surface: expose the device scale

This adds the new public functions
cairo_surface_set_device_scale and cairo_surface_get_device_scale and
updates old users of the internal functions.

src/cairo-default-context.c

@@ -189,9 +189,9 @@ _cairo_default_context_push_group (void *abstract_cr, cairo_content_t content)
 					 parent_surface->device_transform.x0 - extents.x,
 					 parent_surface->device_transform.y0 - extents.y);
 
-	_cairo_surface_set_device_scale (group_surface,
-					 parent_surface->device_transform.xx,
-					 parent_surface->device_transform.yy);
+	cairo_surface_set_device_scale (group_surface,
+					parent_surface->device_transform.xx,
+					parent_surface->device_transform.yy);
 
 	/* If we have a current path, we need to adjust it to compensate for
 	 * the device offset just applied. */

src/cairo-paginated-surface.c

@@ -308,7 +308,7 @@ _paint_fallback_image (cairo_paginated_surface_t *surface,
     image = _cairo_paginated_surface_create_image_surface (surface,
 							   ceil (width  * x_scale),
 							   ceil (height * y_scale));
-    _cairo_surface_set_device_scale (image, x_scale, y_scale);
+    cairo_surface_set_device_scale (image, x_scale, y_scale);
     /* set_device_offset just sets the x0/y0 components of the matrix;
      * so we have to do the scaling manually. */
     cairo_surface_set_device_offset (image, -x*x_scale, -y*y_scale);

src/cairo-surface-subsurface.c

@@ -500,9 +500,9 @@ cairo_surface_create_for_rectangle (cairo_surface_t *target,
 
     surface->snapshot = NULL;
 
-    _cairo_surface_set_device_scale (&surface->base,
-                                     target->device_transform.xx,
-                                     target->device_transform.yy);
+    cairo_surface_set_device_scale (&surface->base,
+                                    target->device_transform.xx,
+                                    target->device_transform.yy);
 
     return &surface->base;
 }
@@ -542,9 +542,9 @@ _cairo_surface_create_for_rectangle_int (cairo_surface_t *target,
 
     surface->snapshot = NULL;
 
-    _cairo_surface_set_device_scale (&surface->base,
-                                     target->device_transform.xx,
-                                     target->device_transform.yy);
+    cairo_surface_set_device_scale (&surface->base,
+                                    target->device_transform.xx,
+                                    target->device_transform.yy);
 
     return &surface->base;
 }

src/cairo-surface.c

@@ -1624,26 +1624,28 @@ cairo_surface_mark_dirty_rectangle (cairo_surface_t *surface,
 slim_hidden_def (cairo_surface_mark_dirty_rectangle);
 
 /**
- * _cairo_surface_set_device_scale:
+ * 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
- * recording surface to an image fallback intended for an eventual
- * vector-oriented backend. Since the recording 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.
+ * Sets an scale that is multiplied to the device coordinates determined
+ * by the CTM when drawing to @surface. One common use for this is to
+ * render to very high resolution display devices at a scale factor, so
+ * that code that assumes 1 pixel will be a certain size will still work.
+ * Setting a transformation via cairo_translate() isn't
+ * sufficient to do this, since functions like
+ * cairo_device_to_user() will expose the hidden scale.
  *
- * Caution: Not all places we use device transform correctly handle
- * both a translate and a scale.  An audit would be nice.
+ * Note that the scale affects drawing to the surface as well as
+ * using the surface in a source pattern.
+ *
+ * Since: 1.14
  **/
 void
-_cairo_surface_set_device_scale (cairo_surface_t *surface,
-				 double		  sx,
-				 double		  sy)
+cairo_surface_set_device_scale (cairo_surface_t *surface,
+				double		 sx,
+				double		 sy)
 {
     cairo_status_t status;
 
@@ -1675,6 +1677,30 @@ _cairo_surface_set_device_scale (cairo_surface_t *surface,
 
     _cairo_observers_notify (&surface->device_transform_observers, surface);
 }
+slim_hidden_def (cairo_surface_set_device_scale);
+
+/**
+ * cairo_surface_get_device_scale:
+ * @surface: a #cairo_surface_t
+ * @x_scale: the scale in the X direction, in device units
+ * @y_scale: the scale in the Y direction, in device units
+ *
+ * This function returns the previous device offset set by
+ * cairo_surface_set_device_scale().
+ *
+ * Since: 1.14
+ **/
+void
+cairo_surface_get_device_scale (cairo_surface_t *surface,
+				double          *x_scale,
+				double          *y_scale)
+{
+    if (x_scale)
+	*x_scale = surface->device_transform.xx;
+    if (y_scale)
+	*y_scale = surface->device_transform.yy;
+}
+slim_hidden_def (cairo_surface_get_device_scale);
 
 /**
  * cairo_surface_set_device_offset:

src/cairo.h

@@ -2455,6 +2455,16 @@ cairo_surface_mark_dirty_rectangle (cairo_surface_t *surface,
 				    int              width,
 				    int              height);
 
+cairo_public void
+cairo_surface_set_device_scale (cairo_surface_t *surface,
+				double           x_scale,
+				double           y_scale);
+
+cairo_public void
+cairo_surface_get_device_scale (cairo_surface_t *surface,
+				double          *x_scale,
+				double          *y_scale);
+
 cairo_public void
 cairo_surface_set_device_offset (cairo_surface_t *surface,
 				 double           x_offset,

src/cairoint.h

@@ -1420,11 +1420,6 @@ cairo_private_no_warn cairo_bool_t
 _cairo_surface_get_extents (cairo_surface_t         *surface,
 			    cairo_rectangle_int_t   *extents);
 
-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) cairo_pure;
 
@@ -1955,6 +1950,7 @@ slim_hidden_proto (cairo_surface_destroy);
 slim_hidden_proto (cairo_surface_finish);
 slim_hidden_proto (cairo_surface_flush);
 slim_hidden_proto (cairo_surface_get_device_offset);
+slim_hidden_proto (cairo_surface_get_device_scale);
 slim_hidden_proto (cairo_surface_get_font_options);
 slim_hidden_proto (cairo_surface_get_mime_data);
 slim_hidden_proto (cairo_surface_has_show_text_glyphs);
@@ -1962,6 +1958,7 @@ slim_hidden_proto (cairo_surface_mark_dirty);
 slim_hidden_proto (cairo_surface_mark_dirty_rectangle);
 slim_hidden_proto_no_warn (cairo_surface_reference);
 slim_hidden_proto (cairo_surface_set_device_offset);
+slim_hidden_proto (cairo_surface_set_device_scale);
 slim_hidden_proto (cairo_surface_set_fallback_resolution);
 slim_hidden_proto (cairo_surface_set_mime_data);
 slim_hidden_proto (cairo_surface_show_page);