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comparison src/video/SDL_blit.h @ 4293:63b54ddd38ea SDL-1.2

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Fixed bug #627 Increased accuracy of alpha blend calculation
author Sam Lantinga <slouken@libsdl.org>
date Sat, 10 Oct 2009 07:48:15 +0000
parents a1b03ba2fcd0
children 2d00ed718720
comparison
equal deleted inserted replaced
4292:464126f4c7db 4293:63b54ddd38ea
382 } 382 }
383 383
384 /* Blend the RGB values of two Pixels based on a source alpha value */ 384 /* Blend the RGB values of two Pixels based on a source alpha value */
385 #define ALPHA_BLEND(sR, sG, sB, A, dR, dG, dB) \ 385 #define ALPHA_BLEND(sR, sG, sB, A, dR, dG, dB) \
386 do { \ 386 do { \
387 dR = (((sR-dR)*(A))>>8)+dR; \ 387 dR = (((sR-dR)*(A)+255)>>8)+dR; \
388 dG = (((sG-dG)*(A))>>8)+dG; \ 388 dG = (((sG-dG)*(A)+255)>>8)+dG; \
389 dB = (((sB-dB)*(A))>>8)+dB; \ 389 dB = (((sB-dB)*(A)+255)>>8)+dB; \
390 } while(0)
391
392 /* Blend the RGB values of two Pixels based on a source alpha value */
393 #define ACCURATE_ALPHA_BLEND(sR, sG, sB, sA, dR, dG, dB) \
394 do { \
395 unsigned tR, tG, tB, tA; \
396 tA = 255 - sA; \
397 tR = 1 + (sR * sA) + (dR * tA); \
398 dR = (tR + (tR >> 8)) >> 8; \
399 tG = 1 + (sG * sA) + (dG * tA); \
400 dG = (tG + (tG >> 8)) >> 8; \
401 tB = 1 + (sB * sA) + (dB * tA); \
402 dB = (tB + (tB >> 8)) >> 8; \
403 } while(0) 390 } while(0)
404 391
405 392
406 /* This is a very useful loop for optimizing blitters */ 393 /* This is a very useful loop for optimizing blitters */
407 #if defined(_MSC_VER) && (_MSC_VER == 1300) 394 #if defined(_MSC_VER) && (_MSC_VER == 1300)