Some screenshots are empty black rectangles

[jiffygist]

When I take a clean PNG screenshot in Doom and Strife the image is entirely black, in case of PCX screenshot the image has status bar on.
In Heretic and Hexen the "take clean screenshot" key is completely ignored.

screenshots.zip

[Noseey]

When I take a clean PNG screenshot in Doom and Strife the image is entirely black, in case of PCX screenshot the image has status bar on.

I tried to reproduce it with Doom using the current dev build and the 7.0.0 Version, but it seems to work fine on my side. What version are you using and do you have similar issues with screenshots in other games?

In Heretic and Hexen the "take clean screenshot" key is completely ignored.

This one is easier to explain: only the binding of the key is present, but it lacks any functionality so far. Still needs to be implemented.😉

[fabiangreffrath]

That's probably the sdl2-compat library?

[jiffygist]

I'm using latest master, my sdl2 version is 2.32.6 and my libpng is 1.6.47
Tested it a bit more, it only happens sometimes (out of 5 screenshots 2 are black), usually it's the first one that's empty
Also it doesn't happen when I export LIBGL_ALWAYS_SOFTWARE=true environment variable or set force_software_renderer 0 in the config

[Noseey]

I'm using latest master, my sdl2 version is 2.32.6 and my libpng is 1.6.47 Tested it a bit more, it only happens sometimes (out of 5 screenshots 2 are black), usually it's the first one that's empty Also it doesn't happen when I export LIBGL_ALWAYS_SOFTWARE=true environment variable or set force_software_renderer 0 in the config

I'm using sdl2 2.32.4 and the same ligpng version. I tried setting force_software_renderer 1 and took multiple screenshots in succession, but still wasn't able to reproduce yet. Since I'm using a different setup, I can not test the LIBGL_ALWAYS_SOFTWARE parameter.

If you have debug capability, maybe it is worth checking if the SDL_RenderReadPixels already returns a black pixel array. Just to see if its more on the readout of the rendering information or the writing of the PNG data:

[jiffygist]

I'm using sdl2 2.32.4 and the same ligpng version. I tried setting force_software_renderer 1 and took multiple screenshots in succession

No, it's ok with software rendering

If you have debug capability, maybe it is worth checking if the SDL_RenderReadPixels already returns a black pixel array. Just to see if its more on the readout of the rendering information or the writing of the PNG data:

Already checked, yeah it does. Return values are ok.

Also noticed it's happening with normal screenshots too, not only clean.

[Noseey]

No, it's ok with software rendering

I tried it also with hardware rendering, but still worked fine.

However, I stumbled upon this thread here:
https://discourse.libsdl.org/t/sdl-renderreadpixels-always-returns-black-rectangle/20371/4

Johnboiles claims that the SDL_RenderReadPixels reads from the backbuffer and according the sdl description: if a previous SDL_RenderPresent has been done, the backbuffer is considered invalidated. That might mean that its content is undefined.

https://wiki.libsdl.org/SDL2/SDL_RenderPresent
The backbuffer should be considered invalidated after each present; do not assume that previous contents will exist between frames. You are strongly encouraged to call SDL_RenderClear() to initialize the backbuffer before starting each new frame's drawing, even if you plan to overwrite every pixel.

Maybe you can play around with when the readout happens in the sequence and move it infront of the RenderPresent to see if the issue disappears. (e. g. if you have a post-rendering hook present, see line 2076 of i_video.c)