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Diffstat (limited to 'libs/cairo-1.16.0/test/line-width-scale.c')
| -rw-r--r-- | libs/cairo-1.16.0/test/line-width-scale.c | 178 |
1 files changed, 178 insertions, 0 deletions
diff --git a/libs/cairo-1.16.0/test/line-width-scale.c b/libs/cairo-1.16.0/test/line-width-scale.c new file mode 100644 index 0000000..037b887 --- /dev/null +++ b/libs/cairo-1.16.0/test/line-width-scale.c @@ -0,0 +1,178 @@ +/* + * 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) |