Implement BACKCOLOR

SMILEBASIC/builtinfunctions.d

@@ -315,6 +315,14 @@ class BuiltinFunction
         p.BGvisible = cast(bool)BG;
         p.sprite.visible = cast(bool)sprite;
     }
+    static void BACKCOLOR(PetitComputer p, int color)
+    {
+        p.backcolor = color;
+    }
+    static int BACKCOLOR(PetitComputer p)
+    {
+        return p.backcolor;
+    }
     static void XON(PetitComputer p, Value mode/*!?!???!?*/)
     {
     }

SMILEBASIC/petitcomputer.d

@@ -487,6 +487,15 @@ class PetitComputer
             m_touch = to;
         }
     }
+    int petitcomBackcolor;
+    void backcolor(int color)
+    {
+        petitcomBackcolor = color;
+    }
+    int backcolor()
+    {
+        return petitcomBackcolor;
+    }
     void render()
     {
         try
@@ -621,6 +630,11 @@ class PetitComputer
                 {
                     chScreen(0, 0, 320, 480);
                 }
+                {
+                    ubyte r, g, b, a;
+                    RGBRead(petitcomBackcolor, r, g, b, a);
+                    glClearColor(r / 255f, g / 255f, b / 255f, 1);
+                }
                 //描画の順位
                 //sprite>GRP>console>BG
                 glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);