create simple skia app for android using jni

platform_tools/android/examples/hello_skia_app/jni/helloskia.cpp

+#include <math.h>
+#include <jni.h>
+#include <android/bitmap.h>
+
+#include "SkCanvas.h"
+#include "SkGraphics.h"
+#include "SkSurface.h"
+#include "SkString.h"
+#include "SkTime.h"
+
+
+/**
+ * Draws something into the given bitmap
+ * @param  env
+ * @param  thiz
+ * @param  dstBitmap   The bitmap to place the results of skia into
+ * @param  elapsedTime The number of milliseconds since the app was started
+ */
+extern "C"
+JNIEXPORT void JNICALL Java_com_example_HelloSkiaActivity_drawIntoBitmap(JNIEnv* env,
+        jobject thiz, jobject dstBitmap, jlong elapsedTime)
+{
+    // Grab the dst bitmap info and pixels
+    AndroidBitmapInfo dstInfo;
+    void* dstPixels;
+    AndroidBitmap_getInfo(env, dstBitmap, &dstInfo);
+    AndroidBitmap_lockPixels(env, dstBitmap, &dstPixels);
+
+    SkImage::Info info = {
+        dstInfo.width, dstInfo.height, SkImage::kPMColor_ColorType, SkImage::kPremul_AlphaType
+    };
+
+    // Create a surface from the given bitmap
+    SkAutoTUnref<SkSurface> surface(SkSurface::NewRasterDirect(info, dstPixels, dstInfo.stride));
+    SkCanvas* canvas = surface->getCanvas();
+
+    // Draw something "interesting"
+
+    // Clear the canvas with a white color
+    canvas->drawColor(SK_ColorWHITE);
+
+    // Setup a SkPaint for drawing our text
+    SkPaint paint;
+    paint.setColor(SK_ColorBLACK); // This is a solid black color for our text
+    paint.setTextSize(SkIntToScalar(30)); // Sets the text size to 30 pixels
+    paint.setAntiAlias(true); // We turn on anti-aliasing so that the text to looks good.
+
+    // Draw some text
+    SkString text("Skia is Best!");
+    SkScalar fontHeight = paint.getFontSpacing();
+    canvas->drawText(text.c_str(), text.size(), // text's data and length
+                     10, fontHeight,            // X and Y coordinates to place the text
+                     paint);                    // SkPaint to tell how to draw the text
+
+    // Adapt the SkPaint for drawing blue lines
+    paint.setAntiAlias(false); // Turning off anti-aliasing speeds up the line drawing
+    paint.setColor(0xFF0000FF); // This is a solid blue color for our lines
+    paint.setStrokeWidth(SkIntToScalar(2)); // This makes the lines have a thickness of 2 pixels
+
+    // Draw some interesting lines using trig functions
+    for (int i = 0; i < 100; i++)
+    {
+        float x = (float)i / 99.0f;
+        float offset = elapsedTime / 1000.0f;
+        canvas->drawLine(sin(x * M_PI + offset) * 800.0f, 0,   // first endpoint
+                         cos(x * M_PI + offset) * 800.0f, 800, // second endpoint
+                         paint);                               // SkPapint to tell how to draw the line
+    }
+
+    // Unlock the dst's pixels
+    AndroidBitmap_unlockPixels(env, dstBitmap);
+}