[Mesa-dev] [PATCH v2 19/31] glsl: fix explicit binding location for bindless samplers/images

[Nicolai Hähnle]

On 04.05.2017 20:54, Marek Olšák wrote:
> On Wed, Apr 26, 2017 at 9:40 AM, Nicolai Hähnle <nhaehnle at gmail.com> wrote:
>> On 24.04.2017 12:35, Samuel Pitoiset wrote:
>>>
>>> The ARB_bindless_texture spec says:
>>>
>>>    "Interactions with GLSL 4.20"
>>>
>>>    "Without GLSL 4.20 support, sampler and image uniforms may only
>>>     be initialized through the OpenGL API. With GLSL 4.20, sampler
>>>     and image uniforms may be initialized in the shader using
>>>
>>>     layout(binding = integer-constant)
>>>
>>>     as described in section 4.4.4 "Opaque-Uniform Layout Qualifiers".
>>>     When ARB_bindless_texture is supported, these initial binding
>>>     values are always taken to mean a texture image or image unit
>>>     number, not a bindless handle."
>>>
>>> Signed-off-by: Samuel Pitoiset <samuel.pitoiset at gmail.com>
>>> ---
>>>  src/compiler/glsl/ast_to_hir.cpp | 20 ++++++++++++++++++++
>>>  1 file changed, 20 insertions(+)
>>>
>>> diff --git a/src/compiler/glsl/ast_to_hir.cpp
>>> b/src/compiler/glsl/ast_to_hir.cpp
>>> index ae81ed95d8..943c25a224 100644
>>> --- a/src/compiler/glsl/ast_to_hir.cpp
>>> +++ b/src/compiler/glsl/ast_to_hir.cpp
>>> @@ -2920,6 +2920,26 @@ apply_explicit_binding(struct
>>> _mesa_glsl_parse_state *state,
>>>        return;
>>>     }
>>>
>>> +   /* The ARB_bindless_texture_spec says:
>>> +    *
>>> +    * "Interactions with GLSL 4.20"
>>> +    *
>>> +    * "Without GLSL 4.20 support, sampler and image uniforms may only be
>>> +    *  initialized through the OpenGL API. With GLSL 4.20, sampler and
>>> image
>>> +    *  uniforms may be initialized in the shader using
>>> +    *
>>> +    *  layout(binding = integer-constant)
>>> +    *
>>> +    *  as described in section 4.4.4 "Opaque-Uniform Layout Qualifiers".
>>> When
>>> +    *  ARB_bindless_texture is supported, these initial binding values
>>> are
>>> +    *  always taken to mean a texture image or image unit number, not a
>>> +    *  bindless handle."
>>> +    */
>>> +   if (state->has_bindless() &&
>>> +       (base_type->is_sampler() || base_type->is_image())) {
>>> +      var->data.bindless = false;
>>> +   }
>>
>>
>> I don't think this is correct. The way I understand the spec, saying
>>
>>   layout (bindless_sampler, binding = 5) uniform sampler2D s;
>>
>> means that s is still bindless, it's just that it's *initial* value is set
>> up as if the application had called
>>
>>   glUniform1i(index of s, 5);
>>
>> You're still allowed to later on change it to a bindless handle by calling
>> one of the glUniformHandleui64* functions.
>
> I don't like this. Are you suggesting that a texture bound to unit 5
> has to be somehow converted to a bindless texture and made resident
> under the hood (in Mesa), so that the bindless shader code works?

I don't think we have much of a choice, unfortunately. I agree it's very 
annoying.

This can only happen for default block uniforms, which st/mesa uploads 
in a special way anyway. Maybe we can also treat default block bindless 
uniforms in a special way?

I don't think this case has been fully implemented in the WIP branches.

Cheers,
Nicolai
-- 
Lerne, wie die Welt wirklich ist,
Aber vergiss niemals, wie sie sein sollte.