詳解Flash AS代碼實現彈弓弓弦彈性形變

我們用Flash ActionScript代碼製作一個模擬彈弓弓弦彈性形變的小遊戲教程，我們一步一步由淺入深來詳細說明製作步驟。思路：準備三個小球元件，使其中一個小球可以拖動，在使它沿著一條線移動，用ActionScript代碼計算移動的角度，最後實現彈弓弓弦彈性形變的一個互動遊戲。一、Flash製作小球隨滑鼠拖動啟動Flash，首先我們繪製兩個元件，非常簡單的。繪製一個小球然後轉變為影片剪輯元件，同樣方法再建議一個不同顏色的小球的影片剪輯。

然後在主場景中直接輸入如下代碼：attachMovie("sling", "sling_1", _root.getNextHighestDepth(), {_x:20, _y:200});attachMovie("sling", "sling_2", _root.getNextHighestDepth(), {_x:480, _y:200});attachMovie("ball", "ball", _root.getNextHighestDepth(), {_x:250, _y:100});_root.createEmptyMovieClip("elastic", _root.getNextHighestDepth());ball.onPress = function() {startDrag(this);};ball.onRelease = function() {stopDrag();};二、Flash製作隨小球移動的弦然後我們通過修改上面的代碼，在兩個小球之間繪製一條線，可以隨中間小球任意移動。attachMovie("sling", "sling_1", _root.getNextHighestDepth(), {_x:20, _y:200});attachMovie("sling", "sling_2", _root.getNextHighestDepth(), {_x:480, _y:200});attachMovie("ball", "ball", _root.getNextHighestDepth(), {_x:250, _y:100});_root.createEmptyMovieClip("elastic", _root.getNextHighestDepth());ball.onPress = function() {startDrag(this);};ball.onRelease = function() {stopDrag();};elastic.onEnterFrame = function() {this.clear();this.lineStyle(2, 0x009900);this.moveTo(sling_1._x, sling_1._y);if (ball._y>182) {dist_x = ball._x-sling_1._x;dist_y = ball._y-sling_1._y;distance_from_sling = Math.sqrt(dist_x*dist_x+dist_y*dist_y);elastic_length = Math.sqrt(distance_from_sling*distance_from_sling-18*18);angle = Math.atan2(dist_y, dist_x)+Math.asin(18/distance_from_sling);this.lineTo(sling_1._x+elastic_length*Math.cos(angle), sling_1._y+elastic_length*Math.sin(angle));} else {this.lineTo(sling_2._x, sling_2._y);}this.moveTo(sling_2._x, sling_2._y);if (ball._y>182) {dist_x = ball._x-sling_2._x;dist_y = ball._y-sling_2._y;distance_from_sling = Math.sqrt(dist_x*dist_x+dist_y*dist_y);elastic_length = Math.sqrt(distance_from_sling*distance_from_sling-18*18);angle = Math.atan2(dist_y, dist_x)+Math.asin(18/distance_from_sling)*-1;this.lineTo(sling_2._x+elastic_length*Math.cos(angle), sling_2._y+elastic_length*Math.sin(angle));} else {this.lineTo(sling_2._x, sling_2._y);}};三、Flash計算弦的形變角度在這裡我們可以很輕鬆的計算出小球在線上的角度來。

稍微做一下改動。attachMovie("sling", "sling_1", _root.getNextHighestDepth(), {_x:20, _y:200});attachMovie("sling", "sling_2", _root.getNextHighestDepth(), {_x:480, _y:200});attachMovie("ball", "ball", _root.getNextHighestDepth(), {_x:250, _y:100});_root.createEmptyMovieClip("elastic", _root.getNextHighestDepth());xspeed = 0;yspeed = 0;fire = false;ball.onPress = function() {fire = false;startDrag(this);};ball.onRelease = function() {stopDrag();fire = true;};ball.onEnterFrame = function() {if (fire) {this._x += (xspeed*0.001);this._y += (yspeed*0.001);}};elastic.onEnterFrame = function() {this.clear();this.lineStyle(2, 0x009900);this.moveTo(sling_1._x, sling_1._y);if (ball._y>182) {dist_x = ball._x-sling_1._x;dist_y = ball._y-sling_1._y;distance_from_sling = Math.sqrt(dist_x*dist_x+dist_y*dist_y);elastic_length = Math.sqrt(distance_from_sling*distance_from_sling-18*18);angle = Math.atan2(dist_y, dist_x)+Math.asin(18/distance_from_sling);saved_angle = angle;this.lineTo(sling_1._x+elastic_length*Math.cos(angle), sling_1._y+elastic_length*Math.sin(angle));this.lineTo(ball._x,ball._y);} else {this.lineTo(sling_2._x, sling_2._y);}this.moveTo(sling_2._x, sling_2._y);if (ball._y>182) {dist_x = ball._x-sling_2._x;dist_y = ball._y-sling_2._y;distance_from_sling = Math.sqrt(dist_x*dist_x+dist_y*dist_y);elastic_length = Math.sqrt(distance_from_sling*distance_from_sling-18*18);angle = Math.atan2(dist_y, dist_x)+Math.asin(18/distance_from_sling)*-1;this.lineTo(sling_2._x+elastic_length*Math.cos(angle), sling_2._y+elastic_length*Math.sin(angle));this.lineTo(ball._x,ball._y);} else {this.lineTo(sling_2._x, sling_2._y);}};四、Flash製作小球與弦的互動運動最後我們讓小球自動運動或者你可以用滑鼠拖動小球。 var ball:MovieClip = _root.attachMovie("ball", "ball", 2, {_x:250, _y:100});var elastic:MovieClip = _root.createEmptyMovieClip("elastic", 1);var point1:MovieClip = _root.attachMovie("sling", "point1", 3, {_x:50, _y:200});var point2:MovieClip = _root.attachMovie("sling", "point2", 4, {_x:450, _y:200});var gravity = 0.1;var angle1:Number = 0;var angle2:Number = 0;var radius:Number = 13.0;// Or whatever half the width of your ball is.var elasticCoefficient:Number = 0.001;// This number will affect the stretchiness of the sling. The greater the number// the tighter the elastic will be.var released:Boolean = true;var forced:Boolean = false;var acc:Object = {x:0, y:0};var vel:Object = {x:0, y:0};_root.onMouseDown = function() {ball._x = _root._xmouse;ball._y = _root._ymouse;ball.startDrag();_root.released = false;vel.x = 0;vel.y = 0;};_root.onMouseUp = function() {ball.stopDrag();_root.released = true;};ball.onPress = function() {ball.startDrag();_root.released = false;vel.x = 0;vel.y = 0;};ball.onRelease = function() {ball.stopDrag();_root.released = true;};_root.onEnterFrame = function() {elastic.clear();elastic.lineStyle(3, 0xFF0000);if (released) {ball._x += vel.x;ball._y += vel.y;}if (ball._y>=187) {/* This area differs from the code in the tutorial.The reason for that is I didn"t read the code, I just looked at the examples.I try to gain experience with problem-solving by doing things as close to by myself as possible. */forced = true;var x1:Number = ball._x-point1._x;var y1:Number = ball._y-point1._y;var x2:Number = point2._x-ball._x;var y2:Number = point2._y-ball._y;var distance1:Number = Math.sqrt(x1*x1+y1*y1);var distance2:Number = Math.sqrt(x2*x2+y2*y2);_root.angle1 = Math.atan2(y1, x1);_root.angle2 = Math.atan2(y2, x2);var xOffset:Number = Math.cos(angle1+Math.PI/2)*radius;var yOffset:Number = Math.sin(angle1+Math.PI/2)*radius;var xOffset2:Number = Math.cos(angle2+Math.PI/2)*radius;var yOffset2:Number = Math.sin(angle2+Math.PI/2)*radius;angle1 += Math.sin(radius/distance1);angle2 += Math.sin(radius/distance2)*-1;elastic.moveTo(point1._x, point1._y);elastic.lineTo(ball._x+xOffset, ball._y+yOffset);elastic.moveTo(point2._x, point2._y);elastic.lineTo(ball._x+xOffset2, ball._y+yOffset2);} else {forced = false;elastic.moveTo(point1._x, point1._y);elastic.lineTo(point2._x, point2._y);}acc.x = 0;acc.y = 0;acc.y = gravity;if (released && forced) {/* This section applies the force of the sling to the ball in terms of acceleration based on the stretching ofthe sling, in the direction of the displacement, scaled by a coefficient that also encapsulates the mass ofthe ball. */acc.x += distance1*Math.sin(angle2)*elasticCoefficient;acc.y += -distance1*Math.cos(angle1)*elasticCoefficient;acc.x += distance2*Math.sin(angle1)*elasticCoefficient;acc.y += -distance2*Math.cos(angle2)*elasticCoefficient;}if (released) {vel.x += acc.x;vel.y += acc.y;}};
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