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Review ImageDraw() alpha blending

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Not sure if math is ok... just left a commented piece of code that uses pre-multiplied alpha.
This commit is contained in:
Ray 2018-04-03 12:42:22 +02:00
parent 0c0ff2802e
commit 533780aadf
1 changed files with 20 additions and 1 deletions
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21
src/textures.c
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@ -1337,11 +1337,30 @@ void ImageDraw(Image *dst, Image src, Rectangle srcRec, Rectangle dstRec)
// Alpha blending implementation
dstCol = dstPixels[j*dst->width + i];
srcCol = srcPixels[(j - dstRec.y)*dstRec.width + (i - dstRec.x)];
/*
// Pre-multiply alpha
Vector3 dstColf = { (float)dstCol.r/255.0f, (float)dstCol.g/255.0f, (float)dstCol.b/255.0f };
dstColf = Vector3Multiply(dstColf, (float)dstCol.a/255.0f);
Vector3 srcColf = { (float)srcCol.r/255.0f, (float)srcCol.g/255.0f, (float)srcCol.b/255.0f };
srcColf = Vector3Multiply(srcColf, (float)srcCol.a/255.0f);
dstColf = Vector3Add(dstColf, srcColf);
if (dstColf.x > 1.0f) dstColf.x = 1.0f;
if (dstColf.y > 1.0f) dstColf.y = 1.0f;
if (dstColf.z > 1.0f) dstColf.z = 1.0f;
dstCol.r = (unsigned char)(dstColf.x*255.0f);
dstCol.g = (unsigned char)(dstColf.y*255.0f);
dstCol.b = (unsigned char)(dstColf.z*255.0f);
dstCol.a = srcCol.a;
*/
dstCol.r = ((srcCol.a*(srcCol.r - dstCol.r)) >> 8) + dstCol.r;
dstCol.g = ((srcCol.a*(srcCol.g - dstCol.g)) >> 8) + dstCol.g;
dstCol.b = ((srcCol.a*(srcCol.b - dstCol.b)) >> 8) + dstCol.b;
dstCol.a = ((srcCol.a*(srcCol.a - dstCol.a)) >> 8) + dstCol.a;
dstCol.a = srcCol.a;
dstPixels[j*dst->width + i] = dstCol;