remove hot .to_u8 call in bus, add fps to display title

src/crab/bus.cr

@@ -28,9 +28,9 @@ class Bus
     when PPU_IO     then @gba.ppu[index]
     when PPU        then @gba.ppu[index]
     when CARTRIDGE  then @gba.cartridge[index - CARTRIDGE.begin]
-    when UNUSED     then 0xFF
-    else                 0xFF
-    end.to_u8
+    when UNUSED     then 0xFF_u8
+    else                 0xFF_u8
+    end
   end
 
   def read_word(index : Int) : Word

src/crab/display.cr

@@ -14,10 +14,22 @@ class Display
     @texture = LibSDL.create_texture @renderer, PIXELFORMAT_BGR555, TEXTUREACCESS_STREAMING, WIDTH, HEIGHT
   end
 
+  def window_title : String
+    "crab - #{@fps} fps"
+  end
+
+  @fps = 30
+  @seconds : Int32 = Time.utc.second
   def draw(framebuffer : Bytes) : Nil
     LibSDL.update_texture @texture, nil, framebuffer, WIDTH * 2
     @renderer.clear
     @renderer.copy @texture
     @renderer.present
+    @fps += 1
+    if Time.utc.second != @seconds
+      @window.title = window_title
+      @fps = 0
+      @seconds = Time.utc.second
+    end
   end
 end