* pixels.c: speed up the RGBA32 -> float32 conversion, using a simple LUT.

git-svn-id: file:///srv/caca.zoy.org/var/lib/svn/libpipi/trunk@2609 92316355-f0b4-4df1-b90c-862c8a59935f

pipi/pixels.c

@@ -28,8 +28,11 @@
 #include "pipi.h"
 #include "pipi_internals.h"
 
-#define C2I(p) (pow(((double)p)/255., 2.2))
-#define I2C(p) ((int)255.999*pow(((double)p), 1./2.2))
+static void init_tables(void);
+
+static float u8tof32_table[256];
+static inline float u8tof32(uint8_t p) { return u8tof32_table[(int)p]; }
+
 
 /* Return a direct pointer to an image's pixels. */
 pipi_pixels_t *pipi_getpixels(pipi_image_t *img, pipi_format_t type)
@@ -68,11 +71,13 @@ pipi_pixels_t *pipi_getpixels(pipi_image_t *img, pipi_format_t type)
         uint8_t *src = (uint8_t *)img->p[PIPI_PIXELS_RGBA32].pixels;
         float *dest = (float *)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++)
                     dest[4 * (y * img->w + x) + i]
-                        = C2I(src[4 * (y * img->w + x) + i]);
+                        = u8tof32(src[4 * (y * img->w + x) + i]);
     }
     else if(img->last_modified == PIPI_PIXELS_RGBA_F
                        && type == PIPI_PIXELS_RGBA32)
@@ -83,8 +88,11 @@ pipi_pixels_t *pipi_getpixels(pipi_image_t *img, pipi_format_t type)
         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]
-                        = I2C(src[4 * (y * img->w + x) + i]);
+                        = (int)(255.999 * pow(p, 1. / 2.2));
+                }
     }
     else
     {
@@ -96,3 +104,18 @@ pipi_pixels_t *pipi_getpixels(pipi_image_t *img, pipi_format_t type)
     return &img->p[type];
 }
 
+
+static void init_tables(void)
+{
+    static int done = 0;
+    int i;
+
+    if(done)
+        return;
+
+    for(i = 0; i < 256; i++)
+        u8tof32_table[i] = pow((double)i / 255., 2.2);
+
+    done = 1;
+}
+