[Mesa-dev] [PATCH v1] mesa: rotation of 0-vector

[Sergii Romantsov]

Hello,
thanks for looking on that.
Will update after any answer on
https://github.com/KhronosGroup/OpenGL-API/issues/41
Hope that is correct place for such things.

On Thu, Sep 13, 2018 at 4:57 AM, Timothy Arceri <tarceri at itsqueeze.com>
wrote:

> On 13/9/18 12:44 am, Brian Paul wrote:
>
>> On 09/12/2018 07:30 AM, Sergii Romantsov wrote:
>>
>>> Specification doesn't define behaviour for rotation of 0-vector.
>>> But khronos.org says that vector has to be normalized.
>>> As workaround assumed that for 0-vector x-position will be
>>> defined as 1.0f.
>>>
>>> Bugzilla: https://na01.safelinks.protection.outlook.com/?url=https%3A%
>>> 2F%2Fbugs.freedesktop.org%2Fshow_bug.cgi%3Fid%3D100960&
>>> amp;data=02%7C01%7Cbrianp%40vmware.com%7Cfde139ec0f4448b
>>> 8090d08d618b3f0ce%7Cb39138ca3cee4b4aa4d6cd83d9dd62f0%7C1%
>>> 7C0%7C636723558454036605&sdata=IAlt%2FkpHJyb5JHRYaOTfhf5
>>> v9V7Xl5iQBNBdqe2PHQs%3D&reserved=0
>>> Signed-off-by: Sergii Romantsov <sergii.romantsov at globallogic.com>
>>> ---
>>>   src/mesa/main/matrix.c | 5 +++++
>>>   1 file changed, 5 insertions(+)
>>>
>>> diff --git a/src/mesa/main/matrix.c b/src/mesa/main/matrix.c
>>> index 8065a83..631b203 100644
>>> --- a/src/mesa/main/matrix.c
>>> +++ b/src/mesa/main/matrix.c
>>> @@ -415,6 +415,11 @@ _mesa_Rotatef( GLfloat angle, GLfloat x, GLfloat y,
>>> GLfloat z )
>>>      FLUSH_VERTICES(ctx, 0);
>>>      if (angle != 0.0F) {
>>> +      /* khronos.org says that ||( x,y,z )|| = 1 (if not, the GL will
>>> normalize this vector)
>>> +      * So that is kind of workaround for empty-vectors.
>>> +      * */
>>>
>>
>> Comment style should be:
>>
>> /* khronos.org says ...
>>   * So that ...
>>   */
>>
>
> Thanks for looking into the bug. However the api docs shouldn't be quoted.
> They are unversioned, are at times wrong and should not be used as a
> definative source when making changes or implementing features. Please only
> quote and use the spec for such things.
>
>
>> You might also note the bug number in the code in case anyone wonders
>> what app would hit this.
>>
>>
>> +      if (x == 0 && y == 0 && z == 0)
>>> +         x = 1.0f;
>>>
>>
> If the spec doesn't define behavior we should probably file a bug against
> the compatibility spec rather than assuming things. Clearly recording the
> problem (including applications it appears in), specifying the current
> behaviors in other drivers and proposing updated wording to the spec is
> usually the fastest way to resolve this type of thing.
>
> Also if this were the correct change it should be made in
> _math_matrix_rotate() this change will make some of the existing code there
> unreachable.
>
> Finally it would be a good idea to have a piglit test for this once any
> spec clarification is done.
>
>
>
>> You may as well use 0.0f in the test too, just to be sure no silly
>> int/float/double conversion happens.
>>
>>         _math_matrix_rotate( ctx->CurrentStack->Top, angle, x, y, z);
>>>         ctx->NewState |= ctx->CurrentStack->DirtyFlag;
>>>      }
>>>
>>>
>> -Brian
>>
>> _______________________________________________
>> mesa-dev mailing list
>> mesa-dev at lists.freedesktop.org
>> https://lists.freedesktop.org/mailman/listinfo/mesa-dev
>>
> _______________________________________________
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>



-- 
Sergii Romantsov
GlobalLogic Inc.
www.globallogic.com
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