CVideo: add get_pixel_scale() to return the active pixel scale.

Multiply font sizes by this to create high-dpi font textures.

src/video.cpp

@@ -103,6 +103,7 @@ CVideo::CVideo(FAKE_TYPES type)
 	, refresh_rate_(0)
 	, offset_x_(0)
 	, offset_y_(0)
+	, pixel_scale_(1)
 {
 	assert(!singleton_);
 	singleton_ = this;
@@ -278,6 +279,8 @@ void CVideo::update_framebuffer()
 	} else {
 		scale = std::min(max_scale, preferences::pixel_scale());
 	}
+	// Cache it for easy access.
+	pixel_scale_ = scale;
 
 	// Update logical size if it doesn't match the current resolution and scale.
 	point lsize(window->get_logical_size());

src/video.hpp

@@ -178,6 +178,18 @@ public:
 	 */
 	int get_height() const;
 
+	/**
+	 * Get the current active pixel scale multiplier.
+	 * This is equal to output_size() / draw_area().
+	 * Currently it is always integer, and the same in both dimensions.
+	 *
+	 * This may differ from preferences::pixel_scale() in some cases,
+	 * For example if the window is too small to fit the desired scale.
+	 *
+	 * @returns     The currently active pixel scale multiplier.
+	 */
+	int get_pixel_scale() const { return pixel_scale_; }
+
 	/** The current game screen dpi. */
 	std::pair<float, float> get_dpi() const;
 
@@ -512,6 +524,7 @@ private:
 	int flip_locked_;
 	int refresh_rate_;
 	int offset_x_, offset_y_;
+	int pixel_scale_;
 };
 
 /** An object which will lock the display for the duration of its lifetime. */