* filter/blur.c: avoid annoying side effects with very small or negative

blur radii.

git-svn-id: file:///srv/caca.zoy.org/var/lib/svn/libpipi/trunk@2619 92316355-f0b4-4df1-b90c-862c8a59935f

pipi/filter/blur.c

@@ -27,6 +27,11 @@
 #include "pipi.h"
 #include "pipi_internals.h"
 
+/* Any standard deviation below this value will be rounded up, in order
+ * to avoid ridiculously low values. exp(-1/(2*0.2*0.2)) is < 10^-5 so
+ * there is little chance that any value below 0.2 will be useful. */
+#define BLUR_EPSILON 0.2
+
 pipi_image_t *pipi_gaussian_blur(pipi_image_t *src, float radius)
 {
     return pipi_gaussian_blur_ext(src, radius, radius, 0.0, 0.0);
@@ -42,6 +47,9 @@ pipi_image_t *pipi_gaussian_blur_ext(pipi_image_t *src, float rx, float ry,
     double K;
     int x, y, i, w, h, kr, kw;
 
+    if(rx < BLUR_EPSILON) rx = BLUR_EPSILON;
+    if(ry < BLUR_EPSILON) ry = BLUR_EPSILON;
+
     w = src->w;
     h = src->h;
 
@@ -54,7 +62,7 @@ pipi_image_t *pipi_gaussian_blur_ext(pipi_image_t *src, float rx, float ry,
 
     buffer = malloc(w * h * 4 * sizeof(double));
 
-    kr = (int)(3. * rx + 0.99999);
+    kr = (int)(3. * rx + 1.99999);
     kw = 2 * kr + 1;
     K = -1. / (2. * rx * rx);
 
@@ -91,7 +99,7 @@ pipi_image_t *pipi_gaussian_blur_ext(pipi_image_t *src, float rx, float ry,
 
     free(kernel);
 
-    kr = (int)(3. * ry + 0.99999);
+    kr = (int)(3. * ry + 1.99999);
     kw = 2 * kr + 1;
     K = -1. / (2. * ry * ry);