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authorMichael Drake <tlsa@netsurf-browser.org>2012-09-28 10:19:34 (GMT)
committer Michael Drake <tlsa@netsurf-browser.org>2012-09-28 10:19:34 (GMT)
commit0804bb7e067e66d4b05a6c45f9736b1e20505b96 (patch)
treee6b5e4ac559963dd0767e2ed39c878202f056c0f
parent46f3c9ea3793d146337c81bf8858d99238c05e86 (diff)
downloadlibnsfb-0804bb7e067e66d4b05a6c45f9736b1e20505b96.tar.gz
libnsfb-0804bb7e067e66d4b05a6c45f9736b1e20505b96.tar.bz2
Add error diffusion to palette based rendering. Only used for bitmap and scaled bitmap plots. Doesn't do serpentine path, since that would need changes to the common bitmap rendering code.
-rw-r--r--include/palette.h130
-rw-r--r--src/palette.c32
-rw-r--r--src/plot/8bpp.c2
-rw-r--r--src/plot/common.c69
-rw-r--r--src/surface/sdl.c2
5 files changed, 206 insertions, 29 deletions
diff --git a/include/palette.h b/include/palette.h
index 845c1bc..f975ef2 100644
--- a/include/palette.h
+++ b/include/palette.h
@@ -27,21 +27,35 @@ struct nsfb_palette_s {
enum nsfb_palette_type_e type; /**< Palette type */
uint8_t last; /**< Last used palette index */
nsfb_colour_t data[256]; /**< Palette for index modes */
+
+ bool dither; /**< Whether to use error diffusion */
+ struct {
+ int width; /**< Length of error value buffer ring*/
+ int current; /**< Current pos in ring buffer*/
+ int *data; /**< Ring buffer error values */
+ int data_len; /**< Max size of ring */
+ } dither_ctx;
};
+
/** Create an empty palette object. */
-bool nsfb_palette_new(struct nsfb_palette_s **palette);
+bool nsfb_palette_new(struct nsfb_palette_s **palette, int width);
/** Free a palette object. */
void nsfb_palette_free(struct nsfb_palette_s *palette);
+/** Init error diffusion for a plot. */
+void nsfb_palette_dither_init(struct nsfb_palette_s *palette, int width);
+
+/** Finalise error diffusion after a plot. */
+void nsfb_palette_dither_fini(struct nsfb_palette_s *palette);
+
/** Generate libnsfb 8bpp default palette. */
void nsfb_palette_generate_nsfb_8bpp(struct nsfb_palette_s *palette);
-
-static inline uint8_t nsfb_palette_best_match(
- const struct nsfb_palette_s *palette,
- nsfb_colour_t c)
+/** Find best palette match for given colour. */
+static inline uint8_t nsfb_palette_best_match(struct nsfb_palette_s *palette,
+ nsfb_colour_t c, int *r_error, int *g_error, int *b_error)
{
uint8_t best_col = 0;
@@ -68,6 +82,9 @@ static inline uint8_t nsfb_palette_best_match(
best_col = col;
best_distance = cur_distance;
+ *r_error = dr;
+ *g_error = dg;
+ *b_error = db;
/* Index into grayscale part */
col = (( c & 0xFF) +
@@ -82,6 +99,9 @@ static inline uint8_t nsfb_palette_best_match(
if (cur_distance < best_distance) {
best_distance = cur_distance;
best_col = col;
+ *r_error = dr;
+ *g_error = dg;
+ *b_error = db;
}
break;
@@ -97,6 +117,9 @@ static inline uint8_t nsfb_palette_best_match(
if (cur_distance < best_distance) {
best_distance = cur_distance;
best_col = col;
+ *r_error = dr;
+ *g_error = dg;
+ *b_error = db;
}
}
break;
@@ -108,4 +131,101 @@ static inline uint8_t nsfb_palette_best_match(
return best_col;
}
+/** Find best palette match for given colour, with error diffusion. */
+static inline uint8_t nsfb_palette_best_match_dither(
+ struct nsfb_palette_s *palette, nsfb_colour_t c)
+{
+ int r, g, b;
+ int current;
+ int error;
+ int width = palette->dither_ctx.width;
+ uint8_t best_col_index;
+
+ if (palette == NULL)
+ return 0;
+
+ if (palette->dither == false)
+ return nsfb_palette_best_match(palette, c, &r, &g, &b);
+
+ current = palette->dither_ctx.current;
+
+ /* Get RGB components of colour, and apply error */
+ r = ( c & 0xFF) + palette->dither_ctx.data[current ];
+ g = ((c >> 8) & 0xFF) + palette->dither_ctx.data[current + 1];
+ b = ((c >> 16) & 0xFF) + palette->dither_ctx.data[current + 2];
+
+ /* Clamp new RGB components to range */
+ if (r < 0) r = 0;
+ if (r > 255) r = 255;
+ if (g < 0) g = 0;
+ if (g > 255) g = 255;
+ if (b < 0) b = 0;
+ if (b > 255) b = 255;
+
+ /* Reset error diffusion slots to 0 */
+ palette->dither_ctx.data[current ] = 0;
+ palette->dither_ctx.data[current + 1] = 0;
+ palette->dither_ctx.data[current + 2] = 0;
+
+ /* Rebuild colour from modified components */
+ c = r + (g << 8) + (b << 16);
+
+ /* Get best match for pixel, and find errors for each component */
+ best_col_index = nsfb_palette_best_match(palette, c, &r, &g, &b);
+
+ /* Advance one set of error diffusion slots */
+ current += 3;
+ if (current >= width)
+ current = 0;
+ palette->dither_ctx.current = current;
+
+ /* Save errors
+ *
+ * [*]-[N]
+ * / | \
+ * [l]-[m]-[r]
+ */
+ error = current;
+
+ /* Error for [N] (next) */
+ if (error != 0) {
+ /* The pixel exists */
+ palette->dither_ctx.data[error ] += r * 7 / 16;
+ palette->dither_ctx.data[error + 1] += g * 7 / 16;
+ palette->dither_ctx.data[error + 2] += b * 7 / 16;
+ }
+
+ error += width - 2 * 3;
+ if (error >= width)
+ error -= width;
+ /* Error for [l] (below, left) */
+ if (error >= 0 && error != 3) {
+ /* The pixel exists */
+ palette->dither_ctx.data[error ] += r * 3 / 16;
+ palette->dither_ctx.data[error + 1] += g * 3 / 16;
+ palette->dither_ctx.data[error + 2] += b * 3 / 16;
+ }
+
+ error += 3;
+ if (error >= width)
+ error -= width;
+ /* Error for [m] (below, middle) */
+ palette->dither_ctx.data[error ] += r * 5 / 16;
+ palette->dither_ctx.data[error + 1] += g * 5 / 16;
+ palette->dither_ctx.data[error + 2] += b * 5 / 16;
+
+ error += 3;
+ if (error >= width)
+ error -= width;
+ /* Error for [r] (below, right) */
+ if (error != 0) {
+ /* The pixel exists */
+ palette->dither_ctx.data[error ] += r / 16;
+ palette->dither_ctx.data[error + 1] += g / 16;
+ palette->dither_ctx.data[error + 2] += b / 16;
+ }
+
+ return best_col_index;
+}
+
#endif /* PALETTE_H */
diff --git a/src/palette.c b/src/palette.c
index eba95cd..d600001 100644
--- a/src/palette.c
+++ b/src/palette.c
@@ -13,12 +13,13 @@
#include <assert.h>
#include <stdbool.h>
#include <stdlib.h>
+#include <string.h>
#include "palette.h"
/** Create an empty palette object. */
-bool nsfb_palette_new(struct nsfb_palette_s **palette)
+bool nsfb_palette_new(struct nsfb_palette_s **palette, int width)
{
*palette = malloc(sizeof(struct nsfb_palette_s));
if (*palette == NULL) {
@@ -28,14 +29,41 @@ bool nsfb_palette_new(struct nsfb_palette_s **palette)
(*palette)->type = NSFB_PALETTE_EMPTY;
(*palette)->last = 0;
+ (*palette)->dither = false;
+ (*palette)->dither_ctx.data_len = width * 3;
+ (*palette)->dither_ctx.data = malloc(width * 3 * sizeof(int));
+ if ((*palette)->dither_ctx.data == NULL) {
+ nsfb_palette_free(*palette);
+ return false;
+ }
+
return true;
}
/** Free a palette object. */
void nsfb_palette_free(struct nsfb_palette_s *palette)
{
- if (palette != NULL)
+ if (palette != NULL) {
+ if (palette->dither_ctx.data != NULL) {
+ free(palette->dither_ctx.data);
+ }
free(palette);
+ }
+}
+
+/** Init error diffusion for a plot. */
+void nsfb_palette_dither_init(struct nsfb_palette_s *palette, int width)
+{
+ palette->dither = true;
+ memset(palette->dither_ctx.data, 0, palette->dither_ctx.data_len);
+ palette->dither_ctx.width = width * 3;
+ palette->dither_ctx.current = 0;
+}
+
+/** Finalise error diffusion after a plot. */
+void nsfb_palette_dither_fini(struct nsfb_palette_s *palette)
+{
+ palette->dither = false;
}
/** Generate libnsfb 8bpp default palette. */
diff --git a/src/plot/8bpp.c b/src/plot/8bpp.c
index 05574d8..0245542 100644
--- a/src/plot/8bpp.c
+++ b/src/plot/8bpp.c
@@ -39,7 +39,7 @@ static uint8_t colour_to_pixel(nsfb_t *nsfb, nsfb_colour_t c)
if (nsfb->palette == NULL)
return 0;
- return nsfb_palette_best_match(nsfb->palette, c);
+ return nsfb_palette_best_match_dither(nsfb->palette, c);
}
#define PLOT_TYPE uint8_t
diff --git a/src/plot/common.c b/src/plot/common.c
index 185e323..c9f9dc1 100644
--- a/src/plot/common.c
+++ b/src/plot/common.c
@@ -16,6 +16,8 @@
#error PLOT_LINELEN must be a macro to increment a line length
#endif
+#include "palette.h"
+
#define SIGN(x) ((x<0) ? -1 : ((x>0) ? 1 : 0))
static bool
@@ -249,8 +251,7 @@ static bool bitmap_scaled(nsfb_t *nsfb, const nsfb_bbox_t *loc,
nsfb_bbox_t clipped; /* clipped display */
/* The part of the scaled image actually displayed is cropped to the
- * current context.
- */
+ * current context. */
clipped.x0 = x;
clipped.y0 = y;
clipped.x1 = x + width;
@@ -271,6 +272,10 @@ static bool bitmap_scaled(nsfb_t *nsfb, const nsfb_bbox_t *loc,
else
rwidth = width;
+ if (nsfb->palette != NULL) {
+ nsfb_palette_dither_init(nsfb->palette, rwidth);
+ }
+
/* get veritcal (y) and horizontal (x) scale factors; both integer
* part and remainder */
dx = bmp_width / width;
@@ -299,7 +304,8 @@ static bool bitmap_scaled(nsfb_t *nsfb, const nsfb_bbox_t *loc,
pvideo = get_xy_loc(nsfb, clipped.x0, clipped.y0);
pvideo_limit = pvideo + PLOT_LINELEN(nsfb->linelen) * rheight;
if (alpha) {
- for (; pvideo < pvideo_limit; pvideo += PLOT_LINELEN(nsfb->linelen)) {
+ for (; pvideo < pvideo_limit;
+ pvideo += PLOT_LINELEN(nsfb->linelen)) {
/* looping through render area vertically */
xoff = xoffs;
rx = rxs;
@@ -322,7 +328,8 @@ static bool bitmap_scaled(nsfb_t *nsfb, const nsfb_bbox_t *loc,
xloop)));
}
/* plot pixel */
- *(pvideo + xloop) = colour_to_pixel(nsfb, abpixel);
+ *(pvideo + xloop) = colour_to_pixel(
+ nsfb, abpixel);
}
/* handle horizontal interpolation */
xoff += dx;
@@ -341,7 +348,8 @@ static bool bitmap_scaled(nsfb_t *nsfb, const nsfb_bbox_t *loc,
}
}
} else {
- for (; pvideo < pvideo_limit; pvideo += PLOT_LINELEN(nsfb->linelen)) {
+ for (; pvideo < pvideo_limit;
+ pvideo += PLOT_LINELEN(nsfb->linelen)) {
/* looping through render area vertically */
xoff = xoffs;
rx = rxs;
@@ -350,7 +358,8 @@ static bool bitmap_scaled(nsfb_t *nsfb, const nsfb_bbox_t *loc,
/* get value of source pixel in question */
abpixel = pixel[yoff + xoff];
/* plot pixel */
- *(pvideo + xloop) = colour_to_pixel(nsfb, abpixel);
+ *(pvideo + xloop) = colour_to_pixel(
+ nsfb, abpixel);
/* handle horizontal interpolation */
xoff += dx;
@@ -369,6 +378,11 @@ static bool bitmap_scaled(nsfb_t *nsfb, const nsfb_bbox_t *loc,
}
}
}
+
+ if (nsfb->palette != NULL) {
+ nsfb_palette_dither_fini(nsfb->palette);
+ }
+
return true;
}
@@ -391,17 +405,16 @@ bitmap(nsfb_t *nsfb,
int height = loc->y1 - loc->y0;
nsfb_bbox_t clipped; /* clipped display */
- if (width == 0 || height == 0)
- return true;
+ if (width == 0 || height == 0)
+ return true;
/* Scaled bitmaps are handled by a separate function */
if (width != bmp_width || height != bmp_height)
return bitmap_scaled(nsfb, loc, pixel, bmp_width, bmp_height,
bmp_stride, alpha);
- /* The part of the scaled image actually displayed is cropped to the
- * current context.
- */
+ /* The part of the image actually displayed is cropped to the
+ * current context. */
clipped.x0 = x;
clipped.y0 = y;
clipped.x1 = x + width;
@@ -416,6 +429,10 @@ bitmap(nsfb_t *nsfb,
if (width > (clipped.x1 - clipped.x0))
width = (clipped.x1 - clipped.x0);
+ if (nsfb->palette != NULL) {
+ nsfb_palette_dither_init(nsfb->palette, width);
+ }
+
xoff = clipped.x0 - x;
yoff = (clipped.y0 - y) * bmp_stride;
height = height * bmp_stride + yoff;
@@ -428,16 +445,22 @@ bitmap(nsfb_t *nsfb,
for (xloop = 0; xloop < width; xloop++) {
abpixel = pixel[yloop + xloop + xoff];
if ((abpixel & 0xFF000000) != 0) {
- /* pixel is not transparent; have to
- * plot something */
- if ((abpixel & 0xFF000000) != 0xFF000000) {
- /* pixel is not opaque; need to
- * blend */
- abpixel = nsfb_plot_ablend(abpixel,
- pixel_to_colour(nsfb, *(pvideo + xloop)));
+ /* pixel is not transparent; have to
+ * plot something */
+ if ((abpixel & 0xFF000000) !=
+ 0xFF000000) {
+ /* pixel is not opaque; need to
+ * blend */
+ abpixel = nsfb_plot_ablend(
+ abpixel,
+ pixel_to_colour(
+ nsfb,
+ *(pvideo +
+ xloop)));
}
- *(pvideo + xloop) = colour_to_pixel(nsfb, abpixel);
+ *(pvideo + xloop) = colour_to_pixel(
+ nsfb, abpixel);
}
}
pvideo += PLOT_LINELEN(nsfb->linelen);
@@ -446,11 +469,17 @@ bitmap(nsfb_t *nsfb,
for (yloop = yoff; yloop < height; yloop += bmp_stride) {
for (xloop = 0; xloop < width; xloop++) {
abpixel = pixel[yloop + xloop + xoff];
- *(pvideo + xloop) = colour_to_pixel(nsfb, abpixel);
+ *(pvideo + xloop) = colour_to_pixel(
+ nsfb, abpixel);
}
pvideo += PLOT_LINELEN(nsfb->linelen);
}
}
+
+ if (nsfb->palette != NULL) {
+ nsfb_palette_dither_fini(nsfb->palette);
+ }
+
return true;
}
diff --git a/src/surface/sdl.c b/src/surface/sdl.c
index 7a86dc1..0554e26 100644
--- a/src/surface/sdl.c
+++ b/src/surface/sdl.c
@@ -458,7 +458,7 @@ static int sdl_initialise(nsfb_t *nsfb)
nsfb->surface_priv = sdl_screen;
if (nsfb->bpp == 8) {
- nsfb_palette_new(&nsfb->palette);
+ nsfb_palette_new(&nsfb->palette, nsfb->width);
set_palette(nsfb);
}