[Mesa-dev] [PATCH] softpipe: fix clamping when using unormalized coordinates

[Brian Paul]

On 11/14/2011 10:24 AM, Morgan Armand wrote:
> On 11/14/2011 3:44 PM, Brian Paul wrote:
>> On 11/13/2011 03:24 AM, Morgan Armand wrote:
>>> ---
>>>    src/gallium/drivers/softpipe/sp_tex_sample.c |    7 ++++---
>>>    1 files changed, 4 insertions(+), 3 deletions(-)
>>>
>>> diff --git a/src/gallium/drivers/softpipe/sp_tex_sample.c b/src/gallium/drivers/softpipe/sp_tex_sample.c
>>> index 72629a0..9b0e54e1 100644
>>> --- a/src/gallium/drivers/softpipe/sp_tex_sample.c
>>> +++ b/src/gallium/drivers/softpipe/sp_tex_sample.c
>>> @@ -491,7 +491,8 @@ wrap_linear_unorm_clamp(const float s[4], unsigned size,
>>>       uint ch;
>>>       for (ch = 0; ch<   4; ch++) {
>>>          /* Not exactly what the spec says, but it matches NVIDIA output */
>>> -      float u = CLAMP(s[ch] - 0.5F, 0.0f, (float) size - 1.0f);
>>> +      float u = CLAMP(s[ch], 0.0f, (float) size);
>>> +      u -= 0.5F;
>>>          icoord0[ch] = util_ifloor(u);
>>
>> If s=0, then icoord0 = -1 and that's not right.  The 'i' coordinates must be in the range [0,size-1].
>>
>> Are you trying to fix a specific bug or piglit test?
>>
>>
>>>          icoord1[ch] = icoord0[ch] + 1;
>>>          w[ch] = frac(u);
>>> @@ -512,8 +513,8 @@ wrap_linear_unorm_clamp_to_border(const float s[4], unsigned size,
>>>          u -= 0.5F;
>>>          icoord0[ch] = util_ifloor(u);
>>>          icoord1[ch] = icoord0[ch] + 1;
>>> -      if (icoord1[ch]>   (int) size - 1)
>>> -         icoord1[ch] = size - 1;
>>> +      if (icoord1[ch]>   (int) size)
>>> +         icoord1[ch] = size;
>>>          w[ch] = frac(u);
>>>       }
>>>    }
>>
>> -Brian
>
> Yes, sorry, I forgot to mention it. This patch fixes texwrap-RECT-bordercolor and texwrap-RECT-proj-bordercolor.
>
>  From what I understand from the spec, we expect to get the border color when sampling with out-of-range coordinates, or the
> correct interpolation between the border color and the texel color when sampling with coordinates in the range [0; 1/2N[ or
> [1-1/2N; max[. That's why I converted the coordinates to [-1;size] instead. get_texel_*d functions handle the case when a texture
> coordinate is out-of-range but it may not the case of all functions so I probably need to check that carefully.
> Please correct me if I misunderstood something.

I think I was wrong above.  I thought you were changing the 
clamp-to-edge behaviour, but that case is implemented in the 
wrap_linear_unorm_clamp_to_edge() function.

In any case, I remember that implementing what the spec says didn't 
match the output from NVIDIA's driver (hence the comment there).

Do you have an NVIDIA GPU to compare against?

I could do some testing/comparing later...

-Brian