* Error diffusion methods now support either raster or serpentine scan.

git-svn-id: file:///srv/caca.zoy.org/var/lib/svn/libpipi/trunk@2656 92316355-f0b4-4df1-b90c-862c8a59935f

examples/dither.c

@@ -17,9 +17,11 @@ int main(int argc, char *argv[])
         fprintf(stderr, "%s: too few arguments\n", argv[0]);
         fprintf(stderr, "Usage: %s <src> <method> <dest>\n", argv[0]);
         fprintf(stderr, "Where <method> is one of:\n");
-        fprintf(stderr, "  1   Floyd-Steinberg (serpentine)\n");
-        fprintf(stderr, "  2   Ostromoukhov (serpentine)\n");
-        fprintf(stderr, "  3   Direct binary search\n");
+        fprintf(stderr, "  1   Floyd-Steinberg (raster)\n");
+        fprintf(stderr, "  2   Floyd-Steinberg (serpentine)\n");
+        fprintf(stderr, "  3   Ostromoukhov (raster)\n");
+        fprintf(stderr, "  4   Ostromoukhov (serpentine)\n");
+        fprintf(stderr, "  5   Direct binary search\n");
         return EXIT_FAILURE;
     }
 
@@ -30,13 +32,17 @@ int main(int argc, char *argv[])
 
     switch(atoi(argv[2]))
     {
-        case 3:
+        case 5:
             newimg = pipi_dbs(img); break;
+        case 4:
+            newimg = pipi_ostromoukhov(img, PIPI_SCAN_SERPENTINE); break;
+        case 3:
+            newimg = pipi_ostromoukhov(img, PIPI_SCAN_RASTER); break;
         case 2:
-            newimg = pipi_ostromoukhov(img); break;
+            newimg = pipi_floydsteinberg(img, PIPI_SCAN_SERPENTINE); break;
         case 1:
         default:
-            newimg = pipi_floydsteinberg(img); break;
+            newimg = pipi_floydsteinberg(img, PIPI_SCAN_RASTER); break;
     }
 
     pipi_free(img);

examples/edd.c

@@ -52,7 +52,7 @@ int main(int argc, char *argv[])
     img = pipi_load(argv[1]);
     pipi_getpixels(img, PIPI_PIXELS_Y_F);
     gauss = pipi_gaussian_blur(img, sigma);
-    dither = pipi_floydsteinberg(img);
+    dither = pipi_floydsteinberg(img, PIPI_SCAN_RASTER);
     pipi_free(img);
 
     /* Compute the standard error */

pipi/dither/floydsteinberg.c

@@ -22,7 +22,7 @@
 #include "pipi.h"
 #include "pipi_internals.h"
 
-pipi_image_t *pipi_floydsteinberg(pipi_image_t *src)
+pipi_image_t *pipi_floydsteinberg(pipi_image_t *src, pipi_scan_t scan)
 {
     pipi_image_t *dst;
     pipi_pixels_t *srcp, *dstp;
@@ -41,11 +41,13 @@ pipi_image_t *pipi_floydsteinberg(pipi_image_t *src)
 
     for(y = 0; y < h; y++)
     {
+        int reverse = (y & 1) && (scan == PIPI_SCAN_SERPENTINE);
+
         for(x = 0; x < w; x++)
         {
             float p, q, e;
-            int x2 = (y & 1) ? x : w - 1 - x;
-            int s = (y & 1) ? 1 : -1;
+            int x2 = reverse ? w - 1 - x : x;
+            int s = reverse ? -1 : 1;
 
             p = srcdata[y * w + x2];
             q = p < 0.5 ? 0. : 1.;

pipi/dither/ostromoukhov.c

@@ -66,7 +66,7 @@ static int const table[][3] =
      {385, 112, 103}, {65, 18, 17}, {395, 104, 101}, {4, 1, 1}
 };
 
-pipi_image_t *pipi_ostromoukhov(pipi_image_t *src)
+pipi_image_t *pipi_ostromoukhov(pipi_image_t *src, pipi_scan_t scan)
 {
     pipi_image_t *dst;
     pipi_pixels_t *srcp, *dstp;
@@ -85,13 +85,15 @@ pipi_image_t *pipi_ostromoukhov(pipi_image_t *src)
 
     for(y = 0; y < h; y++)
     {
+        int reverse = (y & 1) && (scan == PIPI_SCAN_SERPENTINE);
+
         for(x = 0; x < w; x++)
         {
             float p, q, e;
             int x2, s, i;
 
-            x2 = (y & 1) ? x : w - 1 - x;
-            s = (y & 1) ? 1 : -1;
+            x2 = reverse ? w - 1 - x : x;
+            s = reverse ? -1 : 1;
 
             p = srcdata[y * w + x2];
             q = p < 0.5 ? 0. : 1.;

pipi/pipi.h

@@ -24,6 +24,15 @@ extern "C"
 {
 #endif
 
+/* pipi_scan_t: this enum is a list of all possible scanning methods when
+ * parsing an image’s pixels. Not all functions support all scanning paths. */
+typedef enum
+{
+    PIPI_SCAN_RASTER = 0,
+    PIPI_SCAN_SERPENTINE = 1
+}
+pipi_scan_t;
+
 /* pipi_format_t: this enum is a list of all possible pixel formats for
  * our internal images. RGBA32 is the most usual format when an image has
  * just been loaded, but RGBA_F is a lot better for complex operations. */
@@ -68,8 +77,8 @@ extern pipi_image_t *pipi_gaussian_blur(pipi_image_t *, float);
 extern pipi_image_t *pipi_gaussian_blur_ext(pipi_image_t *,
                                             float, float, float, float);
 
-extern pipi_image_t *pipi_floydsteinberg(pipi_image_t *);
-extern pipi_image_t *pipi_ostromoukhov(pipi_image_t *);
+extern pipi_image_t *pipi_floydsteinberg(pipi_image_t *, pipi_scan_t);
+extern pipi_image_t *pipi_ostromoukhov(pipi_image_t *, pipi_scan_t);
 extern pipi_image_t *pipi_dbs(pipi_image_t *);
 extern void pipi_dither_24to16(pipi_image_t *);