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-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);
}
generated by cgit v1.2.3 (git 2.39.1) at 2024-04-18 01:41:03 +0000