* blur.c: improve the Gaussian kernel generation by interpolating its

values in a quincunx pattern.

git-svn-id: file:///srv/caca.zoy.org/var/lib/svn/libpipi/trunk@2719 92316355-f0b4-4df1-b90c-862c8a59935f

pipi/filter/blur.c

@@ -71,11 +71,27 @@ pipi_image_t *pipi_gaussian_blur_ext(pipi_image_t *src, float rx, float ry,
     {
         for(i = -krx; i <= krx; i++)
         {
-            double u = (double)i * cost - (double)j * sint + dx;
-            double v = (double)j * cost + (double)i * sint + dy;
-            double ex = Kx * u * u;
-            double ey = Ky * v * v;
-            double d = exp(ex + ey);
+            static double const samples[] =
+            {
+                -.50, -.50, 0.5,
+                 .50, -.50, 0.5,
+                 .0,  .0, 1,
+                -.50,  .50, 0.5,
+                 .50,  .50, 0.5
+            };
+            double u, v, ex, ey, d = 0.;
+            int k;
+
+            for(k = 0; k < 5; k++)
+            {
+                u = ((double)i + samples[k * 3]) * cost
+                     - ((double)j + samples[k * 3 + 1]) * sint + dx;
+                v = ((double)i + samples[k * 3]) * sint
+                     + ((double)j + samples[k * 3 + 1]) * cost + dy;
+                ex = Kx * u * u;
+                ey = Ky * v * v;
+                d += samples[k * 3 + 2] * exp(ex + ey);
+            }
 
             kernel[(j + kry) * m + i + krx] = d;
             t += d;