Merge branch 'device-scale' into 'master'

Wrapping surface device scale functions

See merge request cairo/cairomm!22

3 files changed, 65 insertions, 0 deletions

diff --git a/cairomm/surface.cc b/cairomm/surface.cc
index d7b9708..9982625 100644
--- a/cairomm/surface.cc
+++ b/cairomm/surface.cc
@@ -162,6 +162,24 @@ void Surface::get_device_offset(double& x_offset, double& y_offset) const
   cairo_surface_get_device_offset(const_cast<cobject*>(cobj()), &x_offset, &y_offset);
 }
 
+void Surface::set_device_scale(double x_scale, double y_scale)
+{
+  cairo_surface_set_device_scale(cobj(), x_scale, y_scale);
+  check_object_status_and_throw_exception(*this);
+}
+
+void Surface::get_device_scale(double& x_scale, double& y_scale) const
+{
+  cairo_surface_get_device_scale(const_cast<cobject*>(cobj()), &x_scale, &y_scale);
+}
+
+double Surface::get_device_scale() const
+{
+  double x_scale = 1, y_scale = 1;
+  get_device_scale(x_scale, y_scale);
+  return (x_scale + y_scale) / 2;
+}
+
 void Surface::set_fallback_resolution(double x_pixels_per_inch, double y_pixels_per_inch)
 {
   cairo_surface_set_fallback_resolution(cobj(), x_pixels_per_inch, y_pixels_per_inch);
diff --git a/cairomm/surface.h b/cairomm/surface.h
index 663bd57..65d7cea 100644
--- a/cairomm/surface.h
+++ b/cairomm/surface.h
@@ -431,6 +431,37 @@ public:
    */
   void get_device_offset(double& x_offset, double& y_offset) const;
 
+  /** Sets a 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::Context::device_to_user() will expose the hidden scale.
+   *
+   * Note that the scale affects drawing to the surface as well as using the
+   * surface in a source pattern.
+   *
+   * @param x_scale 	a scale factor in the X direction
+   * @param y_scale 	a scale factor in the Y direction
+   */
+  void set_device_scale(double x_scale, double y_scale);
+
+  /** Sets x and y scale to the same value.
+   * See set_device_scale(double, double) for details.
+   *
+   * @param scale 	a scale factor in the X and Y direction
+   */
+  inline void set_device_scale(double scale) { set_device_scale(scale, scale); }
+
+  /** Returns a previous device scale set by set_device_scale().
+   */
+  void get_device_scale(double& x_scale, double& y_scale) const;
+
+  /** Returns the x and y average of a previous device scale set by
+   * set_device_scale().
+   */
+  double get_device_scale() const;
+
   /**
    * Set the horizontal and vertical resolution for image fallbacks.
    *
diff --git a/tests/test-surface.cc b/tests/test-surface.cc
index 50069c8..152787c 100644
--- a/tests/test-surface.cc
+++ b/tests/test-surface.cc
@@ -89,6 +89,22 @@ BOOST_AUTO_TEST_CASE(test_content)
   BOOST_CHECK_EQUAL(similar->get_content(), CONTENT_ALPHA);
 }
 
+BOOST_AUTO_TEST_CASE(test_device_scale)
+{
+  auto surface = ImageSurface::create(Surface::Format::ARGB32, 1, 1);
+  const double new_x = 3, new_y = 5;
+  double x, y;
+  surface->set_device_scale(new_x, new_y);
+  surface->get_device_scale(x, y);
+  BOOST_CHECK_EQUAL(x, new_x);
+  BOOST_CHECK_EQUAL(y, new_y);
+  // average x/y scaling
+  BOOST_CHECK_EQUAL(4.0, surface->get_device_scale());
+  // uniform scaling
+  surface->set_device_scale(2);
+  BOOST_CHECK_EQUAL(2.0, surface->get_device_scale());
+}
+
 BOOST_AUTO_TEST_CASE(test_fallback_resolution)
 {
   auto surface = ImageSurface::create(Surface::Format::ARGB32, 1, 1);