Hi,

there seems to be a 7 years old duplicate but I use a current version so I dare to submit this. I'm trying to create a simple shadow of a texture by setting r=g=b=0 and cutting alpha in half:

Uint32 pixels[w*h];
int pitch = w*sizeof(Uint32);
Uint8 r,g,b,a;
Uint32 pft = 0;

SDL_SetRenderTarget(mrc, tex); // holds a valid texture of type RGBA8888
SDL_QueryTexture(tex, &pft, 0, 0, 0); // needed for MapRGBA anyways
SDL_PixelFormat* pf = SDL_AllocFormat(pft); /* XXX free this later? */
SDL_RenderReadPixels(mrc, NULL, pft, pixels, pitch)

... doing my stuff ...

SDL_UpdateTexture(tex, NULL, pixels, pitch);

This works. But SDL_RenderReadPixels(mrc, NULL, 0, pixels, pitch) should work as well according to the docs but it does not. Even if I do not do anything in between reading and updating pixels. The pixels look greenish indicating a different pixel format although it should be the same like the one queried with SDL_QueryTexture as the texture is the current target as well.

Regards,
Michael Speck