PS/PDF: Set image Interpolation flag

If the filter mode is anything other than DEFAILT, FAST or NEAREST set the
Interpolate flag in the image dictionary so that a smoothing filter is
applied when rasterising the vector file.

As we have no control over the implementation of the Interpolate filter
(the PS/PDF specifications leave it undefined) we need to capture the
output of poppler/GS and update our reference images. (For a couple of
tests, the filtering is irrelevant so for those we set the filter to
NEAREST.)

Note that GhostScript's Interpolate filter does not work on rotated images
(and a variety of other transformations) so several of the PS reference
images have use nearest-neighbour sampling instead of a bilinear filter.

1 files changed, 4 insertions, 2 deletions

diff --git a/test/surface-pattern.c b/test/surface-pattern.c
index 6afdcda9..7739cae6 100644
--- a/test/surface-pattern.c
+++ b/test/surface-pattern.c
@@ -30,12 +30,14 @@
 
 #define SIZE 140
 
+/* Not GhostScript does not support /Interpolate on rotated images, so the PS
+ * output looks terrible, but is a known issue. */
+
 static cairo_test_draw_function_t draw;
 
 static const cairo_test_t test = {
     "surface-pattern",
-    "Test transformed repeated surface patterns"
-    "\nExhibiting a strange (very minor) failure in ps backend with device-offset",
+    "Test transformed repeated surface patterns",
     SIZE, SIZE,
     draw
 };