Android 照片选择区域功能实现示例

实现 Android 的照片选择区域功能

主要有参考 pqpo/SmartCropper

显示四条边和八个点，

八个点： 4 个角和 4 条边的中点

/* 裁剪区域,0， 左上 -> LeftTop, 1， 右上 -> RightTop，2， 右下 -> RightBottom, 3， 左下 -> LeftBottom*/Point[] mCropPoints;// 4 条边的中点Point[] mEdgeMidPoints;

绘制

protected void onDrawCropPoint(Canvas canvas) {//绘制蒙版onDrawMask(canvas);//绘制辅助线onDrawGuideLine(canvas);//绘制选区线onDrawLines(canvas);//绘制锚点onDrawPoints(canvas);//绘制放大镜// ... }

具体绘制部分：

绘制八个点

protected void onDrawPoints(Canvas canvas) {if (!checkPoints(mCropPoints)) { return;}// 绘制 4 个角for (Point point : mCropPoints) { canvas.drawCircle(getViewPointX(point), getViewPointY(point), dp2px(POINT_RADIUS), mPointFillPaint); canvas.drawCircle(getViewPointX(point), getViewPointY(point), dp2px(POINT_RADIUS), mPointPaint);}if (mShowEdgeMidPoint) { setEdgeMidPoints(); // 中间锚点 // 绘制 4 条边上的中点 for (Point point : mEdgeMidPoints){canvas.drawCircle(getViewPointX(point), getViewPointY(point), dp2px(POINT_RADIUS), mPointFillPaint);canvas.drawCircle(getViewPointX(point), getViewPointY(point), dp2px(POINT_RADIUS), mPointPaint); }} }

绘制 4 条边上的中点前，

先算出当前 4 条边上中点的位置

public void setEdgeMidPoints(){// 中点不存在，就新建if (mEdgeMidPoints == null){ mEdgeMidPoints = new Point[4]; for (int i = 0; i < mEdgeMidPoints.length; i++){mEdgeMidPoints[i] = new Point(); }}// 维护 4 个顶点的位置，// 通过顶点的位置，算出边上中点的位置int len = mCropPoints.length;for (int i = 0; i < len; i++){ // 为了避免极端情况， // 采用 （ 坐标 + 距离的一半 ） 的方式mEdgeMidPoints[i].set(mCropPoints[i].x + (mCropPoints[(i+1)%len].x - mCropPoints[i].x)/2, mCropPoints[i].y + (mCropPoints[(i+1)%len].y - mCropPoints[i].y)/2);} }2， 拖动

拖动分 2 种情况，角点拖拽，中点平移

8 个类型， 4 个角点拖拽，4 个中点平移

enum DragPointType{LEFT_TOP,RIGHT_TOP,RIGHT_BOTTOM,LEFT_BOTTOM,TOP,RIGHT,BOTTOM,LEFT;// 判断是角点拖拽，不是中点平移public static boolean isEdgePoint(DragPointType type){ return type == TOP || type == RIGHT || type == BOTTOM || type == LEFT;} }

移动的处理

@Override public boolean onTouchEvent(MotionEvent event) {int action = event.getAction();boolean handle = true;switch (action) { case MotionEvent.ACTION_DOWN:// 识别到，当前点mDraggingPoint = getNearbyPoint(event);if (mDraggingPoint == null) { handle = false;}break; case MotionEvent.ACTION_MOVE:// 移动toImagePointSize(mDraggingPoint, event);break; case MotionEvent.ACTION_UP:// 手指抬起，// 操作取消mDraggingPoint = null;break;}// 绘制// 更新完位置后，刷新绘制invalidate();return handle || super.onTouchEvent(event); }

识别到，当前点

private Point getNearbyPoint(MotionEvent event) {// 判断 4 个角点，可用if (checkPoints(mCropPoints)) { for (Point p : mCropPoints) {// 找出当前的点if (isTouchPoint(p, event)) return p; }}// 判断 4 个中点可用if (checkPoints(mEdgeMidPoints)) { for (Point p : mEdgeMidPoints){// 找出当前的点if (isTouchPoint(p, event)) return p; }}return null; }

找出当前的点，的方法

private static final float TOUCH_POINT_CATCH_DISTANCE = 15;private boolean isTouchPoint(Point p, MotionEvent event){float x = event.getX();float y = event.getY();float px = getViewPointX(p);float py = getViewPointY(p);double distance = Math.sqrt(Math.pow(x - px, 2) + Math.pow(y - py, 2));// 也就是，判断距离if (distance < dp2px(TOUCH_POINT_CATCH_DISTANCE)) { return true;}return false; }2.1 ，角点拖拽

先介绍 4 个角点拖拽

private void toImagePointSize(Point dragPoint, MotionEvent event) {if (dragPoint == null) { return;}// 找出当前移动类型，// 是角点拖拽，还是中点平移DragPointType pointType = getPointType(dragPoint);int x = (int) ((Math.min(Math.max(event.getX(), mActLeft), mActLeft + mActWidth) - mActLeft) / mScaleX);int y = (int) ((Math.min(Math.max(event.getY(), mActTop), mActTop + mActHeight) - mActTop) / mScaleY);// 判断可以移动// ... if (DragPointType.isEdgePoint(pointType)){ // ... // 中点平移} else { // 角点拖拽 // 实现很简单， // 更新就好了 dragPoint.y = y; dragPoint.x = x;} }

找出当前移动类型，

是角点拖拽，还是中点平移

// 拿采集的点，找出对应的类型private DragPointType getPointType(Point dragPoint){if (dragPoint == null) return null;DragPointType type;// 看，是不是顶点 / 角点if (checkPoints(mCropPoints)) { for (int i = 0; i < mCropPoints.length; i++) {if (dragPoint == mCropPoints[i]) { // 找到了，直接返回 type = DragPointType.values()[i]; return type;} }}// 看，是不是中点if (checkPoints(mEdgeMidPoints)) { for (int i = 0; i < mEdgeMidPoints.length; i++){if (dragPoint == mEdgeMidPoints[i]){ // 找到了，直接返回 type = DragPointType.values()[4+i]; return type;} }}return null; }2.2，中点平移

private void toImagePointSize(Point dragPoint, MotionEvent event) {if (dragPoint == null) { return;}DragPointType pointType = getPointType(dragPoint);int x = // ...int y = // ...// 判断可以移动// ... if (DragPointType.isEdgePoint(pointType)){ // 中点平移, // 拿到的是，一个偏移向量 int xoff = x - dragPoint.x; int yoff = y - dragPoint.y; moveEdge(pointType, xoff, yoff);} else { // 角点拖拽 // ...} }

拿到偏移向量，修改对应的两个顶点的坐标

private void moveEdge(DragPointType type, int xoff, int yoff){switch (type){ case TOP:// 这边的平移，比较简单// 找到中点，旁边的两个焦点// 再移动位置movePoint(mCropPoints[P_LT], 0, yoff);movePoint(mCropPoints[P_RT], 0, yoff);break; case RIGHT:// 右移处理movePoint(mCropPoints[P_RT], xoff, 0);movePoint(mCropPoints[P_RB], xoff, 0);break; case BOTTOM:// 下移处理// ... case LEFT:// 左移处理// ... default: break;} }

简单的平移代码

拿到偏移向量， 修改坐标，完事

private void movePoint(Point point, int xoff, int yoff){if (point == null) return;int x = point.x + xoff;int y = point.y + yoff;// 检查边界if (x < 0 || x > getDrawable().getIntrinsicWidth()) return;if (y < 0 || y > getDrawable().getIntrinsicHeight()) return;point.x = x;point.y = y; }

中点平移增强

这里的中点平移，拿到平移向量后，

直接添加到中点旁边的两个角点上

效果增强为，中点平移，中点旁边的两个角点顺着两侧边，做平移计算稍微复杂，

知道中点之前的位置，和中点之后的位置，

知道中点与一角点，所在边的斜率，

知道此角点的另一边的斜率

知道角点，平移前的位置，

求解出角点，平移后的位置

这是一个方程式求解网站

变换坐标系，可能简单些相关 github

demo 的 gradle 配置

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