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Fixed signedness issue when blitting on a big endian platform, as reported by capehill

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For example, if sR is 0 and dR is 255, we will get -255*sA casted to an unsigned value. Basically results are quite large numbers instead of the expected 0-255 range.
This commit is contained in:
Sam Lantinga 2017-01-05 08:16:39 -08:00
parent e6e6613ca4
commit d024c724d1
1 changed files with 7 additions and 7 deletions
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14
src/video/SDL_blit.h
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@ -443,19 +443,19 @@ do { \
/* Blend the RGB values of two pixels with an alpha value */
#define ALPHA_BLEND_RGB(sR, sG, sB, A, dR, dG, dB) \
do { \
dR = ((((unsigned)(sR-dR)*(unsigned)A)/255)+dR); \
dG = ((((unsigned)(sG-dG)*(unsigned)A)/255)+dG); \
dB = ((((unsigned)(sB-dB)*(unsigned)A)/255)+dB); \
dR = (Uint8)((((int)(sR-dR)*A)/255)+dR); \
dG = (Uint8)((((int)(sG-dG)*A)/255)+dG); \
dB = (Uint8)((((int)(sB-dB)*A)/255)+dB); \
} while(0)
/* Blend the RGBA values of two pixels */
#define ALPHA_BLEND_RGBA(sR, sG, sB, sA, dR, dG, dB, dA) \
do { \
dR = ((((unsigned)(sR-dR)*(unsigned)sA)/255)+dR); \
dG = ((((unsigned)(sG-dG)*(unsigned)sA)/255)+dG); \
dB = ((((unsigned)(sB-dB)*(unsigned)sA)/255)+dB); \
dA = ((unsigned)sA+(unsigned)dA-((unsigned)sA*dA)/255); \
dR = (Uint8)((((int)(sR-dR)*sA)/255)+dR); \
dG = (Uint8)((((int)(sG-dG)*sA)/255)+dG); \
dB = (Uint8)((((int)(sB-dB)*sA)/255)+dB); \
dA = (Uint8)((int)sA+dA-((int)sA*dA)/255); \
} while(0)