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Corrected alpha blending on ImageDraw()

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This commit is contained in:
raysan5 2018-04-29 18:39:57 +02:00
parent dff1028466
commit c51203ae7e
1 changed files with 23 additions and 29 deletions
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52
src/textures.c
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@ -1312,44 +1312,38 @@ void ImageDraw(Image *dst, Image src, Rectangle srcRec, Rectangle dstRec)
UnloadImage(srcCopy); // Source copy not required any more...
Color srcCol, dstCol;
Vector4 fsrc, fdst, fout; // float based versions of pixel data
// Blit pixels, copy source image into destination
// TODO: Probably out-of-bounds blitting could be considered here instead of so much cropping...
for (int j = dstRec.y; j < (dstRec.y + dstRec.height); j++)
{
for (int i = dstRec.x; i < (dstRec.x + dstRec.width); i++)
{
// Alpha blending implementation
dstCol = dstPixels[j*dst->width + i];
srcCol = srcPixels[(j - dstRec.y)*dstRec.width + (i - dstRec.x)];
// Alpha blending (https://en.wikipedia.org/wiki/Alpha_compositing)
/*
// 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;
*/
fdst = ColorNormalize(dstPixels[j*dst->width + i]);
fsrc = ColorNormalize(srcPixels[(j - dstRec.y)*dstRec.width + (i - dstRec.x)]);
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;
fout.w = fsrc.w + fdst.w*(1.0f - fsrc.w);
if (fout.w <= 0.0f)
{
fout.x = 0.0f;
fout.y = 0.0f;
fout.z = 0.0f;
}
else
{
fout.x = (fsrc.x*fsrc.w + fdst.x*fdst.w*(1 - fsrc.w))/fout.w;
fout.y = (fsrc.y*fsrc.w + fdst.y*fdst.w*(1 - fsrc.w))/fout.w;
fout.z = (fsrc.z*fsrc.w + fdst.z*fdst.w*(1 - fsrc.w))/fout.w;
}
dstPixels[j*dst->width + i] = dstCol;
dstPixels[j*dst->width + i] = (Color){ (unsigned char)(fout.x*255.0f),
(unsigned char)(fout.y*255.0f),
(unsigned char)(fout.z*255.0f),
(unsigned char)(fout.w*255.0f) };
// TODO: Support other blending options
}