shader类渲染图形

public class MainActivity extends Activity {
	@Override
	public void onCreate(Bundle savedInstanceState) {
		super.onCreate(savedInstanceState);
		setContentView(new MyView(this));
	}

	// 自定义视图类
	class MyView extends View {
		private Bitmap bitmap;
		private Shader bitmapShader; // 声明位图渲染对象
		private Shader linearGradient;// 声明线性渲染对象
		private Shader radialGradient;// 声明光束渲染对象
		private Shader sweepGradient;// 声明梯度渲染对象
		private Shader composeShader; // 声明混合渲染对象
		private Paint paint;
		private int[] colors;// 声明颜色数组
		private boolean isFirst = true;

		public MyView(Context context) {
			super(context);
			bitmap = BitmapFactory.decodeResource(getResources(),
					R.drawable.girl);
			paint = new Paint();
			colors = new int[] { Color.RED, Color.GREEN, Color.BLUE };
			bitmapShader = new BitmapShader(bitmap, TileMode.REPEAT,
					TileMode.MIRROR);// 实例化位图渲染对象,x坐标方向重复图形，y坐标方向镜像图形
			linearGradient = new LinearGradient(0, 0, 100, 100, colors, null,
					TileMode.REPEAT);// 实例化线性渲染
			radialGradient = new RadialGradient(100, 100, 80, colors, null,
					TileMode.REPEAT);// 实例化光束渲染
			sweepGradient = new SweepGradient(200, 200, colors, null);// 实例化梯度渲染
			composeShader = new ComposeShader(linearGradient, radialGradient,
					PorterDuff.Mode.DARKEN);// 实例化混合渲染
			setFocusable(true);// 使其获得焦点
		}

		@Override
		protected void onDraw(Canvas canvas) {
			super.onDraw(canvas);
			if (isFirst) {
				String s = "按上/下/左/右/中间键测试！";
				paint.setColor(Color.BLUE);
				canvas.drawText(s, 0, s.length() - 1, 20, 20, paint);
			} else {
				canvas.drawRect(0, 0, getWidth(), getHeight(), paint);// 全屏画矩形
			}
		}

		@Override
		public boolean onKeyDown(int keyCode, KeyEvent event) {
			isFirst = false;
			if (keyCode == KeyEvent.KEYCODE_DPAD_UP) {
				paint.setShader(bitmapShader);// 将画笔渲染设置为位图渲染
			}
			if (keyCode == KeyEvent.KEYCODE_DPAD_DOWN) {
				paint.setShader(linearGradient);// 将画笔渲染设置为线性渲染
			}
			if (keyCode == KeyEvent.KEYCODE_DPAD_LEFT) {
				paint.setShader(radialGradient);// 将画笔渲染设置为光束渲染
			}
			if (keyCode == KeyEvent.KEYCODE_DPAD_RIGHT) {
				paint.setShader(sweepGradient);// 将画笔渲染设置为梯度渲染
			}
			if (keyCode == KeyEvent.KEYCODE_DPAD_CENTER) {
				paint.setShader(composeShader);// 将画笔渲染设置为混合渲染
			}
			postInvalidate();// 重绘界面
			return super.onKeyDown(keyCode, event);
		}
	}
}