Android Paint之Shader渲染详解-CFANZ编程社区

上一篇讲到paint的一些常用方法，其中遗留了一些，这篇先讲解其中的一个Shader渲染，我们知道Shader渲染Android提供了5个子类，有BitmapShader，ComposeShader，LinearGradient，RadialGradient，SweepGradient。Shader中有一个TileMode，共有3种模式，

CLAMP：当图片小于绘制尺寸时要进行边界拉伸来填充

REPEAT：当图片小于绘制尺寸时重复平铺

MIRROR：当图片小于绘制尺寸时镜像平铺

我们先来看一下BitmapShader，

public class ShaderView extends View {
  private Bitmap mBitmap;
  private Shader mBitmapShader = null;
  private Paint mPaint;

  public ShaderView(Context context, AttributeSet attrs) {
    super(context, attrs);
    init();
  }

  private void init() {
    mPaint = new Paint(Paint.ANTI_ALIAS_FLAG);
    mBitmap = BitmapFactory.decodeResource(getResources(), R.drawable.icon);
    mBitmapShader = new BitmapShader(mBitmap, Shader.TileMode.REPEAT,
        Shader.TileMode.MIRROR);
  }

  @Override
  protected void onDraw(Canvas canvas) {
    super.onDraw(canvas);
    mPaint.setShader(mBitmapShader);
    canvas.drawRect(0, 0, mBitmap.getWidth() * 4, mBitmap.getHeight() * 4,
        mPaint);
  }

}

运行结果为

Android Paint之Shader渲染详解_Shader
我们看到左右平铺，上下镜像，在来改一下，只需要把上面的mBitmapShader改一下就可

mBitmapShader = new BitmapShader(mBitmap, Shader.TileMode.CLAMP,
        Shader.TileMode.MIRROR);

Android Paint之Shader渲染详解_LinearGradient_02

看到上下镜像，左右拉伸，再来看一下LinearGradient

public LinearGradient(float x0, float y0, float x1, float y1, int colors[], float positions[],
            TileMode tile)

float x0 ：渐变的x坐标起点

float y0 ：渐变的y坐标起点

float x1 ：渐变的x坐标终点

float y1 ：渐变的y坐标终点

int colors[]：渐变的颜色数组

float positions[]：颜色的相对位置

TileMode tile：上面的3种模式

public class ShaderView extends View {
  private Shader mLinearGradient = null;
  private Paint mPaint;

  public ShaderView(Context context, AttributeSet attrs) {
    super(context, attrs);
    init();
  }

  private void init() {
    mPaint = new Paint(Paint.ANTI_ALIAS_FLAG);
    mLinearGradient = new LinearGradient(0, 0, 100, 100, new int[] {
        Color.RED, Color.YELLOW, Color.BLACK, Color.WHITE },
        new float[] { 0, .1F, .8F, .9F }, Shader.TileMode.REPEAT);
  }

  @Override
  protected void onDraw(Canvas canvas) {
    super.onDraw(canvas);
    mPaint.setShader(mLinearGradient);
    canvas.drawRect(0, 0, 900, 1000, mPaint);
  }
}

Android Paint之Shader渲染详解_BitmapShader_03
我们看到上面的小数数组是渐变的相对位置，如果positions为空，这均匀分布，修改一下

mLinearGradient = new LinearGradient(0, 0, 100, 100, new int[] {
        Color.RED, Color.YELLOW, Color.BLACK, Color.WHITE }, null,
        Shader.TileMode.REPEAT);

Android Paint之Shader渲染详解_Shader_04

再来修改一下模式，因为最后一个是白色容易和手机屏幕混淆，所以添加了一个绿色

mLinearGradient = new LinearGradient(0, 0, 100, 100,
        new int[] { Color.RED, Color.YELLOW, Color.BLACK, Color.WHITE,
            Color.GREEN }, null, Shader.TileMode.CLAMP);

Android Paint之Shader渲染详解_LinearGradient_05

我们看到最后一个颜色是拉伸，再修改一下

mLinearGradient = new LinearGradient(0, 0, 100, 100,
        new int[] { Color.RED, Color.YELLOW, Color.BLACK, Color.WHITE,
            Color.GREEN }, null, Shader.TileMode.MIRROR);

Android Paint之Shader渲染详解_RadialGradient_06

镜像模式，所以感觉有点对称。在看一下LinearGradient的另一个构造方法，

LinearGradient(float x0, float y0, float x1, float y1, int color0, int color1,
            TileMode tile)

其中color0是颜色的起始点，color1是颜色的终止点，我们就演示一个看看

mLinearGradient = new LinearGradient(0, 0, 100, 100, Color.RED,
        Color.YELLOW, Shader.TileMode.MIRROR);

Android Paint之Shader渲染详解_BitmapShader_07

再来看一下RadialGradient

RadialGradient(float x, float y, float radius,
                          int colors[], float positions[], TileMode tile)

它实现的是环形渐变，

x：渐变的中心x坐标

y：渐变的中心y坐标

radius：渐变的半径

colors：梯度渐变的颜色数组

positions：和LinearGradient类似，用来指定颜色数组的相对位置

public class ShaderView extends View {
  private Shader mRadialGradient = null;
  private Paint mPaint;

  public ShaderView(Context context, AttributeSet attrs) {
    super(context, attrs);
    init();
  }

  private void init() {
    mPaint = new Paint(Paint.ANTI_ALIAS_FLAG);
    mRadialGradient = new RadialGradient(200, 400, 100, new int[] {
        Color.YELLOW, Color.RED, Color.BLUE, Color.GREEN }, null,
        Shader.TileMode.REPEAT);
  }

  @Override
  protected void onDraw(Canvas canvas) {
    super.onDraw(canvas);
    mPaint.setShader(mRadialGradient);
    canvas.drawRect(0, 0, 900, 1000, mPaint);
  }
}

Android Paint之Shader渲染详解_SweepGradient_08

运行结果如上，再来修改一下

mRadialGradient = new RadialGradient(200, 400, 100, new int[] {
        Color.YELLOW, Color.RED, Color.BLUE, Color.GREEN }, null,
        Shader.TileMode.CLAMP);

Android Paint之Shader渲染详解_BitmapShader_09

再来修改一下

mRadialGradient = new RadialGradient(200, 400, 100, new int[] {
        Color.YELLOW, Color.RED, Color.BLUE, Color.GREEN }, null,
        Shader.TileMode.MIRROR);

Android Paint之Shader渲染详解_LinearGradient_10

还有个构造方法，这里就不在演示

RadialGradient(float x, float y, float radius,
                          int color0, int color1, TileMode tile)

下面看一下SweepGradient

SweepGradient(float cx, float cy,
                         int colors[], float positions[])

cx，cy：扫描中心的x，y坐标

colors：渐变的数组颜色
positions：渐变的相对位置

public class ShaderView extends View {
  private Shader mSweepGradient = null;
  private Paint mPaint;

  public ShaderView(Context context, AttributeSet attrs) {
    super(context, attrs);
    init();
  }

  private void init() {
    mPaint = new Paint(Paint.ANTI_ALIAS_FLAG);
    mSweepGradient = new SweepGradient(400, 400, new int[] { Color.YELLOW,
        Color.RED, Color.BLUE, Color.GREEN }, new float[] { 0, .2F,
        .6F, .9F });
  }

  @Override
  protected void onDraw(Canvas canvas) {
    super.onDraw(canvas);
    mPaint.setShader(mSweepGradient);
    canvas.drawCircle(400, 400, 300, mPaint);
  }
}

Android Paint之Shader渲染详解_LinearGradient_11

还有最后一个ComposeShader，这个是组合的Shader

public class ShaderView extends View {
  private Shader mSweepGradient = null;
  private Shader mBitmapShader = null;
  private Shader mComposeShader = null;
  private Paint mPaint;
  private Bitmap mBitmap;

  public ShaderView(Context context, AttributeSet attrs) {
    super(context, attrs);
    init();
  }

  private void init() {
    mPaint = new Paint(Paint.ANTI_ALIAS_FLAG);
    mBitmap = BitmapFactory.decodeResource(getResources(), R.drawable.icon);
    mBitmapShader = new BitmapShader(mBitmap, Shader.TileMode.REPEAT,
        Shader.TileMode.MIRROR);
    mSweepGradient = new SweepGradient(mBitmap.getWidth() * 2,
        mBitmap.getWidth() * 2, new int[] { Color.YELLOW,
        Color.RED, Color.BLUE, Color.GREEN }, new float[] { 0, .2F,
        .6F, .9F });
    mComposeShader = new ComposeShader(mBitmapShader, mSweepGradient,
        PorterDuff.Mode.DARKEN);
  }

  @Override
  protected void onDraw(Canvas canvas) {
    super.onDraw(canvas);
    mPaint.setShader(mComposeShader);
    canvas.drawRect(0, 0, mBitmap.getWidth() * 4, mBitmap.getHeight() * 4,
        mPaint);
  }
}