On Fri, Dec 14, 2012 at 04:54:32PM -0800, Eric Anholt wrote:
> Kristian Høgsberg <k...@bitplanet.net> writes:
>
> > ---
> > src/egl/drivers/dri2/egl_dri2.h | 1 +
> > src/egl/drivers/dri2/platform_drm.c | 23 +++++++++++++++++++++++
> > 2 files changed, 24 insertions(+)
> >
> > diff --git a/src/egl/drivers/dri2/egl_dri2.h
> > b/src/egl/drivers/dri2/egl_dri2.h
> > index be359d3..fa2a9f3 100644
> > --- a/src/egl/drivers/dri2/egl_dri2.h
> > +++ b/src/egl/drivers/dri2/egl_dri2.h
> > @@ -189,6 +189,7 @@ struct dri2_egl_surface
> > struct {
> > struct gbm_bo *bo;
> > int locked;
> > + int age;
> > } color_buffers[3], *back, *current;
> > #ifndef HAVE_WAYLAND_PLATFORM
> > __DRIbuffer *dri_buffers[__DRI_BUFFER_COUNT];
> > diff --git a/src/egl/drivers/dri2/platform_drm.c
> > b/src/egl/drivers/dri2/platform_drm.c
> > index 3e04a6c..1923033 100644
> > --- a/src/egl/drivers/dri2/platform_drm.c
> > +++ b/src/egl/drivers/dri2/platform_drm.c
> > @@ -324,11 +324,16 @@ dri2_swap_buffers(_EGLDriver *drv, _EGLDisplay *disp,
> > _EGLSurface *draw)
> > {
> > struct dri2_egl_display *dri2_dpy = dri2_egl_display(disp);
> > struct dri2_egl_surface *dri2_surf = dri2_egl_surface(draw);
> > + int i;
> >
> > if (dri2_surf->base.Type == EGL_WINDOW_BIT) {
> > if (dri2_surf->current)
> > _eglError(EGL_BAD_SURFACE, "dri2_swap_buffers");
> > + for (i = 0; i < ARRAY_SIZE(dri2_surf->color_buffers); i++)
> > + if (dri2_surf->color_buffers[i].bo)
> > + dri2_surf->color_buffers[i].age++;
> > dri2_surf->current = dri2_surf->back;
> > + dri2_surf->current->age = 1;
> > dri2_surf->back = NULL;
>
> OK, if I'm following this right, the ages of my buffers with this code are:
You're missing the if (dri2_surf->color_buffers[i].bo) condition on
incrementing age. We start out with bo = NULL for color_buffer[0..2]
and allocate the bos on demand...
> entering my first swap
> buffers[0] = 0 <- front
> buffers[1] = 0 <- back
>
> after first swap:
> buffers[0] = 1 <- back
> buffers[1] = 1 <- front
and so here back age will be 0 because we pick a new color_buffer from
the pool that doesn't yet have a bo and whose age was never incremented.
> after second swap:
> buffers[0] = 1 <- front
> buffers[1] = 2 <- back
>
> But reading the spec, I think it's supposed to be:
>
> entering my first swap
> buffers[0] = 0 <- front
> buffers[1] = 0 <- back
>
> after first swap:
> buffers[0] = 0 <- back
> buffers[1] = 1 <- front
>
> after second swap:
> buffers[0] = 1 <- front
> buffers[1] = 2 <- back
>
> Note how after the first swap, my backbuffer should have an age of 0, for
> "unknown junk".
Yup, and that's what this patch gets.
Kristian
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