.. so that KMSDRM_CreateDevice() can fail and SDL_VideoInit() would
move on to next bootstrap member which is kmsdrm_legacy. hopefully
fixes bug #5393.
This allows one to build Raspberry Pi versions on an ancient version of
Raspbian and get both the KMSDRM and RPI video targets built into SDL, giving
maximum binary compatibility from linking against an older glibc, etc, but
also making one library that can access video on all RPi models and OS
releases.
Previously the first card with non-empty connectors, encoders
and crtcs would be selected, however KMSDRM_VideoInit could still reject
it if the connector was not connected. This allow finding the first card
(in a multi GPU setup) that is actually connected to a display.
Manuel Alfayate Corchete
I noticed pt2-clone had problems with it's optional hardware mouse on the KMSDRM backend: cursor had a transparent block around it.
So I was investigating and it seems that a GBM cursor needs it's pixels to be alpha-premultiplied instead of straight-alpha.
A
lso, I was previously relying on "manual testing" for the cursor size, but it's far better to use whatever the DRM driver recommends via drmGetCap(): any working driver should make a size recommendation via drmGetCap(), so that's what we use now. I took this decision because I found out that the AMDGPU driver reported working cursor sizes that would appear garbled on screen, and only the recommended cursor size works.
The two are only ever called together, and combining them makes it possible
to eliminate redundant symbol loading and redundant attempts to connect
to a display server.
Manuel Alfayate Corchete
This small patch fixes the KMSDRM_CreateSurfaces() call in KMSDRM_CreateWindow(), that was segfaulting deeper into SDL internals because the windata->viddata pointer wasn't set before the KMSDRM_CreateSurfaces() call.
So that's what this small patch does.
Now, L?VE2D works perfectly well on the Raspberry Pi 3, instead of just segfaulting.
Manuel Alfayate Corchete
This patch is needed so programs that do this work as expected:
1) Start in a different video mode than the mode used by the system and then...
2) Try to go fullscreen with the mode originally used by the system via SetWindowFullScreen() with the SDL_WINDOW_FULLSCREEN_DESKTOP flag.
An example would be pt2-clone in https://github.com/8bitbubsy/pt2-clone.
This program does this:
Starts with:
video.window = SDL_CreateWindow("", SDL_WINDOWPOS_CENTERED,
SDL_WINDOWPOS_CENTERED, screenW, screenH, windowFlags);
and then, *IF* the user has configured it in fullscreen mode in its .ini, it tries to go fullscreen with the desktop mode:
SDL_SetWindowFullscreen(video.window, SDL_WINDOW_FULLSCREEN_DESKTOP);
This sequence of operations is currently failing because SDL_SetDisplayModeForDisplay() in SDL_video.c fails because display->desktop_mode is not being initialized with its correct value: SetDisplayMode() in SDL_kmsdrmvideo.c will not be able to set the mode because it detects the mode to have a driverdata of 0x0 ("if (!modedata)") and rightfully returns an error.
So, the included patch fixes this small problem, and programs that first change the video mode and then try to go fullscreen with the system video mode will now work.
The patch simply fixes an small omission, but its really needed now that dynamic video mode changing was implemented on the KMSDRM backend.
Manuel Alfayate Corchete
On the KMSDRM backend, there is no such thing as a desktop, yet some programs could (and DO) use SDL_GetGlobalMouseState().
So I think its good idea that, in KMSDRM, it returns the same mouse coordinates anyway as SDL_GetMouseState() would return. There is nothing else it could return, as far as I can understand, since there is no desktop anyway.
This small patch does precisely that.
Manuel Alfayate Corchete
The KMSDRM backend was doing things wrong because of some small (but important) misconceptions on how KMS/DRM works: to implement a largely broken non-vsync refresh mechanism, the SwapWindow() function was issuing new pageflips before previous ones had completed, thus causing EBUSY returns, buffer mismanagement, etc... resulting in general breakage on vsync disabling from apps, that would not allow vsync to work again without KMSDRM video re-initialization.
To further clarify, on most DRM drivers async pageflips are NOT working nowadays, so all issued pageflips will complete on next VBLANK, NOT ASAP (calling drmModePageFlip() with the DRM_MODE_PAGE_FLIP_ASYNC flag will return error).
The old code was assuming that can just issue a synchronous (=on VBLANK) pageflip and then pass a 0 timeout to the pull() function so we do not wait for the pageflip event, thinking that this will lead to correct non-vsynced screen updates from the program: That is plain wrong.
Each pageflip has to be waite before issuing a new one, ALWAYS. And if we do not support ASYNC pageflips on the DRM driver level, then we are forced to wait for the next VBLANK. There is no way around it.
I have also added many comments on the KMSDRM code. This is needed for future reference for me or others who may need to look at this code: KMS/DRM terminology regarding what SYNC and ASYNC mean in pageflip terms, and where to do certain things and why, is not trivial. It is not desirable or possible to invest time on researching the same concepts every time there is need to dive into this code. So please leave all these comments in the patch.
