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

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