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List:       cairo
Subject:    [cairo] How to get extents of transformed graphics
From:       Andreas Falkenhahn <andreas () falkenhahn ! com>
Date:       2022-08-28 19:47:44
Message-ID: 938001570.20220828214744 () falkenhahn ! com
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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@falkenhahn.com


["tmp.png" (image/png)]

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