I'm working on a project where I'm putting a 3d cylinder object in front of a static 2d image on a three.js canvas, trying to make the cylinder look like its part of the photo.
In order for the 3d cylinder's perspective to match the photo behind it, it needs to be moved down the y axis. The problem is then it's moved out of the scene. I need a way to render the 3d cylinder how it would look with a -y position, but not actually move down the scene.
See image for details:
A combination of x-axis rotation to around 24 degrees, Lowering the FOV to around 10, and increasing the camera.position.z to about 35 got me the results I needed. Thank you #prisoner849
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I'm using ThreeJS, but this is a general math question.
My end goal is to position an object in my scene using 2D screen space coordinates; however, I want a specific z position in the perspective projection.
As an example, I have a sphere that I want to place towards the bottom left of the screen while having the sphere be 5 units away from the camera. If the camera were to move, the sphere would maintain its perceived size and position.
I can't use an orthographic camera because the sphere needs to be able to move around in the perspective projection. At some point the sphere will be undocked from the screen and interact with the scene using physics.
I'm sure the solution is somewhere in the camera inverse matrix, however, that is beyond my abilities at the current moment.
Any help is greatly appreciated.
Thanks!
Your post includes too many questions, which is out of scope for StackOverflow. But I’ll try to answer just the main one:
Create a plane Mesh using PlaneGeometry.
Rotate it to face the camera, place it 5 units away from the camera.
Add it as a child with camera.add(plane); so whenever the camera moves, the plane moves with it.
Use a Raycaster’s .setfromCamera(cords, cam)
then
.intersectObject(plane)
method to convert x, y screen cords into an x, y, z world position where it
intersects the plane. You can read about it in the docs.
Once it’s working, make the plane invisible with visible = false
You can see the raycaster working in this official example: https://threejs.org/examples/#webgl_geometry_terrain_raycast
I'm trying to add clouds to my scene using the approach in https://codepen.io/teolitto/pen/KwOVvL, which is to make a large number of plane objects at random positions that each rotate continuously around their z axes.
But I would like to be able to move my camera, change its target, etc., and still have the cloud planes look right.
What I need to do is rotate the planes so that as the camera moves and changes target, the cloud planes stay perpendicular to the camera's axis. And I need to do this without changing the planes' rotation around their own z-axis, because otherwise that would break the cloudlike appearance.
I've tried cloudplane.lookAt(camera.position) but of course that doesn't work. It aims all of the planes at the camera, instead of making them all perpendicular to the camera axis. It also sets the object's z-axis, so the clouds don't evolve.
Any advice is appreciated. (I'm new to three.js, so if I have some of the terminology wrong, I apologize for that.)
Edit:
Setting the cloudplane's rotation.x and rotation.y to match the camera's rotation.x and rotation.y seems to get me pretty close, but it doesn't quite get there - its still possible to orbit the camera to a position where the clouds are all invisible because they're all parallel to the camera.
I'm trying to use Three.js to create an ’asteroid field' using particle systems or point clouds or stuff like that. One of the problems I've bumped into with all of these is that when the camera rotates around the z axis, the particles rotate individually with the camera, preserving the same orientation no matter how the camera is turned. I want the simulation to look as if the user is flying through a bunch of asteroids, and obviously asteroids don't magically spin whenever you tilt your head, so I was wondering if there is any way to prevent them from turning when the camera turns. Must particles always be upright?
If you want to rotate sprites you can use attribute SpriteMaterial.rotation:
var sprite = new THREE.Sprite( new THREE.SpriteMaterial({map: texture,rotation: Math.PI/4}));
see this http://threejs.org/examples/webgl_sprites.html
In your case, rotation of all sprites should be equal to camera rotation.
I've built a scene with a cube and a camera placed in the center of the cube. I am able to rotate the cube. Ideally I would like to limit to rotation to horizontal.
Is there any way to count the amount of rotation? For example, being able to know at every amount that I rotated 30 radians in a direction, and if I rotate backgword the amount gets updated accordingly.
Context: trying to take THREE.js and use it to display conic sections.
Method: creating a mesh of vertices and then connect face4's to all of them. Used two faces to produce a front and back side so that when the conic section rotates it won't matter from which angle the camera views it.
Problems encountered: 1. Trying to find a good way to create a intuitive mouse rotation scheme. If you think in spherical coordinates, then it feels like just making up/down change phi and left/right change phi would work. But that requires that you can move the camera. As far as I can tell, there is no way to change actively change the rotation of anything besides the objects. Does anyone know how to change the rotation of the camera or scene? 2. Is there a way to graph functions that is better than creating a mesh? If the mesh has many points then it is too slow, and if the mesh has few points then you cannot easily make out the shape of the conic sections.
Any sort of help would be most excellent.
I'm still starting to learn Three.js, so I'm not sure about the second part of your question.
For the first part, to change the camera, there is a very good way, which could also include zooming and moving the scene: the trackball camera.
For the exact code and how to use it, you can view:
https://github.com/mrdoob/three.js/blob/master/examples/webgl_trackballcamera_earth.html
At the botton of this page (http://mrdoob.com/122/Threejs) you can see the example in action (the globe in the third row from the bottom).
There is an orbit control script for the three.js camera.
I'm not sure if I understand the rotation bit. You do want to rotate an object, but you are correct, the rotation is relative.
When you rotate or move your camera, a matrix is calculated for that position/rotation, and it does indeed rotate the scene while keeping the camera static.
This is irrelevant though, because you work in model/world space, and you position your camera in it, the engine takes care of the rotations under the hood.
What you probably want is to set up an object, hook up your rotation with spherical coordinates, and link your camera as a child to this object. The translation along the cameras Z axis relative to the object should mimic your dolly (zoom is FOV change).
You can rotate the camera by changing its position. See the code I pasted here: https://gamedev.stackexchange.com/questions/79219/three-js-camera-turning-leftside-right
As others are saying OrbitControls.js is an intuitive way for users to manage the camera.
I tackled many of the same issues when building formulatoy.net. I used Morphing Geometries since I found mapping 3d math functions to a UV surface to require v little code and it allowed an easy way to implement different coordinate systems (Cartesian, spherical, cylindrical).
You could use particles instead of a mesh I suppose but a mesh seems best. The lattice material is not too useful if you're trying to understand a surface mathematically. At this point I'm thinking of drawing my own X,Y lines on the surface (or phi, theta lines etc) to better demonstrate cross-sections.
Hope that helps.
You can use trackball controls by which you can zoom in and out of an object,rotate the object,pan it.In trackball controls you are moving the camera around the object.Object still rotates with respect to the screen or renderer centre (0,0,0).