diff options
| author | Sam Lantinga <slouken@libsdl.org> | 2013-07-23 08:06:49 -0700 |
|---|---|---|
| committer | Sam Lantinga <slouken@libsdl.org> | 2013-07-23 08:06:49 -0700 |
| commit | 4862c1fc30a737198e7d5390dc52c3f3de5c9611 (patch) | |
| tree | 18c2f872662696a3664be385643078d5d213b4d5 /include | |
| parent | 03cc44af0339672f1e52d692571711cdf705aabd (diff) | |
Updated blend semantics so blending uses the following formula:
dstRGB = (srcRGB * srcA) + (dstRGB * (1-srcA))
dstA = srcA + (dstA * (1-srcA))
This allows proper compositing semantics without requiring premultiplied alpha.
Needs full unit test coverage and bug fixes!
Diffstat (limited to 'include')
| -rw-r--r-- | include/SDL_blendmode.h | 15 | ||||
| -rw-r--r-- | include/SDL_surface.h | 30 |
2 files changed, 25 insertions, 20 deletions
diff --git a/include/SDL_blendmode.h b/include/SDL_blendmode.h index 37c475aefd..85aa474595 100644 --- a/include/SDL_blendmode.h +++ b/include/SDL_blendmode.h @@ -39,10 +39,17 @@ extern "C" { */ typedef enum { - SDL_BLENDMODE_NONE = 0x00000000, /**< No blending */ - SDL_BLENDMODE_BLEND = 0x00000001, /**< dst = (src * A) + (dst * (1-A)) */ - SDL_BLENDMODE_ADD = 0x00000002, /**< dst = (src * A) + dst */ - SDL_BLENDMODE_MOD = 0x00000004 /**< dst = src * dst */ + SDL_BLENDMODE_NONE = 0x00000000, /**< no blending + dstRGBA = srcRGBA */ + SDL_BLENDMODE_BLEND = 0x00000001, /**< alpha blending + dstRGB = (srcRGB * srcA) + (dstRGB * (1-srcA)) + dstA = srcA + (dstA * (1-srcA)) */ + SDL_BLENDMODE_ADD = 0x00000002, /**< additive blending + dstRGB = (srcRGB * srcA) + dstRGB + dstA = dstA */ + SDL_BLENDMODE_MOD = 0x00000004 /**< color modulate + dstRGB = srcRGB * dstRGB + dstA = dstA */ } SDL_BlendMode; /* Ends C function definitions when using C++ */ diff --git a/include/SDL_surface.h b/include/SDL_surface.h index 76fcfde32c..fece797437 100644 --- a/include/SDL_surface.h +++ b/include/SDL_surface.h @@ -399,44 +399,42 @@ extern DECLSPEC int SDLCALL SDL_FillRects * * The blit function should not be called on a locked surface. * - * The blit semantics for surfaces with and without alpha and colorkey + * The blit semantics for surfaces with and without blending and colorkey * are defined as follows: * \verbatim RGBA->RGB: - SDL_SRCALPHA set: - alpha-blend (using alpha-channel). + Source surface blend mode set to SDL_BLENDMODE_BLEND: + alpha-blend (using the source alpha-channel and per-surface alpha) SDL_SRCCOLORKEY ignored. - SDL_SRCALPHA not set: + Source surface blend mode set to SDL_BLENDMODE_NONE: copy RGB. if SDL_SRCCOLORKEY set, only copy the pixels matching the RGB values of the source color key, ignoring alpha in the comparison. RGB->RGBA: - SDL_SRCALPHA set: - alpha-blend (using the source per-surface alpha value); - set destination alpha to opaque. - SDL_SRCALPHA not set: + Source surface blend mode set to SDL_BLENDMODE_BLEND: + alpha-blend (using the source per-surface alpha) + Source surface blend mode set to SDL_BLENDMODE_NONE: copy RGB, set destination alpha to source per-surface alpha value. both: if SDL_SRCCOLORKEY set, only copy the pixels matching the source color key. RGBA->RGBA: - SDL_SRCALPHA set: - alpha-blend (using the source alpha channel) the RGB values; - leave destination alpha untouched. [Note: is this correct?] + Source surface blend mode set to SDL_BLENDMODE_BLEND: + alpha-blend (using the source alpha-channel and per-surface alpha) SDL_SRCCOLORKEY ignored. - SDL_SRCALPHA not set: + Source surface blend mode set to SDL_BLENDMODE_NONE: copy all of RGBA to the destination. if SDL_SRCCOLORKEY set, only copy the pixels matching the RGB values of the source color key, ignoring alpha in the - comparison. + comparison. RGB->RGB: - SDL_SRCALPHA set: - alpha-blend (using the source per-surface alpha value). - SDL_SRCALPHA not set: + Source surface blend mode set to SDL_BLENDMODE_BLEND: + alpha-blend (using the source per-surface alpha) + Source surface blend mode set to SDL_BLENDMODE_NONE: copy RGB. both: if SDL_SRCCOLORKEY set, only copy the pixels matching the |