Screencasting with xdg-desktop-portal not working for 4K

[tadeokondrak]

When I try to use OBS to capture my screen, it only works if the buffer size is below a certain size.

I've narrowed down the reason for the failure to GBM failing to create buffers past a certain size due to this code:

void ac_modifier_max_extent(const struct radeon_info *info,
                            uint64_t modifier, uint32_t *width, uint32_t *height)
{
   /* DCC is supported with any size. The maximum width per display pipe is 5760, but multiple
    * display pipes can be used to drive the display.
    */
   *width = 16384;
   *height = 16384;

   if (info->gfx_level < GFX12 && ac_modifier_has_dcc(modifier)) {
      bool independent_64B_blocks = AMD_FMT_MOD_GET(DCC_INDEPENDENT_64B, modifier);

      if (info->gfx_level >= GFX10 && !independent_64B_blocks) {
         /* For 4K, DCN requires INDEPENDENT_64B_BLOCKS = 1 and MAX_COMPRESSED_BLOCK_SIZE = 64B. */
         *width = 2560;
         *height = 2560;
      }
   }
}

This code seems to make the allowed modifiers (?) different for buffers of different sizes. I think jay is trying to infer modifiers from a buffer of size (1, 1) and then trying to use them for the full size, which fails because of this.

[tadeokondrak]

And this hack makes it work:

diff --git a/src/portal/ptl_screencast.rs b/src/portal/ptl_screencast.rs
index d27be66d..630b4a76 100644
--- a/src/portal/ptl_screencast.rs
+++ b/src/portal/ptl_screencast.rs
@@ -264,7 +264,7 @@ impl PwClientNodeOwner for StartedScreencast {
         };
         let modifier;
         let planes;
-        match self.allocate_buffer(fmt, modifiers, 1, 1) {
+        match self.allocate_buffer(fmt, modifiers, 3840, 2160) {
             Ok(bo) => {
                 let dmabuf = bo.dmabuf();
                 modifier = dmabuf.modifier;

[tadeokondrak]

Converted to issue