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/*
* Copyright 2010 Soeren Sandmann Pedersen
*
* Permission is hereby granted, free of charge, to any person
* obtaining a copy of this software and associated documentation
* files (the "Software"), to deal in the Software without
* restriction, including without limitation the rights to use, copy,
* modify, merge, publish, distribute, sublicense, and/or sell copies
* of the Software, and to permit persons to whom the Software is
* furnished to do so, subject to the following conditions:
*
* The above copyright notice and this permission notice shall be
* included in all copies or substantial portions of the Software.
*
* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
* EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
* MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
* NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS
* BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN
* ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
* CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
* SOFTWARE.
*
* Author: Soeren Sandmann <sandmann@daimi.au.dk>
*/
/* Exercises a case of seam appearing between two polygons in the image
* backend but not in xlib [using pixman].
*
* The test case draws two abutting quads both individually on the
* leftm combining them with operator ADD, and in one go on the right.
* Both methods should show no signs of seaming at the common edge
* between the two quads, but the individually drawn ones have a
* slight seam.
*
* The cause of the seam is that there are slight differences in the
* output of the analytical coverage rasterization and the
* supersampling rasterization methods, both employed by
* cairo-tor-scan-converter. When drawn individually, the scan
* converter gets a partial view of the geometry at a time, so it ends
* up making different decisions about which scanlines it rasterizes
* with which method, compared to when the geometry is draw all at
* once. Though both methods produce seamless results individually
* (where applicable), they don't produce bit-exact identical results,
* and hence we get seaming where they meet.
*/
#include "cairo-test.h"
static void
draw_quad (cairo_t *cr,
double x1, double y1, double x2, double y2,
double x3, double y3, double x4, double y4)
{
cairo_move_to (cr, x1, y1);
cairo_line_to (cr, x2, y2);
cairo_line_to (cr, x3, y3);
cairo_line_to (cr, x4, y4);
cairo_close_path (cr);
}
static cairo_test_status_t
draw (cairo_t *cr, int width, int height)
{
cairo_set_source_rgb (cr, 0, 0, 0);
cairo_paint (cr);
cairo_scale (cr, 20, 20);
cairo_translate (cr, 5, 1);
/* On the left side, we have two quads drawn one at a time and
* combined with OPERATOR_ADD. This should be seamless, but
* isn't. */
cairo_push_group (cr);
cairo_set_operator (cr, CAIRO_OPERATOR_ADD);
cairo_set_source_rgb (cr, 0, 0.6, 0);
draw_quad (cr,
1.50, 1.50,
2.64, 1.63,
1.75, 2.75,
0.55, 2.63);
cairo_fill (cr);
draw_quad (cr,
0.55, 2.63,
1.75, 2.75,
0.98, 4.11,
-0.35, 4.05);
cairo_fill (cr);
cairo_pop_group_to_source (cr);
cairo_set_operator (cr, CAIRO_OPERATOR_OVER);
cairo_paint (cr);
/* On the right side, we have the same two quads drawn both at the
* same time. This is seamless. */
cairo_translate (cr, 10, 0);
cairo_set_source_rgb (cr, 0, 0.6, 0);
draw_quad (cr,
1.50, 1.50,
2.64, 1.63,
1.75, 2.75,
0.55, 2.63);
draw_quad (cr,
0.55, 2.63,
1.75, 2.75,
0.98, 4.11,
-0.35, 4.05);
cairo_fill (cr);
return CAIRO_TEST_SUCCESS;
}
CAIRO_TEST (bug_seams,
"Check the fidelity of the rasterisation.",
"raster", /* keywords */
"target=raster", /* requirements */
500, 300,
NULL, draw)
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