How to position a particle at the center of the visible screen using Three.js

Question

How to position a particle at the center of the visible screen using Three.js

I have a unique scenario in which I am using a ParticleSystem with thousands of particles spread across the screen. When zooming and panning using the OrbitControls, I am looking to identify the particle closest to the center of the visible area.

There are two main components to this task. Firstly, it is necessary to determine the central vertex of the visible area. Subsequently, we must apply the distance formula to all particles to pinpoint the one nearest to the central vertex. I hope there is a more efficient method than the brute force approach for the second part. While locating the nearest particle can be achieved straightforwardly through brute force, I'm uncertain about how to locate the central vertex of the visible area. Can someone guide me on how to accomplish this?

javascript three.js

Answer 1

Answer №1

If you want to pinpoint a specific location in three-dimensional space, try focusing on a point directly ahead of you, approximately 10 units away, and then identify the nearest particle from that reference point.

Having experimented with this technique previously, I can confidently share this advice with you.

Learn more about Three.js Projector and Ray objects here

This approach is particularly useful for clicking on a spot on your screen and extracting a corresponding vector.

To implement this procedure: 

Initialize a projector object using THREE.Projector()
Set up an initial vector straight_ahead representing a direction relative to the camera
Transform this vector using projector.unprojectVector(straight_ahead, camera)
Adjust the vector to be offset from the camera by a specified distance (e.g., 10 units)
Identify a point in space based on the modified vector's position
Iterate through a collection of particles to find the one closest to the designated point
Keep track of the particle with the shortest distance as min_point

Answer 2

If you want to pinpoint a specific location in three-dimensional space, try focusing on a point directly ahead of you, approximately 10 units away, and then identify the nearest particle from that reference point.

Having experimented with this technique previously, I can confidently share this advice with you.

Learn more about Three.js Projector and Ray objects here

This approach is particularly useful for clicking on a spot on your screen and extracting a corresponding vector.

To implement this procedure: 

Initialize a projector object using THREE.Projector()
Set up an initial vector straight_ahead representing a direction relative to the camera
Transform this vector using projector.unprojectVector(straight_ahead, camera)
Adjust the vector to be offset from the camera by a specified distance (e.g., 10 units)
Identify a point in space based on the modified vector's position
Iterate through a collection of particles to find the one closest to the designated point
Keep track of the particle with the shortest distance as min_point

Answer 3

Answer №2

lookAt = camera.lookAt;
pos = camera.position;

min = MAX_FLOAT, min_index = -1;
foreach(particle in particle_system) {
    d = distance(particle.position, lookAt, pos);
    if( min>d ) { min_index = particle.getIndex; min = d; }
}

Where the distance function is available online, for example: http://en.wikipedia.org/wiki/Distance_from_a_point_to_a_line

This code snippet captures the process of identifying the viewing ray (lookAt vector) and determining the nearest particle to it.

EDIT:

var cam_position = camera.position,
    cam_eyeVec = getEyeVec(camera.projectionMatrix);

var min_dist = 10000000,
    min_index = -1;

for(var i=0; i<particle_count; i++) {
    var d = distance(particle[i].position, cam_eyeVec, cam_position);
    if(min_dist > d) {
         min_index = i;
         min_dist = d;
    }
}

function getEyeVec(projMat) {
    return new THREE.Vector3(projMat[8], projMat[9], projMat[10]);
}

function distance(p, n, a) {
    n = n.normalize();
    var diff = new THREE.Vector3(a.x-p.x, a.y-p.y, a.z-p.z);
    var diff_n = diff.multiply(n);
    var d = ((diff.selfSubstract(diff_n)).selfMultiply(n)).length();
    return d;
}

The calculation for getEyeVec is inspired by - eye and up vectors from viewMatrix. The approach for computing distance is based on - Distance from a point to a line.

Answer 4

lookAt = camera.lookAt;
pos = camera.position;

min = MAX_FLOAT, min_index = -1;
foreach(particle in particle_system) {
    d = distance(particle.position, lookAt, pos);
    if( min>d ) { min_index = particle.getIndex; min = d; }
}

Where the distance function is available online, for example: http://en.wikipedia.org/wiki/Distance_from_a_point_to_a_line

This code snippet captures the process of identifying the viewing ray (lookAt vector) and determining the nearest particle to it.

EDIT:

var cam_position = camera.position,
    cam_eyeVec = getEyeVec(camera.projectionMatrix);

var min_dist = 10000000,
    min_index = -1;

for(var i=0; i<particle_count; i++) {
    var d = distance(particle[i].position, cam_eyeVec, cam_position);
    if(min_dist > d) {
         min_index = i;
         min_dist = d;
    }
}

function getEyeVec(projMat) {
    return new THREE.Vector3(projMat[8], projMat[9], projMat[10]);
}

function distance(p, n, a) {
    n = n.normalize();
    var diff = new THREE.Vector3(a.x-p.x, a.y-p.y, a.z-p.z);
    var diff_n = diff.multiply(n);
    var d = ((diff.selfSubstract(diff_n)).selfMultiply(n)).length();
    return d;
}

The calculation for getEyeVec is inspired by - eye and up vectors from viewMatrix. The approach for computing distance is based on - Distance from a point to a line.

Answer 5

Answer №3

While I may not be well-versed in three.js, I do have expertise in optimization algorithms. One common mistake is looping through all particles every time, which can lead to inefficiency.

A better approach is to sort the particles so that when you know the camera position, you can quickly locate the closest points without iterating through each one individually. It's akin to having an index in a database or navigating a library categorized alphabetically - you don't need to search every single item, just go directly to the relevant section and make finer comparisons as needed.

In a 2D scenario, storing particles in grids with multiple levels can significantly reduce the number of iterations required. For instance, categorizing 1 million particles based on their position relative to the center allows for efficient filtering using simple conditional statements. By organizing particles into grid locations upon creation, you can drastically minimize the computational load by focusing only on the relevant sections during runtime.

To account for particle movement, incorporating basic modular arithmetic calculations can ensure continuous tracking within the designated grid locations. Additionally, implementing a proximity threshold defines what constitutes "close enough," facilitating quicker and more accurate results even with densely clustered particles.

Answer 6

While I may not be well-versed in three.js, I do have expertise in optimization algorithms. One common mistake is looping through all particles every time, which can lead to inefficiency.

A better approach is to sort the particles so that when you know the camera position, you can quickly locate the closest points without iterating through each one individually. It's akin to having an index in a database or navigating a library categorized alphabetically - you don't need to search every single item, just go directly to the relevant section and make finer comparisons as needed.

In a 2D scenario, storing particles in grids with multiple levels can significantly reduce the number of iterations required. For instance, categorizing 1 million particles based on their position relative to the center allows for efficient filtering using simple conditional statements. By organizing particles into grid locations upon creation, you can drastically minimize the computational load by focusing only on the relevant sections during runtime.

To account for particle movement, incorporating basic modular arithmetic calculations can ensure continuous tracking within the designated grid locations. Additionally, implementing a proximity threshold defines what constitutes "close enough," facilitating quicker and more accurate results even with densely clustered particles.

How to position a particle at the center of the visible screen using Three.js

Answer №1

Answer №2

Answer №3

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