[Mesa-dev] [PATCH 30/53] mesa: don't always set _NEW_PROGRAM when linking

[Marek Olšák]

On Tue, Jan 3, 2017 at 10:14 PM, Timothy Arceri
<timothy.arceri at collabora.com> wrote:
> On Tue, 2017-01-03 at 22:07 +0100, Marek Olšák wrote:
>> On Tue, Jan 3, 2017 at 9:57 PM, Timothy Arceri
>> <timothy.arceri at collabora.com> wrote:
>> > On Tue, 2017-01-03 at 20:47 +0100, Marek Olšák wrote:
>> > > On Tue, Jan 3, 2017 at 3:43 AM, Timothy Arceri
>> > > <timothy.arceri at collabora.com> wrote:
>> > > > We only need to set it when linking was successful and the
>> > > > program
>> > > > being linked is currently active.
>> > > >
>> > > > The programs_in_use mask is just used as a flag for now but in
>> > > > a following patch we will use it to update the CurrentProgram
>> > > > array.
>> > > > ---
>> > > >  src/mesa/main/shaderapi.c | 22 +++++++++++++++++++++-
>> > > >  1 file changed, 21 insertions(+), 1 deletion(-)
>> > > >
>> > > > diff --git a/src/mesa/main/shaderapi.c
>> > > > b/src/mesa/main/shaderapi.c
>> > > > index 022afab..6c03dcb 100644
>> > > > --- a/src/mesa/main/shaderapi.c
>> > > > +++ b/src/mesa/main/shaderapi.c
>> > > > @@ -1083,10 +1083,30 @@ _mesa_link_program(struct gl_context
>> > > > *ctx,
>> > > > struct gl_shader_program *shProg)
>> > > >        return;
>> > > >     }
>> > > >
>> > > > -   FLUSH_VERTICES(ctx, _NEW_PROGRAM);
>> > > > +   unsigned programs_in_use = 0;
>> > > > +   if (ctx->_Shader)
>> > > > +      for (unsigned stage = 0; stage < MESA_SHADER_STAGES;
>> > > > stage++) {
>> > > > +         if (ctx->_Shader->CurrentProgram[stage] == shProg) {
>> > > > +            programs_in_use |= 1 << stage;
>> > > > +         }
>> > > > +   }
>> > > >
>> > > >     _mesa_glsl_link_shader(ctx, shProg);
>> > > >
>> > > > +   /* From section 7.3 (Program Objects) of the OpenGL 4.5
>> > > > spec:
>> > > > +    *
>> > > > +    *    "If LinkProgram or ProgramBinary successfully re-
>> > > > links a
>> > > > program
>> > > > +    *     object that is active for any shader stage, then the
>> > > > newly generated
>> > > > +    *     executable code will be installed as part of the
>> > > > current
>> > > > rendering
>> > > > +    *     state for all shader stages where the program is
>> > > > active.
>> > > > +    *     Additionally, the newly generated executable code is
>> > > > made part of
>> > > > +    *     the state of any program pipeline for all stages
>> > > > where
>> > > > the program
>> > > > +    *     is attached."
>> > > > +    */
>> > > > +   if (shProg->data->LinkStatus && programs_in_use) {
>> > > > +      FLUSH_VERTICES(ctx, _NEW_PROGRAM);
>> > > > +   }
>> > >
>> > > This doesn't seem correct. If the context has unflushed vertices,
>> > > calling FLUSH_VERTICES after linking will use the new linked
>> > > program
>> > > instead of the previous program for which the vertices were
>> > > submitted.
>> >
>> > Your probably right but this doesn't make anything worse than it
>> > already is right?
>> >
>> > Before this change we where always calling FLUSH_VERTICES(ctx,
>> > _NEW_PROGRAM);
>>
>> The useless flagging is a different issue.
>>
>> FLUSH_VERTICES should be called before a state change, because it
>> flushes draw calls that the driver hasn't even seen yet. After the
>> driver processes those draw calls, _NEW_PROGRAM is set. That's how it
>> works.
>>
>> If you instead change a state and then call FLUSH_VERTICES, the
>> previous unflushed draw calls will use the new state, which is
>> incorrect.
>
> But the state doesn't change just from linking does it? The new
> programs won't be made current until glUseProgram() is called.

The GL state changes if the program is current and re-linked. (not
sure if all of the internal Mesa state changes too)

Marek