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§;
float py = getViewPointY§;
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;

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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，