Optimize gradient computations

We update the test suite reference images where needed, (pdiff
avoided a few, but most still needed updating). We take advantage
of the need for new reference images to shrink some of the giant
tests to speed them up a bit.

This optimization provides a 2x improvement in linear gradient
generation performance (numbers from an x86 laptop):

image-rgb    paint_linear_rgba_source-512 26.13 -> 11.13: 2.35x speedup
█▍
image-rgb    paint_linear_rgba_source-256  6.47 ->  2.76: 2.34x speedup
█▍
image-rgba      paint_linear_rgb_over-256  6.51 ->  2.86: 2.28x speedup
█▎
image-rgb      paint_linear_rgba_over-512 28.62 -> 13.70: 2.09x speedup
█▏
image-rgba       fill_linear_rgb_over-256  3.24 ->  1.94: 1.66x speedup
▋
image-rgb     stroke_linear_rgba_over-256  5.68 ->  4.10: 1.39x speedup
▍

23 files changed, 18 insertions, 18 deletions

diff --git a/test/clip-operator-ref.png b/test/clip-operator-ref.png
index cc8d83277..9f4eff094 100644
--- a/test/clip-operator-ref.png
+++ b/test/clip-operator-ref.png
diff --git a/test/clip-operator-rgb24-ref.png b/test/clip-operator-rgb24-ref.png
index 7be49f0cb..7ab964c30 100644
--- a/test/clip-operator-rgb24-ref.png
+++ b/test/clip-operator-rgb24-ref.png
diff --git a/test/clip-operator.c b/test/clip-operator.c
index 2e014a942..4d7f81e5c 100644
--- a/test/clip-operator.c
+++ b/test/clip-operator.c
@@ -27,9 +27,9 @@
 #include "cairo-test.h"
 #include <stdio.h>
 
-#define WIDTH 64
-#define HEIGHT 64
-#define PAD 10
+#define WIDTH 16
+#define HEIGHT 16
+#define PAD 2
 
 const char	png_filename[]	= "romedalen.png";
 
diff --git a/test/mask-ref.png b/test/mask-ref.png
index b7cee9919..909d9f295 100644
--- a/test/mask-ref.png
+++ b/test/mask-ref.png
diff --git a/test/mask-rgb24-ref.png b/test/mask-rgb24-ref.png
index 5e60fee7f..703236723 100644
--- a/test/mask-rgb24-ref.png
+++ b/test/mask-rgb24-ref.png
diff --git a/test/mask-svg-argb32-ref.png b/test/mask-svg-argb32-ref.png
index 5ac50a755..4a7f758a8 100644
--- a/test/mask-svg-argb32-ref.png
+++ b/test/mask-svg-argb32-ref.png
diff --git a/test/mask-svg-rgb24-ref.png b/test/mask-svg-rgb24-ref.png
deleted file mode 100644
index 0bf98d901..000000000
--- a/test/mask-svg-rgb24-ref.png
+++ /dev/null
diff --git a/test/mask.c b/test/mask.c
index 84ebf386e..984b82df8 100644
--- a/test/mask.c
+++ b/test/mask.c
@@ -28,9 +28,9 @@
 #include "cairo-test.h"
 #include <stdio.h>
 
-#define WIDTH 64
-#define HEIGHT 64
-#define PAD 10
+#define WIDTH 16
+#define HEIGHT 16
+#define PAD 2
 
 const char	png_filename[]	= "romedalen.png";
 
diff --git a/test/operator-clear-ref.png b/test/operator-clear-ref.png
index ff7afb4d0..a3f8b7f02 100644
--- a/test/operator-clear-ref.png
+++ b/test/operator-clear-ref.png
diff --git a/test/operator-clear-rgb24-ref.png b/test/operator-clear-rgb24-ref.png
index ebb02b3a8..d80da8be7 100644
--- a/test/operator-clear-rgb24-ref.png
+++ b/test/operator-clear-rgb24-ref.png
diff --git a/test/operator-clear.c b/test/operator-clear.c
index 84123fb85..89b50e41c 100644
--- a/test/operator-clear.c
+++ b/test/operator-clear.c
@@ -28,9 +28,9 @@
 #include "cairo-test.h"
 #include <stdio.h>
 
-#define WIDTH 64
-#define HEIGHT 64
-#define PAD 10
+#define WIDTH 16
+#define HEIGHT 16
+#define PAD 2
 
 const char	png_filename[]	= "romedalen.png";
 
diff --git a/test/operator-source-ref.png b/test/operator-source-ref.png
index 9f1a6266a..fe59f7fba 100644
--- a/test/operator-source-ref.png
+++ b/test/operator-source-ref.png
diff --git a/test/operator-source-rgb24-ref.png b/test/operator-source-rgb24-ref.png
index 41316eece..a762d60ab 100644
--- a/test/operator-source-rgb24-ref.png
+++ b/test/operator-source-rgb24-ref.png
diff --git a/test/operator-source.c b/test/operator-source.c
index 9984ca2c9..912fec680 100644
--- a/test/operator-source.c
+++ b/test/operator-source.c
@@ -28,9 +28,9 @@
 #include "cairo-test.h"
 #include <stdio.h>
 
-#define WIDTH 64
-#define HEIGHT 64
-#define PAD 10
+#define WIDTH 16
+#define HEIGHT 16
+#define PAD 2
 
 const char	png_filename[]	= "romedalen.png";
 
diff --git a/test/text-pattern-ref.png b/test/text-pattern-ref.png
index 38529cfe7..ac1dd84e7 100644
--- a/test/text-pattern-ref.png
+++ b/test/text-pattern-ref.png
diff --git a/test/text-pattern-rgb24-ref.png b/test/text-pattern-rgb24-ref.png
index ae87c6f4d..54b214b45 100644
--- a/test/text-pattern-rgb24-ref.png
+++ b/test/text-pattern-rgb24-ref.png
diff --git a/test/trap-clip-ref.png b/test/trap-clip-ref.png
index 3ce2431d2..93302976b 100644
--- a/test/trap-clip-ref.png
+++ b/test/trap-clip-ref.png
diff --git a/test/trap-clip-rgb24-ref.png b/test/trap-clip-rgb24-ref.png
index 6908ca3a5..15068aa56 100644
--- a/test/trap-clip-rgb24-ref.png
+++ b/test/trap-clip-rgb24-ref.png
diff --git a/test/trap-clip-svg-argb32-ref.png b/test/trap-clip-svg-argb32-ref.png
deleted file mode 100644
index 30dfa4f48..000000000
--- a/test/trap-clip-svg-argb32-ref.png
+++ /dev/null
diff --git a/test/trap-clip.c b/test/trap-clip.c
index e98d865d3..ba4d148e5 100644
--- a/test/trap-clip.c
+++ b/test/trap-clip.c
@@ -27,9 +27,9 @@
 #include "cairo-test.h"
 #include <stdio.h>
 
-#define WIDTH 64
-#define HEIGHT 64
-#define PAD 10
+#define WIDTH 16
+#define HEIGHT 16
+#define PAD 2
 
 const char	png_filename[]	= "romedalen.png";
 
diff --git a/test/unbounded-operator-ref.png b/test/unbounded-operator-ref.png
index 231019d86..03c7bc8f7 100644
--- a/test/unbounded-operator-ref.png
+++ b/test/unbounded-operator-ref.png
diff --git a/test/unbounded-operator-rgb24-ref.png b/test/unbounded-operator-rgb24-ref.png
index c12d9bbaa..b2f1a84dc 100644
--- a/test/unbounded-operator-rgb24-ref.png
+++ b/test/unbounded-operator-rgb24-ref.png
diff --git a/test/unbounded-operator.c b/test/unbounded-operator.c
index 7986c7c9c..e04ec8031 100644
--- a/test/unbounded-operator.c
+++ b/test/unbounded-operator.c
@@ -28,9 +28,9 @@
 #include "cairo-test.h"
 #include <stdio.h>
 
-#define WIDTH 64
-#define HEIGHT 64
-#define PAD 10
+#define WIDTH 16
+#define HEIGHT 16
+#define PAD 2
 
 static void
 draw_mask (cairo_t *cr, int x, int y)