自定义ImageView系列 － 区域截图（下）

功能要点：

• 根据控件自身大小计算合适的透明正方形预览区；
• 截取预览区图像并按照指定的尺寸缩放，生成Bitmap对象。
  本文着重介绍上述第2个要点。

有关第一个要点的内容，请参阅上一篇文章：请点此。
本篇文章中我们主要聊两个问题：

• 屏幕指定区域截图；
• 图片缩放。

由于在前文中，我们知道了指定区域的方位，那么解决起来就轻松很多了。只要先截取整个屏幕，然后利用Matrix将图片进行裁剪即可。
截取到指定部分的图像后，再利用Matrix的postScale()方法即可进行缩放。
下面放上代码片段：

public Bitmap getAdjustedBitmap(Activity activity) {
    View view = activity.getWindow().getDecorView();
    view.setDrawingCacheEnabled(true);
    view.buildDrawingCache();
    bitmap = view.getDrawingCache();
    matrix = new Matrix();
    matrix.postScale((CommonSettings.AVATOR\_SIZE * 1.0f) / (previewEdge[1] - previewEdge[0]), (CommonSettings.AVATOR\_SIZE * 1.0f) / (previewEdge[1] - previewEdge[0]));
    return Bitmap.createBitmap(bitmap, previewEdge[0] - 2, previewEdge[2] + myLocationStart[1] - 2, previewEdge[1] - previewEdge[0], previewEdge[1] - previewEdge[0], matrix, false);
}

如上所示，即可完成截图和缩放操作。
接下来放上整个重写的ImageView类的代码，这里面还包含了双指缩放和单指移动操作功能。

 package com.toec.acryptim.view;

import android.app.Activity;
import android.content.Context;
import android.graphics.Bitmap;
import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.Matrix;
import android.graphics.Paint;
import android.util.AttributeSet;
import android.view.MotionEvent;
import android.view.View;
import android.widget.ImageView;

import com.toec.acryptim.R;
import com.toec.acryptim.environment.CommonSettings;

/**
 * 作者：萧文翰
 * 邮箱：wh1990xiao2005@hotmail.com
 * 移动电话：+86 15822932537
 * 微博：http://weibo.com/xwhnew
 * 个人网站：http://www.xwhcoder.com
 */
public class PhotoChooseForAvatorImageView extends ImageView {

private Bitmap bitmap;
private Matrix matrix;

private float point1_old_x, point1_old_y, point1_new_x, point1_new_y,
        point2_old_x, point2_old_y, point2_new_x, point2_new_y,
        distance_old, distance_new;
private float point_old_x, point_old_y, point_new_x, point_new_y;
private boolean isMultiTouch = false;

private int[] myLocationStart;
private int[] myLocationEnd;
private int[] myLocationMid;

private int[] previewEdge;

private int bitmapLocXStart, bitmapLocXEnd, bitmapLocYStart, bitmapLocYEnd;

private Paint rectPaint;
private Paint rectBgPaint;


public PhotoChooseForAvatorImageView(Context context) {
    super(context);
    if (matrix == null) {
        matrix = new Matrix();
    }
}

public PhotoChooseForAvatorImageView(Context context, AttributeSet attrs) {
    super(context, attrs);
    if (matrix == null) {
        matrix = new Matrix();
    }
}

@Override
protected void onDraw(Canvas canvas) {
    super.onDraw(canvas);
    canvas.save();
    if (bitmap != null) {
        canvas.drawBitmap(bitmap, matrix, null);
    }
    if (previewEdge != null) {
        //上
        canvas.drawLine(previewEdge[0], previewEdge[2], previewEdge[1], previewEdge[2], rectPaint);
        //左
        canvas.drawLine(previewEdge[0], previewEdge[2], previewEdge[0], previewEdge[3], rectPaint);
        //下
        canvas.drawLine(previewEdge[0], previewEdge[3], previewEdge[1], previewEdge[3], rectPaint);
        //右
        canvas.drawLine(previewEdge[1], previewEdge[2], previewEdge[1], previewEdge[3], rectPaint);
        //灰色部分
        canvas.drawRect(0, 0, previewEdge[0], myLocationEnd[1], rectBgPaint);
        canvas.drawRect(previewEdge[0], 0, previewEdge[1], previewEdge[2], rectBgPaint);
        canvas.drawRect(previewEdge[1], 0, myLocationEnd[0], myLocationEnd[1], rectBgPaint);
        canvas.drawRect(previewEdge[0], previewEdge[3], previewEdge[1], myLocationEnd[1], rectBgPaint);
    }
    canvas.restore();
}

@Override
public boolean onTouchEvent(MotionEvent event) {
    switch (event.getAction() & MotionEvent.ACTION_MASK) {
        case MotionEvent.ACTION_DOWN:
            // 单点移动 按下
            if (event.getPointerCount() == 1) {
                isMultiTouch = false;
                point_old_x = event.getX();
                point_old_y = event.getY();
            }
            break;
        case MotionEvent.ACTION_UP:
            // 单点移动 抬起
            if (event.getPointerCount() == 1) {
                isMultiTouch = false;
                point_old_x = point_new_x;
                point_old_y = point_new_y;
            }

            break;
        case MotionEvent.ACTION_POINTER_UP:
            // 双点操作 抬起
            if (event.getPointerCount() == 2) {
                isMultiTouch = true;
                point1_old_x = point1_new_x;
                point1_old_y = point1_new_y;
                point2_old_x = point2_new_x;
                point2_old_y = point2_new_y;

            }
            break;
        case MotionEvent.ACTION_POINTER_DOWN:
            // 双点操作 按下
            if (event.getPointerCount() == 2) {
                isMultiTouch = true;
                point1_old_x = event.getX(0);
                point1_old_y = event.getY(0);
                point2_old_x = event.getX(1);
                point2_old_y = event.getY(1);
                distance_old = (float) Math
                        .sqrt(((point1_old_x - point2_old_x)
                                * (point1_old_x - point2_old_x) + (point1_old_y - point2_old_y)
                                * (point1_old_y - point2_old_y)));
            }
            break;
        case MotionEvent.ACTION_MOVE:
            // 双点操作 移动
            if (event.getPointerCount() == 2) {
                isMultiTouch = true;
                point1_new_x = event.getX(0);
                point1_new_y = event.getY(0);
                point2_new_x = event.getX(1);
                point2_new_y = event.getY(1);
                pinch();
            } else {
                // 单点移动 移动
                if (event.getPointerCount() == 1) {
                    if (!isMultiTouch) {
                        point_new_x = event.getX();
                        point_new_y = event.getY();
                        matrix.postTranslate((point_new_x - point_old_x),
                                (point_new_y - point_old_y));
                        point_old_x = point_new_x;
                        point_old_y = point_new_y;
                        invalidate();
                    }
                }
            }
            break;
    }
    return true;
}

// 缩放图片方法
private void pinch() {
    distance_new = (float) Math.sqrt(((point1_new_x - point2_new_x)
            * (point1_new_x - point2_new_x) + (point1_new_y - point2_new_y)
            * (point1_new_y - point2_new_y)));
    matrix.postScale((distance_new / distance_old),
            (distance_new / distance_old), this.getWidth() / 2,
            this.getTop() / 2);
    invalidate();
    distance_old = distance_new;
}

/**
 * 设置Bitmap
 *
 * @param bitmap
 */
public void setImage(Bitmap bitmap) {
    this.bitmap = bitmap;
    //获取控件自身起始点
    myLocationStart = new int[2];
    getLocationOnScreen(myLocationStart);
    //获取控件自身终止点
    myLocationEnd = new int[2];
    myLocationEnd[0] = getWidth() + myLocationStart[0];
    myLocationEnd[1] = getHeight() + myLocationStart[1];
    //计算控件自身中点
    myLocationMid = new int[2];
    myLocationMid[0] = (myLocationStart[0] + myLocationEnd[0]) / 2;
    myLocationMid[1] = (myLocationStart[1] + myLocationEnd[1]) / 2 - myLocationStart[1];
    //设置中间预览框边框色
    rectPaint = new Paint();
    rectPaint.setColor(Color.WHITE);
    rectPaint.setStrokeWidth(2);

    rectBgPaint = new Paint();
    rectBgPaint.setColor(getResources().getColor(R.color.photo_adjust_for_avator_bg));
    //计算中间预览边框位置
    previewEdge = new int[4];
    previewEdge[0] = (myLocationMid[0] - myLocationStart[0]) / 8;
    previewEdge[1] = myLocationEnd[0] - previewEdge[0];
    previewEdge[2] = myLocationMid[1] - ((previewEdge[1] - previewEdge[0]) / 2);
    previewEdge[3] = myLocationMid[1] + ((previewEdge[1] - previewEdge[0]) / 2);
    //计算Bitmap起点
    bitmapLocXStart = myLocationMid[0] - bitmap.getWidth() / 2;
    bitmapLocYStart = myLocationMid[1] - bitmap.getHeight() / 2;
    bitmapLocXEnd = bitmapLocXStart + bitmap.getWidth();
    bitmapLocYEnd = bitmapLocYStart - bitmap.getHeight();
    //调整Bitmap位置
    matrix.postTranslate(bitmapLocXStart, bitmapLocYStart);
    PhotoChooseForAvatorImageView.this.invalidate();
}

/**
 * 截图并返回Bitmap对象
 */
public Bitmap getAdjustedBitmap(Activity activity) {
    View view = activity.getWindow().getDecorView();
    view.setDrawingCacheEnabled(true);
    view.buildDrawingCache();
    bitmap = view.getDrawingCache();
    matrix = new Matrix();
    matrix.postScale((CommonSettings.AVATOR_SIZE * 1.0f) / (previewEdge[1] - previewEdge[0]), (CommonSettings.AVATOR_SIZE * 1.0f) / (previewEdge[1] - previewEdge[0]));
    return Bitmap.createBitmap(bitmap, previewEdge[0] - 2, previewEdge[2] + myLocationStart[1] - 2, previewEdge[1] - previewEdge[0], previewEdge[1] - previewEdge[0], matrix, false);
}

/**
 * 重置Bitmap（回收内存）
 */
public void resetBitmap() {
    bitmap.recycle();
    bitmap = null;
}
}