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gecko/gfx/cairo/pixman-dither.patch
Jeff Muizelaar 091c38ffda Bug 683243. Dither 16 bit gradients. r=BenWa 
This does a 2x2 ordered dither in the same way that Skia does.

One of the things I'm currently unhappy with is that it duplicates
the gradient walker code for 16 bits. We could turn it into a large
macro that does the appropriate things for 16 bit and 32 bit
versions, but that's not particularly appealing.
2012-07-04 11:42:29 -04:00

311 lines
8.7 KiB
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diff --git a/gfx/cairo/libpixman/src/pixman-dither.h b/gfx/cairo/libpixman/src/pixman-dither.h
new file mode 100644
--- /dev/null
+++ b/gfx/cairo/libpixman/src/pixman-dither.h
@@ -0,0 +1,51 @@
+#define R16_BITS 5
+#define G16_BITS 6
+#define B16_BITS 5
+
+#define R16_SHIFT (B16_BITS + G16_BITS)
+#define G16_SHIFT (B16_BITS)
+#define B16_SHIFT 0
+
+#define MASK 0xff
+#define ONE_HALF 0x80
+
+#define A_SHIFT 8 * 3
+#define R_SHIFT 8 * 2
+#define G_SHIFT 8
+#define A_MASK 0xff000000
+#define R_MASK 0xff0000
+#define G_MASK 0xff00
+
+#define RB_MASK 0xff00ff
+#define AG_MASK 0xff00ff00
+#define RB_ONE_HALF 0x800080
+#define RB_MASK_PLUS_ONE 0x10000100
+
+#define ALPHA_8(x) ((x) >> A_SHIFT)
+#define RED_8(x) (((x) >> R_SHIFT) & MASK)
+#define GREEN_8(x) (((x) >> G_SHIFT) & MASK)
+#define BLUE_8(x) ((x) & MASK)
+
+// This uses the same dithering technique that Skia does.
+// It is essentially preturbing the lower bit based on the
+// high bit
+static inline uint16_t dither_32_to_16(uint32_t c)
+{
+ uint8_t b = BLUE_8(c);
+ uint8_t g = GREEN_8(c);
+ uint8_t r = RED_8(c);
+ r = ((r << 1) - ((r >> (8 - R16_BITS) << (8 - R16_BITS)) | (r >> R16_BITS))) >> (8 - R16_BITS);
+ g = ((g << 1) - ((g >> (8 - G16_BITS) << (8 - G16_BITS)) | (g >> G16_BITS))) >> (8 - G16_BITS);
+ b = ((b << 1) - ((b >> (8 - B16_BITS) << (8 - B16_BITS)) | (b >> B16_BITS))) >> (8 - B16_BITS);
+ return ((r << R16_SHIFT) | (g << G16_SHIFT) | (b << B16_SHIFT));
+}
+
+static inline uint16_t dither_8888_to_0565(uint32_t color, pixman_bool_t toggle)
+{
+ // alternate between a preturbed truncation and a regular truncation
+ if (toggle) {
+ return dither_32_to_16(color);
+ } else {
+ return CONVERT_8888_TO_0565(color);
+ }
+}
diff --git a/gfx/cairo/libpixman/src/pixman-linear-gradient.c b/gfx/cairo/libpixman/src/pixman-linear-gradient.c
--- a/gfx/cairo/libpixman/src/pixman-linear-gradient.c
+++ b/gfx/cairo/libpixman/src/pixman-linear-gradient.c
@@ -26,16 +26,18 @@
*/
#ifdef HAVE_CONFIG_H
#include <config.h>
#endif
#include <stdlib.h>
#include "pixman-private.h"
+#include "pixman-dither.h"
+
static pixman_bool_t
linear_gradient_is_horizontal (pixman_image_t *image,
int x,
int y,
int width,
int height)
{
linear_gradient_t *linear = (linear_gradient_t *)image;
@@ -222,25 +224,28 @@ linear_get_scanline_narrow (pixman_iter_
return iter->buffer;
}
static uint16_t convert_8888_to_0565(uint32_t color)
{
return CONVERT_8888_TO_0565(color);
}
+
+
static uint32_t *
linear_get_scanline_16 (pixman_iter_t *iter,
const uint32_t *mask)
{
pixman_image_t *image = iter->image;
int x = iter->x;
int y = iter->y;
int width = iter->width;
uint16_t * buffer = (uint16_t*)iter->buffer;
+ pixman_bool_t toggle = ((x ^ y) & 1);
pixman_vector_t v, unit;
pixman_fixed_32_32_t l;
pixman_fixed_48_16_t dx, dy;
gradient_t *gradient = (gradient_t *)image;
linear_gradient_t *linear = (linear_gradient_t *)image;
uint16_t *end = buffer + width;
pixman_gradient_walker_t walker;
@@ -294,34 +299,47 @@ linear_get_scanline_16 (pixman_iter_t *
t = ((dx * v.vector[0] + dy * v.vector[1]) -
(dx * linear->p1.x + dy * linear->p1.y) * v2) * invden;
inc = (dx * unit.vector[0] + dy * unit.vector[1]) * invden;
}
next_inc = 0;
if (((pixman_fixed_32_32_t )(inc * width)) == 0)
{
- register uint16_t color;
+ register uint32_t color;
+ uint16_t dither_diff;
+ uint16_t color16;
+ uint16_t color16b;
- color = convert_8888_to_0565(_pixman_gradient_walker_pixel (&walker, t));
- while (buffer < end)
- *buffer++ = color;
+ color = _pixman_gradient_walker_pixel (&walker, t);
+ color16 = dither_8888_to_0565(color, toggle);
+ color16b = dither_8888_to_0565(color, toggle^1);
+ // compute the difference
+ dither_diff = color16 ^ color16b;
+ while (buffer < end) {
+ *buffer++ = color16;
+ // use dither_diff to toggle between color16 and color16b
+ color16 ^= dither_diff;
+ toggle ^= 1;
+ }
}
else
{
int i;
i = 0;
while (buffer < end)
{
if (!mask || *mask++)
{
- *buffer = convert_8888_to_0565(_pixman_gradient_walker_pixel (&walker,
- t + next_inc));
+ *buffer = dither_8888_to_0565(_pixman_gradient_walker_pixel (&walker,
+ t + next_inc),
+ toggle);
}
+ toggle ^= 1;
i++;
next_inc = inc * i;
buffer++;
}
}
}
else
{
@@ -340,18 +358,20 @@ linear_get_scanline_16 (pixman_iter_t *
invden = pixman_fixed_1 * (double) pixman_fixed_1 /
(l * (double) v.vector[2]);
v2 = v.vector[2] * (1. / pixman_fixed_1);
t = ((dx * v.vector[0] + dy * v.vector[1]) -
(dx * linear->p1.x + dy * linear->p1.y) * v2) * invden;
}
- *buffer = convert_8888_to_0565(_pixman_gradient_walker_pixel (&walker, t));
+ *buffer = dither_8888_to_0565(_pixman_gradient_walker_pixel (&walker, t),
+ toggle);
}
+ toggle ^= 1;
++buffer;
v.vector[0] += unit.vector[0];
v.vector[1] += unit.vector[1];
v.vector[2] += unit.vector[2];
}
}
@@ -369,17 +389,18 @@ linear_get_scanline_wide (pixman_iter_t
pixman_expand ((uint64_t *)buffer, buffer, PIXMAN_a8r8g8b8, iter->width);
return buffer;
}
void
_pixman_linear_gradient_iter_init (pixman_image_t *image, pixman_iter_t *iter)
{
- if (linear_gradient_is_horizontal (
+ // XXX: we can't use this optimization when dithering
+ if (0 && linear_gradient_is_horizontal (
iter->image, iter->x, iter->y, iter->width, iter->height))
{
if (iter->flags & ITER_16)
linear_get_scanline_16 (iter, NULL);
else if (iter->flags & ITER_NARROW)
linear_get_scanline_narrow (iter, NULL);
else
linear_get_scanline_wide (iter, NULL);
diff --git a/gfx/cairo/libpixman/src/pixman-radial-gradient.c b/gfx/cairo/libpixman/src/pixman-radial-gradient.c
--- a/gfx/cairo/libpixman/src/pixman-radial-gradient.c
+++ b/gfx/cairo/libpixman/src/pixman-radial-gradient.c
@@ -29,16 +29,18 @@
#ifdef HAVE_CONFIG_H
#include <config.h>
#endif
#include <stdlib.h>
#include <math.h>
#include "pixman-private.h"
+#include "pixman-dither.h"
+
static inline pixman_fixed_32_32_t
dot (pixman_fixed_48_16_t x1,
pixman_fixed_48_16_t y1,
pixman_fixed_48_16_t z1,
pixman_fixed_48_16_t x2,
pixman_fixed_48_16_t y2,
pixman_fixed_48_16_t z2)
{
@@ -489,16 +491,17 @@ radial_get_scanline_16 (pixman_iter_t *i
* <=> for every p, the radiuses associated with the two t solutions
* have opposite sign
*/
pixman_image_t *image = iter->image;
int x = iter->x;
int y = iter->y;
int width = iter->width;
uint16_t *buffer = iter->buffer;
+ pixman_bool_t toggle = ((x ^ y) & 1);
gradient_t *gradient = (gradient_t *)image;
radial_gradient_t *radial = (radial_gradient_t *)image;
uint16_t *end = buffer + width;
pixman_gradient_walker_t walker;
pixman_vector_t v, unit;
/* reference point is the center of the pixel */
@@ -575,25 +578,27 @@ radial_get_scanline_16 (pixman_iter_t *i
unit.vector[0], unit.vector[1], 0);
ddc = 2 * dot (unit.vector[0], unit.vector[1], 0,
unit.vector[0], unit.vector[1], 0);
while (buffer < end)
{
if (!mask || *mask++)
{
- *buffer = convert_8888_to_0565(
+ *buffer = dither_8888_to_0565(
radial_compute_color (radial->a, b, c,
radial->inva,
radial->delta.radius,
radial->mindr,
&walker,
- image->common.repeat));
+ image->common.repeat),
+ toggle);
}
+ toggle ^= 1;
b += db;
c += dc;
dc += ddc;
++buffer;
}
}
else
{
@@ -621,31 +626,33 @@ radial_get_scanline_16 (pixman_iter_t *i
radial->delta.x, radial->delta.y,
radial->delta.radius);
/* / pixman_fixed_1 / pixman_fixed_1 */
c = fdot (pdx, pdy, -radial->c1.radius,
pdx, pdy, radial->c1.radius);
/* / pixman_fixed_1 / pixman_fixed_1 */
- *buffer = convert_8888_to_0565 (
+ *buffer = dither_8888_to_0565 (
radial_compute_color (radial->a, b, c,
radial->inva,
radial->delta.radius,
radial->mindr,
&walker,
- image->common.repeat));
+ image->common.repeat),
+ toggle);
}
else
{
*buffer = 0;
}
}
++buffer;
+ toggle ^= 1;
v.vector[0] += unit.vector[0];
v.vector[1] += unit.vector[1];
v.vector[2] += unit.vector[2];
}
}
iter->y++;
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