/* * 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); } #define ARRAY_SIZE(arr) (sizeof(arr)/sizeof(arr[0])) 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)