Hi I'm currently new in farseer physics engine,
anyway,
I have read tutorial about farseer 3.31 here
http://roy-t.nl/index.php/2012/09/06/farseer-physics-3-3-1-and-xna-joints/
in the tutorial he's trying to attach/join paddle body to world withJointFactory.CreateFixedRevoluteJoint ,
unfortunately in farseer 3.5 there is no CreateFixedRevoluteJoint method,
it's only CreateRevoluteJoint which is joint two bodies,
so how can I revolute joint one body to world object ?
Use a RevoluteJoint. And make your paddle rotate around another object. Like so:
Body motorPaddle = CreateMotorPaddle();
Body motorPaddleAxle = BodyFactory.CreateCircle(World, 0.1f, 1f);
var j = JointFactory.CreateRevoluteJoint
(
World,
motorPaddle,
motorPaddleAxle,
new Vector2(0.0f, 0.0f),
new Vector2(-14.0f, 10.0f)
);
// set speed and torque
j.MotorSpeed = MathHelper.Pi;
j.MotorImpulse = 100;
j.MotorEnabled = true;
j.MaxMotorTorque = 100;
More details here
Related
I'm wondering how I would go about calling the individual children of cube (mesh0, mesh1) so I'm able to set different styles / animations to them both.
AFRAME.registerComponent('multi_box', {
schema: {},
update: function() {
for (var i = 0; i < 2; i++) {
var material = new THREE.MeshBasicMaterial({color: "blue"});
var geometry = new THREE.BoxGeometry(1, 1, 1);
var cube = new THREE.Mesh(geometry, material);
cube.position.x = i == 0 ? -1 : 1;
cube.position.y = 0.5;
cube.position.z = -5;
this.el.setObject3D("mesh"+i, cube); //unique name for each object
}
console.log(this.el.object3DMap)
}
});
Codepen link: https://codepen.io/ubermario/pen/wrwjVG
I can console.log them both and see that they are unique objects to each other but I'm having trouble calling them:
var meshtest = this.el.getObject3D('mesh0')
console.log(meshtest.position)
I'v tried this method but with no luck: aframe get object3d children
Any help is appreciated :)
Instancing
In your for cycle, you create
a new geometry instance
a new material instance
a new mesh that connect the previous two
Each new keyword creates a unique instance that is independent of the others. In your case mesh0 and mesh1 are fully independent of each other. If you change any property of an instance, like for example material color or position, the other(s) will not be affected by that. In fact you do that by assigning a different x position to each cube.
Storage
Your component holds a map of 3D objects. Each is identified by a unique name. You generate this name by concatenating the prefix mesh with the iteration number (value of i).
You can later access the cubes just the same way you created them. Either by name
this.el.getObject3D('mesh0')
this.el.getObject3D('mesh1')
//etc.
or by index
this.el.object3D.children[0]
this.el.object3D.children[1]
and you can manipulate them further. For example you can put his on Ln19 in your Codepen:
this.el.getObject3D('mesh0').position.y = 2;
this.el.object3D.children[1].position.z = -3;
Just for completeness: If you would omit the +i at the end, you would overwrite the same key again and again, so mesh would reference just the last cube and others would get lost.
Changing properties
Three.js has a nice API, but in javascript you always need to think what happens behind the scenes. You will see that while learning new stuff. For example:
this.el.object3D.children[1].position.z = -3;
this.el.object3D.children[1].material.color.set('#ffff00');
this.el.object3D.children[1].material.color = [1, 1, 0];
As you can see the position can be changed directly, but color needs a setter sometimes. Things get more complicated with vectors where you need to watch which methods change the current instance and which produce a new one. You could easily forget to clone it. Say you had:
var pos = new THREE.Vector3(-1, 0.5, -5)
for (var i = 0; i < 2; i++) {
var material = new THREE.MeshBasicMaterial({color: "blue"});
var geometry = new THREE.BoxGeometry(1, 1, 1);
var cube = new THREE.Mesh(geometry, material);
//wrong, since it will assign the object reference,
//i.e. always the same object.
//Thus, the cubes will be at one position in the end
cube.position = pos;
//right
cube.pos = pos.clone();
pos.x += 1;
this.el.setObject3D("mesh"+i, cube); //unique name for each object
}
The difference is a bit more moderate topic on reference and value types. You will find many tutorials for that, for example this small gist I just found.
I hope this was helpful and wish you good progress in learning!
I am trying to have the camera orbit around an arbitrary axis in world space. I've already spent so many hours trying to solve this issue without luck. I do not want to add a library like THREE.OrbitControls just to have this feature. Can anyone tell me what I'm doing wrong in the following code?
Camera.prototype.orbit = function(axis, spd, pt) {
var axis = axis.normalize(),
currCamQuaternion = new THREE.Quaternion(this.position.x, this.position.y, this.position.z, 0),
rotQuaternion = new THREE.Quaternion();
rotQuaternion.setFromAxisAngle(axis, spd);
var halfCamQuaternion = rotQuaternion.clone().multiply(currCamQuaternion),
fullCamQuaternion = halfCamQuaternion.clone().multiply(rotQuaternion.clone().conjugate());
this.position.copy(new THREE.Vector3(fullCamQuaternion.x, fullCamQuaternion.y, fullCamQuaternion.z));
this.lookAt(pt);
}
Im trying to make portals with ThreeJS. I found this page Mini-Portals That explains how to make portals with OpenGL. So i tried to replicate the portal view function in TJS. Now this is my result:
The left portal(right camera) is normal camera and right portal(left camera) is the view matrix gotten from tutorial. As you can see the portal view on the right is quite weird.
The main issue here is that the scaling of the images is all wrong and the angle im seeing the images in portal is wrong. Currently its flat and show where i pointed the camera, but what i want is portal where the scaling is correct(image on portal is same scale as the world itself) and what is see in portal depends on the angle where im watching.
What am i doing wrong and what should i do to fix it?
For people who want a great Portal system with Three.js :
https://github.com/markotaht/Portals
Its been a while. But i have found a way to do what i needed. The 4th parameter in not needed. Basically i send camera, and my 2 portal objects(Meshes) to my function. Instead of using the matrix multiplication way(does not work in ThreeJS because ThreeJS does some weird stuff with it) I split the matrices into pieces. Then manually calculate the new position and rotation and construct the new matrix from it. And i set this new matrix as my cameras worldMatrix. Voila a working portal. Next step is oblique view fusrum, because we want our nearplane to be the portal otherwise we can have some objects between the camera and portal.
And the rendering procedure itself uses stencil buffer to render the portals correctly. If anyone needs, this will help you: https://th0mas.nl/2013/05/19/rendering-recursive-portals-with-opengl/
function portal_view(camera, src_portal, dst_portal, kordaja) {
src_portal.updateMatrixWorld()
dst_portal.updateMatrixWorld()
camera.updateMatrixWorld()
var camerapos = new THREE.Vector3();
var camerarot = new THREE.Quaternion();
var camerascale = new THREE.Vector3();
camera.matrix.decompose(camerapos,camerarot,camerascale);
var srcpos = new THREE.Vector3();
var srcquat = new THREE.Quaternion();
var srcscale = new THREE.Vector3();
src_portal.matrix.decompose(srcpos, srcquat, srcscale);
var destquat = new THREE.Quaternion();
var destpos = new THREE.Vector3();
var destscale = new THREE.Vector3();
dst_portal.matrix.decompose(destpos,destquat,destscale);
var diff = camerapos.clone().sub(srcpos);
var ydiff = src_portal.rotation.y - dst_portal.rotation.y - Math.PI;
diff.applyAxisAngle(new THREE.Vector3(0,1,0),-ydiff);
var newcampos = diff.add(destpos);
var yrotvec = new THREE.Quaternion().setFromAxisAngle(new THREE.Vector3(0,1,0),-ydiff);
console.log(yrotvec)
srcquat = srcquat.multiply(destquat.inverse());
camerarot = camerarot.multiply(yrotvec);
var inverse_view_to_source = new THREE.Matrix4();
inverse_view_to_source.compose(newcampos,camerarot,camerascale);
return inverse_view_to_source;
}
NOTE:
I moved my answer to the answers so i can mark an answer.
I am using bullet/ammo.js with three.js. I have a 3d mesh and I want to use the exact shape for collision detection with a soft body. Is there a way I can create a 3d rigid body (in bullet) from a mesh (in three.js)?
Here is an example:
http://kidzinski.com/miamisura/lazy3d/ (please wait a second for the 3d model to download). I have a cloth falling on a 3d body and I need to simulate collision of this cloth with the body.
I am new to these frameworks sorry if I fundamentally misunderstood something.
It looks like you can do some work to turn an arbitrary Three.js mesh into a Bullet concave mesh. This is supported by Physi.js, which is a plug and play solution to link Three.js directly to ammo.js. I personally wouldn't recommend using the project (Physi.js) but you can look at the source code to see how they implement concave meshes.
First they loop over the geometry to create a custom list of "triangle" data objects on these lines of physi.js
for ( i = 0; i < geometry.faces.length; i++ ) {
face = geometry.faces[i];
if ( face instanceof THREE.Face3) {
triangles.push([
...
Then these triangles are passed off to Ammo.js to make a new Ammo.btBvhTriangleMeshShape on these lines:
for ( i = 0; i < description.triangles.length; i++ ) {
...
triangle_mesh.addTriangle( _vec3_1, _vec3_2, _vec3_3, true );
}
...
shape = new Ammo.btBvhTriangleMeshShape( triangle_mesh, true, true );
This should be a good starting point for building your own Ammo.js custom mesh.
There are lots of threads around the web, that Physijs Concave mesh does not work with collission. It seems, that btBvhTriangleMeshShape is not intended to work with collission in ammo.js, as I found out searching for that topic in bullet related forums.
What worked for me, is btConvexHullShape:
var triangle, triangle_mesh = new Ammo.btTriangleMesh;
var btConvexHullShape = new Ammo.btConvexHullShape();
var _vec3_1 = new Ammo.btVector3(0,0,0);
var _vec3_2 = new Ammo.btVector3(0,0,0);
var _vec3_3 = new Ammo.btVector3(0,0,0);
for ( i = 0; i < triangles.length; i++ ) {
triangle = triangles[i];
_vec3_1.setX(triangle[0].x);
_vec3_1.setY(triangle[0].y);
_vec3_1.setZ(triangle[0].z);
btConvexHullShape.addPoint(_vec3_1,true);
_vec3_2.setX(triangle[1].x);
_vec3_2.setY(triangle[1].y);
_vec3_2.setZ(triangle[1].z);
btConvexHullShape.addPoint(_vec3_2,true);
_vec3_3.setX(triangle[2].x);
_vec3_3.setY(triangle[2].y);
_vec3_3.setZ(triangle[2].z);
btConvexHullShape.addPoint(_vec3_3,true);
triangle_mesh.addTriangle(
_vec3_1,
_vec3_2,
_vec3_3,
true
);
}
return btConvexHullShape;
In the process of learning physic based 3d with threejs, I also want to mention the following best practice: when using complex models, create a low poly model that you can push to that converter function instead of the original model, or you will encounter a stack overflow.
I am a complete newbie to 3d programming and have been working with three.js just over a week now. I have managed to load multiple collada and obj files, and managed to get perspectives, trackballs, everything working from examples. However, now I am stuck and need some help. For reference you can see the file i'm posting about at the following url:
http://shaman-labz.appspot.com/webgl_loader_obj_mtl.html
This page is basically straight from the examples, except that i am loading up an obj file, which has all these objects as meshes. what i am working on now is after loading the obj, i am going to iterate through all the geometries in the object and extract them so that i can drop them in the scene one a time when i need them, or have them float around like bubbles or something. I was thinking to maybe try to use the fresnel example, but this is where i'm hitting up against the boundaries of my understanding, and some terminology escapes me.
My question is, when this runs, the object that returns and is added to the scene after load has all these gems in it together.
So instead of the following lines:
var loader = new THREE.OBJMTLLoader();
loader.addEventListener( 'load', function ( event ) {
var object = event.content;
object.position.y = - 100;
scene.add( object );
});
loader.load( 'obj/gems/24.obj', 'obj/gems/24.mtl' );
So what i'm doing is when the object returns, i look at the internals in debug/break mode, and i see that it's an object3D and object.children is an array of 25 meshes...and each of those meshes would be one of my 'gems' that i want to work with individually.
So here's where i get lost...when i grab the 'mesh' do i need to strip out the underlying geometry and create a new mesh?
on this page, you can see what i tried to accomplish:
http://shaman-labz.appspot.com/webgl_loader_obj_mtl2.html
the only major difference is in this section of code:
var loader = new THREE.OBJMTLLoader();
loader.addEventListener( 'load', function ( event ) {
var object = event.content;
var pos=0;
for(var i=0; i< object.children.length; i++){
var m = object.children[i];
var gem = new THREE.Object3D();
gem.name=m.name;
gem.add(m);
gem.position.x = -10;
gem.position.y = -10;
gem.position.z = pos;
scene.add( gem );
pos = pos - 10;
}
});
loader.load( 'obj/gems/24.obj', 'obj/gems/24.mtl' );
notice that only 13 of the 25 gems show up from the collection, and also note how they are scattered, indicating that they are somehow still linked to some higher-order relationships that i am unable to set with position properly (it's like each mesh is somehow offset relative to it's original positioning in the original object loaded...thinking this has to do with world matrix?