ActionScript 3缩放和滚动问题

由于内置的触摸手势的空气不是很方便,我实现了一个自制的缩放功能,使用 MultitouchInputMode.TOUCH_POINT .

import flash.events.Event;
import flash.geom.Rectangle;
import flash.events.MouseEvent;
import flash.ui.MultitouchInputMode;
import flash.events.TouchEvent;
import flash.geom.Point;


//Vars

var touchpoints:Array = []
var touch_mode:String = null
var touch_start:Point
var map_start:Point
var map_zoom:Number
var map_width:Number
var map_height:Number
var zoom_startdist:Number

//Config

var max_zoom:Number = 6
var min_zoom:Number = 1
var map_bounds:Rectangle = new Rectangle(0,0,mapMC.width,mapMC.height) // this defines the area in which the map should fit


//Allow Touch Gestures

Multitouch.inputMode = MultitouchInputMode.TOUCH_POINT;

//Zoom and Drag Event Listeners

stage.addEventListener(TouchEvent.TOUCH_BEGIN, touchBegin)
stage.addEventListener(TouchEvent.TOUCH_MOVE, touchMoved)
stage.addEventListener(TouchEvent.TOUCH_END, touchEnd)

// Touch Handlers

function touchBegin(e:TouchEvent){
    if(touchpoints.length<2){ // only accept 2 active touchpoints, ignore the 3rd,4th,etc
        touchpoints.push({id:e.touchPointID,x:e.stageX,y:e.stageY})
        touchpointsChanged()
    }
}
function touchMoved(e:TouchEvent){
    var touchpoint:Object = getTouchPointById(e.touchPointID) // get current touchpoint...
    if(touchpoint){
        // ... and update the position
        touchpoint.x = e.stageX 
        touchpoint.y = e.stageY
        touchpointMoved()
    }
}
function touchEnd(e:TouchEvent){
    removeTouchPoint(e.touchPointID)
    touchpointsChanged()
}



// Pan & Zoom logic

function touchpointsChanged(){
    if(touchpoints.length==1){ // 1 touch point => panning
        startPan()
    }else if(touchpoints.length==2){ // 2 touch points => zooming
        startZoom()
    }
}

function startPan(){
    touch_mode = 'pan'
    touch_start = new Point(touchpoints[0].x,touchpoints[0].y)
    map_start = new Point(mapMC.x,mapMC.y)
}

function startZoom(){
    touch_mode = 'zoom'
    touch_start = getZoomCenter()
    zoom_startdist = getZoomDist()
    map_start = new Point(mapMC.x,mapMC.y)
    map_zoom = mapMC.scaleX
    map_width = mapMC.width
    map_height = mapMC.height
}

function touchpointMoved(){
    switch(touch_mode){
        case 'pan':
            mapMC.x = map_start.x + touchpoints[0].x - touch_start.x
            mapMC.y = map_start.y + touchpoints[0].y - touch_start.y
        break
        case 'zoom':
            var current_scale:Number = map_zoom*getZoomFactor() // get current zoom factor (relative to the previous zoom of the map)

            current_scale = Math.min(max_zoom,Math.max(min_zoom,current_scale)) // limit zoom (as defined in -> Config)

            mapMC.scaleX = mapMC.scaleY = current_scale

            // Set map position to the current center of zoom
            var zoom_pos:Point = getZoomCenter()
            mapMC.x = map_start.x + zoom_pos.x - touch_start.x
            mapMC.y = map_start.y + zoom_pos.y - touch_start.y

            // Correct map position regarding the scaling
            mapMC.x += -(current_scale-map_zoom)*map_width*((touch_start.x-map_start.x)/map_width)/map_zoom
            mapMC.y += -(current_scale-map_zoom)*map_height*((touch_start.y-map_start.y)/map_height)/map_zoom

        break
    }

    // Make sure the map doesnt leave its defined area - see Config (map_bounds)
    if(mapMC.x>map_bounds.x)
        mapMC.x = map_bounds.x
    else if(mapMC.x+mapMC.width<map_bounds.x+map_bounds.width)
        mapMC.x = map_bounds.x+map_bounds.width-mapMC.width

    if(mapMC.y>map_bounds.y)
        mapMC.y = map_bounds.y
    else if(mapMC.y+mapMC.height<map_bounds.y+map_bounds.height)
        mapMC.y = map_bounds.y+map_bounds.height-mapMC.height
}


// Helper functions

function getTouchPointById(id:int):Object{
    for(var i:uint=0;i<touchpoints.length;i++){
        if(touchpoints[i].id==id)
            return touchpoints[i]
    }
    return null
}

function removeTouchPoint(id:int){
    for(var i:uint=0;i<touchpoints.length;i++){
        if(touchpoints[i].id==id){
            touchpoints.splice(i,1)
            return
        }
    }
}

function getZoomCenter():Point{
    //get the average of the 2 touchpoints
    return new Point((touchpoints[0].x+touchpoints[1].x)/2,(touchpoints[0].y+touchpoints[1].y)/2)
}
function getZoomDist():Number{
    // calculate the distance between the 2 touchpoints
    return getDist(touchpoints[0].x,touchpoints[0].y,touchpoints[1].x,touchpoints[1].y)
}
function getZoomFactor():Number{
    // calculate the difference of distance between the 2 touchpoints from when the zoom gesture started
    return getZoomDist()/zoom_startdist
}
function getDist(x1:Number,y1:Number,x2:Number,y2:Number){
    // pythagoras, yo
    var deltaX:Number = x2-x1
    var deltaY:Number = y2-y1
    return Math.sqrt(deltaX*deltaX + deltaY*deltaY)
}

如果有什么不清楚的地方,请告诉我,我会尽量多加评论。