gstate: Handle device scale on surface as source

When creating a transformed pattern we must apply the device
transform *before* the transform set on the pattern itself, otherwise
e.g. its translation will not be affected by the device scale.

We also fix up the device_transform related handling in
_cairo_default_context_pop_group().  With a device scale we can
no longer just use the device_transform_inverse to unset the
device offset for the extents, so we make that a simple translate
instead.

We also remove some weird code that tries to handle the device
transform but seems unnecessary (maybe a workaround for applying
the device transform in the wrong order?). With that code removed
things work fine, but with it things get translated wrongly when
there is a scale.

4 files changed, 23 insertions, 16 deletions

diff --git a/src/cairo-default-context.c b/src/cairo-default-context.c
index 5132259f..af5d53fa 100644
--- a/src/cairo-default-context.c
+++ b/src/cairo-default-context.c
@@ -213,7 +213,8 @@ _cairo_default_context_pop_group (void *abstract_cr)
     cairo_default_context_t *cr = abstract_cr;
     cairo_surface_t *group_surface;
     cairo_pattern_t *group_pattern;
-    cairo_matrix_t group_matrix, device_transform_matrix;
+    cairo_surface_t *parent_surface;
+    cairo_matrix_t group_matrix;
     cairo_status_t status;
 
     /* Verify that we are at the right nesting level */
@@ -227,29 +228,21 @@ _cairo_default_context_pop_group (void *abstract_cr)
     status = _cairo_gstate_restore (&cr->gstate, &cr->gstate_freelist);
     assert (status == CAIRO_STATUS_SUCCESS);
 
+    parent_surface = _cairo_gstate_get_target (cr->gstate);
+
     group_pattern = cairo_pattern_create_for_surface (group_surface);
     status = group_pattern->status;
     if (unlikely (status))
         goto done;
 
     _cairo_gstate_get_matrix (cr->gstate, &group_matrix);
-    /* Transform by group_matrix centered around device_transform so that when
-     * we call _cairo_gstate_copy_transformed_pattern the result is a pattern
-     * with a matrix equivalent to the device_transform of group_surface. */
-    if (_cairo_surface_has_device_transform (group_surface)) {
-	cairo_pattern_set_matrix (group_pattern, &group_surface->device_transform);
-	_cairo_pattern_transform (group_pattern, &group_matrix);
-	_cairo_pattern_transform (group_pattern, &group_surface->device_transform_inverse);
-    } else {
-	cairo_pattern_set_matrix (group_pattern, &group_matrix);
-    }
+    cairo_pattern_set_matrix (group_pattern, &group_matrix);
 
     /* If we have a current path, we need to adjust it to compensate for
      * the device offset just removed. */
-    cairo_matrix_multiply (&device_transform_matrix,
-                           &_cairo_gstate_get_target (cr->gstate)->device_transform,
-			   &group_surface->device_transform_inverse);
-    _cairo_path_fixed_transform (cr->path, &device_transform_matrix);
+    _cairo_path_fixed_translate (cr->path,
+				 _cairo_fixed_from_int (parent_surface->device_transform.x0 - group_surface->device_transform.x0),
+				 _cairo_fixed_from_int (parent_surface->device_transform.y0 - group_surface->device_transform.y0));
 
 done:
     cairo_surface_destroy (group_surface);
diff --git a/src/cairo-gstate.c b/src/cairo-gstate.c
index 33b45ed8..742b347d 100644
--- a/src/cairo-gstate.c
+++ b/src/cairo-gstate.c
@@ -954,7 +954,7 @@ _cairo_gstate_copy_transformed_pattern (cairo_gstate_t  *gstate,
         surface = surface_pattern->surface;
 
 	if (_cairo_surface_has_device_transform (surface))
-	    _cairo_pattern_transform (pattern, &surface->device_transform);
+	    _cairo_pattern_pretransform (pattern, &surface->device_transform);
     }
 
     if (! _cairo_matrix_is_identity (ctm_inverse))
diff --git a/src/cairo-pattern-private.h b/src/cairo-pattern-private.h
index dfd843fc..bbcfadd8 100644
--- a/src/cairo-pattern-private.h
+++ b/src/cairo-pattern-private.h
@@ -237,6 +237,10 @@ cairo_private void
 _cairo_pattern_transform (cairo_pattern_t      *pattern,
 			  const cairo_matrix_t *ctm_inverse);
 
+cairo_private void
+_cairo_pattern_pretransform (cairo_pattern_t      *pattern,
+                             const cairo_matrix_t *ctm);
+
 cairo_private cairo_bool_t
 _cairo_pattern_is_opaque_solid (const cairo_pattern_t *pattern);
 
diff --git a/src/cairo-pattern.c b/src/cairo-pattern.c
index 940227d2..57b930b9 100644
--- a/src/cairo-pattern.c
+++ b/src/cairo-pattern.c
@@ -2128,6 +2128,16 @@ cairo_pattern_get_extend (cairo_pattern_t *pattern)
 slim_hidden_def (cairo_pattern_get_extend);
 
 void
+_cairo_pattern_pretransform (cairo_pattern_t	*pattern,
+			     const cairo_matrix_t  *ctm)
+{
+    if (pattern->status)
+	return;
+
+    cairo_matrix_multiply (&pattern->matrix, &pattern->matrix, ctm);
+}
+
+void
 _cairo_pattern_transform (cairo_pattern_t	*pattern,
 			  const cairo_matrix_t  *ctm_inverse)
 {