Stop importing DMA-BUFs on wl_surface.commit

[emersion]

Right now, we create wlr_client_buffer objects on surface commit. This works fine for wl_shm buffers (especially when we can just update the previous buffer), however this imports DMA-BUFs via EGL too often. We'd only need to import them once when the wl_buffer is created, and then we could re-use the same EGLImage for all subsequent commits.

Some drivers are known to have slow DMA-BUF import paths. This also makes us import too often the DMA-BUFs to KMS when using direct scan-out.

[emersion]

Well, apparently re-importing the DMA-BUFs is necessary on some drivers to see the changes to the underlying buffer.

[emersion]

However, when we use external EGL textures, the underlying changes are guaranteed to be visible without re-importing.

Also, it seems like to see the external changes for a regular texture (not external), we don't need to re-import the DMA-BUF as an EGLImage -- we can just re-create the texture from the same EGLImage.

[J0nnyMak0]

This proposal sounds like it can potentially fix #2636?

[emersion]

I don't think so. Before the regression we were already importing DMA-BUFs on each commit.

[emersion]

We could add a wlr_texture_invalidate function. However, it's important to note that shm buffers work pretty differently from DMA-BUFs.

With the GLES2 renderer and a DMA-BUF texture:

• On wl_buffer creation: import as an EGLImage
• On wl_surface.commit: re-create the texture if it's not EXTERNAL_OES

With the GLES2 renderer and a shm texture:

• On wl_buffer creation: do nothing
• On wl_surface.commit: upload the damaged region to the texture

With the Pixman renderer and a shm texture:

• On wl_buffer creation: we can't hook into that, it's all handled inside libwayland
• On wl_surface.commit: create the pixman image
• When accessing the pixman image, make sure to call wl_shm_buffer_{begin,end}_access

[emersion]

#2851 tries to address this issue by passing a wlr_buffer reference to the renderer for upload/import. The renderer can then make the decision to leave the buffer unlocked (upload: shm+GLES2) or lock the buffer (import: DMA-BUF+GLES2 or shm+Pixman).

This does require us to always have a wlr_buffer around for each wl_buffer. This is easy enough to do for linux-dmabuf buffers, but is a little bit more tedious with wl_shm buffers (because it's all implemented by libwayland, and wlr_buffer_impl.get_data_ptr does not play well with wl_shm_buffer_begin_access/end_access)

[emersion]

Fixed in #2851