Centering is a user preference, to adjust the screen, not a theme

setting.  It's usually tied to the screen resolution (will usually
need readjustment anyway if the resolution changes).  Treat the
values as pixels, as if we were using glViewport to do this.
(Reduces dependencies on ScreenDimensions.h, and we don't need
to worry about calling ChangeCentering when the theme changes.)

stepmania/src/RageDisplay.cpp

@@ -29,6 +29,8 @@ static int			g_iFramesRenderedSinceLastCheck,
 					g_iNumChecksSinceLastReset;
 static RageTimer g_LastFrameEndedAt( RageZeroTimer );
 
+static int g_iTranslateX = 0, g_iTranslateY = 0, g_iAddWidth = 0, g_iAddHeight = 0;
+
 RageDisplay*		DISPLAY	= NULL;
 
 Preference<bool>  LOG_FPS( "LogFPS", true );
@@ -602,13 +604,25 @@ RageMatrix RageDisplay::GetFrustumMatrix( float l, float r, float b, float t, fl
 	return m;
 }
 
-void RageDisplay::ChangeCentering( int trans_x, int trans_y, int add_width, int add_height )
+void RageDisplay::ChangeCentering( int iTranslateX, int iTranslateY, int iAddWidth, int iAddHeight )
+{
+	g_iTranslateX = iTranslateX;
+	g_iTranslateY = iTranslateY;
+	g_iAddWidth = iAddWidth;
+	g_iAddHeight = iAddHeight;
+
+	UpdateCentering();
+}
+
+void RageDisplay::UpdateCentering()
 {
 	// in screen space, left edge = -1, right edge = 1, bottom edge = -1. top edge = 1
-	float fPercentShiftX = SCALE( trans_x, 0, SCREEN_WIDTH, 0, +2.0f );
+	float fWidth = (float) GetActualVideoModeParams().width;
-	float fPercentShiftY = SCALE( trans_y, 0, SCREEN_HEIGHT, 0, -2.0f );
+	float fHeight = (float) GetActualVideoModeParams().height;
-	float fPercentScaleX = SCALE( add_width, 0, SCREEN_WIDTH, 1.0f, 2.0f );
+	float fPercentShiftX = SCALE( g_iTranslateX, 0, fWidth, 0, +2.0f );
-	float fPercentScaleY = SCALE( add_height, 0, SCREEN_HEIGHT, 1.0f, 2.0f );
+	float fPercentShiftY = SCALE( g_iTranslateY, 0, fHeight, 0, -2.0f );
+	float fPercentScaleX = SCALE( g_iAddWidth, 0, fWidth, 1.0f, 2.0f );
+	float fPercentScaleY = SCALE( g_iAddHeight, 0, fHeight, 1.0f, 2.0f );
 
 	RageMatrix m1;
 	RageMatrix m2;

stepmania/src/RageDisplay.h

@@ -313,6 +313,7 @@ protected:
 	// Matrix that adjusts position and scale of image on the screen
 	//
 	RageMatrix m_Centering;
+	void UpdateCentering();
 
 	// Called by the RageDisplay derivitives
 	const RageMatrix* GetCentering() { return &m_Centering; }