ozone: Add an opaque fb to ScanoutBuffer for primary planes.

ui/ozone/platform/drm/common/drm_util.cc

 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "ui/ozone/platform/drm/common/drm_util.h"
 
 #include <drm_fourcc.h>
 #include <stdint.h>
 #include <stdlib.h>
 #include <sys/mman.h>
@@ skipping 403 matching lines @@
     case DRM_FORMAT_NV12:
       return gfx::BufferFormat::YUV_420_BIPLANAR;
     case DRM_FORMAT_YV12:
       return gfx::BufferFormat::YVU_420;
     default:
       NOTREACHED();
       return gfx::BufferFormat::BGRA_8888;
   }
 }
 
-int GetFourCCFormatForFramebuffer(gfx::BufferFormat format) {
-  // Currently, drm supports 24 bitcolordepth for hardware overlay.
+int GetFourCCFormatForOpaqueFramebuffer(gfx::BufferFormat format) {
+  // DRM atomic interface doesn't currently support specifying an alpha
+  // blending. We can simulate disabling alpha bleding creating an fb
+  // with a format without the alpha channel.
   switch (format) {
     case gfx::BufferFormat::RGBA_8888:
     case gfx::BufferFormat::RGBX_8888:
       return DRM_FORMAT_XBGR8888;
     case gfx::BufferFormat::BGRA_8888:
     case gfx::BufferFormat::BGRX_8888:
       return DRM_FORMAT_XRGB8888;
     case gfx::BufferFormat::BGR_565:
       return DRM_FORMAT_RGB565;
     case gfx::BufferFormat::UYVY_422:
       return DRM_FORMAT_UYVY;
     default:
       NOTREACHED();
       return 0;
   }
 }
 }  // namespace ui