How to update Verge3D objects with JavaScript

All objects by default automatically update their matrices if they have been added to the scene with


    const object = new v3d.Object3D();
    app.scene.add(object);

or if they are the child of another object that has been added to the scene:


    const object1 = new v3d.Object3D();
    const object2 = new v3d.Object3D();

    object1.add(object2);
    app.scene.add(object1); // object1 and object2 will automatically update their matrices

However, if you know the object will be static, you can disable this and update the transform matrix manually just when needed.


    object.matrixAutoUpdate = false;
    object.updateMatrix();

BufferGeometry

BufferGeometries store information (such as vertex positions, face indices, normals, colors, UVs, and any custom attributes) in buffers — that is, typed arrays. This makes them generally faster than standard Geometries, at the cost of being somewhat harder to work with.

With regards to updating BufferGeometries, the most important thing to understand is that you cannot resize buffers (this is very costly, basically the equivalent to creating a new geometry). You can however update the content of buffers.

This means that if you know an attribute of your BufferGeometry will grow, say the number of vertices, you must pre-allocate a buffer large enough to hold any new vertices that may be created. Of course, this also means that there will be a maximum size for your BufferGeometry - there is no way to create a BufferGeometry that can efficiently be extended indefinitely.

We'll use the example of a line that gets extended at render time. We'll allocate space in the buffer for 500 vertices but draw only two at first, using BufferGeometry.drawRange.


    const MAX_POINTS = 500;

    // geometry
    const geometry = new v3d.BufferGeometry();

    // attributes
    const positions = new Float32Array(MAX_POINTS * 3); // 3 coords per vertex
    geometry.setAttribute('position', new v3d.BufferAttribute(positions, 3));

    // draw range
    const drawCount = 2; // draw the first 2 vertices, only
    geometry.setDrawRange(0, drawCount);

    // material
    const material = new v3d.LineBasicMaterial({ color: 0xff0000 });

    // line
    const line = new v3d.Line(geometry, material);
    scene.add(line);

Next we'll randomly add points to the line using a pattern like:


    const positions = line.geometry.attributes.position.array;

    let x, y, z, index;
    x = y = z = index = 0;

    for (let i = 0, l = MAX_POINTS; i < l; i++) {
        positions[index++] = x;
        positions[index++] = y;
        positions[index++] = z;

        x += (Math.random() - 0.5) * 30;
        y += (Math.random() - 0.5) * 30;
        z += (Math.random() - 0.5) * 30;
    }

If you want to change the number of points rendered after the first render, do this:


    line.geometry.setDrawRange(0, newValue);

If you want to change the position data values after the first render, you need to set the needsUpdate flag like so:


    line.geometry.attributes.position.needsUpdate = true; // required after the first render

If you change the position data values after the initial render, you may need to recompute bounding volumes so other features of the engine like view frustum culling or helpers properly work.


    line.geometry.computeBoundingBox();
    line.geometry.computeBoundingSphere();

Materials

All uniforms values can be changed freely (e.g. colors, textures, opacity, etc), values are sent to the shader every frame.

Also WebGL state-related parameters can change any time (depthTest, blending, polygonOffset, etc).

The following properties can't be easily changed at runtime (once the material is rendered at least once):

numbers and types of uniforms
presence or not of
- texture
- fog
- vertex colors
- morphing
- shadow map
- alpha test
- transparent

Changes in these require building of new shader program. You'll need to set

material.needsUpdate = true

Bear in mind this might be quite slow and induce jerkiness in framerate (especially on Windows, as shader compilation is slower in DirectX than OpenGL).

For smoother experience you can emulate changes in these features to some degree by having "dummy" values like zero intensity lights, white textures, or zero density fog.

You can freely change the material used for geometry chunks, however you cannot change how an object is divided into chunks (according to face materials).

If you need to have different configurations of materials during runtime:

If the number of materials / chunks is small, you could pre-divide the object beforehand (e.g. hair / face / body / upper clothes / trousers for a human, front / sides / top / glass / tire / interior for a car).

If the number is large (e.g. each face could be potentially different), consider a different solution, such as using attributes / textures to drive different per-face look.

Textures

Image, canvas, video and data textures need to have the following flag set if they are changed:


    texture.needsUpdate = true;

Render targets update automatically.

Cameras

A camera's position and target is updated automatically. If you need to change:

fov
aspect
near
far

then you'll need to recompute the projection matrix:


    camera.aspect = window.innerWidth / window.innerHeight;
    camera.updateProjectionMatrix();