Fast Colour Blending Function

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mike_g	Created : 23 August 2007 Edited : 23 August 2007 Language : Blitz Fast Colour Blending Function
Heres a fast colour blending function using some techniques I was shown over on the DBF boards. I thought I would share it as its something I find it useful. It avoids floating point maths and RGB colour conversions. \|edit\| Oh, and the alpha component should be a number between 0 and 255 \|edit\| Function ColourBlend( rgb_1, rgb_2, alpha_1 ) alpha_2 = 256 - alpha_1 rb_1 = ((rgb_1 And $00FF00FF) * alpha_1) And $FF00FF00 g_1 = ((rgb_1 And $0000FF00) * alpha_1) And $00FF0000 rb_2 = ((rgb_2 And $00FF00FF) * alpha_2) And $FF00FF00 g_2 = ((rgb_2 And $0000FF00) * alpha_2) And $00FF0000 rb_1 = rb_1 + rb_2 g_1 = g_1 + g_2 Return (rb_1 Or g_1) Sar 8 End Function --v And heres a test prog for it: Global cursor = CreateImage(100, 100) SetBuffer ImageBuffer(cursor) For i = 1 To 10 Color (i20), (i2), (i8) Oval (i10), (i10), 100-(i10), 100-(i10) , 1 Next SetBuffer BackBuffer() RotateImage cursor, 180 Global x_pos = 10 Global y_pos = 10 Global alpha = 127 While Not KeyHit(1) Cls DrawText() LockBuffer BackBuffer() DrawBackGround() DrawAlphaSprite() UnlockBuffer BackBuffer() KeyInput() Flip False Wend ;---------------------------------------------------------------------; ;********************* COLOUR BLEND ****************************; ;---------------------------------------------------------------------; Function ColourBlend( rgb_1, rgb_2, alpha_1 ) alpha_2 = 256 - alpha_1 rb_1 = ((rgb_1 And $00FF00FF) alpha_1) And $FF00FF00 g_1 = ((rgb_1 And $0000FF00) * alpha_1) And $00FF0000 rb_2 = ((rgb_2 And $00FF00FF) * alpha_2) And $FF00FF00 g_2 = ((rgb_2 And $0000FF00) * alpha_2) And $00FF0000 rb_1 = rb_1 + rb_2 g_1 = g_1 + g_2 Return (rb_1 Or g_1) Sar 8 End Function ;---------------------------------------------------------------------; ;********************** DEMO FUNCTIONS ***************************; ;---------------------------------------------------------------------; Function DrawText() Color 255, 255, 255 Text 280, 20, "MOVE WITH" Text 280, 40, "ARROW KEYS" Text 280, 60, "- AND = ALTERS" Text 280, 80, "ALPHA" End Function Function DrawBackground() For y = 0 To 255 Color 100, 100+(y/2), y Line 20, 20+y, 275, 20+y Next End Function Function DrawAlphaSprite() LockBuffer ImageBuffer(cursor) For y = 1 To 99 draw_y = y+y_pos For x = 1 To 99 col1 = ReadPixelFast(x, y, ImageBuffer(cursor)) If col1 <> -16777216 col2 = ReadPixelFast(x+x_pos, draw_y) WritePixelFast(x+x_pos, draw_y, ColourBlend( col1, col2, alpha )) EndIf Next Next UnlockBuffer ImageBuffer(cursor) End Function Function KeyInput() If KeyDown(203) x_pos = x_pos - 3 If KeyDown(205) x_pos = x_pos + 3 If KeyDown(200) And y_pos > 3 Then y_pos = y_pos - 3 If KeyDown(208) And y_pos < GraphicsHeight()-100 Then y_pos = y_pos + 3 If KeyDown(12) And alpha > 3 Then alpha = alpha -3 If KeyDown(13) And alpha < 253 Then alpha = alpha +3 End Function --v

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Friday, 24 August 2007, 00:21
shroom_monk	That looks pretty useful. I could use that in future...

Fast Colour Blending Function

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