Upside down and backwards

Pekka Paalanen ppaalanen at
Sun Mar 4 23:42:00 PST 2012

On Sun, 4 Mar 2012 20:37:48 -0800
Mandeep Singh Baines <msb at> wrote:

> Hi,
> I have recently started playing around with EGL_PLATFORM=drm. Using
> eglkms.c and compositor-drm.c as examples, I've been able to port some
> simple EGL/GLESv2 applications without much effort. But the one weird
> thing is that everything gets rendered upside down and backwards. I
> guess I could solve this with the projection matrix but just wondering
> why I'm getting this effect. How does compositor-drm deal with this.

Look for WL_OUTPUT_FLIPPED in weston.

I guess and if I remember right, flipped y-axis is because OpenGL
back/front buffer of a window has origin at top-left with y growing
down, but FBOs have origin at bottom-left with y growing up. Or maybe
it was vice versa, I didn't check.


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