Box2d tutorial 2-mouse Interaction

Box2d tutorial 1-create a collision world

Box2d tutorial 2-mouse Interaction

Box2d tutorial 3-Rigid Body binding

Box2d tutorial 4-complex appearance of complex rigid bodies

Box2d tutorial 5-Collision Detection

The mouse interaction of box2d is not to allow the mouse to interact with the displayed object, but to create a mouse joint. the two ends of the joint are the rigid body and the ground respectively. When you click the mouse, create a very small area, traverse and obtain the rigid body under the area. After obtaining the rigid body, create the mouse joint. As the mouse moves, the joint rigid body moves along. When the mouse is released, the mouse joints are destroyed.

ImportantCodeAs follows:

 1   Private   Function Handleenterframe (EVT: Event): void
 2 {
3               //  Update mouse position  
  4 Updatemouseworld ();
 5               //  Constantly call the mouse drag Method  
  6 Mousedrag ();
 7   
 8               VaR Timestep: Number = 1/30;
9               VaR Velocityinterations: Int = 10;
 10               VaR Positioniterations: Int = 10;
 11   
 12 World. Step (timestep, velocityinterations, positioniterations );
 13               //  In version 2.1, the force is removed to improve efficiency.  
  14 World. clearforces ();
 15              //  Draw  
  16 World. drawdebugdata ();
 17 }
 18   Private   Function Updatemouseworld (): void
 19 {
 20               //  Mouse position in the physical world  
  21 _ Mousexworldphys = This. mousex/pixel_to_meter;
 22 _ Mouseyworldphys = This. Mousey/pixel_to_meter;
 23               //  Mouse position on the screen  
  24 _ Mousexworld = This. mousex;
 25 _ Mouseyworld = This. Mousey;
 26 }
 27           Private   Function Getbodyatmouse (includestatic: Boolean = False ): B2body
 28 {
 29               //  Create a small boundary area  
  30 _ Mousepvec. Set (_ mousexworldphys, _ mouseyworldphys );
 31               VaR AABB: b2aabb = new b2aabb ();
 32 AABB. lowerbound. Set (_ mousexworldphys-0.001, _ mouseyworldphys-0.001 );
 33 AABB. upperbound. Set (_ mousexworldphys + 0.001, _ mouseyworldphys + 0.001 );
 34               VaR Body: b2body = Null ;
 35               VaR Fixture: b2fixture;
 36   
 37               //  Get the rigid body under the mouse in the form of a callback function  
 38               Function Getbodycallback (fixture: b2fixture ): Boolean 
 39 {
 40                   VaR Shape: b2shape = fixture. getshape ();
 41                   If (Fixture. getbody (). GetType ()! = B2body. b2_staticbody | required destatic)
 42 {
 43                       VaR Inside:Boolean = Shape. testpoint (fixture. getbody (). gettransform (), _ mousepvec );
 44                       If (Inside)
 45 {
 46 Body = fixture. getbody ();
 47                           Return   False ;
 48 }
 49 }
50                   Return   True ;
 51 }
 52 World. queryaabb (getbodycallback, AABB );
 53               Return Body;
 54 }
 55   
 56           Private   Function Mousedrag (): void
57 {
 58               //  If you press the mouse, but there is no mouse Joint  
  59               //  Create mouse Joints  
  60               If (Mousedown &&! _ Mousejoint)
 61 {
 62                   VaR Body: b2body = getbodyatmouse ();
63                   If (Body)
 64 {
 65                       VaR MD: b2mousejointdef = new b2mousejointdef ();
 66 Md. bodya = World. getgroundbody ();
 67 Md. bodyb = body;
 68   
 69 Md.tar get. Set (_ mousexworldphys, _ mouseyworldphys );
 70 Md. collideconnected = True ;
 71 Md. maxforce = 300.0 * body. getmass ();
 72 _ Mousejoint = World. createjoint (MD) as b2mousejoint;
 73 Body. setawake ( True );
 74 }
 75 }
 76               // If the mouse is released, the mouse joints are destroyed.  
  77               If (! Mousedown)
 78 {
 79                   If (_ Mousejoint)
 80 {
 81 World. destroyjoint (_ mousejoint );
 82 _ Mousejoint = Null ;
83 }
 84 }
 85               //  If you already have a mouse joint, the joint target is always set to the mouse position.  
  86               If (_ Mousejoint)
 87 {
 88                   VaR P2: b2vec2 = new b2vec2 (_ mousexworldphys, _ mouseyworldphys );
 89 _ Mousejoint. settarget (P2 );
 90 }
 91 }
 92   
 93           Public   Function Handlemousedown (E: mouseevent): void
 94 {
 95 Mousedown = True ;
 96 }
97   
 98           Public   Function Handlemouseup (E: mouseevent): void
 99 {
 100 Mousedown = False ;
 101 }

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