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Correction for alpha blending issues in texture mod compositing (#9029)

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Warr1024 2019-10-18 13:17:35 -04:00 committed by SmallJoker
parent b7e358703f
commit 15b6922ae6
1 changed files with 20 additions and 2 deletions
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22
src/client/tile.cpp
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@ -1811,6 +1811,24 @@ bool TextureSource::generateImagePart(std::string part_of_name,
return true; return true;
} }
/*
Calculate the color of a single pixel drawn on top of another pixel.
This is a little more complicated than just video::SColor::getInterpolated
because getInterpolated does not handle alpha correctly. For example, a
pixel with alpha=64 drawn atop a pixel with alpha=128 should yield a
pixel with alpha=160, while getInterpolated would yield alpha=96.
*/
static inline video::SColor blitPixel(const video::SColor &src_c, const video::SColor &dst_c, u32 ratio)
{
if (dst_c.getAlpha() == 0)
return src_c;
video::SColor out_c = src_c.getInterpolated(dst_c, (float)ratio / 255.0f);
out_c.setAlpha(dst_c.getAlpha() + (255 - dst_c.getAlpha()) *
src_c.getAlpha() * ratio / (255 * 255));
return out_c;
}
/* /*
Draw an image on top of an another one, using the alpha channel of the Draw an image on top of an another one, using the alpha channel of the
source image source image
@ -1830,7 +1848,7 @@ static void blit_with_alpha(video::IImage *src, video::IImage *dst,
s32 dst_y = dst_pos.Y + y0; s32 dst_y = dst_pos.Y + y0;
video::SColor src_c = src->getPixel(src_x, src_y); video::SColor src_c = src->getPixel(src_x, src_y);
video::SColor dst_c = dst->getPixel(dst_x, dst_y); video::SColor dst_c = dst->getPixel(dst_x, dst_y);
dst_c = src_c.getInterpolated(dst_c, (float)src_c.getAlpha()/255.0f); dst_c = blitPixel(src_c, dst_c, src_c.getAlpha());
dst->setPixel(dst_x, dst_y, dst_c); dst->setPixel(dst_x, dst_y, dst_c);
} }
} }
@ -1853,7 +1871,7 @@ static void blit_with_alpha_overlay(video::IImage *src, video::IImage *dst,
video::SColor dst_c = dst->getPixel(dst_x, dst_y); video::SColor dst_c = dst->getPixel(dst_x, dst_y);
if (dst_c.getAlpha() == 255 && src_c.getAlpha() != 0) if (dst_c.getAlpha() == 255 && src_c.getAlpha() != 0)
{ {
dst_c = src_c.getInterpolated(dst_c, (float)src_c.getAlpha()/255.0f); dst_c = blitPixel(src_c, dst_c, src_c.getAlpha());
dst->setPixel(dst_x, dst_y, dst_c); dst->setPixel(dst_x, dst_y, dst_c);
} }
} }