Fix mask usage in image-compositor

src/cairo-image-compositor.c

@@ -2610,14 +2610,14 @@ _inplace_src_spans (void *abstract_renderer, int y, int h,
 		    unsigned num_spans)
 {
     cairo_image_span_renderer_t *r = abstract_renderer;
-    uint8_t *m;
+    uint8_t *m, *base = (uint8_t*)pixman_image_get_data(r->mask);
     int x0;
 
     if (num_spans == 0)
 	return CAIRO_STATUS_SUCCESS;
 
     x0 = spans[0].x;
-    m = r->_buf;
+    m = base;
     do {
 	int len = spans[1].x - spans[0].x;
 	if (len >= r->u.composite.run_length && spans[0].coverage == 0xff) {
@@ -2655,7 +2655,7 @@ _inplace_src_spans (void *abstract_renderer, int y, int h,
 				      spans[0].x, y,
 				      spans[1].x - spans[0].x, h);
 
-	    m = r->_buf;
+	    m = base;
 	    x0 = spans[1].x;
 	} else if (spans[0].coverage == 0x0) {
 	    if (spans[0].x != x0) {
@@ -2684,7 +2684,7 @@ _inplace_src_spans (void *abstract_renderer, int y, int h,
 #endif
 	    }
 
-	    m = r->_buf;
+	    m = base;
 	    x0 = spans[1].x;
 	} else {
 	    *m++ = spans[0].coverage;

test/Makefile.sources

@@ -34,6 +34,7 @@ test_sources = \
 	bug-source-cu.c					\
 	bug-extents.c					\
 	bug-seams.c					\
+	bug-image-compositor.c				\
 	caps.c						\
 	checkerboard.c					\
 	caps-joins.c					\

test/bug-image-compositor.c

+#include "cairo-test.h"
+
+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_set_source_rgb (cr, 1., 1., 1.);
+    cairo_set_line_width (cr, 1.);
+
+    cairo_pattern_t *p = cairo_pattern_create_linear (0, 0, width, height);
+    cairo_pattern_add_color_stop_rgb (p, 0, 0.99, 1, 1);
+    cairo_pattern_add_color_stop_rgb (p, 1, 1, 1, 1);
+    cairo_set_source (cr, p);
+
+    cairo_move_to (cr, 0.5, -1);
+    for (int i = 0; i < width; i+=3) {
+	cairo_rel_line_to (cr, 2, 2);
+	cairo_rel_line_to (cr, 1, -2);
+    }
+
+    cairo_set_operator (cr, CAIRO_OPERATOR_SOURCE);
+    cairo_stroke (cr);
+
+    cairo_pattern_destroy(p);
+
+    return CAIRO_TEST_SUCCESS;
+}
+
+
+CAIRO_TEST (bug_image_compositor,
+	    "Crash in image-compositor",
+	    "stroke, stress", /* keywords */
+	    NULL, /* requirements */
+	    10000, 1,
+	    NULL, draw)
+	    
+