add Supports4BitPalettes

stepmania/src/RageDisplay.h

@@ -140,6 +140,13 @@ public:
 	virtual void SetBlendMode( BlendMode mode ) = 0;
 
 	virtual bool SupportsTextureFormat( PixelFormat pixfmt ) = 0;
+
+	/* This really indicates whether 4-bit palettes will actually use less memory
+	 * than 8-bit ones.  Note that 4-bit palettes are uploaded as 8-bit paletted
+	 * surfaces with color index values in the range 0..15; not as 4-bit "packed
+	 * indexes". */
+	virtual bool Supports4BitPalettes() { return false; }
+
 	/* return 0 if failed or internal texture resource handle 
 	 * (unsigned in OpenGL, texture pointer in D3D) */
 	virtual unsigned CreateTexture(