This bug report was migrated from our old Bugzilla tracker.

Reported in version: don't know
Reported for operating system, platform: Linux, x86_64

Comments on the original bug report:

On 2017-10-29 02:08:57 +0000, Ellie wrote:

SDL_HideWindow will also suspend rendering with SDL_RenderPresent(). I planned to use a hidden window for offscreen rendering (the main window is handled by something else than SDL and has no OpenGL context) but due to this problem I can't. It'd be nice if there was a way to make this work without being forced to have an additional useless window visible.

On 2017-10-29 02:11:18 +0000, Ellie wrote:

I forgot to mention what I'm actually doing: I'm using SDL_RenderReadPixels to extract the pixels after rendering a frame, and with the hidden window I simply get a pitch black texture instead of the actual image. If I change nothing else except commenting the line that hides the window, everything works fine and I can extract the proper image.

On 2017-12-27 12:09:47 +0000, Ellie wrote:

Anyone?

I need off-screen rendering in a couple of places, and this makes it really challenging ot use SDL2 for that purpose.

Any sort of feedback on whether this is unavoidable per design or a fixable bug would already be nice, because if there is no hope this ever gets addressed I'll have to look into other options than SDL2.

On 2018-01-03 18:01:49 +0000, Sam Lantinga wrote:

Ryan, can you take a look at this? Is there something we need to set to allow off-screen rendering?

On 2018-01-04 18:50:00 +0000, Ryan C. Gordon wrote:

Does this work if you use a render target instead of rendering directly to the hidden window?

--ryan.

On 2018-01-04 21:19:50 +0000, Ellie wrote:

I didn't try render targets, because the API doesn't appear to support SDL_TEXTUREACCESS_TARGET and SDL_TEXTUREACCESS_STREAMING at the same time since they are enumerations and not flags. Therefore, I'd either need a way to combine SDL_TEXTUREACCESS_TARGET and SDL_TEXTUREACCESS_STREAMING on one SDL_Texture, or I have no other way than to rely on SDL_RenderReadPixels() to get the end result again, which is what I used in the end. Did I miss something so that I can do this with render targets without using OpenGL code myself?

On 2018-02-02 03:26:31 +0000, Ryan C. Gordon wrote:

So my suspicion is that X11 won't render to an unmapped window; hiding a window unmaps it. You might be able to place the window entirely offscreen (at like, position -10000,-10000) to get around this, but I haven't tried.

That being said: SDL_RenderReadPixels() works from render targets, and you don't need to mark them as streaming. I think these will work even if the window is unmapped.

--ryan.

On 2018-02-07 18:27:50 +0000, Ryan C. Gordon wrote:

Going to close this as WONTFIX for now. If you try any of these things (moving the window way offscreen or a render target) and nothing works, we can brainstorm some more.

--ryan.