Cannot plot points in Z direction using regl

Question

I am starting with regl and I am trying to make a small demo for plotting points in all three axis. I have used this link to start with.

In the example above the points were initialized as

const points = d3.range(numPoints).map(i => ({
                x: //Code,
                y: //Code,
                color: [1, 0, 0],
            }));

I modified it to the one below to get a spiral that goes into infinity

const points = d3.range(numPoints).map(i => ({
                x: 200+radius*Math.cos(i*Math.PI/180),
                y: 200+radius*Math.sin(i*Math.PI/180),
                z: i,
                color: [1, 0, 0],
            }));

I modified the vertex shader to account for the additional axis. The following is the code which draws the points

const drawPoints = regl({
                frag:`
                precision highp float;
                varying vec3 fragColor;
                void main() 
                {
                    gl_FragColor = vec4(fragColor, 1);
                }
                `,

                vert:`
                attribute vec3 position;
                attribute vec3 color;
                varying vec3 fragColor;
                uniform float pointWidth;
                uniform float stageWidth;
                uniform float stageHeight;
                uniform float stageDepth;
                vec3 normalizeCoords(vec3 position) 
                {
                    float x = position[0];
                    float y = position[1];
                    float z = position[2];
                    return vec3(2.0 * ((x / stageWidth) - 0.5),-(2.0 * ((y / stageHeight) - 0.5)),1.0 * ((z / stageDepth) - 0.0));
                }
                void main()
                {
                    gl_PointSize = pointWidth;
                    fragColor = color;
                    gl_Position = vec4(normalizeCoords(position), 1.0);
                }
                `,
                attributes:
                {
                    position: points.map(d => [d.x, d.y, d.z]),
                    color: points.map(d => d.color),
                },
                uniforms:
                {
                    pointWidth: regl.prop('pointWidth'),
                    stageWidth: regl.prop('stageWidth'),
                    stageHeight: regl.prop('stageHeight'),
                    stageDepth: regl.prop('stageDepth'),
                },

                count: points.length,
                depth: 
                {
                    enable: true,
                    mask: true,
                    func: 'less',
                    range: [0, 1]
                },
                primitive: 'points',



            });
frameLoop = regl.frame(() => {
        // clear the buffer
        regl.clear({
            // background color (black)
            color: [0, 0, 0, 1],
            depth: 1,
        });

        drawPoints({
            pointWidth,
            stageWidth: width,
            stageHeight: height,
        });

        if (frameLoop) {
            frameLoop.cancel();
        }
    });

But the result of this is a circle which is plotted on the same plane. The third input to the position doesn't seem to have any effect. I tried interchanging the y and z values in the position and I obtained a sine curve. So the value of z is getting assigned properly. Another thing I noted is that if the value of z is zero, nothing is plotted. Any other value of z doesn't seem to produce any effect.

Answer 1

The reason the added z coordinate has no effect is because you currently have no concept of "depth projection" in your rendering pipeline.

Typically, you'll need to add a "projection matrix" to your rendering pipeline which will account for the z coordinate in vertices, when mapping those 3D vertex positions to your 2D screen.

You should be able to add this projection fairly simply by using something like the canvas-orbit-camera module. Once you'd added that module to your project, consider making the following adjustments to your code (see comments tagged with [Add]):

// Your init code ..

// [Add] Register camera middleware with canvas
const camera = require('canvas-orbit-camera')(canvas)

// Your init code ..

const drawPoints = regl({
    frag:`
    precision highp float;
    varying vec3 fragColor;
    void main() 
    {
        gl_FragColor = vec4(fragColor, 1);
    }
    `,

    vert:`
    attribute vec3 position;
    attribute vec3 color;
    varying vec3 fragColor;
    uniform float pointWidth;
    uniform float stageWidth;
    uniform float stageHeight;
    uniform float stageDepth;

    uniform mat4 proj; // [Add] Projection matrix uniform

    vec3 normalizeCoords(vec3 position) 
    {
        float x = position[0];
        float y = position[1];
        float z = position[2];
        return vec3(2.0 * ((x / stageWidth) - 0.5),-(2.0 * ((y / stageHeight) - 0.5)),1.0 * ((z / stageDepth) - 0.0));
    }
    void main()
    {
        gl_PointSize = pointWidth;
        fragColor = color;
        gl_Position = proj * vec4(normalizeCoords(position), 1.0); // [Add] Multiply vertex by projection matrix
    }
    `,
    attributes:
    {
        position: points.map(d => [d.x, d.y, d.z]),
        color: points.map(d => d.color),
    },
    uniforms:
    {
        pointWidth: regl.prop('pointWidth'),
        stageWidth: regl.prop('stageWidth'),
        stageHeight: regl.prop('stageHeight'),
        stageDepth: regl.prop('stageDepth'),

        // [Add] Projection matrix calculation
        proj: ({viewportWidth, viewportHeight}) =>
            mat4.perspective([],
                Math.PI / 2,
                viewportWidth / viewportHeight,
                0.01,
                1000),
    },

    count: points.length,
    depth: 
    {
        enable: true,
        mask: true,
        func: 'less',
        range: [0, 1]
    },
    primitive: 'points',
});

frameLoop = regl.frame(() => {
    // clear the buffer
    regl.clear({
        // background color (black)
        color: [0, 0, 0, 1],
        depth: 1,
    });

    // [Add] Camera re computation
    camera.tick()

    drawPoints({
        pointWidth,
        stageWidth: width,
        stageHeight: height,
    });

    if (frameLoop) {
        frameLoop.cancel();
    }
});

Hope this helps!