You’re looking for an unproject function, which converts screen coordinates into a ray cast from the camera position into the 3D world. You must then perform ray/triangle intersection tests to find the closest triangle to the camera which also intersects the ray. I have an example of unprojecting available at jax/camera.js#L568 — but you’ll still … Read more
If you want to rotate a vector you should construct what is known as a rotation matrix. Rotation in 2D Say you want to rotate a vector or a point by θ, then trigonometry states that the new coordinates are x’ = x cos θ − y sin θ y’ = x sin θ + … Read more
Here is a solution in Java that gives you both: from 3D to 1D from 1D to 3D Below is a graphical illustration of the path I chose to traverse the 3D matrix, the cells are numbered in their traversal order: Conversion functions: public int to1D( int x, int y, int z ) { return … Read more
If you want to rotate an object around an arbitrary line in world space, you can use the following method. The line is specified by a 3D point and a direction vector (axis). THREE.Object3D.prototype.rotateAroundWorldAxis = function() { // rotate object around axis in world space (the axis passes through point) // axis is assumed to … Read more
Typical depth buffers in a 3D graphics pipeline are not linear. Perspective division causes depths in normalized device coordinates to be on a different scale. (See also here.) So the z-coordinate you’re feeding into unprojectPoint isn’t actually the one you want. How, then, to find the normalized-depth coordinate matching a plane in world space? Well, … Read more
For smooth surfaces (no edges) I do it like this: create space for per vertex double N[3]; //normal int cnt; per vertex init N={0.0,0.0,0.0} cnt=0; compute per face normal normal must be normalized length=1.0 !!! add this Normal to all vertexes used in face and increment cnt to all vertexes used in face per vertex … Read more
I’ve written for my project the following function; it receives an THREE.Object3D instance and a camera as a parameters and returns the position on the screen. function toScreenPosition(obj, camera) { var vector = new THREE.Vector3(); var widthHalf = 0.5*renderer.context.canvas.width; var heightHalf = 0.5*renderer.context.canvas.height; obj.updateMatrixWorld(); vector.setFromMatrixPosition(obj.matrixWorld); vector.project(camera); vector.x = ( vector.x * widthHalf ) + widthHalf; … Read more
I see this question is a bit old, but I decided to give an answer anyway for those who find this question by searching. The standard way to represent 2D/3D transformations nowadays is by using homogeneous coordinates. [x,y,w] for 2D, and [x,y,z,w] for 3D. Since you have three axes in 3D as well as translation, … Read more
Here is an overview of a few methods to render with transparency in OpenGL, with advantages and disadvantages for each. Alpha Testing This is a very limited method, but is sufficient for the specific case the poster asked about. The example shown does not really need transparency because everything is either fully opaque or fully … Read more
What you really have is Volumetric data. I guess that you have is a value of C for every X,Y,Z. And it actually depends a lot in what type of data you have. You’d need to give more information for an specific answer. In general have a look to Volumetric data visualization techniques, but there … Read more