dmabuf: Create buffers without the SCANOUT flag

gbm_bo_create_with_modifiers implies the GBM_BO_USE_SCANOUT flag, which
disables complex (tiled or compressed) formats that cannot be used for
scanout. This reduces performance. We don't need to scan out buffers
created for sceencasting/etc., so this is suboptimal.

By switching to gbm_bo_create_with_modifiers2, we can explicitly pass
the flags and avoid falling back to lower performance formats. Also add
a config check and fall back to the old version, to retain compatibility
with older mesa versions.

CMakeLists.txt

@@ -248,6 +248,11 @@ if (${gbm_VERSION} GREATER_EQUAL 21.1)
 else()
     set(HAVE_GBM_BO_GET_FD_FOR_PLANE 0)
 endif()
+if (${gbm_VERSION} GREATER_EQUAL 21.3)
+    set(HAVE_GBM_BO_CREATE_WITH_MODIFIERS2 1)
+else()
+    set(HAVE_GBM_BO_CREATE_WITH_MODIFIERS2 0)
+endif()
 
 pkg_check_modules(Libxcvt IMPORTED_TARGET libxcvt>=0.1.1 REQUIRED)
 add_feature_info(Libxcvt Libxcvt_FOUND "Required for generating modes in the drm backend")

src/backends/drm/gbm_dmabuf.h

@@ -58,11 +58,20 @@ inline gbm_bo *createGbmBo(gbm_device *device, const QSize &size, quint32 format
 {
     gbm_bo *bo = nullptr;
     if (modifiers.count() > 0 && !(modifiers.count() == 1 && modifiers[0] == DRM_FORMAT_MOD_INVALID)) {
+#if HAVE_GBM_BO_CREATE_WITH_MODIFIERS2
+        bo = gbm_bo_create_with_modifiers2(device,
+                                           size.width(),
+                                           size.height(),
+                                           format,
+                                           modifiers.constData(), modifiers.count(),
+                                           GBM_BO_USE_RENDERING);
+#else
         bo = gbm_bo_create_with_modifiers(device,
                                           size.width(),
                                           size.height(),
                                           format,
                                           modifiers.constData(), modifiers.count());
+#endif
     }
 
     if (!bo && (modifiers.isEmpty() || modifiers.contains(DRM_FORMAT_MOD_INVALID))) {

src/config-kwin.h.cmake

@@ -14,6 +14,7 @@
 #cmakedefine01 HAVE_X11_XCB
 #cmakedefine01 HAVE_X11_XINPUT
 #cmakedefine01 HAVE_GBM_BO_GET_FD_FOR_PLANE
+#cmakedefine01 HAVE_GBM_BO_CREATE_WITH_MODIFIERS2
 #cmakedefine01 HAVE_MEMFD
 #cmakedefine01 HAVE_BREEZE_DECO
 #cmakedefine01 HAVE_SCHED_RESET_ON_FORK