Factor out checkerboard function in gm and sampleapp into tools.

gm/colorwheel.cpp

 /*
  * Copyright 2014 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #include "Resources.h"
 #include "SkData.h"
 #include "SkDecodingImageGenerator.h"
+#include "checkerboard.h"
 #include "gm.h"
 #include "sk_tool_utils.h"
 
-static void checkerboard(
-        SkCanvas* canvas, int w, int h, int size, SkColor c1, SkColor c2) {
-    SkAutoCanvasRestore autoCanvasRestore(canvas, true);
-    canvas->clipRect(SkRect::MakeWH(SkIntToScalar(w), SkIntToScalar(h)));
-    canvas->drawColor(c1);
-    SkPaint paint;
-    paint.setColor(c2);
-    SkScalar s = SkIntToScalar(size);
-    for (int y = 0; y < h; y += size) {
-        SkScalar ty = SkIntToScalar(y);
-        bool oddRow = (y % (2 * size)) != 0;
-        for (int x = oddRow ? size : 0; x < w; x += (2 * size)) {
-            SkScalar tx = SkIntToScalar(x);
-            canvas->drawRect(SkRect::MakeXYWH(tx, ty, s, s), paint);
-        }
-    }
-}
-
 static void draw_bitmap(SkCanvas* canvas, const char* resource, int x, int y) {
     SkBitmap bitmap;
     if (GetResourceAsBitmap(resource, &bitmap)) {
         canvas->drawBitmap(bitmap, SkIntToScalar(x), SkIntToScalar(y));
     } else {
         SkDebugf("\nCould not decode file '%s'. Did you forget"
                  " to set the resourcePath?\n", resource);
     }
 }
 
 /*
   This GM tests whether the image decoders properly decode each color
   channel.  Four copies of the same image should appear in the GM, and
   the letter R should be red, B should be blue, G green, C cyan, M
   magenta, Y yellow, and K black. In all but the JPEG version of the
   image, the letters should be on a white disc on a transparent
   background (rendered as a checkerboard).  The JPEG image has a grey
   background and compression artifacts.
  */
 DEF_SIMPLE_GM(colorwheel, canvas, 256, 256) {
-    canvas->clear(SK_ColorWHITE);
-    checkerboard(canvas, 256, 556, 8, 0xFF999999, 0xFF666666);
+    skiagm::Checkerboard(canvas);
     draw_bitmap(canvas, "color_wheel.png", 0, 0);  // top left
     draw_bitmap(canvas, "color_wheel.gif", 128, 0);  // top right
     draw_bitmap(canvas, "color_wheel.webp", 0, 128);  // bottom left
     draw_bitmap(canvas, "color_wheel.jpg", 128, 128);  // bottom right
 }
 
 DEF_SIMPLE_GM(colorwheelnative, canvas, 128, 28) {
     SkPaint paint;
     sk_tool_utils::set_portable_typeface(&paint, NULL, SkTypeface::kBold);
     paint.setTextSize(18.0f);
 
     canvas->clear(SK_ColorLTGRAY);
     paint.setColor(SK_ColorRED);
     canvas->drawText("R", 1, 8.0f, 20.0f, paint);
     paint.setColor(SK_ColorGREEN);
     canvas->drawText("G", 1, 24.0f, 20.0f, paint);
     paint.setColor(SK_ColorBLUE);
     canvas->drawText("B", 1, 40.0f, 20.0f, paint);
     paint.setColor(SK_ColorCYAN);
     canvas->drawText("C", 1, 56.0f, 20.0f, paint);
     paint.setColor(SK_ColorMAGENTA);
     canvas->drawText("M", 1, 72.0f, 20.0f, paint);
     paint.setColor(SK_ColorYELLOW);
     canvas->drawText("Y", 1, 88.0f, 20.0f, paint);
     paint.setColor(SK_ColorBLACK);
     canvas->drawText("K", 1, 104.0f, 20.0f, paint);
 }