[cairo] Fwd: Cairo fill extents results with rotation transform

[Heiko Lewin]

PS: Try this

cairo_set_source_rgb(state->cr, 1.0, 0.0, 0.0);
cairo_translate(state->cr, 500, 500); cairo_rotate(state->cr, M_PI / 4);
cairo_translate(state->cr, -500, -500); cairo_rectangle(state->cr, 400,
400, 200, 200); double x0, y0, x1, y1;

   cairo_identity_matrix(state->cr);

   cairo_fill_extents(state->cr, &x0, &y0, &x1, &y1);
cairo_fill(state->cr); ...

Am 17.04.2021 um 22:15 schrieb Heiko Lewin:
>
> Hello!
>
> The _entents-functions return coordinates in the current
> user-coordinate-system, that is the same transform as when drawing the
> rectangle needs to be applied for meaningful results.
>
> Am 17.04.2021 um 22:03 schrieb Moazin K:
>> Hi all,
>>
>> While playing with the `*_extents` functions of Cairo, I discovered
>> that `cairo_fill_extents` and `cairo_stroke_extents` give slightly
>> poor results when a rotation transform has been applied on the path.
>>
>> My code is pretty simple:
>>
>> cairo_set_source_rgb(state->cr, 1.0, 0.0, 0.0);
>>   cairo_translate(state->cr, 500, 500);
>>   cairo_rotate(state->cr, M_PI / 4);
>>   cairo_translate(state->cr, -500, -500);
>>   cairo_rectangle(state->cr, 400, 400, 200, 200);
>>   double x0, y0, x1, y1;
>>   cairo_fill_extents(state->cr, &x0, &y0, &x1, &y1);
>>   cairo_fill(state->cr);
>>
>>   cairo_identity_matrix(state->cr);
>>   cairo_set_source_rgb(state->cr, 0.0, 0.0, 1.0);
>>   cairo_set_line_width(state->cr, 1);
>>   cairo_rectangle(state->cr, x0, y0, x1 - x0 + 1, y1 - y0 + 1);
>>   cairo_stroke(state->cr);
>>
>> Extents come out to be:
>> [x0 y0 x1 y1] -> [299.999266 299.999266 700.000734 700.000734]
>>
>> The picture `cairo-rotate-problem.png` visualizes this. I think the
>> result should be as shown in
>> `cairo-rotate-problem-right-result-imho.png`. Please tell me if this
>> is the expected behavior or a bug or enhancement and I can
>> appropriately create an issue on the Gitlab issue tracker.
>>
>> It didn't make sense to me why the function behaves this way, when
>> calculating the tight bounds is actually easy. I can get my desired
>> results by removing the transform, calculating extents and then
>> transforming those extents to get a quadrilateral on which I can fit
>> a rectangle to get the tight bounds.
>>
>> Thank you,
>> Moazin
>>
>>
>
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