[test] Avoid redundant writes/reads of test surfaces via png.

As Behdad suggested, we can dramatically speed up the test suite by
short-circuiting the write to a png file, only to then immediately read it
back in. So for the raster based surfaces, we avoid the round-trip through
libpng by implementing a new boilerplate method to directly extract the image
buffer from the test result. A secondary speedup is achieved by caching the
most recent reference image.

1 files changed, 18 insertions, 20 deletions

diff --git a/test/buffer-diff.h b/test/buffer-diff.h
index 61daa897d..64bce920a 100644
--- a/test/buffer-diff.h
+++ b/test/buffer-diff.h
@@ -36,21 +36,6 @@ typedef struct _buffer_diff_result {
     unsigned int max_diff;
 } buffer_diff_result_t;
 
-/* Compares two image surfaces
- *
- * Provides number of pixels changed and maximum single-channel
- * difference in result.
- *
- * Also fills in a "diff" surface intended to visually show where the
- * images differ.
- */
-void
-compare_surfaces (const cairo_test_context_t  *ctx,
-	          cairo_surface_t	*surface_a,
-		  cairo_surface_t	*surface_b,
-		  cairo_surface_t	*surface_diff,
-		  buffer_diff_result_t *result);
-
 /* Compares two image buffers ignoring the alpha channel.
  *
  * Provides number of pixels changed and maximum single-channel
@@ -60,8 +45,8 @@ compare_surfaces (const cairo_test_context_t  *ctx,
  * images differ.
  */
 void
-buffer_diff_noalpha (unsigned char *buf_a,
-		     unsigned char *buf_b,
+buffer_diff_noalpha (const unsigned char *buf_a,
+		     const unsigned char *buf_b,
 		     unsigned char *buf_diff,
 		     int	    width,
 		     int	    height,
@@ -82,7 +67,7 @@ buffer_diff_noalpha (unsigned char *buf_a,
  * images differ.
  */
 cairo_status_t
-image_diff (const cairo_test_context_t *ctx,
+png_diff (const cairo_test_context_t *ctx,
 	    const char *filename_a,
 	    const char *filename_b,
 	    const char *filename_diff,
@@ -92,9 +77,9 @@ image_diff (const cairo_test_context_t *ctx,
 	    int		by,
 	    buffer_diff_result_t *result);
 
-/* Like image_diff, but blending the contents of b over white first. */
+/* Like png_diff, but blending the contents of b over white first. */
 cairo_status_t
-image_diff_flattened (const cairo_test_context_t *ctx,
+png_diff_flattened (const cairo_test_context_t *ctx,
 	              const char *filename_a,
 		      const char *filename_b,
 		      const char *filename_diff,
@@ -104,4 +89,17 @@ image_diff_flattened (const cairo_test_context_t *ctx,
                       int         by,
 		      buffer_diff_result_t *result);
 
+/* The central algorithm to compare two images, and return the differences
+ * in the surface_diff.
+ *
+ * Provides number of pixels changed and maximum single-channel
+ * difference in result.
+ */
+cairo_status_t
+image_diff (const cairo_test_context_t *ctx,
+	    cairo_surface_t *surface_a,
+	    cairo_surface_t *surface_b,
+	    cairo_surface_t *surface_diff,
+	    buffer_diff_result_t *result);
+
 #endif