利用PorterDuffXfermode绘制图片文字

PorterDuffXfermode是Android中用来对图层进行操作的类，类似于数学中的交集、并集，将上层（src）和下层（dst)进行特定的方式进行混合显示。

构造方法：PorterDuffXfermode(PorterDuff.Mode mode)

下图显示对应的PorterDuff.Mode所对应的效果

这次实现的图片文字是用的SrcIn模式，也就是先画文字然后画图，取其交集区域显示上层图层

完整代码展示

package com.yuyigufen.customview;

import android.content.Context;
import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.Paint;
import android.graphics.PorterDuff;
import android.graphics.PorterDuffXfermode;
import android.support.annotation.Nullable;
import android.util.AttributeSet;
import android.view.View;

/**
* Created by Administrator on 2018/6/1 0001.
*/

public class MyTextImageView extends View {

private Paint paint;

public MyTextImageView(Context context) {
this(context,null);
}

public MyTextImageView(Context context, @Nullable AttributeSet attrs) {
super(context, attrs);
paint = new Paint(Paint.ANTI_ALIAS_FLAG);
}

@Override
protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
setMeasuredDimension(measureWidth(widthMeasureSpec),measureWidth(heightMeasureSpec));
}
private int measureWidth(int width){
int size = MeasureSpec.getSize(width);
int mode = MeasureSpec.getMode(width);
if(MeasureSpec.EXACTLY==mode){
return size;
}else {
if(MeasureSpec.AT_MOST==mode){
return size<200?size:200;
}
return 200;
}
}

@Override
protected void onDraw(Canvas canvas) {
super.onDraw(canvas);
//        创建一个新画布，然后在新画布上进行绘制
int layerId = canvas.saveLayer(0, 0, getWidth(),getHeight() , null, Canvas.ALL_SAVE_FLAG);
paint.setTextSize(100);
//    这里使用STROKE模式通过设置StrokeWidth增加文字的宽度
paint.setStyle(Paint.Style.STROKE);
paint.setStrokeWidth(8);
float i = paint.measureText("图片文字");
canvas.drawText("图片文字",(getWidth()-i)/2,getHeight()/2,paint);
//        设置取交集显示
PorterDuffXfermode porterDuffXfermode = new PorterDuffXfermode(PorterDuff.Mode.SRC_IN);
paint.setXfermode(porterDuffXfermode);
Bitmap bitmap = BitmapFactory.decodeResource(getResources(), R.mipmap.fff);
//        将图片缩放为控件大小
Bitmap scaledBitmap = Bitmap.createScaledBitmap(bitmap, getWidth(), getHeight(), true);
canvas.drawBitmap(scaledBitmap,5,5,paint);
paint.setXfermode(null);
//        将绘制完的画布贴到控件上
canvas.restoreToCount(layerId);
}
}

效果展示