Change framebuffer.clear to use background color

pkg/stm32/lib/lcd.dart

 // Copyright (c) 2016, the Dartino project authors. Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE.md file.
 
 library stm32.lcd;
 
 import 'dart:dartino.ffi';
 
 final _lcdHeight = ForeignLibrary.main.lookup('lcd_height');
 final _lcdWidth = ForeignLibrary.main.lookup('lcd_width');
@@ skipping 63 matching lines @@
   /// Align text to the center.
   center,
   /// Align text to the right.
   right,
 }
 
 class FrameBuffer {
   int get height => _lcdHeight.icall$0();
   int get width => _lcdWidth.icall$0();
 
-  clear([Color color = Color.black]) {
+  Color _backgroundColor = Color.white;
+
+  clear([Color color]) {
+    color ??= _backgroundColor;
     _lcdClear.icall$1(color.rgb8888);
   }
 
+  set backgroundColor(Color color) {
+    _backgroundColor = color;
+    _lcdSetBackgroundColor.icall$1(color.rgb8888);
+  }
+
   set foregroundColor(Color color) {
     _lcdSetForegroundColor.icall$1(color.rgb8888);
   }
 
-  set backgroundColor(Color color) {
-    _lcdSetBackgroundColor.icall$1(color.rgb8888);
-  }
-
   Color readPixel(int x, int y) {
     return new Color.fromRgb8888(_lcdReadPixel.icall$2(x, y));
   }
 
   void drawPixel(int x, int y, [Color color = Color.white]) {
     _lcdDrawPixel.icall$3(x, y, color.rgb8888);
   }
 
   void drawLine(int x1, int y1, int x2, int y2, [Color color = Color.white]) {
     _lcdSetForegroundColor.icall$1(color.rgb8888);
@@ skipping 10 matching lines @@
     int alignMode;
     switch (align) {
       case TextAlign.left: alignMode = 3; break;
       case TextAlign.center: alignMode = 1; break;
       case TextAlign.right: alignMode = 2; break;
     }
     _lcdDisplayString.icall$4(x, y, m, alignMode);
     m.free();
   }
 }