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Andrei Lesnitsky
Andrei Lesnitsky

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WebGL Month. Day 19. Rendering multiple objects

#beginners #javascript #webgl

This is a series of blog posts related to WebGL. New post will be available every day

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Hey 👋

Welcome to WebGL month.

In previous tutorials we've been rendering only a signle object, but typical 3D scene consists of a multiple objects.
Today we're going to learn how to render many objects on scene.

Since we're rendering objects with a solid color, let's get rid of colorIndex attribute and pass a signle color via uniform

📄 src/3d.js

  const { vertices, normals } = parseObj(monkeyObj);  - const faceColors = [ - [0.5, 0.5, 0.5, 1.0] - ]; - - const colors = []; - - for (var j = 0; j < vertices.length / 3; ++j) { - colors.push(0, 0, 0, 0); - } - - faceColors.forEach((color, index) => { - gl.uniform4fv(programInfo.uniformLocations[`colors[${index}]`], color); - }); + gl.uniform3fv(programInfo.uniformLocations.color, [0.5, 0.5, 0.5]);   const vertexBuffer = new GLBuffer(gl, gl.ARRAY_BUFFER, vertices, gl.STATIC_DRAW); - const colorsBuffer = new GLBuffer(gl, gl.ARRAY_BUFFER, new Float32Array(colors), gl.STATIC_DRAW);  const normalsBuffer = new GLBuffer(gl, gl.ARRAY_BUFFER, normals, gl.STATIC_DRAW);   vertexBuffer.bind(gl); gl.vertexAttribPointer(programInfo.attributeLocations.position, 3, gl.FLOAT, false, 0, 0);  - colorsBuffer.bind(gl); - gl.vertexAttribPointer(programInfo.attributeLocations.colorIndex, 1, gl.FLOAT, false, 0, 0); -  normalsBuffer.bind(gl); gl.vertexAttribPointer(programInfo.attributeLocations.normal, 3, gl.FLOAT, false, 0, 0);
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📄 src/shaders/3d.v.glsl

 attribute vec3 position; attribute vec3 normal; - attribute float colorIndex;   uniform mat4 modelMatrix; uniform mat4 viewMatrix; uniform mat4 projectionMatrix; uniform mat4 normalMatrix; - uniform vec4 colors[6]; + uniform vec3 color;  uniform vec3 directionalLightVector;   varying vec4 vColor; vec3 transformedNormal = (normalMatrix * vec4(normal, 1.0)).xyz; float intensity = dot(transformedNormal, normalize(directionalLightVector));  - vColor.rgb = vec3(0.3, 0.3, 0.3) + colors[int(colorIndex)].rgb * intensity; + vColor.rgb = vec3(0.3, 0.3, 0.3) + color * intensity;  vColor.a = 1.0; }
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We'll need a helper class to store object related info

📄 src/Object3D.js

export class Object3D { constructor() { } }
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Each object should contain it's own vertices and normals

📄 src/Object3D.js

+ import { parseObj } from "./gl-helpers"; +  export class Object3D { - constructor() { - - } + constructor(source) { + const { vertices, normals } = parseObj(source); + + this.vertices = vertices; + this.normals = normals; + }  }
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As well as a model matrix to store object transform

📄 src/Object3D.js

 import { parseObj } from "./gl-helpers"; + import { mat4 } from "gl-matrix";   export class Object3D { constructor(source) {   this.vertices = vertices; this.normals = normals; + + this.modelMatrix = mat4.create();  } }
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Since normal matrix is computable from model matrix it makes sense to define a getter

📄 src/Object3D.js

 this.normals = normals;   this.modelMatrix = mat4.create(); + this._normalMatrix = mat4.create(); + } + + get normalMatrix () { + mat4.invert(this._normalMatrix, this.modelMatrix); + mat4.transpose(this._normalMatrix, this._normalMatrix); + + return this._normalMatrix;  } }
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Now we can refactor our code and use new helper class

📄 src/3d.js

 import { compileShader, setupShaderInput, parseObj } from './gl-helpers'; import { GLBuffer } from './GLBuffer'; import monkeyObj from '../assets/objects/monkey.obj'; + import { Object3D } from './Object3D';   const canvas = document.querySelector('canvas'); const gl = canvas.getContext('webgl');   const programInfo = setupShaderInput(gl, program, vShaderSource, fShaderSource);  - const { vertices, normals } = parseObj(monkeyObj); + const monkey = new Object3D(monkeyObj);   gl.uniform3fv(programInfo.uniformLocations.color, [0.5, 0.5, 0.5]);  - const vertexBuffer = new GLBuffer(gl, gl.ARRAY_BUFFER, vertices, gl.STATIC_DRAW); - const normalsBuffer = new GLBuffer(gl, gl.ARRAY_BUFFER, normals, gl.STATIC_DRAW); + const vertexBuffer = new GLBuffer(gl, gl.ARRAY_BUFFER, monkey.vertices, gl.STATIC_DRAW); + const normalsBuffer = new GLBuffer(gl, gl.ARRAY_BUFFER, monkey.normals, gl.STATIC_DRAW);   vertexBuffer.bind(gl); gl.vertexAttribPointer(programInfo.attributeLocations.position, 3, gl.FLOAT, false, 0, 0); normalsBuffer.bind(gl); gl.vertexAttribPointer(programInfo.attributeLocations.normal, 3, gl.FLOAT, false, 0, 0);  - const modelMatrix = mat4.create();  const viewMatrix = mat4.create(); const projectionMatrix = mat4.create(); - const normalMatrix = mat4.create();   mat4.lookAt( viewMatrix, 100, );  - gl.uniformMatrix4fv(programInfo.uniformLocations.modelMatrix, false, modelMatrix);  gl.uniformMatrix4fv(programInfo.uniformLocations.viewMatrix, false, viewMatrix); gl.uniformMatrix4fv(programInfo.uniformLocations.projectionMatrix, false, projectionMatrix);   gl.viewport(0, 0, canvas.width, canvas.height);  - gl.drawArrays(gl.TRIANGLES, 0, vertexBuffer.data.length / 3); -  function frame() { - mat4.rotateY(modelMatrix, modelMatrix, Math.PI / 180); - - mat4.invert(normalMatrix, modelMatrix); - mat4.transpose(normalMatrix, normalMatrix); + mat4.rotateY(monkey.modelMatrix, monkey.modelMatrix, Math.PI / 180);  - gl.uniformMatrix4fv(programInfo.uniformLocations.modelMatrix, false, modelMatrix); - gl.uniformMatrix4fv(programInfo.uniformLocations.normalMatrix, false, normalMatrix); + gl.uniformMatrix4fv(programInfo.uniformLocations.modelMatrix, false, monkey.modelMatrix); + gl.uniformMatrix4fv(programInfo.uniformLocations.normalMatrix, false, monkey.normalMatrix);   gl.drawArrays(gl.TRIANGLES, 0, vertexBuffer.data.length / 3);
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Now let's import more objects

📄 src/3d.js

 import { compileShader, setupShaderInput, parseObj } from './gl-helpers'; import { GLBuffer } from './GLBuffer'; import monkeyObj from '../assets/objects/monkey.obj'; + import torusObj from '../assets/objects/torus.obj'; + import coneObj from '../assets/objects/cone.obj'; +  import { Object3D } from './Object3D';   const canvas = document.querySelector('canvas'); const programInfo = setupShaderInput(gl, program, vShaderSource, fShaderSource);   const monkey = new Object3D(monkeyObj); + const torus = new Object3D(torusObj); + const cone = new Object3D(coneObj);   gl.uniform3fv(programInfo.uniformLocations.color, [0.5, 0.5, 0.5]);
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and store them in a collection

📄 src/3d.js

 const torus = new Object3D(torusObj); const cone = new Object3D(coneObj);  + const objects = [ + monkey, + torus, + cone, + ]; +  gl.uniform3fv(programInfo.uniformLocations.color, [0.5, 0.5, 0.5]);   const vertexBuffer = new GLBuffer(gl, gl.ARRAY_BUFFER, monkey.vertices, gl.STATIC_DRAW);
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and instead of issuing a draw call for just a monkey, we'll iterate over collection

📄 src/3d.js

 gl.viewport(0, 0, canvas.width, canvas.height);   function frame() { - mat4.rotateY(monkey.modelMatrix, monkey.modelMatrix, Math.PI / 180); + objects.forEach((object) => { + mat4.rotateY(object.modelMatrix, object.modelMatrix, Math.PI / 180);  - gl.uniformMatrix4fv(programInfo.uniformLocations.modelMatrix, false, monkey.modelMatrix); - gl.uniformMatrix4fv(programInfo.uniformLocations.normalMatrix, false, monkey.normalMatrix); + gl.uniformMatrix4fv(programInfo.uniformLocations.modelMatrix, false, object.modelMatrix); + gl.uniformMatrix4fv(programInfo.uniformLocations.normalMatrix, false, object.normalMatrix);  - gl.drawArrays(gl.TRIANGLES, 0, vertexBuffer.data.length / 3); + gl.drawArrays(gl.TRIANGLES, 0, vertexBuffer.data.length / 3); + });   requestAnimationFrame(frame); }
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Ok, but why do we still have only monkey rendered?

No wonder, vertex and normals buffer stays the same, so we just render the same object N times. Let's update vertex and normals buffer each time we want to render an object

📄 src/3d.js

 gl.uniformMatrix4fv(programInfo.uniformLocations.modelMatrix, false, object.modelMatrix); gl.uniformMatrix4fv(programInfo.uniformLocations.normalMatrix, false, object.normalMatrix);  + vertexBuffer.setData(gl, object.vertices, gl.STATIC_DRAW); + normalsBuffer.setData(gl, object.normals, gl.STATIC_DRAW); +  gl.drawArrays(gl.TRIANGLES, 0, vertexBuffer.data.length / 3); });
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Multiple objects 1

Cool, we've rendered multiple objects, but they are all in the same spot. Let's fix that

Each object will have a property storing a position in space

📄 src/3d.js

  const programInfo = setupShaderInput(gl, program, vShaderSource, fShaderSource);  - const monkey = new Object3D(monkeyObj); - const torus = new Object3D(torusObj); - const cone = new Object3D(coneObj); + const monkey = new Object3D(monkeyObj, [0, 0, 0]); + const torus = new Object3D(torusObj, [-3, 0, 0]); + const cone = new Object3D(coneObj, [3, 0, 0]);   const objects = [ monkey,
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📄 src/Object3D.js

 import { mat4 } from "gl-matrix";   export class Object3D { - constructor(source) { + constructor(source, position) {  const { vertices, normals } = parseObj(source);   this.vertices = vertices; this.normals = normals; + this.position = position;   this.modelMatrix = mat4.create(); this._normalMatrix = mat4.create();
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and this position should be respected by model matrix

📄 src/Object3D.js

 this.position = position;   this.modelMatrix = mat4.create(); + mat4.fromTranslation(this.modelMatrix, position);  this._normalMatrix = mat4.create(); }
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And one more thing. We can also define a color specific to each object

📄 src/3d.js

  const programInfo = setupShaderInput(gl, program, vShaderSource, fShaderSource);  - const monkey = new Object3D(monkeyObj, [0, 0, 0]); - const torus = new Object3D(torusObj, [-3, 0, 0]); - const cone = new Object3D(coneObj, [3, 0, 0]); + const monkey = new Object3D(monkeyObj, [0, 0, 0], [1, 0, 0]); + const torus = new Object3D(torusObj, [-3, 0, 0], [0, 1, 0]); + const cone = new Object3D(coneObj, [3, 0, 0], [0, 0, 1]);   const objects = [ monkey, cone, ];  - gl.uniform3fv(programInfo.uniformLocations.color, [0.5, 0.5, 0.5]); -  const vertexBuffer = new GLBuffer(gl, gl.ARRAY_BUFFER, monkey.vertices, gl.STATIC_DRAW); const normalsBuffer = new GLBuffer(gl, gl.ARRAY_BUFFER, monkey.normals, gl.STATIC_DRAW);   gl.uniformMatrix4fv(programInfo.uniformLocations.modelMatrix, false, object.modelMatrix); gl.uniformMatrix4fv(programInfo.uniformLocations.normalMatrix, false, object.normalMatrix);  + gl.uniform3fv(programInfo.uniformLocations.color, object.color); +  vertexBuffer.setData(gl, object.vertices, gl.STATIC_DRAW); normalsBuffer.setData(gl, object.normals, gl.STATIC_DRAW);
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📄 src/Object3D.js

 import { mat4 } from "gl-matrix";   export class Object3D { - constructor(source, position) { + constructor(source, position, color) {  const { vertices, normals } = parseObj(source);   this.vertices = vertices; this.modelMatrix = mat4.create(); mat4.fromTranslation(this.modelMatrix, position); this._normalMatrix = mat4.create(); + + this.color = color;  }   get normalMatrix () {
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Multiple objects 2

Yay! We now can render multiple objects with individual transforms and colors 🎉

That's it for today, see you tomorrow 👋

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