[cairo] How to get extents of transformed graphics

[Andreas Falkenhahn]

I've tried this:

	width = fabs(x2 - floor(x1));
	height = fabs(y2 - floor(y1));

	width = ceil(width * 4.6);
	height = ceil(height * 4.6);

Still cuts off a line of the "C" shape. I've also tried this:

	width = fabs(ceil(x2) - floor(x1));
	height = fabs(ceil(y2) - floor(y1));

	width = ceil(width * 4.6);
	height = ceil(height * 4.6);

No success either. A line is cut off.

Any more ideas? You can find my test program below...

On 08.09.2022 at 19:03 Behdad Esfahbod wrote:

> Try flooring x1,y1 before subtracting them from x2,y2 for computing the size of your surface.


> behdad
> http://behdad.org/

> On Thu, Sep 8, 2022 at 10:21 AM Andreas Falkenhahn <andreas at falkenhahn.com> wrote:

> Is there really nobody who knows how to solve this? There surely
> must be a way to find out the *exact* extents of transformed
> graphics? The idea is to find out the exact dimensions in order to
> allocate a Cairo surface that *exactly* matches the size of the path.
>  
>  On 28.08.2022 at 21:47 Andreas Falkenhahn wrote:
>  
 >> Hi,
>  
 >> is there any way to get the *exact* extents of transformed
 >> graphics? AFAICS, cairo_fill_extents() is in user coordinates, i.e.
 >> it doesn't take any transformation settings into account. So I've
 >> tried to apply the transformation manually to what I get from
 >> cairo_fill_extents() but I don't seem to get it 100% right. It looks
 >> like one row is missing at the bottom. 
>  
 >> This is what I've tried:
>  
 >>         cairo_t *cr;
 >>         cairo_surface_t *surface;
 >>         cairo_matrix_t cm;
 >>         int k;
 >>         double tx = 0, ty = 0;
 >>         double x1, y1, x2, y2;
 >>         
 >>         surface = cairo_image_surface_create(CAIRO_FORMAT_A8, 1000, 1000);
 >>         cr = cairo_create(surface);
>  
 >>         for(k = 0; k < 2; k++) {
 >>         
 >>                 cairo_new_path(cr);
 >>                 cairo_move_to(cr, tx, ty);
 >>                 cairo_set_font_size(cr, 100);
 >>                 cairo_text_path(cr, "C");                          
 >>                 
 >>                 if(!k) {        
 >>                 
 >>                         double width, height;
 >>                         
 >>                         cairo_fill_extents(cr, &x1, &y1, &x2, &y2);
 >>                         
 >>                         tx = -x1;
 >>                         ty = -y1;               
 >>                         
 >>                         width = fabs(x2 - x1);
 >>                         height = fabs(y2 - y1);
>  
 >>                         width = ceil(width * 4.6);
 >>                         height = ceil(height * 4.6);
 >>                         
 >>                         cairo_destroy(cr);
 >>                         cairo_surface_destroy(surface);
 >>                         
 >>                         surface =
 >> cairo_image_surface_create(CAIRO_FORMAT_A8, width, height);
 >>                         cr = cairo_create(surface);                
 >>                                 
 >>                         cairo_matrix_init(&cm, 4.6, 0, 0, 4.6, 0, 0);
 >>                         cairo_set_matrix(cr, &cm);                 
 >>                 }
 >>         }
 >>         
 >>         cairo_fill(cr);
>  
 >>         cairo_surface_flush(surface);
 >>         cairo_surface_write_to_png(surface, "tmp.png");
 >>         
 >>         cairo_destroy(cr);
 >>         cairo_surface_destroy(surface);
>  
 >> I'm attaching the resulting image. As you can see, there's at least
 >> one row of the "C" shape missing at the bottom of the image.
>  
 >> Any ideas how to get this right? Is this some sort of floating
 >> point inaccuracy and should I just add 1 to width/height to solve
 >> this or am I doing something wrong here and there is a better way?
>  
>  
>  
>  -- 
>  Best regards,
>   Andreas Falkenhahn                            mailto:andreas at falkenhahn.com
>  
>  


-- 
Best regards,
 Andreas Falkenhahn                            mailto:andreas at falkenhahn.com