Konrad
This kind of blending is rather quite useful and in my opinion should be available for all renderers. I do need it myself, but since I didn't want to use a custom blending mode which is supported only by certain renderers (e.g. not in software which is quite important for me) I did write implementation of SDL_BLENDMODE_MUL for all renderers altogether.
SDL_BLENDMODE_MUL implements following equation:
dstRGB = (srcRGB * dstRGB) + (dstRGB * (1-srcA))
dstA = (srcA * dstA) + (dstA * (1-srcA))
Background:
https://i.imgur.com/UsYhydP.png
Blended texture:
https://i.imgur.com/0juXQcV.png
Result for SDL_BLENDMODE_MOD:
https://i.imgur.com/wgNSgUl.png
Result for SDL_BLENDMODE_MUL:
https://i.imgur.com/Veokzim.png
I think I did cover all possibilities within included patch, but I didn't write any tests for SDL_BLENDMODE_MUL, so it would be lovely if someone could do it.
SDL now builds with gcc 7.2 with the following command line options:
-Wall -pedantic-errors -Wno-deprecated-declarations -Wno-overlength-strings --std=c99
Simon Hug
The RGBA_FROM_PIXEL macro in src/video/blit.h [1] is not designed to work with more than 8 bits per channel and the ARGB2101010 format makes it read outside of the array bounds causing access violations. This can happen during blitting with the BlitNtoNPixelAlpha and SDL_Blit_Slow functions.
When SDL_InitFormat tries to calculate the loss of the channels [2], the Uint8 will wrap around and it will end up at 254 for the 10-bit channels. Clearly way over the 9 entries of the SDL_expand_byte array. (Not that a signed integer would help.) Then the macro tries to access the lookup table with the channel value which could be up to 1023. If the previous indirection didn't cause an access violation this one will.
I guess it's not worth modifying this macro for a format that only a few will use. It will only make the other blitters slower. I don't have good ideas to solve this issue.
Attached is a test case that does three blits. A copy one that work and the two that use the functions mentioned above.
[1] https://hg.libsdl.org/SDL/file/cd1994d4f3c6/src/video/SDL_blit.h#l303
[2] https://hg.libsdl.org/SDL/file/cd1994d4f3c6/src/video/SDL_pixels.c#l540
The internal function SDL_EGL_LoadLibrary() did not delete and remove a mostly
uninitialized data structure if loading the library first failed. A later try to
use EGL then skipped initialization and assumed it was previously successful
because the data structure now already existed. This led to at least one crash
in the internal function SDL_EGL_ChooseConfig() because a NULL pointer was
dereferenced to make a call to eglBindAPI().
