fix gradient ordering edge case

Gradients in XPS code are ordered by offset. If however two offsets are
equal, the order of the colors depends on the sort algorithm instead of
the original order in the document. This is shown e.g. in 2245*.xps:

<GradientStop Offset="0" Color="#ff00ff00" />
<GradientStop Offset="0.5" Color="#ff0000ff" />
<GradientStop Offset="0.5" Color="#ff00ff00" />
<GradientStop Offset="1" Color="#ff00ffff" />

Tracking the original order of gradient stops and always sorting earlier
stops first makes gradient ordering consistent.

1 files changed, 3 insertions, 1 deletions

diff --git a/source/xps/xps-gradient.c b/source/xps/xps-gradient.c
index 88ed470b..7d03f89d 100644
--- a/source/xps/xps-gradient.c
+++ b/source/xps/xps-gradient.c
@@ -14,6 +14,7 @@ struct stop
 {
 	float offset;
 	float r, g, b, a;
+	int index;
 };
 
 static int cmp_stop(const void *a, const void *b)
@@ -25,7 +26,7 @@ static int cmp_stop(const void *a, const void *b)
 		return -1;
 	if (diff > 0)
 		return 1;
-	return 0;
+	return astop->index - bstop->index;
 }
 
 static inline float lerp(float a, float b, float x)
@@ -57,6 +58,7 @@ xps_parse_gradient_stops(xps_document *doc, char *base_uri, fz_xml *node,
 			if (offset && color)
 			{
 				stops[count].offset = fz_atof(offset);
+				stops[count].index = count;
 
 				xps_parse_color(doc, base_uri, color, &colorspace, sample);