Add bubbles GM for drawing/blending 50 circles.

gm/bubbles.cpp

Index: gm/bubbles.cpp
diff --git a/gm/bubbles.cpp b/gm/bubbles.cpp
new file mode 100644
index 0000000000000000000000000000000000000000..86c3daa661e27b254cb3e715d062a18265bd9401
--- /dev/null
+++ b/gm/bubbles.cpp
@@ -0,0 +1,44 @@
+/*
+ * Copyright 2016 Google, Inc. 
+ *
+ * Use of this source code is governed by a BSD-style license that can be
+ * found in the LICENSE file.
+ */
+
+#include "gm.h"
+
+/*
+ * Draw 50 semi-transparent circles with pseudo-random positions, radii, and
+ * colors, using the default blend mode (SRC OVER). Use of SkRandom with 
+ * default seed means results SHOULD be identical across multiple platforms. 
+ */
+DEF_SIMPLE_GM(bubbles, canvas, 512, 512) {
+	canvas->clear(SK_ColorWHITE);
+
+	SkPaint p;
+	p.setAntiAlias(true);
+
+	SkRandom rand;
+
+	auto pos_min    = SkIntToScalar(0);
+	auto pos_max    = SkIntToScalar(511);
+	auto radius_min = SkIntToScalar(0);
+	auto radius_max = SkIntToScalar(128);
+	auto color_min  = SkIntToScalar(0);
+	auto color_max  = SkIntToScalar(255);
+
+	const int NUM_BUBBLES = 50;
+	for (int i = 0; i < NUM_BUBBLES; i++) {
+		auto cx     = rand.nextRangeScalar(pos_min, pos_max);
+		auto cy     = rand.nextRangeScalar(pos_min, pos_max);
+		auto radius = rand.nextRangeScalar(radius_min, radius_max);
+
+		auto a = (U8CPU)128;
+		auto r = (U8CPU)rand.nextRangeScalar(color_min, color_max);
+		auto g = (U8CPU)rand.nextRangeScalar(color_min, color_max);
+		auto b = (U8CPU)rand.nextRangeScalar(color_min, color_max);
+		p.setColor(SkColorSetARGB(a, r, g, b));
+
+		canvas->drawCircle(cx, cy, radius, p);
+	}
+}