{"id":396,"date":"2009-09-04T11:44:49","date_gmt":"2009-09-04T18:44:49","guid":{"rendered":"https:\/\/actionsnippet.com\/?p=2114"},"modified":"2009-09-04T11:44:49","modified_gmt":"2009-09-04T18:44:49","slug":"quickbox2d-groupindex-platforms","status":"publish","type":"post","link":"https:\/\/actionsnippet.com\/?p=396","title":{"rendered":"QuickBox2D groupIndex Platforms"},"content":{"rendered":"
\r\nimport com.actionsnippet.qbox.*;\r\nimport Box2D.Common.Math.*;\r\nimport Box2D.Collision.Shapes.*;\r\n\r\n[SWF(width = 800, height = 600, backgroundColor = 0x000000)]\r\n\r\nvar sim:QuickBox2D = new QuickBox2D(this);\r\n\r\nsim.createStageWalls();\r\n\r\nvar boxNum:int = 8;\r\nvar boxes:Array = [];\r\nvar xp:Number, yp:Number, w:Number;\r\nfor (var i:int = 0; i<boxNum; i++){\r\n\txp = 3 + Math.random() * 10;\r\n\typ = 4 + i * 2;\r\n\tw = 2 + Math.random() * 3;\r\n\tboxes.push(sim.addBox({x: xp, y: yp, width: w, height: 0.5, density:0, groupIndex:-1, fillColor:0xFF6532}));\r\n}\r\n\r\nvar char:QuickObject = sim.addBox({x:2, y:18, width:1, height:2, allowSleep:false, groupIndex:-1, fillColor:0x0099CC});\r\n\r\nsim.start();\r\n\r\nvar charVel:b2Vec2;\r\nvar charVelAng:Number;\r\n\r\naddEventListener(Event.ENTER_FRAME, onLoop);\r\nfunction onLoop(evt:Event):void {\r\n\t \r\n\tcharVel = char.body.GetLinearVelocity();\r\n\tcharVelAng =  char.body.GetAngularVelocity();\r\n\tvar filter:b2FilterData;\r\n\t\r\n\tif (key[Keyboard.RIGHT]){\r\n\t\tcharVel.x += 1\r\n\t\tchar.body.SetLinearVelocity(charVel);\r\n\t\tcharVelAng += 1;\r\n\t\tchar.body.SetAngularVelocity(charVelAng);\r\n\t}\r\n\tif (key[Keyboard.LEFT]){\r\n\t\tcharVel.x -=1;\r\n\t\tchar.body.SetLinearVelocity(charVel);\r\n\t\tcharVelAng -= 1;\r\n\t\tchar.body.SetAngularVelocity(charVelAng);\r\n\t}\r\n\tif (key[Keyboard.UP] && sim.w.GetContactCount() > 0){\r\n\t\t charVel.y = -10;\r\n\t\t trace(charVel.y);\r\n\t\t char.body.SetLinearVelocity(charVel);\r\n\t\t charVelAng *= 0.8;\r\n\t\t char.body.SetAngularVelocity(charVelAng);\r\n\t}\r\n\tfor (var i:int = 0; i<boxes.length; i++){\r\n\t\tvar rect:Rectangle = char.userData.getRect(this);\r\n\t\tif (rect.bottom \/ 30 < boxes[i].y){\r\n\t\t\tfilter = boxes[i].shape.GetFilterData();\r\n\t\t\tfilter.groupIndex = 1;\r\n\t\t\tboxes[i].shape.SetFilterData(filter);\r\n\t\t}else{\r\n\t\t\tfilter = boxes[i].shape.GetFilterData();\r\n\t\t\tif (filter.groupIndex != -1){\r\n\t\t\t\tfilter.groupIndex = -1;\r\n\t\t\t\tboxes[i].shape.SetFilterData(filter);\r\n\t\t\t}\r\n\t\t}\r\n\t}\r\n}\r\n\r\nvar key:Object = new Object();\r\nstage.addEventListener(KeyboardEvent.KEY_DOWN, onKeyPressed);\r\nstage.addEventListener(KeyboardEvent.KEY_UP, onKeyReleased);\r\nfunction onKeyPressed(evt:KeyboardEvent):void{ key[evt.keyCode] = true; }\r\nfunction onKeyReleased(evt:KeyboardEvent):void{ key[evt.keyCode] = false; }\r\n<\/pre>\n
NOTE: This requires the QuickBox2D<\/a> mini-library<\/i><\/p>\n
This snippet shows how to use groupIndex to create simple platforms for a character to jump on.  A few people have asked me about this so I figured I’d post about it. It works by altering the groupIndex of each platform based on the characters position – if the character is below a platform, both the character and the platform have groupIndex -1 (meaning they will not collide). As soon as the character is above a platform, the platforms groupIndex is set to 1 (allowing the character to walk on the platform despite having just passed through it.<\/p>\n

\nHave a look at the swf…<\/p>\n

\n<\/a>