Android Paint之MaskFilter详解

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这一篇来简单分析一下Paint的setMaskFilter(MaskFilter maskfilter)方法，其中MaskFilter有两个子类，一个BlurMaskFilter一个是EmbossMaskFilter，这里先来看一下BlurMaskFilter这个类的源码

public enum Blur {
        /**
         * Blur inside and outside the original border.
         */
        NORMAL(0),

        /**
         * Draw solid inside the border, blur outside.
         */
        SOLID(1),

        /**
         * Draw nothing inside the border, blur outside.
         */
        OUTER(2),

        /**
         * Blur inside the border, draw nothing outside.
         */
        INNER(3);
        
        Blur(int value) {
            native_int = value;
        }
        final int native_int;
    }
    
    /**
     * Create a blur maskfilter.
     *
     * @param radius The radius to extend the blur from the original mask. Must be > 0.
     * @param style  The Blur to use
     * @return       The new blur maskfilter
     */
    public BlurMaskFilter(float radius, Blur style) {
        native_instance = nativeConstructor(radius, style.native_int);
    }

构造方法很简单，传入一个半径，是绘制阴影模糊的半径，其中类型有以上4种，这里就不在一一叙述，先看一下代码然后在直接看运行结果

public class MaskFilterView extends View {
  private Paint paint;
  private TextPaint mTextPaint;
  private BlurMaskFilter bmf1;
  private BlurMaskFilter bmf2;
  private BlurMaskFilter bmf3;
  private BlurMaskFilter bmf4;

  public MaskFilterView(Context context, AttributeSet attrs) {
    super(context, attrs);
    paint = new Paint(Paint.ANTI_ALIAS_FLAG);
    paint.setColor(Color.RED);
    paint.setStyle(Style.FILL_AND_STROKE);
    mTextPaint = new TextPaint(Paint.ANTI_ALIAS_FLAG);
    mTextPaint.setTextSize(64);
    mTextPaint.setColor(Color.BLUE);
    mTextPaint.setTextAlign(Align.CENTER);

    bmf1 = new BlurMaskFilter(100, Blur.NORMAL);
    bmf2 = new BlurMaskFilter(100, Blur.SOLID);
    bmf3 = new BlurMaskFilter(100, Blur.OUTER);
    bmf4 = new BlurMaskFilter(100, Blur.INNER);

  }

  @Override
  protected void onDraw(Canvas canvas) {
    super.onDraw(canvas);
    canvas.translate(0, 200);
    canvas.drawColor(Color.WHITE);
    paint.setMaskFilter(bmf1);
    canvas.drawCircle(300, 300, 150, paint);
    canvas.drawText("NORMAL", 300, 600, mTextPaint);

    paint.setMaskFilter(bmf2);
    canvas.drawCircle(300, 900, 150, paint);
    canvas.drawText("SOLID", 300, 1200, mTextPaint);

    paint.setMaskFilter(bmf3);
    canvas.drawCircle(800, 300, 150, paint);
    canvas.drawText("OUTER", 800, 600, mTextPaint);

    paint.setMaskFilter(bmf4);
    canvas.drawCircle(800, 900, 150, paint);
    canvas.drawText("INNER", 800, 1200, mTextPaint);
  }
}

在Androidmanifest中要加上下面这段代码，否则不会出现任何模糊效果

android:hardwareAccelerated="false"

来看一下运行的结果

效果很明显，这里就不在详述。下面再来看一下EmbossMaskFilter这个类，先看一下他的构造方法

/**
     * Create an emboss maskfilter
     *
     * @param direction  array of 3 scalars [x, y, z] specifying the direction of the light source
     * @param ambient    0...1 amount of ambient light
     * @param specular   coefficient for specular highlights (e.g. 8)
     * @param blurRadius amount to blur before applying lighting (e.g. 3)
     * @return           the emboss maskfilter
     */
    public EmbossMaskFilter(float[] direction, float ambient, float specular, float blurRadius) {
        if (direction.length < 3) {
            throw new ArrayIndexOutOfBoundsException();
        }
        native_instance = nativeConstructor(direction, ambient, specular, blurRadius);
    }

其中direction表示x,y,z的三个方向，ambient表示的是光的强度，范围为[0-1]，specular是反射亮度的系数，blurRadius是指模糊的半径，看一下代码

package test.view;

import android.annotation.SuppressLint;
import android.content.Context;
import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.EmbossMaskFilter;
import android.graphics.Paint;
import android.graphics.Paint.Style;
import android.util.AttributeSet;
import android.view.View;

public class MaskFilterView extends View {
  private Paint paint;
  EmbossMaskFilter emboss;

  public MaskFilterView(Context context, AttributeSet attrs) {
    super(context, attrs);
    paint = new Paint(Paint.ANTI_ALIAS_FLAG);
    paint.setColor(Color.RED);
    paint.setStyle(Style.STROKE);
    paint.setStrokeWidth(32);
    paint.setTextSize(368);
    float[] direction = new float[] { 1, 1, 1 };
    // 设置环境光亮度
    float light = 0.1f;
    // 选择要应用的反射等级
    float specular = 8;
    // 向mask应用一定级别的模糊
    float blur = 3;
    emboss = new EmbossMaskFilter(direction, light, specular, blur);

  }

  @Override
  protected void onDraw(Canvas canvas) {
    super.onDraw(canvas);
    canvas.drawText("山大王", 30, 400, paint);
  }

  @SuppressLint("NewApi")
  public void setparam(float x, float y, float z, float light,
      float specular, float blur) {
    emboss = new EmbossMaskFilter(new float[] { x, y, z }, light, specular,
        blur);
    paint.setMaskFilter(emboss);
    invalidate();
  }
}

看一下运行结果，这个会根据不同的值产生不同的结果，下面只截取已其中的一个