Hook up device scaling so fallback_resolution starts working.

Add new, private _cairo_surface_set_device_scale for getting at the
scaling components of device_transform. Use this in paginated surface
when replaying to an image surface. The fallback-resolution test now
clearly shows that image fallback resolution can be controlled by the
user. Hurrah!

src/cairo-paginated-surface.c

@@ -217,13 +217,20 @@ _paint_page (cairo_paginated_surface_t *surface)
 
     if (_cairo_analysis_surface_has_unsupported (analysis))
     {
+	double x_scale = surface->base.x_fallback_resolution / 72.0;
+	double y_scale = surface->base.y_fallback_resolution / 72.0;
+	cairo_matrix_t matrix;
+
 	image = _cairo_image_surface_create_with_content (surface->content,
-							  surface->width,
-							  surface->height);
+							  surface->width * x_scale,
+							  surface->height * y_scale);
+	_cairo_surface_set_device_scale (image, x_scale, y_scale);
 
 	_cairo_meta_surface_replay (surface->meta, image);
 
 	pattern = cairo_pattern_create_for_surface (image);
+	cairo_matrix_init_scale (&matrix, x_scale, y_scale);
+	cairo_pattern_set_matrix (pattern, &matrix);
 
 	_cairo_surface_paint (surface->target, CAIRO_OPERATOR_SOURCE, pattern);
 

src/cairo-surface.c

@@ -611,6 +611,45 @@ cairo_surface_mark_dirty_rectangle (cairo_surface_t *surface,
     }
 }
 
+/**
+ * _cairo_surface_set_device_scale:
+ * @surface: a #cairo_surface_t
+ * @sx: a scale factor in the X direction
+ * @sy: a scale factor in the Y direction
+ *
+ * Private function for setting an extra scale factor to affect all
+ * drawing to a surface. This is used, for example, when replaying a
+ * meta surface to an image fallback intended for an eventual
+ * vector-oriented backend. Since the meta surface will record
+ * coordinates in one backend space, but the image fallback uses a
+ * different backend space, (differing by the fallback resolution
+ * scale factors), we need a scale factor correction.
+ *
+ * Caution: There is no guarantee that a surface with both a
+ * device_scale and a device_offset will be treated in consistent
+ * fashion. So, for now, just don't do that. (And we'll need to
+ * examine this issue in more detail if we were to ever want to export
+ * support for device scaling.)
+ **/
+void
+_cairo_surface_set_device_scale (cairo_surface_t *surface,
+				 double		  sx,
+				 double		  sy)
+{
+    assert (! surface->is_snapshot);
+
+    if (surface->status)
+	return;
+
+    if (surface->finished) {
+	_cairo_surface_set_error (surface, CAIRO_STATUS_SURFACE_FINISHED);
+	return;
+    }
+
+    surface->device_transform.xx = sx;
+    surface->device_transform.yy = sy;
+}
+
 /**
  * cairo_surface_set_device_offset:
  * @surface: a #cairo_surface_t

src/cairoint.h

@@ -1855,6 +1855,11 @@ _cairo_surface_composite_shape_fixup_unbounded (cairo_surface_t            *dst,
 cairo_private cairo_bool_t
 _cairo_surface_is_opaque (const cairo_surface_t *surface);
 
+cairo_private void
+_cairo_surface_set_device_scale (cairo_surface_t *surface,
+				 double		  sx,
+				 double		  sy);
+
 cairo_private cairo_bool_t
 _cairo_surface_has_device_transform (cairo_surface_t *surface);