gstate: Reduce degenerate dash to solid

If the dash specifies that the pen is always on (i.e. the total of the
off segments is zero), then we can eliminate the dash pattern.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>

1 files changed, 30 insertions, 5 deletions

diff --git a/src/cairo-gstate.c b/src/cairo-gstate.c
index 23e8b189..650ed371 100644
--- a/src/cairo-gstate.c
+++ b/src/cairo-gstate.c
@@ -518,8 +518,8 @@ _cairo_gstate_get_line_join (cairo_gstate_t *gstate)
 cairo_status_t
 _cairo_gstate_set_dash (cairo_gstate_t *gstate, const double *dash, int num_dashes, double offset)
 {
-    unsigned int i;
-    double dash_total;
+    double dash_total, on_total, off_total;
+    int i;
 
     free (gstate->stroke_style.dash);
 
@@ -539,12 +539,26 @@ _cairo_gstate_set_dash (cairo_gstate_t *gstate, const double *dash, int num_dash
 
     memcpy (gstate->stroke_style.dash, dash, gstate->stroke_style.num_dashes * sizeof (double));
 
-    dash_total = 0.0;
-    for (i = 0; i < gstate->stroke_style.num_dashes; i++) {
+    on_total = off_total = dash_total = 0.0;
+    for (i = 0; i < num_dashes; i++) {
 	if (gstate->stroke_style.dash[i] < 0)
 	    return _cairo_error (CAIRO_STATUS_INVALID_DASH);
 
+	if (gstate->stroke_style.dash[i] == 0) {
+	    if (i > 0 && i < num_dashes - 1) {
+		gstate->stroke_style.dash[i-1] +=
+		    gstate->stroke_style.dash[i+1];
+		gstate->stroke_style.num_dashes -= 2;
+		i++;
+		continue;
+	    }
+	}
+
 	dash_total += gstate->stroke_style.dash[i];
+	if ((i & 1) == 0)
+	    on_total += gstate->stroke_style.dash[i];
+	else
+	    off_total += gstate->stroke_style.dash[i];
     }
 
     if (dash_total == 0.0)
@@ -552,8 +566,19 @@ _cairo_gstate_set_dash (cairo_gstate_t *gstate, const double *dash, int num_dash
 
     /* An odd dash value indicate symmetric repeating, so the total
      * is twice as long. */
-    if (gstate->stroke_style.num_dashes & 1)
+    if (gstate->stroke_style.num_dashes & 1) {
 	dash_total *= 2;
+	on_total += off_total;
+    }
+
+    if (dash_total - on_total < CAIRO_FIXED_ERROR_DOUBLE) {
+	/* Degenerate dash -> solid line */
+	free (gstate->stroke_style.dash);
+	gstate->stroke_style.dash = NULL;
+	gstate->stroke_style.num_dashes = 0;
+	gstate->stroke_style.dash_offset = 0.0;
+	return CAIRO_STATUS_SUCCESS;
+    }
 
     /* The dashing code doesn't like a negative offset or a big positive
      * offset, so we compute an equivalent offset which is guaranteed to be