Android Shader应用开发之雷达扫描效果

package com.example.apple.shaderdemo;import android.content.Context;import android.graphics.Bitmap;import android.graphics.BitmapFactory;import android.graphics.BitmapShader;import android.graphics.Canvas;import android.graphics.Color;import android.graphics.Matrix;import android.graphics.Paint;import android.graphics.Shader;import android.graphics.SweepGradient;import android.support.annotation.Nullable;import android.util.AttributeSet;import android.view.View;public class ShaderView3 extends View {    private Paint mSweepPaint;    private Paint mBitmapPaint;    private int mWidth;    private Bitmap mBitmap;    private int degrees = 0;    Matrix mSweepMatrix = new Matrix();    Matrix mBitmapMatrix = new Matrix();    private SweepGradient mSweepGradient;    private BitmapShader mBitmapShader;  private float mScale;  public ShaderView3(Context context) {    super(context);    init();  }  public ShaderView3(Context context, @Nullable AttributeSet attrs) {    super(context, attrs);    init();  }    public void setDegrees(int degrees) {    this.degrees = degrees;    postInvalidate();//在主线程里执行OnDraw  }  private void init() {//    1.准备好画笔    mSweepPaint = new Paint();    mBitmapPaint = new Paint();//    2.图片着色器    mBitmap = BitmapFactory.decodeResource(getResources(), R.drawable.ccc);    mBitmapShader = new BitmapShader(mBitmap, Shader.TileMode.CLAMP, Shader.TileMode.CLAMP);//    3.将图片着色器设置给画笔    mBitmapPaint.setShader(mBitmapShader);  }  @Override  protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {    super.onMeasure(widthMeasureSpec, heightMeasureSpec);//    获取这个自定义view的宽高，注意在onMeasure里获取，在构造函数里得到的是0    mWidth = getMeasuredWidth();//    根据你所设置的view的尺寸和bitmap的尺寸计算一个缩放比例，否则的话，得到的图片是一个局部，而不是一整张图片    mScale = (float) mWidth / (float) mBitmap.getWidth();//    4.梯度扫描着色器    mSweepGradient = new SweepGradient(mWidth / 2, mWidth / 2, new int[]{Color.argb(200, 200, 0, 0), Color.argb(10, 30, 0, 0)}, null);//    5.将梯度扫描着色器设置给另外一支画笔    mSweepPaint.setShader(mSweepGradient);  }  @Override  protected void onDraw(Canvas canvas) {    super.onDraw(canvas);//    迫不得已的时候，才在onDraw方法写代码，能提前准备的要在之前去准备，//    不要写在onDraw里面，因为onDraw会不停地刷新绘制，写的代码越多，越影响效率//    将图片缩放至你指定的自定义View的宽高    mBitmapMatrix.setScale(mScale, mScale);    mBitmapShader.setLocalMatrix(mBitmapMatrix);//   设置扫描圈旋转角度    mSweepMatrix.setRotate(degrees, mWidth / 2, mWidth / 2);    mSweepGradient.setLocalMatrix(mSweepMatrix);//    5. 使用设置好图片着色器的画笔，画圆，先画出下层的女神图片，在画出上层的扫描图片    canvas.drawCircle(mWidth / 2, mWidth / 2, mWidth / 2, mBitmapPaint);    canvas.drawCircle(mWidth / 2, mWidth / 2, mWidth / 2, mSweepPaint);  }}