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.
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.
Anthony Pesch
* Remove triple buffering support. As far as I can tell, this goes against the libdrm API; the EGL implementations themselves control the buffering. Removing it isn't absolutely necessary as it seemingly works on the Pi at least, but I noticed this while doing my work and explained my reasoning in the commit.
* Replace the crtc_ready logic which allocates an extra bo to perform the initial CRTC configuration (which is required before calling drmModePageFlip) with a call to drmModeSetCrtc after the front and back buffers are allocated, avoiding this allocation.
* Standardized the SDL_*Data variable names and null checks to improve readability. Given that there were duplicate fields in each SDL_*Data structure, having generic names such as "data" at times was very confusing.
* Removed unused fields from the SDL_*Data structures and moves all display related fields out of SDL_VideoData and into SDL_DisplayData. Not required since the code only supports a single display right now, but this was helpful in reading and understanding the code initially.
* Implement KMSDRM_GetDisplayModes / KMSDRM_SetDisplayMode to provide dynamic modeset support.
These changes have been tested on a Raspberry Pi 4 and a Dell XPS laptop with an HD 520.
As an update, I went back over the triple buffer changes and left them in. I didn't entirely get the code originally, I had just seen it calling KMSDRM_gbm_surface_lock_front_buffer twice for a single swap and had removed it because I was paranoid of bugs stemming from it while working on the modeset changes.
I've made a few small changes to the logic that had thrown me off originally and rebased the changes:
* The condition wrapping the call to release buffer was incorrect.
* The first call to KMSDRM_gbm_surface_lock_front_buffer has been removed. I don't understand why it existed.
* Added additional comments describing what was going on in the code (as it does fix the buffer release pattern of the original code before it).
Manuel Alfayate Corchete
This fixes a problem with KMSDRM on some graphics hardware where only bigger cursor sizes are supported, such as current Intel gfx. (The kernel-side driver is what limits this: had to look for failing IOCTLs...)
That caused SDL_SetCursor() to fail silently, and we were left with a missing cursor without further explanation.
With this patch, different "standard" sizes are tried and a bigger one is used (with an intermediate and clean buffer only used to write the new cursor to the BO where it will live after) if we get, let's say, 16x16 which is pretty common but our hardware does not support that.
Manuel
The attached patch adds support for KMS/DRM context graphics.
It builds with no problem on X86_64 GNU/Linux systems, provided the needed libraries are present, and on ARM GNU/Linux systems that have KMS/DRM support and a GLES2 implementation.
Tested on Raspberry Pi: KMS/DRM is what the Raspberry Pi will use as default in the near future, once the propietary DispmanX API by Broadcom is overtaken by open graphics stack, it's possible to boot current Raspbian system in KMS mode by adding "dtoverlay=vc4-kms-v3d" to config.txt on Raspbian's boot partition.
X86 systems use KMS right away in every current GNU/Linux system.
Simple build instructions:
$./autogen.sh
$./configure --enable-video-kmsdrm
$make
