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[网页设计]Box2D自定义重力


需要给刚体添加一个自定义的属性:m_customGravity,这样就可以动态的修改每一个刚体自定义的重力,查找box2d源码大约在5486行,加上红色的一句代码

 

b2Island.prototype.Solve = function (step, gravity, allowSleep) {   var i = 0;   var j = 0;   var b;   var joint;   for (i = 0;   i < this.m_bodyCount; ++i) {     b = this.m_bodies[i];     if (b.GetType() != b2Body.b2_dynamicBody) continue;     gravity = b.m_customGravity || gravity;          b.m_linearVelocity.x += step.dt * (gravity.x + b.m_invMass * b.m_force.x);     b.m_linearVelocity.y += step.dt * (gravity.y + b.m_invMass * b.m_force.y);     b.m_angularVelocity += step.dt * b.m_invI * b.m_torque;     b.m_linearVelocity.Multiply(b2Math.Clamp(1.0 - step.dt * b.m_linearDamping, 0.0, 1.0));     b.m_angularVelocity *= b2Math.Clamp(1.0 - step.dt * b.m_angularDamping, 0.0, 1.0);   }..............代码略...........................................................................................};

 

使用的方法:

//创建一个圆形刚体
var circle = new Circle({x:mousePoint.x,y:mousePoint.y,r:20,type:sc.dynamicBody});
//给该刚体加上m_customGravity属性,并赋值垂直重力为1
circle.b2Obj.body.m_customGravity = new xengine.EasyB2D.b2Vec2(0,1);