I have struggled for the past 3 weeks trying to figure this out. If anyone could help me I would appreciate it so much.
I'm developing a game similar to Geometry Wars in where I have a triangle in the middle of the screen which you can move around.
The problem is I need the triangle to rotate and face toward the direction of the mouse curser. I don't need to worry about the z-axis per-say as I always have the camera in a fixed position (z=500) and I am treating the scene as a "2D scene" - all the action occurs on the z=0 plane.
Calculating the angle between the triangle and the mouse is elementary:
targetAngle = Math.atan2(mouseCoord.y-this.position.y, mouseCoord.x-this.position.x)
where this is the mesh.
The problem is that the mouseCoords are in standed Dom window format whilst the position of the triangle is in Three.js format.
Q) How would I convert the mouse coords to represent the coords on the z=0 plane where the triangle is?
I have tryed so many ways including ray intersection but nothing works ;(
Thank you all for your help and thank you so much for an amazing framework!!!!
I don't actually see the problem. use the THREE.vector3 with the z coord in 0. then use something like triangle.rotate(THREE.vector3(targetAngle,0,0) or something
I suspect your intersection isn't working because of a CSS offset by your canvas within the DOM.
If you need the triangle to look at something specific, you should simply be able to use the "lookAt" method of the triangle.
To have it look at the camera for example:
triangleMesh.lookAt(camera.position);
Related
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 was looking at demo by Mrdoob on dragging cubes.
http://threejs.org/examples/webgl_interactive_draggablecubes.html
I have understood the basic code to add cubes and some other basic functionality. But i'm not getting what for? PLANE has been used in the code. I am understanding its being used obviously for dragging the cubes somehow, but why hasn't object's TRANSLATION property been used here?
view-source:http://threejs.org/examples/webgl_interactive_draggablecubes.html
And why are we subtracting the PLANE position from offset and then offset from intersects[ 0 ].point
In this example, the plane is being used as something for a ray to intersect, in order to get a position to work with in the scene. If there were nothing to intersect the ray with, there wouldn't be any reliable way to know what the mouse is pointing at.
I'm quite new to three.js and lacking some basic understanding of the coordinate systems obviously.
I have an Object3D "group" that has some children (planes). I use "group" to rotate the group of planes, which works fine. Now camera can move and parent object can rotate. One can click on the planes to select them. What I want now is to let the selected plane fly into the camera.
If I just move the plane to the camera position it flys in any direction but mostly not to the camera. Certainly because "group" seems to be the "world" for the child objects. If I move a plane along the z-axis the plane move along the z-axis of the parent.
I don't understand which coordinates I need to take (or transform) to move the plane bound to "group" in front of the camera.
Basically I demoed with three.js what famo.us did, just spent some two hours on it or so. I faked the wanted effect with an additional plane that is not grouped and which I can just move to camera without transformations. The demo is available here:
http://hwg.rattat.net/famo.html.
Would be nice if somebody could tell me how to get this working. I could still live with the fake, when I would be able to place the additional plane exactly over the selected plane.
Thanks in advance,
Christian
The question of converting local coordinates to world coordinates has been addressed at THREE.js: Calculate world space position of a point on an object . There might also be helping information at how to: get the global/world position of a child object .
I'm a newbie to KineticJS and have been going through the tutorials. I want to take an image that has a 'front' and rotate it a random number of degrees and then have it move forward a number of pixels/inches in that new direction.
I was able to use this rotation tutorial to rotate my image.
I see how to use transitionTo to send an image to an x/y coordinate.
I'm having trouble tying the two together. I feel like I need randomly generate e a new x/y coordinate and then determine the degree difference between where my image is pointing and a line drawn from the center of the image to the new x/y point.
Does anyone have any tips for doing something like this? How would one draw two lines from one point and determine the angle between them?
Thanks in advance.
You have to calculate the new coordinates thanks to the law of cosines.
http://en.wikipedia.org/wiki/Law_of_cosines
Once you have calculated the angle, you have to be careful because you will get an absolute angle.
Don't hesitate if you need more help. I also have to do this calculation using KineticJS.
Good luck !
The JS Math Object will be useful I guess : http://www.w3schools.com/jsref/jsref_obj_math.asp
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).