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fix: update blend functions to respect alpha channel (fixes #82) (#83)

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* fix: update linear_blend to respect alpha channel

* fix: update masked_blend to respect alpha channel

Unclear if this is the right implementation.

* misc: remove unnecessary fixed declaration

* misc: update mask_blend

* update changes.md

* misc: fix typo in changes.md
This commit is contained in:
Brendan Hagan
2024-08-23 19:49:56 -04:00
committed by GitHub
parent ddd49b50d7
commit bd875779f5
2 changed files with 41 additions and 9 deletions
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src/gfx/blend_image.cpp
+36 -6
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@@ -55,23 +55,53 @@ void linear_blend(Image& img1, const Image& img2, double x1,double y1, double x2
data1 += 3;
data2 += 3;
}
}
// Blend Alpha for the two images.
if (img1.HasAlpha() && img2.HasAlpha()) {
Byte *alpha1 = img1.GetAlpha(), *alpha2 = img2.GetAlpha();
for (int y = 0; y < height; ++y) {
for (int x = 0; x < width; ++x) {
int mult = x * xm + y * ym + d;
if (mult < 0) mult = 0;
if (mult > fixed) mult = fixed;
alpha1[0] = alpha1[0] + mult * (alpha2[0] - alpha1[0]) / fixed;
alpha1 += 1;
alpha2 += 1;
}
}
}
}
// ----------------------------------------------------------------------------- : Mask Blend
void mask_blend(Image& img1, const Image& img2, const Image& mask) {
if (img2.GetWidth() != img1.GetWidth() || img2.GetHeight() != img1.GetHeight()
|| mask.GetWidth() != img1.GetWidth() || mask.GetHeight() != img1.GetHeight()) {
throw Error(_("Images used for blending must have the same size"));
int width = img1.GetWidth(), height = img1.GetHeight();
if (img2.GetWidth() != width || img2.GetHeight() != height) {
throw Error(_("Images used for blending in masked_blend function must have the same size"));
}
UInt size = img1.GetWidth() * img1.GetHeight() * 3;
if (mask.GetWidth() != width || mask.GetHeight() != height) {
throw Error(_("Mask used for blending in masked_blend function must have the same size as the images"));
}
UInt size = width * height;
// these have the following structure:
// [pixel1red, pixel1green, pixel1blue, pixel2red, pixel2green, pixel2blue, pixel3red, etc...]
Byte *data1 = img1.GetData(), *data2 = img2.GetData(), *dataM = mask.GetData();
// for each subpixel...
for (UInt i = 0 ; i < size ; ++i) {
for (UInt i = 0; i < (size * 3); ++i) {
data1[i] = (data1[i] * dataM[i] + data2[i] * (255 - dataM[i])) / 255;
}
if (img1.HasAlpha() && img2.HasAlpha()) {
// these have the following structure:
// [pixel1alpha, pixel2alpha, pixel3alpha, etc...]
Byte *alpha1 = img1.GetAlpha(), *alpha2 = img2.GetAlpha();
for (UInt i = 0; i < size; ++i) {
// use mask's red channel to blend alpha (all mask channels should be identical since it's grey scale)
alpha1[i] = (alpha1[i] * dataM[i * 3] + alpha2[i] * (255 - dataM[i * 3])) / 255;
}
}
}
// ----------------------------------------------------------------------------- : Alpha