Add "device_affinity" keyword argument to Bitmap.new binding

0 (default) prefers accelerated GPU.
1 prefers CPU (initializes as a Mega Surface).

There are at least 3 situations where CPU is likely to be faster:

1. Raster effects implemented in Ruby (e.g. via set_pixel).
2. Operations on background threads.
3. Platforms without accelerated OpenGL (e.g. LLVMPipe).

binding/bitmap-binding.cpp

@@ -66,16 +66,38 @@ void bitmapInitProps(Bitmap *b, VALUE self) {
 
 RB_METHOD_GUARD(bitmapInitialize) {
     Bitmap *b = 0;
-    
-    if (argc == 1) {
-        char *filename;
-        rb_get_args(argc, argv, "z", &filename RB_ARG_END);
-        
-        GFX_GUARD_EXC(b = new Bitmap(filename);)
-    } else {
-        int width, height;
-        rb_get_args(argc, argv, "ii", &width, &height RB_ARG_END);
-        
+
+    VALUE arg1;
+    VALUE arg2;
+
+    VALUE kwargs;
+    rb_scan_args(argc, argv, "11:", &arg1, &arg2, &kwargs);
+
+    ID table[1];
+    table[0] = rb_intern("device_affinity");
+    VALUE deviceAffinity;
+    rb_get_kwargs(kwargs, table, 0, 1, &deviceAffinity);
+
+    if (RB_TYPE_P(arg1, RUBY_T_STRING)) {
+        // filename constructor, arg1 is filename
+        SafeStringValue(arg1);
+
+        int affinity = 0;
+        if (deviceAffinity != Qundef && deviceAffinity != Qnil) {
+            affinity = NUM2INT(deviceAffinity);
+        }
+
+        bool forceMega = false;
+        if (affinity == 1) {
+            forceMega = true;
+        }
+
+        GFX_GUARD_EXC(b = new Bitmap(RSTRING_PTR(arg1), forceMega);)
+    }
+    else {
+        // width,height constructor
+        int width = NUM2INT(arg1);
+        int height = NUM2INT(arg2);
         GFX_GUARD_EXC(b = new Bitmap(width, height);)
     }
     

src/display/bitmap.cpp

@@ -488,7 +488,7 @@ struct BitmapOpenHandler : FileSystem::OpenHandler
     }
 };
 
-Bitmap::Bitmap(const char *filename)
+Bitmap::Bitmap(const char *filename, bool forceMega)
 {
     std::string hiresPrefix = "Hires/";
     std::string filenameStd = filename;
@@ -498,7 +498,7 @@ Bitmap::Bitmap(const char *filename)
         // Look for a high-res version of the file.
         std::string hiresFilename = hiresPrefix + filenameStd;
         try {
-            hiresBitmap = new Bitmap(hiresFilename.c_str());
+            hiresBitmap = new Bitmap(hiresFilename.c_str(), forceMega);
             hiresBitmap->setLores(this);
         }
         catch (const Exception &e)
@@ -631,7 +631,7 @@ Bitmap::Bitmap(const char *filename)
 
     SDL_Surface *imgSurf = handler.surface;
 
-    initFromSurface(imgSurf, hiresBitmap, false);
+    initFromSurface(imgSurf, hiresBitmap, forceMega);
 }
 
 Bitmap::Bitmap(int width, int height, bool isHires)

src/display/bitmap.h

@@ -38,7 +38,7 @@ struct BitmapPrivate;
 class Bitmap : public Disposable
 {
 public:
-	Bitmap(const char *filename);
+	Bitmap(const char *filename, bool forceMega = false);
 	Bitmap(int width, int height, bool isHires = false);
 	Bitmap(void *pixeldata, int width, int height);
 	Bitmap(TEXFBO &other);