Add new LWJGL API Display.getPixelScaleFactor() for use in high DPI

modes, like HiDPI retina mode on OS X.

src/java/org/lwjgl/opengl/Display.java

@@ -1348,4 +1348,27 @@ public final class Display {
 
 		return height;
 	}
+	
+	/**
+	 * @return this method will return the pixel scale factor of the Display window.
+	 *
+	 * This method should be used when running in high DPI mode. In such modes Operating
+	 * Systems will scale the Display window to avoid the window shrinking due to high
+	 * resolutions. The OpenGL frame buffer will however use the higher resolution and
+	 * not be scaled to match the Display window size.
+	 * 
+	 * OpenGL methods that require pixel dependent values e.g. glViewport, glTexImage2D,
+	 * glReadPixels, etc can convert the scaled Display and Mouse coordinates to the 
+	 * correct high resolution value by multiplying them by the pixel scale factor.
+	 * 
+	 * e.g. Display.getWidth() * Display.getPixelScaleFactor() will return the high DPI
+	 * width of the OpenGL frame buffer. Whereas Display.getWidth() will be the same as
+	 * the OpenGL frame buffer in non high DPI mode.
+	 * 
+	 * Where high DPI mode is not available this method will just return 1.0f therefore
+	 * not have any effect on values that are multiplied by it.
+	 */
+	public static float getPixelScaleFactor() {
+		return display_impl.getPixelScaleFactor();
+	}
 }

src/java/org/lwjgl/opengl/DisplayImplementation.java

@@ -192,4 +192,9 @@ interface DisplayImplementation extends InputImplementation {
 	 * @return this method will return the top-left y position of the Display window.
 	 */
 	int getY();
+	
+	/**
+	 * @return this method will return the pixel scale factor of the Display window useful for high resolution modes.
+	 */
+	float getPixelScaleFactor();
 }

src/java/org/lwjgl/opengl/LinuxDisplay.java

@@ -1459,6 +1459,10 @@ final class LinuxDisplay implements DisplayImplementation {
 		return false;
 	}
 
+	public float getPixelScaleFactor() {
+		return 1f;
+	}
+	
 	/**
 	 * Helper class for managing Compiz's workarounds. We need this to enable Legacy
 	 * Fullscreen Support in Compiz, else we'll have trouble with fullscreen windows

src/java/org/lwjgl/opengl/MacOSXDisplay.java

@@ -622,5 +622,9 @@ final class MacOSXDisplay implements DisplayImplementation {
 	public boolean wasResized() {
 		return nWasResized(window);
 	}
+	
+	public float getPixelScaleFactor() {
+		return 1f;
+	}
 
 }

src/java/org/lwjgl/opengl/WindowsDisplay.java

@@ -1191,6 +1191,10 @@ final class WindowsDisplay implements DisplayImplementation {
 		}
 		return false;
 	}
+	
+	public float getPixelScaleFactor() {
+		return 1f;
+	}
 
 	private static final class Rect {
 		public int top;