[cairo] [PATCH pixman 1/4] Compute filter size using boundary of xformed ellipse, not rectangle

[Bill Spitzak]

This is much more accurate and less blurry. In particular the filtering does
not change as the image is rotated.
---
 demos/scale.c |   43 ++-----------------------------------------
 1 file changed, 2 insertions(+), 41 deletions(-)

diff --git a/demos/scale.c b/demos/scale.c
index d00307e..0b6c715 100644
--- a/demos/scale.c
+++ b/demos/scale.c
@@ -55,50 +55,11 @@ get_widget (app_t *app, const char *name)
     return widget;
 }
 
-static double
-min4 (double a, double b, double c, double d)
-{
-    double m1, m2;
-
-    m1 = MIN (a, b);
-    m2 = MIN (c, d);
-    return MIN (m1, m2);
-}
-
-static double
-max4 (double a, double b, double c, double d)
-{
-    double m1, m2;
-
-    m1 = MAX (a, b);
-    m2 = MAX (c, d);
-    return MAX (m1, m2);
-}
-
 static void
 compute_extents (pixman_f_transform_t *trans, double *sx, double *sy)
 {
-    double min_x, max_x, min_y, max_y;
-    pixman_f_vector_t v[4] =
-    {
-	{ { 1, 1, 1 } },
-	{ { -1, 1, 1 } },
-	{ { -1, -1, 1 } },
-	{ { 1, -1, 1 } },
-    };
-
-    pixman_f_transform_point (trans, &v[0]);
-    pixman_f_transform_point (trans, &v[1]);
-    pixman_f_transform_point (trans, &v[2]);
-    pixman_f_transform_point (trans, &v[3]);
-
-    min_x = min4 (v[0].v[0], v[1].v[0], v[2].v[0], v[3].v[0]);
-    max_x = max4 (v[0].v[0], v[1].v[0], v[2].v[0], v[3].v[0]);
-    min_y = min4 (v[0].v[1], v[1].v[1], v[2].v[1], v[3].v[1]);
-    max_y = max4 (v[0].v[1], v[1].v[1], v[2].v[1], v[3].v[1]);
-
-    *sx = (max_x - min_x) / 2.0;
-    *sy = (max_y - min_y) / 2.0;
+  *sx = hypot (trans->m[0][0], trans->m[0][1]) / trans->m[2][2];
+  *sy = hypot (trans->m[1][0], trans->m[1][1]) / trans->m[2][2];
 }
 
 typedef struct
-- 
1.7.9.5