[cairo] Extents under rotation

[Uli Schlachter]

On 08.12.2013 16:19, Donn wrote:
> On 07/12/2013 20:22, Uli Schlachter wrote:
>> Uhm. So the above code should do just this, right?
> Uli,thanks for your input again.
>
> I put together this code (in Vala) using your idea:
[...]
>             cr.arc (0.0, 0.0, 30.0, 0, 2*Math.PI);
>             cr.set_source_rgb(1,1,0);
>             cr.fill_preserve();
>
>             cr.save();
>             cr.identity_matrix();
>             cr.path_extents(out x1, out y1, out x2, out y2);
>
>               //Draw this device rect in green
>               cr.new_path();
>               cr.rectangle(x1,y1,(x2-x1),(y2-y1));
>               cr.set_source_rgb(0,1,0);
>               cr.set_line_width(3);
>               cr.stroke();
>
>             cr.restore();
>
>             //Go from device into user
>             cr.device_to_user(ref x1, ref y1);
>             cr.device_to_user(ref x2, ref y2);
>
>             //Draw this user rect in white.
>             cr.new_path();
>             cr.move_to(x1,y1);
>             cr.line_to(x2,y1);
>             cr.line_to(x2,y2);
>             cr.line_to(x1,y2);
>             cr.close_path();
>
[...]

That's not what I suggested. You cannot just transform the top-left and 
bottom-right corner of the extents and assume that the other ones can be deduced 
from that (this is not an axis-aligned rectangle in user space!).

Attached is a working version. The diff to your version is also attached.

Cheers,
Uli
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