On 09/11/2015 10:55 AM, Ilia Mirkin wrote:
> On Fri, Sep 11, 2015 at 12:36 PM, Marius Predut <marius.pre...@intel.com>
> wrote:
>> Comparison with a signed expression and unsigned value
>> is converted to unsigned value, reason for minus value is interpreted
>> as a big unsigned value. For this case the "for" loop
>> is going into unexpected behavior.
>>
>> v1: Brian Paul: code style fix.
>> v2: Ian Romanick: glDrawArrays(GL_QUADS, 0, (n * 4) + k) fail , k < 4.
>>
>> Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=38109
>> Signed-off-by: Marius Predut <marius.pre...@intel.com>
>> ---
>> src/mesa/tnl_dd/t_dd_dmatmp.h | 7 +++++++
>> 1 file changed, 7 insertions(+)
>>
>> diff --git a/src/mesa/tnl_dd/t_dd_dmatmp.h b/src/mesa/tnl_dd/t_dd_dmatmp.h
>> index 7be3954..f99d977 100644
>> --- a/src/mesa/tnl_dd/t_dd_dmatmp.h
>> +++ b/src/mesa/tnl_dd/t_dd_dmatmp.h
>> @@ -627,6 +627,13 @@ static void TAG(render_quads_verts)( struct gl_context
>> *ctx,
>> LOCAL_VARS;
>> GLuint j;
>>
>> + /* Page 18 (page 32 of the PDF) of the OpenGL 2.1 spec says:
>> + * The total number of vertices between Begin and End is 4n + k,
>> + * where 0 ≤ k ≤ 3; if k is not zero, the final k vertices are
>> ignored.
>> + */
>> + count = (count / 4) * 4;
>
> Might be just me, but I'd find
>
> count &= ~0x3
>
> to be a lot clearer. Don't know if the compiler can make such an
> optimization.
I think it can if count is unsigned. Of course, GLsizei is not
unsigned. It is already invalid for count < 0, so your optimization is
safe.
> However this seems wrong... you're supposed to draw
> start..count, so that's the value that has to be div-by-4. Further up,
> when there's native quad support, the logic does:
I don't think that's right. Count is the number of vertices, not the
index of the last vertex. Calling
glDrawArrays(GL_QUADS, 47000, 4);
still draws one quad.
Look at the pseudocode on page 28 (page 42 of the PDF) of the OpenGL 2.1
spec:
"The command
void DrawArrays(enum mode, int first, sizei count);
constructs a sequence of geometric primitives using elements first
through first + count − 1 of each enabled array. mode specifies
what kind of primitives are constructed; it accepts the same token
values as the mode parameter of the Begin command. The effect of
DrawArrays(mode, first, count);
is the same as the effect of the command sequence
if (mode or count is invalid)
generate appropriate error
else {
Begin(mode);
for (int i = 0; i < count; i++)
ArrayElement(first + i);
End();
}"
Combining that with the language previously quoted, I think this change
is right.
> /* Emit whole number of quads in total. dmasz is already a multiple
> * of 4.
> */
> count -= (count-start)%4;
>
> Which seems more accurate.
>
>> + if(count == 0) return;
>
> if (count == 0)
>
> note the space. That's the style used in all of mesa.
>
> $ git grep '\sif(' | wc -l
> 1076
> $ git grep '\sif (' | wc -l
> 58071
>
> I guess a few 'if(' instances snuck through, mostly in src/gallium.
> But the overwhelming majority are of the 'if (' style.
>
>> +
>> INIT(GL_TRIANGLES);
>>
>> for (j = start; j < count-3; j += 4) {
>> --
>> 1.9.1
>>
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