[Mesa-dev] [PATCH 15/20] glsl/es3.1: Allow textureGather and textureGatherOffset in GLSL ES 3.10

[Chris Forbes]

Nevermind, pre-coffee. On re-reading the GLSL ES 3.1 spec, the offset
is required to be constant wherever texture offsets are used.

On Fri, May 1, 2015 at 10:03 AM, Ilia Mirkin <imirkin at alum.mit.edu> wrote:
> On Thu, Apr 30, 2015 at 5:56 PM, Chris Forbes <chrisf at ijw.co.nz> wrote:
>>>  /* Only ARB_texture_gather but not GLSL 4.0 or ARB_gpu_shader5.
>>>   * used for relaxation of const offset requirements.
>>>   */
>>>  static bool
>>> -texture_gather_only(const _mesa_glsl_parse_state *state)
>>> +texture_gather_only_or_es31(const _mesa_glsl_parse_state *state)
>>>  {
>>>     return !state->is_version(400, 0) &&
>>>            !state->ARB_gpu_shader5_enable &&
>>> -          state->ARB_texture_gather_enable;
>>> +          (state->ARB_texture_gather_enable ||
>>> +           state->is_version(0, 310));
>>>  }
>>
>> I don't think this is correct. This is used to enable the restricted
>> versions of textureGather/textureGatherOffset which require a constant
>> offset. This restriction doesn't appear to exist in ES3.1 -- it's more
>> or less the GS5 version.
>>
>> An example pair, where at most one should be enabled:
>>     _texture(ir_tg4, texture_gather_only, glsl_type::vec4_type,
>> glsl_type::sampler2D_type, glsl_type::vec2_type, TEX_OFFSET),
>>     _texture(ir_tg4, gpu_shader5, glsl_type::vec4_type,
>> glsl_type::sampler2D_type, glsl_type::vec2_type, TEX_OFFSET_NONCONST),
>
> From my read of GLSL ES 3.10, it requires const offsets. Non-const
> support is added in EXT_gpu_shader5:
>
>       * extending the textureGather() built-in functions provided by
>         OpenGL ES Shading Language 3.10:
>
>         * allowing shaders to use arbitrary offsets computed at run-time to
>           select a 2x2 footprint to gather from; and
>
>   -ilia