blob: 037b887fdddf447f30bbf96ca430a47b6bbaedd2 [file] [log] [blame]
/*
* Copyright © 2006 Red Hat, Inc.
*
* Permission to use, copy, modify, distribute, and sell this software
* and its documentation for any purpose is hereby granted without
* fee, provided that the above copyright notice appear in all copies
* and that both that copyright notice and this permission notice
* appear in supporting documentation, and that the name of
* Red Hat, Inc. not be used in advertising or publicity pertaining to
* distribution of the software without specific, written prior
* permission. Red Hat, Inc. makes no representations about the
* suitability of this software for any purpose. It is provided "as
* is" without express or implied warranty.
*
* RED HAT, INC. DISCLAIMS ALL WARRANTIES WITH REGARD TO THIS
* SOFTWARE, INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY AND
* FITNESS, IN NO EVENT SHALL RED HAT, INC. BE LIABLE FOR ANY SPECIAL,
* INDIRECT OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES WHATSOEVER
* RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION
* OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF OR
* IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
*
* Author: Carl D. Worth <cworth@cworth.org>
*/
#include "cairo-test.h"
/* This test exercises the various interactions between
* cairo_set_line_width and cairo_scale. Specifically it shows how
* separate transformations can affect the pen for stroking compared
* to the path itself.
*
* This was inspired by an image by Maxim Shemanarev demonstrating the
* flexible-pipeline nature of his Antigrain Geometry project:
*
* http://antigrain.com/tips/line_alignment/conv_order.gif
*
* It also uncovered some behavior in cairo that I found surprising.
* Namely, cairo_set_line_width was not transforming the width
* according the the current CTM, but instead delaying that
* transformation until the time of cairo_stroke.
*
* This delayed behavior was released in cairo 1.0 so we're going to
* document this as the way cairo_set_line_width works rather than
* considering this a bug.
*/
#define LINE_WIDTH 13
#define SPLINE 50.0
#define XSCALE 0.5
#define YSCALE 2.0
#define WIDTH (XSCALE * SPLINE * 6.0)
#define HEIGHT (YSCALE * SPLINE * 2.0)
static void
spline_path (cairo_t *cr)
{
cairo_save (cr);
{
cairo_move_to (cr,
- SPLINE, 0);
cairo_curve_to (cr,
- SPLINE / 4, - SPLINE,
SPLINE / 4, SPLINE,
SPLINE, 0);
}
cairo_restore (cr);
}
/* If we scale before setting the line width or creating the path,
* then obviously both will be scaled. */
static void
scale_then_set_line_width_and_stroke (cairo_t *cr)
{
cairo_scale (cr, XSCALE, YSCALE);
cairo_set_line_width (cr, LINE_WIDTH);
spline_path (cr);
cairo_stroke (cr);
}
/* This is used to verify the results of
* scale_then_set_line_width_and_stroke.
*
* It uses save/restore pairs to isolate the scaling of the path and
* line_width and ensures that both are scaled.
*/
static void
scale_path_and_line_width (cairo_t *cr)
{
cairo_save (cr);
{
cairo_scale (cr, XSCALE, YSCALE);
spline_path (cr);
}
cairo_restore (cr);
cairo_save (cr);
{
cairo_scale (cr, XSCALE, YSCALE);
cairo_set_line_width (cr, LINE_WIDTH);
cairo_stroke (cr);
}
cairo_restore (cr);
}
/* This is the case that was surprising.
*
* Setting the line width before scaling doesn't change anything. The
* line width will be interpreted under the CTM in effect at the time
* of cairo_stroke, so the line width will be scaled as well as the
* path here.
*/
static void
set_line_width_then_scale_and_stroke (cairo_t *cr)
{
cairo_set_line_width (cr, LINE_WIDTH);
cairo_scale (cr, XSCALE, YSCALE);
spline_path (cr);
cairo_stroke (cr);
}
/* Here then is the way to achieve the alternate result.
*
* This uses save/restore pairs to isolate the scaling of the path and
* line_width and ensures that the path is scaled while the line width
* is not.
*/
static void
scale_path_not_line_width (cairo_t *cr)
{
cairo_save (cr);
{
cairo_scale (cr, XSCALE, YSCALE);
spline_path (cr);
}
cairo_restore (cr);
cairo_save (cr);
{
cairo_set_line_width (cr, LINE_WIDTH);
cairo_stroke (cr);
}
cairo_restore (cr);
}
static cairo_test_status_t
draw (cairo_t *cr, int width, int height)
{
int i;
void (* const figures[4]) (cairo_t *cr) = {
scale_then_set_line_width_and_stroke,
scale_path_and_line_width,
set_line_width_then_scale_and_stroke,
scale_path_not_line_width
};
cairo_set_source_rgb (cr, 1.0, 1.0, 1.0); /* white */
cairo_paint (cr);
cairo_set_source_rgb (cr, 0.0, 0.0, 0.0); /* black */
for (i = 0; i < 4; i++) {
cairo_save (cr);
cairo_translate (cr,
WIDTH/4 + (i % 2) * WIDTH/2,
HEIGHT/4 + (i / 2) * HEIGHT/2);
(figures[i]) (cr);
cairo_restore (cr);
}
return CAIRO_TEST_SUCCESS;
}
CAIRO_TEST (line_width_scale,
"Tests interaction of cairo_set_line_width with cairo_scale",
"stroke", /* keywords */
NULL, /* requirements */
WIDTH, HEIGHT,
NULL, draw)