[Bf-codereview] [PATCH] Fix FDO 34495: Selecting objects in Blender slow due to GL_SELECT

[Laura Ekstrand]

Hi Antony,

Ah, ok, I see.

GL select is a very ill-defined part of the GL 1.0 spec, which is why
driver developers are reluctant to optimize it.  I collaborate on the Mesa
project, and some of the other developers thought it would be a good idea
for me to try to see if I can help with Blender's GL usage in any way.  It
would be helpful to us and Blender both if we could get Blender running on
OpenGL core 3.0.  I'm completely new to the Blender project (I've used
Blender a little), so I'm not sure how much work there is to do toward this
goal.

Have you tried any other strategies besides GL select and occlusion
queries?  In my master's thesis, I used a common technique to make
selections whereby you color-code each selectable object with a different
value and read back the color to tell which object was picked.  It's kind
of like this:
http://content.gpwiki.org/OpenGL_Selection_Using_Unique_Color_IDs, only I
used shaders and painted each object or fragment with a different value to
get a fine-grained result.

Thanks.

Laura

On Fri, Sep 4, 2015 at 11:40 PM, Antony Riakiotakis <kalast at gmail.com>
wrote:

> Hi Laura, the two modes are not equivalent. GL Select is more precise
> than occlusion queries, that's why we tend to prefer one over the
> other.
>
> On 5 September 2015 at 06:45, Laura Ekstrand <laura at jlekstrand.net> wrote:
> > Refer to bug: https://bugs.freedesktop.org/show_bug.cgi?id=34495,
> Comment 78
> >
> > The default selection mode (File > User Preferences > System >
> Selection) of
> > Automatic preferred using glRenderMode(GL_SELECT) unless the user's GPU
> was an
> > ATI. Since glRenderMode(GL_SELECT) is deprecated, driver developers rely
> on
> > software fallbacks for its implementation.  These software fallbacks are
> slow.
> >
> > Since all drivers (including all open source drivers) now implement
> > GL_ARB_OCCLUSION_QUERY, this patch sets the selection mode to always
> > use occlusion query unless:
> >
> > 1. GL_ARB_OCCLUSION_QUERY is not present in the driver, or
> > 2. The user has selected the GL_SELECT selection mode manually using
> File >
> > User Preferences > System > Selection.
> > ---
> >  source/blender/gpu/intern/gpu_select.c | 3 +--
> >  1 file changed, 1 insertion(+), 2 deletions(-)
> >
> > diff --git a/source/blender/gpu/intern/gpu_select.c
> b/source/blender/gpu/intern/gpu_select.c
> > index 4978229..0d0dd33 100644
> > --- a/source/blender/gpu/intern/gpu_select.c
> > +++ b/source/blender/gpu/intern/gpu_select.c
> > @@ -243,6 +243,5 @@ bool GPU_select_query_check_support(void)
> >  bool GPU_select_query_check_active(void)
> >  {
> >         return GLEW_ARB_occlusion_query &&
> > -              ((U.gpu_select_method == USER_SELECT_USE_OCCLUSION_QUERY)
> ||
> > -               ((U.gpu_select_method == USER_SELECT_AUTO) &&
> GPU_type_matches(GPU_DEVICE_ATI, GPU_OS_ANY, GPU_DRIVER_ANY)));
> > +               (U.gpu_select_method !=
> USER_SELECT_USE_SELECT_RENDERMODE);
> >  }
> > --
> > 2.4.3
> >
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