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.c

@@ -2,6 +2,10 @@
 
 #include <X11/Xutil.h>
 #include <stdbool.h>
+#include <GL/gl.h>
+
+// OpenGL 3.x+
+#include <GL/glx.h>
 
 #include "capnhook/hook/lib.h"
 
@@ -26,11 +30,21 @@ typedef Window (*XCreateWindow_t)(
 typedef Display *(*XOpenDisplay_t)(const char *display_name);
 typedef XVisualInfo *(*glXChooseVisual_t)(
     Display *dpy, int screen, int *attribList);
+typedef void (*glViewport_t)(GLint x, GLint y, GLsizei width, GLsizei height);
 
 static bool patch_gfx_initialized;
 static XCreateWindow_t patch_gfx_real_XCreateWindow;
 static XOpenDisplay_t patch_gfx_real_XOpenDisplay;
 static glXChooseVisual_t patch_gfx_real_GlXChooseVisual;
+static glViewport_t patch_gfx_real_glViewport;
+
+static bool _patch_gfx_scaling_enabled;
+static uint16_t _patch_gfx_screen_width;
+static uint16_t _patch_gfx_screen_height;
+static uint16_t _patch_gfx_viewport_width;
+static uint16_t _patch_gfx_viewport_height;
+static uint16_t _patch_gfx_viewport_pos_x;
+static uint16_t _patch_gfx_viewport_pos_y;
 
 static char *patch_gfx_attrib_list_to_str(int *attrib_list)
 {
@@ -82,6 +96,11 @@ Window XCreateWindow(
     }
   }
 
+  if (_patch_gfx_scaling_enabled) {
+    width = _patch_gfx_screen_width;
+    height = _patch_gfx_screen_height;
+  }
+
   return patch_gfx_real_XCreateWindow(
       display,
       parent,
@@ -152,8 +171,80 @@ XVisualInfo *glXChooseVisual(Display *dpy, int screen, int *attribList)
   return res;
 }
 
+void glViewport(GLint x, GLint y, GLsizei width, GLsizei height)
+{
+  if (!patch_gfx_real_glViewport) {
+    void* handle = cnh_lib_load("libGL.so");
+
+    patch_gfx_real_glViewport =
+        (glViewport_t) cnh_lib_get_func_addr_handle(handle, "glViewport");
+  }
+
+  // 0/0 at the bottom left
+  if (_patch_gfx_scaling_enabled) {
+    x = _patch_gfx_viewport_pos_x;
+    y = _patch_gfx_viewport_pos_y;
+    width = _patch_gfx_viewport_width;
+    height = _patch_gfx_viewport_height;
+  }
+
+  patch_gfx_real_glViewport(x, y, width, height);
+}
+
 void patch_gfx_init()
 {
+  _patch_gfx_scaling_enabled = false;
   patch_gfx_initialized = true;
   log_info("Initialized");
 }
+
+// Note, consider improving scaling, see http://www.david-amador.com/2013/04/opengl-2d-independent-resolution-rendering/
+void patch_gfx_scale(enum patch_gfx_scale_mode scale_mode)
+{
+  switch (scale_mode) {
+    case PATCH_GFX_SCALE_MODE_SD_480_TO_PILLARBOX_HD_720:
+      _patch_gfx_screen_width = 1280;
+      _patch_gfx_screen_height = 720;
+      _patch_gfx_viewport_width = 960;
+      _patch_gfx_viewport_height = 720;
+      _patch_gfx_viewport_pos_x = 160;
+      _patch_gfx_viewport_pos_y = 0;
+      break;
+
+    case PATCH_GFX_SCALE_MODE_SD_480_TO_PILLARBOX_HD_1080:
+      _patch_gfx_screen_width = 1920;
+      _patch_gfx_screen_height = 1080;
+      _patch_gfx_viewport_width = 1440;
+      _patch_gfx_viewport_height = 1080;
+      _patch_gfx_viewport_pos_x = 240;
+      _patch_gfx_viewport_pos_y = 0;
+      break;
+
+    case PATCH_GFX_SCALE_MODE_SD_480_TO_SD_960:
+      _patch_gfx_screen_width = 1280;
+      _patch_gfx_screen_height = 960;
+      _patch_gfx_viewport_width = 1280;
+      _patch_gfx_viewport_height = 960;
+      _patch_gfx_viewport_pos_x = 0;
+      _patch_gfx_viewport_pos_y = 0;
+      break;
+
+    case PATCH_GFX_SCALE_MODE_HD_720_TO_HD_1080:
+      _patch_gfx_screen_width = 1920;
+      _patch_gfx_screen_height = 1080;
+      _patch_gfx_viewport_width = 1920;
+      _patch_gfx_viewport_height = 1080;
+      _patch_gfx_viewport_pos_x = 0;
+      _patch_gfx_viewport_pos_y = 0;
+      break;
+
+    case PATCH_GFX_SCALE_MODE_INVALID:
+    default:
+      log_error("Invalid scale mode: %d. Scaling disabled", scale_mode);
+      return;
+  }
+
+  log_info("Scaling enabled, mode: %d", scale_mode);
+
+  _patch_gfx_scaling_enabled = true;
+}

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);