commit 8509bb51a947f6e966228fe8879000be5461e29c
Author: Owen W. Taylor <otaylor@fishsoup.net>
Date:   Fri Apr 4 23:45:19 2008 -0400

    Make pattern bounds tighter for pixel-exact transformations
    cairo-matrix.c cairoint.: Add _cairo_matrix_is_pixel_exact
    cairo-pattern.c: Treat pixel-exact transformations like
      they were always FILTER_NEAREST

diff --git a/src/cairo-matrix.c b/src/cairo-matrix.c
index d10d156..7262d90 100644
--- a/src/cairo-matrix.c
+++ b/src/cairo-matrix.c
@@ -600,6 +600,36 @@ _cairo_matrix_is_integer_translation (const cairo_matrix_t *matrix,
     return FALSE;
 }
 
+/* By pixel exact here, we mean a matrix that is composed only of
+ * 90 degree rotations, flips, and and integer translations. If
+ * we transform an image with a pixel-exact matrix, filtering
+ * is not useful.
+ */
+cairo_private cairo_bool_t
+_cairo_matrix_is_pixel_exact(const cairo_matrix_t *matrix)
+{
+    cairo_fixed_t x0_fixed, y0_fixed;
+
+    if (matrix->xy == 0.0 && matrix->yx == 0.0) {
+	if (!(matrix->xx == 1.0 || matrix->xx == -1.0))
+	    return FALSE;
+	if (!(matrix->yy == 1.0 || matrix->yy == -1.0))
+	    return FALSE;
+    } else if (matrix->xx == 0.0 && matrix->yy == 0.0) {
+	if (!(matrix->xy == 1.0 || matrix->xy == -1.0))
+	    return FALSE;
+	if (!(matrix->yx == 1.0 || matrix->yx == -1.0))
+	    return FALSE;
+    } else {
+	return FALSE;
+    }
+    
+    x0_fixed = _cairo_fixed_from_double (matrix->x0);
+    y0_fixed = _cairo_fixed_from_double (matrix->y0);
+    
+    return _cairo_fixed_is_integer (x0_fixed) && _cairo_fixed_is_integer (y0_fixed);
+}
+				     
 /*
   A circle in user space is transformed into an ellipse in device space.
 
diff --git a/src/cairo-pattern.c b/src/cairo-pattern.c
index e1d4b5c..6aed729 100644
--- a/src/cairo-pattern.c
+++ b/src/cairo-pattern.c
@@ -2000,10 +2000,15 @@ _cairo_pattern_get_extents (cairo_pattern_t         *pattern,
 	case CAIRO_FILTER_GOOD:
 	case CAIRO_FILTER_BEST:
 	case CAIRO_FILTER_BILINEAR:
-	    x1 -= 0.5;
-	    y1 -= 0.5;
-	    x2 += 0.5;
-	    y2 += 0.5;
+	    /* We assume that the backend will not blur out the image
+	     * when a pixel-for-pixel copy is possible.
+	     */
+	    if (!_cairo_matrix_is_pixel_exact(&imatrix)) {
+		x1 -= 0.5;
+		y1 -= 0.5;
+		x2 += 0.5;
+		y2 += 0.5;
+	    }
 	    break;
 	case CAIRO_FILTER_FAST:
 	case CAIRO_FILTER_NEAREST:
diff --git a/src/cairoint.h b/src/cairoint.h
index 01ad567..768e6b3 100644
--- a/src/cairoint.h
+++ b/src/cairoint.h
@@ -2051,6 +2051,9 @@ cairo_private cairo_bool_t
 _cairo_matrix_is_integer_translation(const cairo_matrix_t *matrix,
 				     int *itx, int *ity);
 
+cairo_private cairo_bool_t
+_cairo_matrix_is_pixel_exact(const cairo_matrix_t *matrix);
+				     
 cairo_private double
 _cairo_matrix_transformed_circle_major_axis(cairo_matrix_t *matrix, double radius);