gl-renderer, simple-dmabuf-v4l: fix dmabuf y-invert

Graphics / Wayland / Weston - Pekka Paalanen [collabora.co.uk] - 15 August 2016 12:07 UTC

Invert the Y_INVERT flag for the EGL import fo dmabufs. This fixes weston-simple-dmabuf-intel to show the same image on both GL-composited and with direct scanout on a hardware plane. Before, the image would y-flip when switching between these two cases. Now the orientation also matches the color values written in simple-dmabuf-intel.c.

The GL-renderer uses the OpenGL convention of texture coordinates, where the origin is at the bottom-left of an image. This can be observed in texture_region() where the texcoords are inverted if y_invert is false, since the surface coordinates have origin at top-left. Both wl_shm and dmabuf buffers have origin at the top-left.

When wl_shm buffer is imported with glTexImage2D, it gets inverted because glTexImage2D is defined to read in the bottom row first. The shm data is top row first. This incidentally also means, that buffer pixel 0,0 ends up at texture coordinates 0,0. This is now inverted compared to the GL coordinate convention, and therefore gl_renderer_attach_shm() sets y_inverted to true. This causes texture_region() to NOT invert the texcoords. Wayland surface coordinates have origin at top-left, hence the double-inversion.

Dmabuf buffers also have the origin at top-left. However, they are imported via EGL to GL, where they should get the GL oriented coordinates but they do not. It is as if pixel 0,0 ends up at texcoords 0,0 - the same thing as with wl_shm buffers. Therefore we need to invert the invert flag.

Too bad EGL_EXT_image_dma_buf_import does not seem to specify the image orientation. The GL spec implied result seems to conflict with the reality in Mesa 11.2.2.

I asked about this in the Mesa developer mailing list. The question with no answers: https://lists.freedesktop.org/archives/mesa-dev/2016-June/120249.html and the thread I hijacked to get some answers: https://lists.freedesktop.org/archives/mesa-dev/2016-June/120733.html which culminated to the conclusion: https://lists.freedesktop.org/archives/mesa-dev/2016-June/120955.html that supports this patch.

simple-dmabuf-v4l is equally fixed to not add Y_INVERT. There is no rational reason to have it, and removing is necessary together with the GL-renderer change to keep the image the right way up. This has been tested with VIVID.

319397e gl-renderer, simple-dmabuf-v4l: fix dmabuf y-invert
clients/simple-dmabuf-v4l.c | 7 ++++++-
libweston/gl-renderer.c | 8 +++++++-
2 files changed, 13 insertions(+), 2 deletions(-)

Upstream: cgit.freedesktop.org

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