test/zero-alpha.c

   1 /*
   2  * Copyright © 2006 Red Hat, Inc.
   3  *
   4  * Permission to use, copy, modify, distribute, and sell this software
   5  * and its documentation for any purpose is hereby granted without
   6  * fee, provided that the above copyright notice appear in all copies
   7  * and that both that copyright notice and this permission notice
   8  * appear in supporting documentation, and that the name of
   9  * Red Hat, Inc. not be used in advertising or publicity pertaining to
  10  * distribution of the software without specific, written prior
  11  * permission. Red Hat, Inc. makes no representations about the
  12  * suitability of this software for any purpose.  It is provided "as
  13  * is" without express or implied warranty.
  14  *
  15  * RED HAT, INC. DISCLAIMS ALL WARRANTIES WITH REGARD TO THIS
  16  * SOFTWARE, INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY AND
  17  * FITNESS, IN NO EVENT SHALL RED HAT, INC. BE LIABLE FOR ANY SPECIAL,
  18  * INDIRECT OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES WHATSOEVER
  19  * RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION
  20  * OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF OR
  21  * IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
  22  *
  23  * Author: Carl D. Worth <cworth@cworth.org>
  24  */
  25
  26 #include "cairo-test.h"
  27
  28 #define SIZE 3
  29 #define REPS 10
  30
  31 /* History:
  32  *
  33  * 2006-06-13 Paul Giblock reports a "Stange alpha channel problem" on
  34  * the cairo mailing list.
  35  *
  36  * 2006-06-13 Carl Worth writes this test in an attempt to reproduce
  37  * the problem. The test first fills in a 3x3 rectangle with red, then
  38  * starts pounding on that center pixel with various forms of
  39  * zero-alpha rendering to see if its value can ever be made to
  40  * change.
  41  *
  42  * 2006-06-13 Paul Giblock reports that this only happens with the
  43  * xlib backend, and then only on some systems.
  44  */
  45 static cairo_test_status_t
  46 draw (cairo_t *cr, int width, int height)
  47 {
  48     int i;
  49     cairo_surface_t *surface;
  50     uint32_t zero = 0;
  51
  52     /* First paint background red. */
  53     cairo_set_source_rgb (cr, 1.0, 0.0, 0.0); /* red */
  54     cairo_paint (cr);
  55
  56     /* Then we paint zero-alpha in several ways (always REPS times): */
  57
  58     /* 1. fill a rectangle with a zero-alpha solid source. */
  59     cairo_set_source_rgba (cr, 0.0, 0.0, 0.0, 0.0); /* transparent */
  60     cairo_rectangle (cr, 1.0, 1.0, 1.0, 1.0);
  61     for (i=0; i < REPS; i++)
  62         cairo_fill_preserve (cr);
  63     cairo_new_path (cr);
  64
  65     /* 2. paint with a zero-alpha image surface source. */
  66     surface = cairo_image_surface_create_for_data ((unsigned char *) &zero,
  67                                                    CAIRO_FORMAT_ARGB32, 1, 1, 4);
  68     cairo_set_source_surface (cr, surface, 1, 1);
  69     for (i=0; i < REPS; i++)
  70         cairo_paint (cr);
  71
  72     /* 3. clip to rectangle then paint with zero-alpha solid source. */
  73     cairo_rectangle (cr, 1.0, 1.0, 1.0, 1.0);
  74     cairo_clip (cr);
  75     cairo_set_source_rgba (cr, 0.0, 0.0, 0.0, 0.0); /* transparent */
  76     for (i=0; i < REPS; i++)
  77         cairo_paint (cr);
  78
  79     /* 4. With the clip still there, paint our image surface. */
  80     cairo_set_source_surface (cr, surface, 1, 1);
  81     for (i=0; i < REPS; i++)
  82         cairo_paint (cr);
  83
  84     cairo_surface_destroy (surface);
  85
  86     return CAIRO_TEST_SUCCESS;
  87 }
  88
  89 CAIRO_TEST (zero_alpha,
  90             "Testing that drawing with zero alpha has no effect",
  91             "alpha", /* keywords */
  92             NULL, /* requirements */
  93             SIZE, SIZE,
  94             NULL, draw)