patch/gfx: Implement scaling using different screen and viewport resolutions

Define a set of fixed modes covering our use-cases to allow rendering
4:3 games to a pillarbox on widescreen monitors.

src/main/hook/patch/gfx.h

@@ -1,12 +1,27 @@
+#pragma once
+
 /**
- * Hook module to run the games on non NVIDIA cards
+ * Different modes for scaling different source resolutions to target
+ * resolutions including keeping the aspect ratio
  */
-#ifndef PATCH_GFX_H
-#define PATCH_GFX_H
+enum patch_gfx_scale_mode {
+    PATCH_GFX_SCALE_MODE_INVALID = 0,
+    PATCH_GFX_SCALE_MODE_SD_480_TO_PILLARBOX_HD_720 = 1,
+    PATCH_GFX_SCALE_MODE_SD_480_TO_PILLARBOX_HD_1080 = 2,
+    PATCH_GFX_SCALE_MODE_SD_480_TO_SD_960 = 3,
+    PATCH_GFX_SCALE_MODE_HD_720_TO_HD_1080 = 4,
+};
 
 /**
  * Initialize the patch module
+ *
+ * This takes care of running the games on non NVIDIA cards
  */
 void patch_gfx_init();
 
-#endif
+/**
+ * Scale the rendered output according to the given mode (see enum)
+ *
+ * @param scale_mode The scaling mode to apply
+ */
+void patch_gfx_scale(enum patch_gfx_scale_mode scale_mode);