Do correct calculation of pen dimensions for stroke optimization

1 files changed, 17 insertions, 0 deletions

diff --git a/src/cairo-stroke-style.c b/src/cairo-stroke-style.c
index a7c17b2fd..3bc234e90 100644
--- a/src/cairo-stroke-style.c
+++ b/src/cairo-stroke-style.c
@@ -84,3 +84,20 @@ _cairo_stroke_style_fini (cairo_stroke_style_t *style)
     }
     style->num_dashes = 0;
 }
+
+/*
+ * For a stroke in the given style, compute the maximum distance
+ * from the path that vertices could be generated.  In the case
+ * of rotation in the ctm, the distance will not be exact.
+ */
+void
+_cairo_stroke_style_max_distance_from_path (const cairo_stroke_style_t *style,
+                                            const cairo_matrix_t *ctm,
+                                            double *dx, double *dy)
+{
+    double style_expansion = MAX(style->line_cap == CAIRO_LINE_CAP_SQUARE ? M_SQRT1_2 : 0.5,
+                                 style->line_join == CAIRO_LINE_JOIN_MITER ? style->miter_limit : 0.5);
+
+    *dx = style->line_width * style_expansion * (fabs(ctm->xx) + fabs(ctm->xy));
+    *dy = style->line_width * style_expansion * (fabs(ctm->yy) + fabs(ctm->yx));
+}