wayland-dma-buf: doc the odd format mapping

This format mapping looks wrong at first hand, so explain why it is like
it is.

See also https://gitlab.gnome.org/GNOME/mutter/issues/323
This commit is contained in:
Pekka Paalanen 2018-10-16 14:45:14 +03:00 committed by Ray Strode
parent 1c044a8fa0
commit 63a6ead7d9

View File

@ -3,6 +3,7 @@
/* /*
* Copyright (C) 2016 Red Hat Inc. * Copyright (C) 2016 Red Hat Inc.
* Copyright (C) 2017 Intel Corporation * Copyright (C) 2017 Intel Corporation
* Copyright (C) 2018 DisplayLink (UK) Ltd.
* *
* This program is free software; you can redistribute it and/or * This program is free software; you can redistribute it and/or
* modify it under the terms of the GNU General Public License as * modify it under the terms of the GNU General Public License as
@ -85,6 +86,13 @@ meta_wayland_dma_buf_buffer_attach (MetaWaylandBuffer *buffer,
switch (dma_buf->drm_format) switch (dma_buf->drm_format)
{ {
/*
* NOTE: The cogl_format here is only used for texture color channel
* swizzling as compared to COGL_PIXEL_FORMAT_ARGB. It is *not* used
* for accessing the buffer memory. EGL will access the buffer
* memory according to the DRM fourcc code. Cogl will not mmap
* and access the buffer memory at all.
*/
case DRM_FORMAT_XRGB8888: case DRM_FORMAT_XRGB8888:
cogl_format = COGL_PIXEL_FORMAT_RGB_888; cogl_format = COGL_PIXEL_FORMAT_RGB_888;
break; break;