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steve_ancell	Created : 08 August 2016 Edited : 08 August 2016 Monkey-X Box2D: Learning from my perspective... Hopefully!
Learning Box2D with Monkey-X: Based on my personal experience. So, I decided to have a go at using the Box2D/monkeybox2d module. At the moment I've been attempting to break down some tutorials, which were kindly provided by skid over at monkey-x.com, into small chunks in order to make it more understandable. This was done to help me understand how to use the Box2D module, but maybe whoever else is reading this may also benefit from this too. Over time I will break down, or maybe just break it altogether, what I learn into code snippets that I hope can become useful to me and whoever. I will start with showing results as a debug drawing and then hopefully transition over to proper graphics as this progresses, I just hope I don't wind up boring you all in the process. I have so far isolated the part that creates the world with noting else in it, I will add more to this blog as I go along. Creating the world: This is the bare-essentials for setting up a Box2D environment. Although stuff could probably be done in the C_Game class, which is what I originally intended as to try simplifying what does what, it seems to be easier to handle if the Box2D stuff is inside of another class like I've done here with the C_Box2D class. Strict 'I am da masta! Import mojo 'It seems that this needs a bit of mojo. Import box2d.collision 'Based on what I've seen so far, this subframe of C_Box2D is needed for what I'm doing here. 'These constants were in the example on the Monkey-X site, I'm not entirely sure what they are for at this time but should become clearer as I progress. Const WORLDSCALE:Float = 1.0 / 8 Const TIMESTEP:Float = 1.0 / 20 'frantic 2x clock, as it was said in the original example, I think this thing needs to lay off the caffeine! Const FRAMERATE:Int = 30 Const SPEEDLOOPS:Int = 20 'WTF! I bet that makes it a bit dizzy. Const POSLOOPS:Int = 20 Function Main:Int() New C_Game() Return 0 End Class C_Box2D Field world:b2World 'Well I think this one is obvious, it would be a bit hard to live in a world without well... a world! Method New() Init(New b2Vec2(0, 10)) 'Initiate the world and give it a vector that defines gravity. End Method Init:Void(gravity:b2Vec2) world = New b2World(gravity, True) 'And then create the world and apply the gravity to it. I haven't a scooby what the other parameter is for yet, sleep apparently; perhaps it's just being a lazy fucker! world.SetWarmStarting(True) 'No clue on this yet. Local dbgDraw:= New C_DebugDraw() 'Create the debug draw hanlder, I assume this isn't needed once proper graphics are used. dbgDraw.SetDrawScale(1.0 / WORLDSCALE) 'I assume this is for setting the size of the drawing or something. 'If you remove this everything looks microscopically small. dbgDraw.SetFillAlpha(1.0) 'I guess this may have something to do with how prominent the visible bits are; but who knows?, fucknoze! 'I tried changing and removing this, it didn't seem to make any difference. dbgDraw.SetLineThickness(1.0) 'I guess this has something to do with the outlines. 'Changing or removing this doesn't seem to make any difference either. dbgDraw.SetFlags(b2DebugDraw.e_shapeBit \| b2DebugDraw.e_jointBit)'\| b2DebugDraw.e_pairBit) 'Buggernoze what this bit does but, after looking at the b2DebugDraw class, 'I'm guessing that it tells the debug draw handler what information to draw. world.SetDebugDraw(dbgDraw) 'I suppose this bit assigns the debug draw handler to the world. End Method Update:Void() 'Not entirely sure what these are doing yet. world.TimeStep(TIMESTEP, SPEEDLOOPS, POSLOOPS) 'This one seems to go through all the background maths, movement and collision stuff, and what ever else it has to do. world.ClearForces() End Method Draw:Void() world.DrawDebugData() End End Class C_DebugDraw Extends b2DebugDraw Method Clear:Void() 'You need to Declare this method, otherwise b2DebugDraw.Clear() will be called and will do the Cls(0, 0, 0) thing and therefore override your own Cls colour. End End Class C_Game Extends App Field world:C_Box2D Field renderCount% Field ball:b2Body Field square:b2Body Method OnCreate:Int() SetUpdateRate(30) '_______________________________________________________________________________________________ 'This section clears then creates a new world: ResetWorld() '_______________________________________________________________________________________________ Return 0 End Method OnUpdate:Int() world.Update() Return 0 End Method OnRender:Int() renderCount = (renderCount + 1) Cls(10, 30, 160) world.Draw() Return 0 End Method ResetWorld:Void() world = New C_Box2D() End End --v Next: Will be adding some rectangles to the environment, stay tuned! __________________________________________________________ In this installment I will be adding some stuff that fills the environment with, well..., stuff!. In this case it will be stationary and falling rectangles. I've added a few methods and static globals, listed below. Inside C_Box2D: Global FixtureDef:= New b2FixtureDef() Global BodyDef:=New b2BodyDef() Global Impulse:=New b2Vec2 CreateBody AddSquareFixture ApplyImpulse Inside C_Game MakeWorld Const STATIC_BODY:Int Const KINEMATIC_BODY:Int Const DYNAMIC_BODY:Int AddRect Strict 'I am da masta! Import mojo 'It seems that this needs a bit of mojo. Import box2d.collision 'Based on what I've seen so far, this subframe of C_Box2D is needed for what I'm doing here. 'These constants were in the example on the Monkey-X site, I'm not entirely sure what they are for at this time but should become clearer as I progress. Const WORLDSCALE:Float = 1.0 / 8 Const TIMESTEP:Float = 1.0 / 20 'frantic 2x clock, as it was said in the original example, I think this thing needs to lay off the caffeine! Const FRAMERATE:Int = 30 Const SPEEDLOOPS:Int = 20 'WTF! I bet that makes it a bit dizzy. Const POSLOOPS:Int = 20 'These constants have been added for this section; I'm not sure why just yet, all I know is they are needed. Const STATICBIT% = 1 Const DYNAMICBIT%=2 Function Main:Int() New C_Game() Return 0 End Class C_Box2D Field world:b2World 'Well I think this one is obvious, it would be a bit hard to live in a world without well... a world! Method New() Init(New b2Vec2(0, 10)) 'Initiate the world and give it a vector that defines gravity. End Method Init:Void(gravity:b2Vec2) world = New b2World(gravity, True) 'And then create the world and apply the gravity to it. I haven't a scooby what the other parameter is for yet, sleep apparently; perhaps it's just being a lazy fucker! world.SetWarmStarting(True) 'No clue on this yet. Local dbgDraw:= New C_DebugDraw() 'Create the debug draw hanlder, I assume this isn't needed once proper graphics are used. dbgDraw.SetDrawScale(1.0 / WORLDSCALE) 'I assume this is for setting the size of the drawing or something. 'If you remove this everything looks microscopically small. dbgDraw.SetFillAlpha(1.0) 'I guess this may have something to do with how prominent the visible bits are; but who knows?, fucknoze! 'I tried changing and removing this, it didn't seem to make any difference. dbgDraw.SetLineThickness(1.0) 'I guess this has something to do with the outlines. 'Changing or removing this doesn't seem to make any difference either. dbgDraw.SetFlags(b2DebugDraw.e_shapeBit \| b2DebugDraw.e_jointBit)'\| b2DebugDraw.e_pairBit) 'Buggernoze what this bit does but, after looking at the b2DebugDraw class, 'I'm guessing that it tells the debug draw handler what information to draw. world.SetDebugDraw(dbgDraw) 'I suppose this bit assigns the debug draw handler to the world. End Method Update:Void() 'Not entirely sure what these are doing yet. world.TimeStep(TIMESTEP, SPEEDLOOPS, POSLOOPS) 'This one seems to go through all the background maths, movement and collision stuff, and what ever else it has to do. world.ClearForces() End Method Draw:Void() world.DrawDebugData() End 'These static globals have been added for this bit, they are here for ready-baked action as far as I can tell. Global FixtureDef:= New b2FixtureDef() Global BodyDef:=New b2BodyDef() Global Impulse:=New b2Vec2 'This creates a b2Body object which is used with fixtures, think of this as a mass that you attach other fixtures onto. Method CreateBody:b2Body(x#,y#,bodytype%) BodyDef.type = bodytype BodyDef.fixedRotation=False BodyDef.position.Set(x, y) Return world.CreateBody(BodyDef) End 'This takes in a b2Body object that was created with CreateBody, attaches it to a fixture and then returns that fixture. Again, fucknoze what bits and mask do at this point. Method AddSquareFixture:b2Fixture(body:b2Body, w:Float, h:Float, bits:Int, mask:Int) Local shape:= New b2PolygonShape shape.SetAsBox wWORLDSCALE,hWORLDSCALE FixtureDef.shape=shape FixtureDef.density=10 FixtureDef.filter.categoryBits=bits FixtureDef.filter.maskBits=mask Local fixture:=body.CreateFixture(FixtureDef) fixture.SetRestitution(0.1) fixture.SetFriction(0.9) Return fixture End 'This gives the body a shove in the right direction. Method ApplyImpulse:Void(body:b2Body,x#,y#) Impulse.x=x Impulse.y=y body.ApplyForce Impulse, body.GetPosition() End End 'Used for drawing the debug info. Class C_DebugDraw Extends b2DebugDraw Method Clear:Void() 'You need to Declare this method, otherwise b2DebugDraw.Clear() will be called and will do the Cls(0, 0, 0) thing and therefore override your own Cls colour. End End Class C_Game Extends App Field world:C_Box2D Field renderCount% Field ball:b2Body Field square:b2Body Method OnCreate:Int() 'This section sets up the world and set the framerate: SetUpdateRate(30) '_______________________________________________________________________________________________ 'This section clears then adds stuff to the world: ResetWorld() MakeWorld() '_______________________________________________________________________________________________ Return 0 End Method OnUpdate:Int() world.Update() If KeyHit(KEY_F1) ResetWorld() MakeWorld() EndIf If KeyHit(KEY_F2) AddRect(30, 0, Rnd(10, 50), Rnd(10, 50), DYNAMIC_BODY) EndIf Return 0 End Method OnRender:Int() renderCount = (renderCount + 1) Cls(10, 30, 160) world.Draw() DrawText("Hit [F1] to reset", 20, 20) DrawText("Hit [F2] to drop another box", 20, 40) Return 0 End Method ResetWorld:Void() world = New C_Box2D() End Method MakeWorld:Void() AddRect(20, 20, 200, 10, STATIC_BODY, 29) 'First platform (angled). The angle property in b2Body doesn't seem to work the way I expected, perhaps it's in radians or some other bollocks, 'looks like I need to do some more research. AddRect(40, 45, 120, 10, STATIC_BODY) 'Second platform AddRect(40, 55, 310, 10, STATIC_BODY) 'The floor AddRect(20, 0, 50, 40, DYNAMIC_BODY) 'Where the fuck did that come from?, the sky by the looks of it! End Const STATIC_BODY:Int = 0 Const KINEMATIC_BODY:Int = 1 Const DYNAMIC_BODY:Int = 2 'This constructs a rectangular body. Method AddRect:b2Body(x:Float, y:Float, width:Float, height:Float, bodyType:Int = DYNAMIC_BODY, angle:Float = 0) Local rect:b2Body rect = world.CreateBody(x, y, bodyType) world.AddSquareFixture(rect, width, height, DYNAMICBIT, STATICBIT \| DYNAMICBIT) world.ApplyImpulse(rect, 0, 0) rect.SetAngle(angle) Return rect End End --v

Comments
Monday, 08 August 2016, 03:56
steve_ancell	Instead of keep adding comments I will just edit the main blog as I add stuff, this will help to keep any other comments separate from the stuff above.
Monday, 08 August 2016, 04:00
Jayenkai	"Only adding to the main blog" will only ever add to the main blog. It won't flag up the new content as an unread post in the sidebar. As such, be sure to post a comment, like "Today I tackled X/achieved Y/broke Z" if it's been a while since the last update. (eg a few hours, not spamming every 10 seconds )
Monday, 08 August 2016, 04:02
steve_ancell	OKies, I'll do it like that instead.
Monday, 08 August 2016, 05:11
steve_ancell	Added a new method, AddBall... Now it has balls!!! That's it for the time being, I am now off to learn how to apply forces, and torque to balls. I did say torque, not talk; not that I talk to balls, unlike Tom Hanks, but then again some do. Strict 'I am da masta! Import mojo 'It seems that this needs a bit of mojo. Import box2d.collision 'Based on what I've seen so far, this subframe of C_Box2D is needed for what I'm doing here. 'These constants were in the example on the Monkey-X site, I'm not entirely sure what they are for at this time but should become clearer as I progress. Const WORLDSCALE:Float = 1.0 / 8 Const TIMESTEP:Float = 1.0 / 20 'frantic 2x clock, as it was said in the original example, I think this thing needs to lay off the caffeine! Const FRAMERATE:Int = 30 Const SPEEDLOOPS:Int = 20 'WTF! I bet that makes it a bit dizzy. Const POSLOOPS:Int = 20 'These constants have been added for this section; I'm not sure why just yet, all I know is they are needed. Const STATICBIT% = 1 Const DYNAMICBIT%=2 Function Main:Int() New C_Game() Return 0 End Class C_Box2D Field world:b2World 'Well I think this one is obvious, it would be a bit hard to live in a world without well... a world! Method New() Init(New b2Vec2(0, 10)) 'Initiate the world and give it a vector that defines gravity. End Method Init:Void(gravity:b2Vec2) world = New b2World(gravity, True) 'And then create the world and apply the gravity to it. I haven't a scooby what the other parameter is for yet, sleep apparently; perhaps it's just being a lazy fucker! world.SetWarmStarting(True) 'No clue on this yet. Local dbgDraw:= New C_DebugDraw() 'Create the debug draw hanlder, I assume this isn't needed once proper graphics are used. dbgDraw.SetDrawScale(1.0 / WORLDSCALE) 'I assume this is for setting the size of the drawing or something. 'If you remove this everything looks microscopically small. dbgDraw.SetFillAlpha(1.0) 'I guess this may have something to do with how prominent the visible bits are; but who knows?, fucknoze! 'I tried changing and removing this, it didn't seem to make any difference. dbgDraw.SetLineThickness(1.0) 'I guess this has something to do with the outlines. 'Changing or removing this doesn't seem to make any difference either. dbgDraw.SetFlags(b2DebugDraw.e_shapeBit \| b2DebugDraw.e_jointBit)'\| b2DebugDraw.e_pairBit) 'Buggernoze what this bit does but, after looking at the b2DebugDraw class, 'I'm guessing that it tells the debug draw handler what information to draw. world.SetDebugDraw(dbgDraw) 'I suppose this bit assigns the debug draw handler to the world. End Method Update:Void() 'Not entirely sure what these are doing yet. world.TimeStep(TIMESTEP, SPEEDLOOPS, POSLOOPS) 'This one seems to go through all the background maths, movement and collision stuff, and what ever else it has to do. world.ClearForces() End Method Draw:Void() world.DrawDebugData() End 'These static globals have been added for this bit, they are here for ready-baked action as far as I can tell. Global FixtureDef:= New b2FixtureDef() Global BodyDef:=New b2BodyDef() Global Impulse:=New b2Vec2 'This creates a b2Body object which is used with fixtures, think of this as a mass that you attach other fixtures onto. Method CreateBody:b2Body(x#,y#,bodytype%) BodyDef.type = bodytype BodyDef.fixedRotation=False BodyDef.position.Set(x, y) Return world.CreateBody(BodyDef) End 'This takes in a b2Body object that was created with CreateBody, attaches it to a fixture and then returns that fixture. Again, fucknoze what bits and mask do at this point. Method AddSquareFixture:b2Fixture(body:b2Body, w:Float, h:Float, bits:Int, mask:Int) Local shape:= New b2PolygonShape shape.SetAsBox wWORLDSCALE,hWORLDSCALE FixtureDef.shape=shape FixtureDef.density=10 FixtureDef.filter.categoryBits=bits FixtureDef.filter.maskBits=mask Local fixture:=body.CreateFixture(FixtureDef) fixture.SetRestitution(0.1) fixture.SetFriction(0.9) Return fixture End 'This does something similar to AddSquareFixture only this time it constructs a round fixture. Method AddRadialFixture:b2Fixture(body:b2Body, r:Float, bits:Int, mask:Int) FixtureDef.shape = New b2CircleShape(r * WORLDSCALE) FixtureDef.density = 10 FixtureDef.filter.categoryBits=bits FixtureDef.filter.maskBits = mask Local fixture:= body.CreateFixture(FixtureDef) fixture.SetRestitution(0.1) fixture.SetFriction(0.9) Return fixture End 'This gives the body a shove in the right direction. Method ApplyImpulse:Void(body:b2Body,x#,y#) Impulse.x=x Impulse.y=y body.ApplyForce Impulse, body.GetPosition() End End 'Used for drawing the debug info. Class C_DebugDraw Extends b2DebugDraw Method Clear:Void() 'You need to Declare this method, otherwise b2DebugDraw.Clear() will be called and will do the Cls(0, 0, 0) thing and therefore override your own Cls colour. End End Class C_Game Extends App Field world:C_Box2D Field renderCount% Field ball:b2Body Field square:b2Body Method OnCreate:Int() 'This section sets up the world and set the framerate: SetUpdateRate(30) '_______________________________________________________________________________________________ 'This section clears then adds stuff to the world: ResetWorld() MakeWorld() '_______________________________________________________________________________________________ Return 0 End Method OnUpdate:Int() world.Update() If KeyHit(KEY_F1) ResetWorld() MakeWorld() EndIf If KeyHit(KEY_F2) AddBall(20, 40, Rnd(10, 50)) EndIf Return 0 End Method OnRender:Int() renderCount = (renderCount + 1) Cls(10, 30, 160) world.Draw() DrawText("Hit [F1] to reset", 20, 20) DrawText("Hit [F2] to drop another ball", 20, 40) Return 0 End Method ResetWorld:Void() world = New C_Box2D() End Method MakeWorld:Void() AddRect(20, 20, 200, 10, STATIC_BODY, 29) 'First platform (angled). The angle property in b2Body doesn't seem to work the way I expected, perhaps it's in radians or some other bollocks, 'looks like I need to do some more research. AddRect(40, 45, 120, 10, STATIC_BODY) 'Second platform AddRect(40, 55, 310, 10, STATIC_BODY) 'The floor ' AddRect(20, 0, 50, 40, DYNAMIC_BODY) 'Where the fuck did that come from?, the sky by the looks of it! AddBall(20, 40, 10, DYNAMIC_BODY) End Const STATIC_BODY:Int = 0 Const KINEMATIC_BODY:Int = 1 Const DYNAMIC_BODY:Int = 2 'This constructs a rectangular body. Method AddRect:b2Body(x:Float, y:Float, width:Float, height:Float, bodyType:Int = DYNAMIC_BODY, angle:Float = 0) Local rect:b2Body rect = world.CreateBody(x, y, bodyType) world.AddSquareFixture(rect, width, height, DYNAMICBIT, STATICBIT \| DYNAMICBIT) world.ApplyImpulse(rect, 0, 0) rect.SetAngle(angle) Return rect End Method AddBall:b2Body(x:Float, y:Float, radius:Float, bodyType:Int = DYNAMIC_BODY) Local ball:b2Body ball = world.CreateBody(10, 0, DYNAMIC_BODY) world.AddRadialFixture(ball, radius, DYNAMICBIT, STATICBIT \| DYNAMICBIT) world.ApplyImpulse(ball, Rnd(-.1,.1), 0) Return ball End End --v
Tuesday, 09 August 2016, 07:06
steve_ancell	Today I've been toying around with torque. I've now defined a 2dBody in the ball field and applied torque to that. I also changed the platforms for a bit of fun. Left and right arrows roll the ball in the relevant direction. I did originally include a DrawText command to show this on screen, but DrawText seems to make the framerate rather shite. Strict 'I am da masta! Import mojo 'It seems that this needs a bit of mojo. Import box2d.collision 'Based on what I've seen so far, this subframe of C_Box2D is needed for what I'm doing here. 'These constants were in the example on the Monkey-X site, I'm not entirely sure what they are for at this time but should become clearer as I progress. Const WORLDSCALE:Float = 1.0 / 8 Const TIMESTEP:Float = 1.0 / 20 'frantic 2x clock, as it was said in the original example, I think this thing needs to lay off the caffeine! Const FRAMERATE:Int = 30 Const SPEEDLOOPS:Int = 20 'WTF! I bet that makes it a bit dizzy. Const POSLOOPS:Int = 20 'These constants have been added for this section; I'm not sure why just yet, all I know is they are needed. Const STATICBIT% = 1 Const DYNAMICBIT%=2 Function Main:Int() New C_Game() Return 0 End Class C_Box2D Field world:b2World 'Well I think this one is obvious, it would be a bit hard to live in a world without well... a world! Method New() Init(New b2Vec2(0, 10)) 'Initiate the world and give it a vector that defines gravity. End Method Init:Void(gravity:b2Vec2) world = New b2World(gravity, True) 'And then create the world and apply the gravity to it. I haven't a scooby what the other parameter is for yet, sleep apparently; perhaps it's just being a lazy fucker! world.SetWarmStarting(True) 'No clue on this yet. Local dbgDraw:= New C_DebugDraw() 'Create the debug draw hanlder, I assume this isn't needed once proper graphics are used. dbgDraw.SetDrawScale(1.0 / WORLDSCALE) 'I assume this is for setting the size of the drawing or something. 'If you remove this everything looks microscopically small. dbgDraw.SetFillAlpha(1.0) 'I guess this may have something to do with how prominent the visible bits are; but who knows?, fucknoze! 'I tried changing and removing this, it didn't seem to make any difference. dbgDraw.SetLineThickness(1.0) 'I guess this has something to do with the outlines. 'Changing or removing this doesn't seem to make any difference either. dbgDraw.SetFlags(b2DebugDraw.e_shapeBit \| b2DebugDraw.e_jointBit)'\| b2DebugDraw.e_pairBit) 'Buggernoze what this bit does but, after looking at the b2DebugDraw class, 'I'm guessing that it tells the debug draw handler what information to draw. world.SetDebugDraw(dbgDraw) 'I suppose this bit assigns the debug draw handler to the world. End Method Update:Void() 'Not entirely sure what these are doing yet. world.TimeStep(TIMESTEP, SPEEDLOOPS, POSLOOPS) 'This one seems to go through all the background maths, movement and collision stuff, and what ever else it has to do. world.ClearForces() End Method Draw:Void() world.DrawDebugData() End Global FixtureDef:= New b2FixtureDef() Global BodyDef:= New b2BodyDef() Global Impulse:=New b2Vec2 Method CreateBody:b2Body(x#,y#,bodytype%) BodyDef.type = bodytype BodyDef.fixedRotation=False BodyDef.position.Set(x, y) Return world.CreateBody(BodyDef) End Method AddSquareFixture:b2Fixture(body:b2Body, w:Float, h:Float, bits:Int, mask:Int) Local shape:= New b2PolygonShape shape.SetAsBox wWORLDSCALE,hWORLDSCALE FixtureDef.shape=shape FixtureDef.density=10 FixtureDef.filter.categoryBits=bits FixtureDef.filter.maskBits=mask Local fixture:=body.CreateFixture(FixtureDef) fixture.SetRestitution(0.1) fixture.SetFriction(0.9) Return fixture End Method AddRadialFixture:b2Fixture(body:b2Body, r:Float, bits:Int, mask:Int) FixtureDef.shape = New b2CircleShape(r * WORLDSCALE) FixtureDef.density = 10 FixtureDef.filter.categoryBits=bits FixtureDef.filter.maskBits = mask Local fixture:= body.CreateFixture(FixtureDef) fixture.SetRestitution(0.1) fixture.SetFriction(0.9) Return fixture End Method ApplyImpulse:Void(body:b2Body,x#,y#) Impulse.x = x Impulse.y=y body.ApplyForce Impulse, body.GetPosition() End End 'Used for drawing the debug info. Class C_DebugDraw Extends b2DebugDraw Method Clear:Void() End End Class C_Game Extends App Field world:C_Box2D Field renderCount% Field ball:b2Body Field square:b2Body Method OnCreate:Int() 'This section sets up the world and set the framerate: SetUpdateRate(30) ResetWorld() MakeWorld() Return 0 End Method OnUpdate:Int() world.Update() If KeyHit(KEY_F1) ResetWorld() MakeWorld() EndIf If KeyDown(KEY_LEFT) ball.ApplyTorque(-800) EndIf If KeyDown(KEY_RIGHT) ball.ApplyTorque(800) EndIf Return 0 End Method OnRender:Int() ' renderCount = (renderCount + 1) Cls(10, 30, 160) world.Draw() 'Comment-out the following 2 lines if you want to speed things up, Box2D doesn't seem to like DrawText. ' DrawText("Hit [F1] to reset", 20, 20) ' DrawText("[Left arrow] roll left : [Right arrow] roll right", 20, 40) Return 0 End Method ResetWorld:Void() world = New C_Box2D() End Method MakeWorld:Void() AddRect(1, 20, 100, 10, STATIC_BODY, F_DegToRad(-90)) 'Ramp top-left AddRect(79, 20, 100, 10, STATIC_BODY, F_DegToRad(90)) 'Ramp top-right AddRect(10, 41, 100, 10, STATIC_BODY, F_DegToRad(45)) 'Ramp left-bottom AddRect(70, 41, 100, 10, STATIC_BODY, F_DegToRad(-45)) 'Ramp right-bottom AddRect(40, 50, 162, 10, STATIC_BODY) 'Floor ball = AddBall(40, 35, 10, DYNAMIC_BODY) End Const STATIC_BODY:Int = 0 Const KINEMATIC_BODY:Int = 1 Const DYNAMIC_BODY:Int = 2 Method AddRect:b2Body(x:Float, y:Float, width:Float, height:Float, bodyType:Int = DYNAMIC_BODY, angle:Float = 0) Local rect:b2Body rect = world.CreateBody(x, y, bodyType) world.AddSquareFixture(rect, width, height, DYNAMICBIT, STATICBIT \| DYNAMICBIT) world.ApplyImpulse(rect, 0, 0) rect.SetAngle(angle) Return rect End Method AddBall:b2Body(x:Float, y:Float, radius:Float, bodyType:Int = DYNAMIC_BODY) Local ball:b2Body ball = world.CreateBody(x, y, DYNAMIC_BODY) world.AddRadialFixture(ball, radius, DYNAMICBIT, STATICBIT \| DYNAMICBIT) world.ApplyImpulse(ball, Rnd(-.1,.1), 0) Return ball End End 'It seems evident that Box2D uses radians, so I "turned out" a couple of functions to help dealing with this. Function F_DegToRad:Float(deg:Float) Return (deg * PI) / 180 End Function F_RadToDeg:Float(rad:Float) Return (180 / PI) * rad End --v Next: Not sure yet, maybe I'll look into adding graphics for the next installment. Stay tuned!
Friday, 12 August 2016, 09:00
steve_ancell	I'm a big kid, look what I can do!... Me been playing with compound shapes. Remove the F_DebugMessage commands from OnUpdate in the C_Game class if you want the simulation to run at full chat. Strict Import mojo Import box2d.collision Const WORLDSCALE:Float = 1.0 / 8 Const TIMESTEP:Float = 1.0 / 20 Const FRAMERATE:Int = 30 Const SPEEDLOOPS:Int = 20 Const POSLOOPS:Int = 20 Const STATICBIT:Int = 1 Const DYNAMICBIT:Int = 2 Const STATIC_BODY:Int = b2Body.b2_staticBody Const KINEMATIC_BODY:Int = b2Body.b2_kinematicBody Const DYNAMIC_BODY:Int = b2Body.b2_Body Global debugMessageList:String[] Global world:b2World = New b2World() Global FixtureDef:b2FixtureDef = New b2FixtureDef() Global BodyDef:b2BodyDef = New b2BodyDef() Global Impulse:b2Vec2 = New b2Vec2() Global ground:b2Body Global leftWall:b2Body Global rightWall:b2Body Global square:b2Body Global poly:b2Body Global ball:b2Body Global actor:C_Actor Function Main:Int() New C_Game() Return 0 End Class C_DebugDraw Extends b2DebugDraw Method Clear:Void() End End Class C_Game Extends App Method OnCreate:Int() F_ResetWorld() F_MakeWorld() Return 0 End Method OnUpdate:Int() F_UpdateWorld() F_Input() 'Remove debug message requests to make the simulation run quicker. F_DebugMessage("BallPos_Y: " + ball.GetPosition().y) F_DebugMessage("SquarePos_Y: " + square.GetPosition().y) F_DebugMessage("CompoundShapePos_Y: " + actor.body.GetPosition().y) Return 0 End Method OnRender:Int() Cls(10, 30, 160) F_DrawWorld() F_DisplayDebugMessages() Return 0 End End Class C_Actor Field name:String Field body:b2Body Field polyList:b2Body[] Method New(name:String = "") Self.name = name body = F_CreateBody(0, 0, DYNAMIC_BODY) End Method SetPos:Void(x:Float, y:Float) body.SetPosition(New b2Vec2(x, y)) End Method AddPoly:Void(verts:Float[]) Local index:Int body.CreateFixture(F_CreateFixtureDef(F_CreateShape(verts), DYNAMICBIT, STATICBIT \| DYNAMICBIT)) End End Function F_Input:Void() If KeyHit(KEY_F1) F_ResetWorld() F_MakeWorld() EndIf End Function F_InitWorld:Void(gravity:b2Vec2) Local dbgDraw:C_DebugDraw If world world = Null EndIf world = New b2World(gravity, True) world.SetWarmStarting(True) dbgDraw = New C_DebugDraw() dbgDraw.SetDrawScale(1.0 / WORLDSCALE) dbgDraw.SetFillAlpha(1.0) dbgDraw.SetLineThickness(1.0) dbgDraw.SetFlags(b2DebugDraw.e_shapeBit \| b2DebugDraw.e_jointBit)'\| b2DebugDraw.e_pairBit) world.SetDebugDraw(dbgDraw) End Function F_ResetWorld:Void() F_InitWorld(New b2Vec2(0, 10)) End Function F_MakeWorld:Void() Local verts:Float[] ground = F_AddRect(40, 50, 300, 10, STATIC_BODY) leftWall = F_AddRect(5, 40, 10, 100, STATIC_BODY) rightWall = F_AddRect(75, 40, 10, 100, STATIC_BODY) square = F_AddRect(30, 0, 30, 30, DYNAMIC_BODY) ball = F_AddBall(30, -10, 20) verts =[0.0, 0.0, 3.0, 0.0, 4.0, 3.0] actor = New C_Actor("A") actor.SetPos(26, 20) actor.AddPoly(verts) verts =[0.0, 0.0, -3.0, 0.0, -4.0, 3.0] actor.AddPoly(verts) End Function F_DrawWorld:Void() world.DrawDebugData() End Function F_UpdateWorld:Void() world.TimeStep(TIMESTEP, SPEEDLOOPS, POSLOOPS) world.ClearForces() End Function F_CreateBody:b2Body(x:Float, y:Float, bodytype:Int) BodyDef.type = bodytype BodyDef.fixedRotation=False BodyDef.position.Set(x, y) Return world.CreateBody(BodyDef) End Function F_CreateShape:b2Shape(verts:Float[]) Local shape:b2PolygonShape Local n:Int = verts.Length() / 2 Local vertsList:b2Vec2[] = New b2Vec2[n] Local x:Float Local y:Float Local i:Int shape = New b2PolygonShape() For i = 0 Until n x = verts[i * 2 + 0] y = verts[i * 2 + 1] vertsList[i] = New b2Vec2(x, y) Next shape.SetAsArray(vertsList, n) Return shape End Function F_CreateFixtureDef:b2FixtureDef(shape:b2Shape, bits:Int, mask:Int) FixtureDef.shape = shape FixtureDef.density = 10 FixtureDef.filter.categoryBits = bits FixtureDef.filter.maskBits = mask Return FixtureDef End Function F_AddFixture:b2Fixture(body:b2Body, shape:b2Shape, bits:Int, mask:Int) Local fixture:b2Body fixture = body.CreateFixture(F_CreateFixtureDef(shape, bits, mask)) Return fixture End Function F_AddPolygonFixture:b2Fixture(body:b2Body, pts:Float[], bits:Int, mask:Int) Local shape:b2PolygonShape Local n:Int = pts.Length() / 2 Local points:b2Vec2[] = New b2Vec2[n] Local x:Float = pts[i * 2 + 0] Local y:Float = pts[i * 2 + 1] Local i:Int shape = New b2PolygonShape() For i = 0 Until n x = pts[i * 2 + 0] y = pts[i * 2 + 1] points[i] = New b2Vec2(x, y) Next shape.SetAsArray(points, n) Return F_AddFixture(body, shape, bits, mask) End Function F_AddSquareFixture:b2Fixture(body:b2Body, w:Float, h:Float, bits:Int, mask:Int) Local shape:b2PolygonShape Local fixture:b2Fixture shape = New b2PolygonShape() shape.SetAsBox(w * WORLDSCALE, h * WORLDSCALE) FixtureDef.shape = shape FixtureDef.density = 10 FixtureDef.filter.categoryBits = bits FixtureDef.filter.maskBits = mask fixture = body.CreateFixture(FixtureDef) fixture.SetRestitution(0.1) fixture.SetFriction(0.9) Return fixture End Function F_AddRadialFixture:b2Fixture(body:b2Body, radius:Float, bits:Int, mask:Int) Local fixture:b2Fixture FixtureDef.shape = New b2CircleShape(radius * WORLDSCALE) FixtureDef.density = 10 FixtureDef.filter.categoryBits = bits FixtureDef.filter.maskBits = mask fixture = body.CreateFixture(FixtureDef) fixture.SetRestitution(0.1) fixture.SetFriction(0.9) Return fixture End Function F_ApplyImpulse:Void(body:b2Body, x:Float, y:Float) Impulse.x = x Impulse.y = y body.ApplyForce Impulse, body.GetPosition() End Function F_AddPoly:b2Body(x:Float, y:Float, verts:Float[], bodyType:Int = DYNAMIC_BODY, angle:Float = 0) Local poly:b2Body poly = F_CreateBody(x, y, bodyType) F_AddPolygonFixture(poly, verts, DYNAMICBIT, STATICBIT \| DYNAMICBIT) Return poly End Function F_AddRect:b2Body(x:Float, y:Float, width:Float, height:Float, bodyType:Int = DYNAMIC_BODY, angle:Float = 0) Local rect:b2Body rect = F_CreateBody(x, y, bodyType) F_AddSquareFixture(rect, width, height, DYNAMICBIT, STATICBIT \| DYNAMICBIT) F_ApplyImpulse(rect, 0, 0) rect.SetAngle(angle) Return rect End Function F_AddBall:b2Body(x:Float, y:Float, radius:Float, bodyType:Int = DYNAMIC_BODY, angle:Float = 0) Local ball:b2Body ball = F_CreateBody(x, y, bodyType) F_AddRadialFixture(ball, radius, DYNAMICBIT, STATICBIT \| DYNAMICBIT) F_ApplyImpulse(ball, Rnd(-0.1, 0.1), 0) Return ball End Function F_DegToRad:Float(deg:Float) Return (deg * PI) / 180 End Function F_RadToDeg:Float(rad:Float) Return (180 / PI) * rad End Function F_DebugMessage:Void(message:String = "") Local index:Int index = debugMessageList.Length() debugMessageList = debugMessageList.Resize(index + 1) debugMessageList[index] = message End Function F_DisplayDebugMessages:Void() Local index:Int For index = 0 To(debugMessageList.Length() -1) DrawText(debugMessageList[index], 10, index * 20) Next debugMessageList = debugMessageList.Resize(0) End --v
Friday, 12 August 2016, 13:40
steve_ancell	One problem has arisen, the left polygon in the compound shape doesn't seem to be colliding with the circle. Back to the drawing board in search of a solution
Saturday, 13 August 2016, 09:14
steve_ancell	I've found that compound shapes collide a whole lot better whn the vertices are added when the first vector is added at top left and the rest are added in a clockwise fashion. Also been using actual images with this, I will post in here again once I get something more stable going.
Saturday, 20 August 2016, 06:32
steve_ancell	I've been having a roustabout with top-down car physics. A bit crappy and uncontrollable I know, but it's a start. From the code, most of this is quite self explanatory. [Edit]Oops!, I forgot to include the media \|edit\| This goes in "root\Try_04.data\Graphics" Strict Import mojo Import box2d.collision Const WORLDSCALE:Float = 1.0 / 8 Const TIMESTEP:Float = 1.0 / 20 Const FRAMERATE:Int = 30 Const SPEEDLOOPS:Int = 20 Const POSLOOPS:Int = 20 Const STATICBIT:Int = 1 Const DYNAMICBIT:Int = 2 Const STATIC_BODY:Int = b2Body.b2_staticBody Const KINEMATIC_BODY:Int = b2Body.b2_kinematicBody Const DYNAMIC_BODY:Int = b2Body.b2_Body Global debugMessageList:String[] Global world:b2World = New b2World() Global worldGravity:b2Vec2 = New b2Vec2(0, 0) 'Because this is a top-down thing we need to turn off gravity. 'Defining these variables now saves a lot of work later. Global FixtureDef:b2FixtureDef = New b2FixtureDef() Global BodyDef:b2BodyDef = New b2BodyDef() Global Impulse:b2Vec2 = New b2Vec2() Global RevoluteJointDef:b2RevoluteJointDef = New b2RevoluteJointDef() Global JointDef:b2JointDef = New b2JointDef() 'The content. Global topWall:b2Body Global bottomWall:b2Body Global leftWall:b2Body Global rightWall:b2Body Global car:C_Car Function Main:Int() New C_Game() Return 0 End Class C_DebugDraw Extends b2DebugDraw Method Clear:Void() 'A dummy method, for preventing the real Box2D one from being used. End End Class C_Game Extends App Method OnCreate:Int() F_ResetWorld() F_MakeWorld() Return 0 End Method OnUpdate:Int() F_UpdateWorld() F_UpdateCar(car) F_Input() Return 0 End Method OnRender:Int() Cls(10, 30, 160) F_DrawWorld() car.Draw() F_DisplayDebugMessages() Return 0 End End Class C_Car Field name:String Field gfx:Image Field body:b2Body Field frontWheelLeft:b2Body Field frontWheelRight:b2Body Field rearWheelLeft:b2Body Field rearWheelRight:b2Body Field acceleration:Float = 0 Field power:Float = 10 Field speed:Float = 0 Field speedMax:Float = 50 Field speedDecay:Float = 1 Field brakingPower:Float = 0.1 Field steerAngle:Float = 0 Field steerSpeed:Float = 5 Field steerMax:Float = 20 Method New(name:String = "") Self.name = name End Method SetPos:Void(x:Float, y:Float) body.SetPosition(New b2Vec2(x, y)) End Method Draw:Void() Local x:Float = body.GetPosition().x * F_ScaleX() Local y:Float = body.GetPosition().y * F_ScaleY() Local angle:Float = F_RadToDeg(body.GetAngle()) If gfx DrawImage(gfx, x, y, -angle, 1, 1) Else ' F_DebugMessage("Failed to load image!") EndIf End End Function F_Input:Void() Local isBeingSteered:Int = 0 If KeyHit(KEY_F1) F_ResetWorld() F_MakeWorld() EndIf If KeyDown(KEY_UP) car.acceleration = 0.01 Else car.acceleration = 0.00 EndIf If KeyDown(KEY_DOWN) car.acceleration = -0.01 EndIf If KeyDown(KEY_LEFT) isBeingSteered = 1 car.steerAngle = (car.steerAngle - car.steerSpeed) EndIf If KeyDown(KEY_RIGHT) isBeingSteered = 1 car.steerAngle = (car.steerAngle + car.steerSpeed) EndIf If isBeingSteered = 0 If car.steerAngle < 0 car.steerAngle = (car.steerAngle + car.steerSpeed) EndIf If car.steerAngle > 0 car.steerAngle = (car.steerAngle - car.steerSpeed) EndIf EndIf End Function F_InitWorld:Void(gravity:b2Vec2 = worldGravity) Local dbgDraw:C_DebugDraw If world world = Null EndIf world = New b2World(gravity, True) world.SetWarmStarting(True) dbgDraw = New C_DebugDraw() dbgDraw.SetDrawScale(1.0 / WORLDSCALE) dbgDraw.SetFillAlpha(1.0) dbgDraw.SetLineThickness(1.0) dbgDraw.SetFlags(b2DebugDraw.e_shapeBit \| b2DebugDraw.e_jointBit)'\| b2DebugDraw.e_pairBit) world.SetDebugDraw(dbgDraw) End Function F_ResetWorld:Void() F_InitWorld() End Function F_MakeWorld:Void() topWall = F_AddRect(40, 1, 300, 10, STATIC_BODY) bottomWall = F_AddRect(40, 59, 300, 10, STATIC_BODY) leftWall = F_AddRect(1, 30, 10, 240, STATIC_BODY) rightWall = F_AddRect(79, 30, 10, 240, STATIC_BODY) car = F_AddCar(40, 40) End Function F_DrawWorld:Void() world.DrawDebugData() End Function F_UpdateWorld:Void() world.TimeStep(TIMESTEP, SPEEDLOOPS, POSLOOPS) world.ClearForces() 'This is basically needed to prevent forces from the last frame being added to current forces. End Function F_CreateBody:b2Body(x:Float, y:Float, bodytype:Int) BodyDef.type = bodytype BodyDef.fixedRotation=False BodyDef.position.Set(x, y) Return world.CreateBody(BodyDef) End Function F_AddSquareFixture:b2Fixture(body:b2Body, w:Float, h:Float, bits:Int, mask:Int) Local shape:b2PolygonShape Local fixture:b2Fixture shape = New b2PolygonShape() shape.SetAsBox(w * WORLDSCALE, h * WORLDSCALE) FixtureDef.shape = shape FixtureDef.density = 10 FixtureDef.filter.categoryBits = bits FixtureDef.filter.maskBits = mask fixture = body.CreateFixture(FixtureDef) fixture.SetRestitution(0.1) fixture.SetFriction(0.9) Return fixture End Function F_AddRect:b2Body(x:Float, y:Float, width:Float, height:Float, bodyType:Int = DYNAMIC_BODY, angle:Float = 0) Local rect:b2Body rect = F_CreateBody(x, y, bodyType) F_AddSquareFixture(rect, width, height, DYNAMICBIT, STATICBIT \| DYNAMICBIT) rect.SetAngle(angle) Return rect End Function F_AddCar:C_Car(x:Float, y:Float, angle:Float = 0) Local body:b2Body Local shape:b2PolygonShape = New b2PolygonShape() Local actor:C_Car = New C_Car("Car") Local frontWheelLeft:b2Body Local frontWheelRight:b2Body Local rearWheelLeft:b2Body Local rearWheelRight:b2Body 'Not the best place for a LoadImage command though to be honest, this is only here for my convenience at them moment. I will include the media with the forum post. 'Uncomment these lines if you want to include graphics. ' actor.gfx = LoadImage("Graphics/car_red.png") ' actor.gfx.SetHandle(actor.gfx.Width() / 2, actor.gfx.Height() / 2) '----------------- 'Create main car body shape.SetAsBox(2.25, 1.25) BodyDef.fixedRotation = False FixtureDef.shape = shape body = world.CreateBody(BodyDef) body.SetType(DYNAMIC_BODY) body.CreateFixture(FixtureDef) body.SetPosition(New b2Vec2(x, y)) body.SetLinearDamping(1) actor.body = body '----------------- '----------------- 'Create front left wheel shape.SetAsBox(0.5, 0.25) BodyDef.fixedRotation = False FixtureDef.shape = shape frontWheelLeft = world.CreateBody(BodyDef) frontWheelLeft.SetType(DYNAMIC_BODY) frontWheelLeft.CreateFixture(FixtureDef) frontWheelLeft.SetPosition(New b2Vec2(body.GetWorldCenter().x +2, body.GetWorldCenter().y -1.5)) actor.frontWheelLeft = frontWheelLeft '----------------- '----------------- 'Create front right wheel shape.SetAsBox(0.5, 0.25) BodyDef.fixedRotation = False FixtureDef.shape = shape frontWheelRight = world.CreateBody(BodyDef) frontWheelRight.SetType(DYNAMIC_BODY) frontWheelRight.CreateFixture(FixtureDef) frontWheelRight.SetPosition(New b2Vec2(body.GetWorldCenter().x +2, body.GetWorldCenter().y +1.5)) actor.frontWheelRight = frontWheelRight '----------------- '----------------- 'Create rear left wheel shape.SetAsBox(0.5, 0.25) BodyDef.fixedRotation = False FixtureDef.shape = shape rearWheelLeft = world.CreateBody(BodyDef) rearWheelLeft.SetType(DYNAMIC_BODY) rearWheelLeft.CreateFixture(FixtureDef) rearWheelLeft.SetPosition(New b2Vec2(body.GetWorldCenter().x -2, body.GetWorldCenter().y -1.5)) actor.rearWheelLeft = rearWheelLeft '----------------- '----------------- 'Create rear right wheel shape.SetAsBox(0.5, 0.25) BodyDef.fixedRotation = False FixtureDef.shape = shape rearWheelRight = world.CreateBody(BodyDef) rearWheelRight.SetType(DYNAMIC_BODY) rearWheelRight.CreateFixture(FixtureDef) rearWheelRight.SetPosition(New b2Vec2(body.GetWorldCenter().x -2, body.GetWorldCenter().y +1.5)) actor.rearWheelRight = rearWheelRight '----------------- 'Join the front wheels to the body. RevoluteJointDef.Initialize(frontWheelLeft, body, frontWheelLeft.GetWorldCenter()) world.CreateJoint(RevoluteJointDef) RevoluteJointDef.Initialize(frontWheelRight, body, frontWheelRight.GetWorldCenter()) world.CreateJoint(RevoluteJointDef) 'Join the rear wheels to the body. RevoluteJointDef.Initialize(rearWheelLeft, body, rearWheelLeft.GetWorldCenter()) world.CreateJoint(RevoluteJointDef) RevoluteJointDef.Initialize(rearWheelRight, body, rearWheelRight.GetWorldCenter()) world.CreateJoint(RevoluteJointDef) 'Join the front wheels to the rear wheels, if you were to comment out the following 4 lines then you will discover why this is needed. RevoluteJointDef.Initialize(frontWheelLeft, rearWheelLeft, frontWheelLeft.GetWorldCenter()) world.CreateJoint(RevoluteJointDef) RevoluteJointDef.Initialize(frontWheelRight, rearWheelRight, frontWheelRight.GetWorldCenter()) world.CreateJoint(RevoluteJointDef) body.SetAngle(F_DegToRad(angle)) Return actor End Function F_UpdateCar:Void(actor:C_Car) Local body:b2Body = actor.body Local frontWheelLeft:b2Body = actor.frontWheelLeft Local frontWheelRight:b2Body = actor.frontWheelRight Local rearWheelLeft:b2Body = actor.rearWheelLeft Local rearWheelRight:b2Body = actor.rearWheelRight Local angle:Float Local move:b2Vec2 'Apply any sideways force to the ahead direction to cancel out the sideways force. F_KillOrthogonalVelocity(frontWheelLeft) F_KillOrthogonalVelocity(frontWheelRight) F_KillOrthogonalVelocity(rearWheelLeft) F_KillOrthogonalVelocity(rearWheelRight) 'Prevent the fronts wheels from steering to far left. If actor.steerAngle < - actor.steerMax actor.steerAngle = -actor.steerMax EndIf 'Prevent the fronts wheels from steering to far right. If actor.steerAngle > actor.steerMax actor.steerAngle = actor.steerMax EndIf 'Cap reverse acceleration. If actor.acceleration < - 1 actor.acceleration = -1 EndIf 'Cap forward acceleration. If actor.acceleration > 1 actor.acceleration = 1 EndIf 'Apply current acceleration and power to the current speed. I think this is a rather crap way of doing this though, I will look into this more another time. actor.speed = actor.speed + (actor.power * actor.acceleration) 'Cap the forward and reverse speeds. If actor.speed < - actor.speedMax actor.speed = -actor.speedMax EndIf If actor.speed > actor.speedMax actor.speed = actor.speedMax EndIf 'Get the angle of the main body, then get the offset angle in reference to the steering angle. angle = F_RadToDeg(body.GetAngle()) angle = (angle + actor.steerAngle) 'And the apply the above to the front wheels. frontWheelLeft.SetAngle(F_DegToRad(angle)) frontWheelRight.SetAngle(F_DegToRad(angle)) 'Create a vector that is based on the speed and sine/cosine steering angle. move = New b2Vec2(Cos(angle) * actor.speed, Sin(angle) * actor.speed) 'And then apply that to the front wheels. frontWheelLeft.ApplyForce(move, frontWheelLeft.GetWorldCenter()) frontWheelLeft.SetLinearVelocity(move) frontWheelRight.ApplyForce(move, frontWheelRight.GetWorldCenter()) frontWheelRight.SetLinearVelocity(move) End Function F_KillOrthogonalVelocity:Void(body:b2Body) 'I ripped-off this function from another example elswhere on the internet, and then I modified it to work with Monkey-X. 'In Laymen's terms it takes sideways force and then applies it in a forward direction. Local localVelocity:b2Vec2 Local velocity:b2Vec2 Local sidewaysAxis:b2Vec2 localVelocity = New b2Vec2(0, 0) velocity = body.GetLinearVelocityFromLocalPoint(localVelocity) sidewaysAxis = body.GetTransform().R.col2.Copy() sidewaysAxis.Multiply(b2Math.Dot(velocity, sidewaysAxis)) body.SetLinearVelocity(sidewaysAxis) End 'Get the scales of the width and height of the screen, so that graphics fit in accross different sized devices. Function F_ScaleX:Float() Return DeviceWidth() / (DeviceWidth() * WORLDSCALE) End Function F_ScaleY:Float() Return DeviceHeight() / (DeviceHeight() * WORLDSCALE) End 'Convert degrees to radians. Function F_DegToRad:Float(deg:Float) Return (deg * PI) / 180 End 'Convert radians to degrees. Function F_RadToDeg:Float(rad:Float) Return (180 / PI) * rad End 'For debugging purposes. This works from anywhere in the program, not just the render method, only use when necessary as DrawText seems to slow down Box2D debug rendering. 'Data is cleared after rendering. Function F_DebugMessage:Void(message:String = "") Local index:Int index = debugMessageList.Length() debugMessageList = debugMessageList.Resize(index + 1) debugMessageList[index] = message End 'Call this as the final command in the render method. Function F_DisplayDebugMessages:Void() Local index:Int For index = 0 To(debugMessageList.Length() -1) DrawText(debugMessageList[index], 10, index * 20) Next debugMessageList = debugMessageList.Resize(0) End --v
Sunday, 21 August 2016, 14:49
steve_ancell	I have found that top down car physics is easier to impliment with a single rectangular body without the wheels. It's now a lot easier to control but it now moves like it's on a track, it needs to have some sort of sideways inertia to give it the feeling of drift on tight corners. i'm planning on trying some sort of dual-mass approach, in the meantime here is the code for what I've done recently. Strict Import mojo Import box2d.collision Const WORLDSCALE:Float = 1.0 / 8 Const TIMESTEP:Float = 1.0 / 20 Const FRAMERATE:Int = 30 Const SPEEDLOOPS:Int = 20 Const POSLOOPS:Int = 20 Const STATICBIT:Int = 1 Const DYNAMICBIT:Int = 2 Const STATIC_BODY:Int = b2Body.b2_staticBody Const KINEMATIC_BODY:Int = b2Body.b2_kinematicBody Const DYNAMIC_BODY:Int = b2Body.b2_Body Global debugMessageList:String[] Global world:b2World = New b2World() Global worldGravity:b2Vec2 = New b2Vec2(0, 0) 'Because this is a top-down thing we need to turn off gravity. 'Defining these variables now saves a lot of work later. Global FixtureDef:b2FixtureDef = New b2FixtureDef() Global BodyDef:b2BodyDef = New b2BodyDef() Global Impulse:b2Vec2 = New b2Vec2() Global RevoluteJointDef:b2RevoluteJointDef = New b2RevoluteJointDef() Global JointDef:b2JointDef = New b2JointDef() 'The content. Global topWall:b2Body Global bottomWall:b2Body Global leftWall:b2Body Global rightWall:b2Body Global car:C_Car Function Main:Int() New C_Game() Return 0 End Class C_DebugDraw Extends b2DebugDraw Method Clear:Void() 'A dummy method, for preventing the real Box2D one from being used. End End Class C_Game Extends App Method OnCreate:Int() F_ResetWorld() F_MakeWorld() Return 0 End Method OnUpdate:Int() F_UpdateWorld() F_UpdateCar(car) F_Input() Return 0 End Method OnRender:Int() Cls(10, 30, 160) F_DrawWorld() car.Draw() F_DisplayDebugMessages() Return 0 End End Class C_Car Field name:String Field gfx:Image Field body:b2Body Field frontWheelLeft:b2Body Field frontWheelRight:b2Body Field rearWheelLeft:b2Body Field rearWheelRight:b2Body Field acceleration:Float = 0 Field power:Float = 10 Field speed:Float = 0 Field speedMax:Float = 50 Field speedDecay:Float = 1 Field brakingPower:Float = 0.1 Field steerAngle:Float = 0 Field steerSpeed:Float = 5 Field steerMax:Float = 10 Method New(name:String = "") Self.name = name End Method SetPos:Void(x:Float, y:Float) body.SetPosition(New b2Vec2(x, y)) End Method Draw:Void() Local x:Float = body.GetPosition().x * F_ScaleX() Local y:Float = body.GetPosition().y * F_ScaleY() Local angle:Float = F_RadToDeg(body.GetAngle()) If gfx DrawImage(gfx, x, y, -angle, 1, 1) Else ' F_DebugMessage("Failed to load image!") EndIf End End Function F_Input:Void() If KeyHit(KEY_F1) F_ResetWorld() F_MakeWorld() EndIf If KeyDown(KEY_UP) car.speed = (car.speed + 0.01) EndIf If KeyDown(KEY_DOWN) car.speed = (car.speed - 0.01) EndIf If KeyDown(KEY_LEFT) car.steerAngle = (car.steerAngle - car.steerSpeed) EndIf If KeyDown(KEY_RIGHT) car.steerAngle = (car.steerAngle + car.steerSpeed) EndIf End Function F_InitWorld:Void(gravity:b2Vec2 = worldGravity) Local dbgDraw:C_DebugDraw If world world = Null EndIf world = New b2World(gravity, True) world.SetWarmStarting(True) dbgDraw = New C_DebugDraw() dbgDraw.SetDrawScale(1.0 / WORLDSCALE) dbgDraw.SetFillAlpha(1.0) dbgDraw.SetLineThickness(1.0) dbgDraw.SetFlags(b2DebugDraw.e_shapeBit \| b2DebugDraw.e_jointBit)'\| b2DebugDraw.e_pairBit) world.SetDebugDraw(dbgDraw) End Function F_ResetWorld:Void() F_InitWorld() End Function F_MakeWorld:Void() topWall = F_AddRect(40, 1, 300, 10, STATIC_BODY) bottomWall = F_AddRect(40, 59, 300, 10, STATIC_BODY) leftWall = F_AddRect(1, 30, 10, 240, STATIC_BODY) rightWall = F_AddRect(79, 30, 10, 240, STATIC_BODY) car = F_AddCar(40, 40) End Function F_DrawWorld:Void() world.DrawDebugData() End Function F_UpdateWorld:Void() world.TimeStep(TIMESTEP, SPEEDLOOPS, POSLOOPS) world.ClearForces() 'This is basically needed to prevent forces from the last frame being added to current forces. End Function F_CreateBody:b2Body(x:Float, y:Float, bodytype:Int) BodyDef.type = bodytype BodyDef.fixedRotation=False BodyDef.position.Set(x, y) Return world.CreateBody(BodyDef) End Function F_AddSquareFixture:b2Fixture(body:b2Body, w:Float, h:Float, bits:Int, mask:Int) Local shape:b2PolygonShape Local fixture:b2Fixture shape = New b2PolygonShape() shape.SetAsBox(w * WORLDSCALE, h * WORLDSCALE) FixtureDef.shape = shape FixtureDef.density = 10 FixtureDef.filter.categoryBits = bits FixtureDef.filter.maskBits = mask fixture = body.CreateFixture(FixtureDef) fixture.SetRestitution(0.1) fixture.SetFriction(0.9) Return fixture End Function F_AddRect:b2Body(x:Float, y:Float, width:Float, height:Float, bodyType:Int = DYNAMIC_BODY, angle:Float = 0) Local rect:b2Body rect = F_CreateBody(x, y, bodyType) F_AddSquareFixture(rect, width, height, DYNAMICBIT, STATICBIT \| DYNAMICBIT) rect.SetAngle(angle) Return rect End Function F_AddCar:C_Car(x:Float, y:Float, angle:Float = 0) Local actor:C_Car = New C_Car("Car") Local body:b2Body Local shape:b2PolygonShape = New b2PolygonShape() ' actor.gfx = LoadImage("Graphics/car_red.png") ' actor.gfx.SetHandle(actor.gfx.Width() / 2, actor.gfx.Height() / 2) shape.SetAsBox(2.25, 1.25) BodyDef.fixedRotation = False FixtureDef.shape = shape body = world.CreateBody(BodyDef) body.SetType(DYNAMIC_BODY) body.CreateFixture(FixtureDef) body.SetPosition(New b2Vec2(x, y)) actor.body = body Return actor End Function F_UpdateCar:Void(actor:C_Car) Local body:b2Body = actor.body Local angle:Float = F_RadToDeg(body.GetAngle()) Local steerAngle:Float = actor.steerAngle Local steerSpeed:Float = actor.steerSpeed Local speed:Float = actor.speed Local power:Float = actor.power Local move:b2Vec2 speed = (speed * power) move = New b2Vec2(Cos(angle) * speed, Sin(angle) * speed) F_KillOrthogonalVelocity(body) body.SetAngle(F_DegToRad(steerAngle)) body.ApplyForce(move, body.GetWorldCenter()) body.SetLinearVelocity(move) ' F_DebugMessage("Speed: " + speed) ' F_DebugMessage("Power: " + power) End Function F_KillOrthogonalVelocity:Void(body:b2Body) 'I ripped-off this function from another example elswhere on the internet, and then I modified it to work with Monkey-X. 'In Laymen's terms it takes sideways force and then applies it in a forward direction. Local localVelocity:b2Vec2 Local velocity:b2Vec2 Local sidewaysAxis:b2Vec2 localVelocity = New b2Vec2(0, 0) velocity = body.GetLinearVelocityFromLocalPoint(localVelocity) sidewaysAxis = body.GetTransform().R.col2.Copy() sidewaysAxis.Multiply(b2Math.Dot(velocity, sidewaysAxis)) body.SetLinearVelocity(sidewaysAxis) End 'Get the scales of the width and height of the screen, so that graphics fit in accross different sized devices. Function F_ScaleX:Float() Return DeviceWidth() / (DeviceWidth() * WORLDSCALE) End Function F_ScaleY:Float() Return DeviceHeight() / (DeviceHeight() * WORLDSCALE) End 'Convert degrees to radians. Function F_DegToRad:Float(deg:Float) Return (deg * PI) / 180 End 'Convert radians to degrees. Function F_RadToDeg:Float(rad:Float) Return (180 / PI) * rad End 'For debugging purposes. This works from anywhere in the program, not just the render method, only use when necessary as DrawText seems to slow down Box2D debug rendering. 'Data is cleared after rendering. Function F_DebugMessage:Void(message:String = "") Local index:Int index = debugMessageList.Length() debugMessageList = debugMessageList.Resize(index + 1) debugMessageList[index] = message End 'Call this as the final command in the render method. Function F_DisplayDebugMessages:Void() Local index:Int For index = 0 To(debugMessageList.Length() -1) DrawText(debugMessageList[index], 10, index * 20) Next debugMessageList = debugMessageList.Resize(0) End --v

Monkey-X Box2D: Learning from my perspective... Hopefully!

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