[Mesa-dev] [PATCH] meta: Use result of texture coordinate clamping operation

[Ian Romanick]

I'm pretty sure our implementation of this extension is complete
rubbish.  I have attached an image from the blit-scaled test.  This
result cannot be useful to anyone.

On 09/09/2015 11:16 AM, Ian Romanick wrote:
> On 09/09/2015 11:13 AM, Ian Romanick wrote:
>> From: Ian Romanick <ian.d.romanick at intel.com>
>>
>> Previously the result of the complicated clamp() expression just dropped
>> on the floor: clamp does not modify any of its parameters.  Looking at
>> the surrounding code, I believe this is supposed to modify the value of
>> tex_coord.
>>
>> This change (along with a change to avoid the use of
>> brw_blorp_framebuffer) does not affect any existing piglit tests.  I'm
>> not sure what this clamp is trying to accomplish, so I'm not sure how to
>> write a test to exercise this path.
> 
> I just noticed that the piglit test contains the same incorrect shader
> as meta for the "reference" implementation.
> 
>> I also noticed another bug in this code.  There is no way the array
>> texture case could possibly work.  This will generate code for the
>> TEXEL_FETCH macro like:
>>
>>     #define TEXEL_FETCH(coord) texelFetch(texSampler, ivec3(coord), sample_map[int(2 * fract(coord.x))]);
>>
>> Since the coord parameter of this macro is a vec2 at all invocations, no
>> expansion of this macro will even compile.
>>
>> Signed-off-by: Ian Romanick <ian.d.romanick at intel.com>
>> Cc: Anuj Phogat <anuj.phogat at gmail.com>
>> Cc: Topi Pohjolainen <topi.pohjolainen at intel.com>
>> Cc: Jordan Justen <jordan.l.justen at intel.com>
>> ---
>>  src/mesa/drivers/common/meta_blit.c | 4 ++--
>>  1 file changed, 2 insertions(+), 2 deletions(-)
>>
>> diff --git a/src/mesa/drivers/common/meta_blit.c b/src/mesa/drivers/common/meta_blit.c
>> index 71d18de..a41fe42 100644
>> --- a/src/mesa/drivers/common/meta_blit.c
>> +++ b/src/mesa/drivers/common/meta_blit.c
>> @@ -187,8 +187,8 @@ setup_glsl_msaa_blit_scaled_shader(struct gl_context *ctx,
>>                                 "   vec2 tex_coord = texCoords - s_0_offset;\n"
>>                                 "\n"
>>                                 "   tex_coord *= scale;\n"
>> -                               "   clamp(tex_coord.x, 0.0f, scale.x * src_width - 1.0f);\n"
>> -                               "   clamp(tex_coord.y, 0.0f, scale.y * src_height - 1.0f);\n"
>> +                               "   tex_coord.x = clamp(tex_coord.x, 0.0f, scale.x * src_width - 1.0f);\n"
>> +                               "   tex_coord.y = clamp(tex_coord.y, 0.0f, scale.y * src_height - 1.0f);\n"
>>                                 "   interp = fract(tex_coord);\n"
>>                                 "   tex_coord = ivec2(tex_coord) * scale_inv;\n"
>>                                 "\n"
> 
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