SDL2 texture blend help

[Dmitry]

On Monday, 11 December 2017 at 04:57:44 UTC, Ivan Trombley wrote:
> Experimenting with compositing images in SDL2, I get a dark 
> edge around my textures. In the image below, you can see the 
> top example where I composite the cyan image on top of the 
> blue/magenta image looks correct but the bottom example, which 
> is done using SDL_RenderCopy is not correct.

Won't this help?
https://stackoverflow.com/questions/45781683/how-to-get-correct-sourceover-alpha-compositing-in-sdl-with-opengl