Real world catapult prototype using Box2D – Adding wheels
Talking about Crush the Castle game, Actionscript 3, Box2D and Flash.
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Did you enjoy the catapult prototype?
Here I am with the second part, adding wheels controlled by left and right arrows.
Have a look:
Now you can move the catapult with left and arrow keys, and shoot with a mouse click
If you feel the catapult is running on an icy surface, that’s because I did not set any friction. I’ll do it next time, when I’ll also come with a decent code, meanwhile check this:
package {
import flash.display.Sprite;
import flash.events.Event;
import flash.events.MouseEvent;
import flash.events.KeyboardEvent;
import Box2D.Dynamics.*;
import Box2D.Collision.*;
import Box2D.Collision.Shapes.*;
import Box2D.Common.Math.*;
import Box2D.Dynamics.Joints.*;
public class main extends Sprite {
public var world:b2World=new b2World(new b2Vec2(0,10.0),true);
public var world_scale:int=30;
var arm_joint:b2RevoluteJointDef = new b2RevoluteJointDef();
var front_wheel_joint:b2RevoluteJointDef = new b2RevoluteJointDef();
var rear_wheel_joint:b2RevoluteJointDef = new b2RevoluteJointDef();
var arm_revolute_joint_def:b2RevoluteJoint;
var front_wheel_joint_def:b2RevoluteJoint;
var rear_wheel_joint_def:b2RevoluteJoint;
var catapult_body:b2BodyDef = new b2BodyDef();
var catapult_itself:b2Body;
public function main():void {
debug_draw();
draw_box(250,400,2000,30,false,"ground");
catapult_body.position.Set(350/world_scale,200/world_scale);
catapult_body.type=b2Body.b2_dynamicBody;
var main_part:b2PolygonShape = new b2PolygonShape();
main_part.SetAsOrientedBox(125/world_scale, 20/world_scale, new b2Vec2(0,0),0);
var fixed_arm:b2PolygonShape = new b2PolygonShape();
fixed_arm.SetAsOrientedBox(20/world_scale, 60/world_scale, new b2Vec2(-80/world_scale,-40/world_scale),0);
catapult_itself=world.CreateBody(catapult_body);
catapult_itself.CreateFixture2(main_part,200);
catapult_itself.CreateFixture2(fixed_arm,200);
var catapult_arm:b2BodyDef = new b2BodyDef();
catapult_arm.allowSleep=false;
catapult_arm.position.Set(210/world_scale,110/world_scale);
catapult_arm.type=b2Body.b2_dynamicBody;
var arm_part:b2PolygonShape = new b2PolygonShape();
arm_part.SetAsOrientedBox(150/world_scale, 10/world_scale, new b2Vec2(0,0),0);
var stopper:b2PolygonShape = new b2PolygonShape();
stopper.SetAsOrientedBox(10/world_scale, 20/world_scale, new b2Vec2(-140/world_scale,-30/world_scale),0);
var catapult_arm_itself:b2Body=world.CreateBody(catapult_arm);
catapult_arm_itself.CreateFixture2(arm_part,1);
catapult_arm_itself.CreateFixture2(stopper,1);
//
arm_joint.enableMotor=true;
arm_joint.enableLimit=true;
arm_joint.Initialize(catapult_itself, catapult_arm_itself,new b2Vec2(0,0));
arm_joint.localAnchorA=new b2Vec2(-80/world_scale,-90/world_scale);
arm_joint.localAnchorB=new b2Vec2(60/world_scale,0);
arm_revolute_joint_def=world.CreateJoint(arm_joint) as b2RevoluteJoint;
arm_revolute_joint_def.SetMotorSpeed(1000);
arm_revolute_joint_def.SetLimits(-Math.PI,Math.PI/3);
arm_revolute_joint_def.SetMaxMotorTorque(1);
//
var rear_wheel:b2BodyDef= new b2BodyDef();
rear_wheel.position.Set(250/world_scale, 200/world_scale);
rear_wheel.type=b2Body.b2_dynamicBody;
var rear_wheel_shape:b2CircleShape=new b2CircleShape(40/world_scale);
var the_rear_wheel_itself:b2Body=world.CreateBody(rear_wheel);
the_rear_wheel_itself.CreateFixture2(rear_wheel_shape,20);
var front_wheel:b2BodyDef= new b2BodyDef();
front_wheel.position.Set(450/world_scale, 200/world_scale);
front_wheel.type=b2Body.b2_dynamicBody;
var front_wheel_shape:b2CircleShape=new b2CircleShape(40/world_scale);
var the_front_wheel_itself:b2Body=world.CreateBody(front_wheel);
the_front_wheel_itself.CreateFixture2(front_wheel_shape,20);
//
front_wheel_joint.enableMotor=true;
front_wheel_joint.Initialize(catapult_itself, the_front_wheel_itself,new b2Vec2(0,0));
front_wheel_joint.localAnchorA=new b2Vec2(80/world_scale,0);
front_wheel_joint.localAnchorB=new b2Vec2(0,0);
front_wheel_joint_def=world.CreateJoint(front_wheel_joint) as b2RevoluteJoint;
front_wheel_joint_def.SetMaxMotorTorque(1000000);
//
rear_wheel_joint.enableMotor=true;
rear_wheel_joint.Initialize(catapult_itself, the_rear_wheel_itself,new b2Vec2(0,0));
rear_wheel_joint.localAnchorA=new b2Vec2(-80/world_scale,0);
rear_wheel_joint.localAnchorB=new b2Vec2(0,0);
rear_wheel_joint_def=world.CreateJoint(rear_wheel_joint) as b2RevoluteJoint;
rear_wheel_joint_def.SetMaxMotorTorque(1000000);
//
var cannonball:b2BodyDef= new b2BodyDef();
cannonball.position.Set(90/world_scale, 90/world_scale);
cannonball.type=b2Body.b2_dynamicBody;
var ball:b2CircleShape=new b2CircleShape(10/world_scale);
var the_cannonball_itself:b2Body=world.CreateBody(cannonball);
the_cannonball_itself.CreateFixture2(ball,20);
addEventListener(Event.ENTER_FRAME, update);
stage.addEventListener(MouseEvent.CLICK,fire);
stage.addEventListener(KeyboardEvent.KEY_DOWN, key_down);
}
public function key_down(event:KeyboardEvent):void {
switch (event.keyCode) {
case 39 :
rear_wheel_joint_def.SetMotorSpeed(10);
front_wheel_joint_def.SetMotorSpeed(10);
break;
case 37 :
rear_wheel_joint_def.SetMotorSpeed(-10);
front_wheel_joint_def.SetMotorSpeed(-10);
break;
}
}
public function fire(e:MouseEvent):void {
arm_revolute_joint_def.SetMaxMotorTorque(10000);
}
public function draw_box(px,py,w,h,d,ud):void {
var ground:b2BodyDef= new b2BodyDef();
ground.position.Set(px/world_scale, py/world_scale);
if (d) {
ground.type=b2Body.b2_dynamicBody;
}
var my_box:b2PolygonShape = new b2PolygonShape();
my_box.SetAsBox(w/2/world_scale, h/2/world_scale);
var my_fixture:b2FixtureDef = new b2FixtureDef();
my_fixture.shape=my_box;
var the_ground_itself:b2Body=world.CreateBody(ground);
the_ground_itself.SetUserData(ud);
the_ground_itself.CreateFixture(my_fixture);
}
public function debug_draw():void {
var debug_draw:b2DebugDraw = new b2DebugDraw();
var debug_sprite:Sprite = new Sprite();
addChild(debug_sprite);
debug_draw.SetSprite(debug_sprite);
debug_draw.SetDrawScale(world_scale);
debug_draw.SetFlags(b2DebugDraw.e_shapeBit|b2DebugDraw.e_jointBit);
debug_draw.SetFillAlpha(0.5);
world.SetDebugDraw(debug_draw);
}
public function update(e:Event):void {
world.Step(1/30,10,10);
world.ClearForces();
world.DrawDebugData();
}
}
}
No need to download anything, just paste the new code in the catapult prototype file.
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