* pixels.c: add Floyd-Steinberg dithering to the float32 -> rgba32

conversion.

git-svn-id: file:///srv/caca.zoy.org/var/lib/svn/libpipi/trunk@2616 92316355-f0b4-4df1-b90c-862c8a59935f

pipi/pixels.c

@@ -28,6 +28,8 @@
 #include "pipi.h"
 #include "pipi_internals.h"
 
+#define GAMMA 2.2
+
 static void init_tables(void);
 
 static float u8tof32_table[256];
@@ -85,13 +87,30 @@ pipi_pixels_t *pipi_getpixels(pipi_image_t *img, pipi_format_t type)
         float *src = (float *)img->p[PIPI_PIXELS_RGBA_F].pixels;
         uint8_t *dest = (uint8_t *)img->p[type].pixels;
 
+        init_tables();
+
         for(y = 0; y < img->h; y++)
             for(x = 0; x < img->w; x++)
                 for(i = 0; i < 4; i++)
                 {
-                    double p = src[4 * (y * img->w + x) + i];
-                    dest[4 * (y * img->w + x) + i]
-                        = (int)(255.999 * pow(p, 1. / 2.2));
+                    double p, e;
+                    uint8_t d;
+
+                    p = src[4 * (y * img->w + x) + i];
+                    d = (int)(255.999 * pow(p, 1. / GAMMA));
+                    dest[4 * (y * img->w + x) + i] = d;
+
+                    e = p - u8tof32(d);
+                    if(x < img->w - 1)
+                        src[4 * (y * img->w + x + 1) + i] += e * .4375;
+                    if(y < img->h - 1)
+                    {
+                        if(x < img->w - 1)
+                            src[4 * ((y + 1) * img->w + x - 1) + i] += e * .1875;
+                        src[4 * ((y + 1) * img->w + x) + i] += e * .3125;
+                        if(x < img->w - 1)
+                            src[4 * ((y + 1) * img->w + x + 1) + i] += e * .0625;
+                    }
                 }
     }
     else
@@ -114,7 +133,7 @@ static void init_tables(void)
         return;
 
     for(i = 0; i < 256; i++)
-        u8tof32_table[i] = pow((double)i / 255., 2.2);
+        u8tof32_table[i] = pow((double)i / 255., GAMMA);
 
     done = 1;
 }