How to map different textures to different faces of a cube in WebGL?

Question

I have the following cube coordinates:

var vertices = [
    // Front face
    -1.0, -1.0,  1.0,
     1.0, -1.0,  1.0,
     1.0,  1.0,  1.0,
    -1.0,  1.0,           


        

Answer 1

The arguably best way to put different images on a cube is to put all the images into one texture and use UV coordinates to select a different part of the textures for each face of the cube.

See example on this page with lots of explanation

Or here

"use strict";
var m4 = twgl.m4;
var gl = document.getElementById("c").getContext("webgl");
// compiles shader, links and looks up locations
var programInfo = twgl.createProgramInfo(gl, ["vs", "fs"]);

var arrays = {
  position: [1, 1, -1, 1, 1, 1, 1, -1, 1, 1, -1, -1, -1, 1, 1, -1, 1, -1, -1, -1, -1, -1, -1, 1, -1, 1, 1, 1, 1, 1, 1, 1, -1, -1, 1, -1, -1, -1, -1, 1, -1, -1, 1, -1, 1, -1, -1, 1, 1, 1, 1, -1, 1, 1, -1, -1, 1, 1, -1, 1, -1, 1, -1, 1, 1, -1, 1, -1, -1, -1, -1, -1],
  texcoord: [
 // select the bottom left image
    0   , 0  ,
    0   , 0.5,
    0.25, 0.5,
    0.25, 0  ,
    // select the bottom middle image
    0.25, 0  ,
    0.5 , 0  ,
    0.5 , 0.5,
    0.25, 0.5,
    // select to bottom right image
    0.5 , 0  ,
    0.5 , 0.5,
    0.75, 0.5,
    0.75, 0  ,
    // select the top left image
    0   , 0.5,
    0.25, 0.5,
    0.25, 1  ,
    0   , 1  ,
    // select the top middle image
    0.25, 0.5,
    0.25, 1  ,
    0.5 , 1  ,
    0.5 , 0.5,
    // select the top right image
    0.5 , 0.5,
    0.75, 0.5,
    0.75, 1  ,  
    0.5 , 1  ,
  ],
  indices:  [0, 1, 2, 0, 2, 3, 4, 5, 6, 4, 6, 7, 8, 9, 10, 8, 10, 11, 12, 13, 14, 12, 14, 15, 16, 17, 18, 16, 18, 19, 20, 21, 22, 20, 22, 23],
};
// calls gl.createBuffer, gl.bindBuffer, gl.bufferData for each array
var bufferInfo = twgl.createBufferInfoFromArrays(gl, arrays);

// calls gl.createTexture, gl.bindTexture, gl.texImage2D, gl.texParameteri
var tex = twgl.createTexture(gl, {
  src: "https://webglfundamentals.org/webgl/resources/noodles.jpg",
  crossOrigin: "",
});

var uniforms = {
  u_texture: tex,
};

function render(time) {
  time *= 0.001;
  twgl.resizeCanvasToDisplaySize(gl.canvas);
  gl.viewport(0, 0, gl.canvas.width, gl.canvas.height);

  gl.enable(gl.DEPTH_TEST);
  gl.enable(gl.CULL_FACE);
  gl.clear(gl.COLOR_BUFFER_BIT | gl.DEPTH_BUFFER_BIT);

  var projection = m4.perspective(30 * Math.PI / 180, gl.canvas.clientWidth / gl.canvas.clientHeight, 0.5, 10);
  var eye = [1, 4, -6];
  var target = [0, 0, 0];
  var up = [0, 1, 0];

  var camera = m4.lookAt(eye, target, up);
  var view = m4.inverse(camera);
  var viewProjection = m4.multiply(view, projection);
  var world = m4.rotationY(time);

  uniforms.u_worldViewProjection = m4.multiply(world, viewProjection);

  gl.useProgram(programInfo.program);
  // calls gl.bindBuffer, gl.enableVertexAttribArray, gl.vertexAttribPointer
  twgl.setBuffersAndAttributes(gl, programInfo, bufferInfo);
  // calls gl.uniformXXX, gl.activeTexture, gl.bindTexture
  twgl.setUniforms(programInfo, uniforms);
  // calls gl.drawArray or gl.drawElements
  twgl.drawBufferInfo(gl, gl.TRIANGLES, bufferInfo);

  requestAnimationFrame(render);
}
requestAnimationFrame(render);

body { margin: 0px; }
canvas { width: 100vw; height: 100vh; display: block; }

<script id="vs" type="notjs">
uniform mat4 u_worldViewProjection;

attribute vec4 position;
attribute vec2 texcoord;

varying vec2 v_texCoord;

void main() {
  v_texCoord = texcoord;
  gl_Position = u_worldViewProjection * position;
}
  </script>
  <script id="fs" type="notjs">
precision mediump float;

varying vec2 v_texCoord;

uniform sampler2D u_texture;
void main() {
  gl_FragColor = texture2D(u_texture, v_texCoord);
}
  </script>
<script src="https://twgljs.org/dist/twgl-full.min.js"></script>
<canvas id="c"></canvas>

There are many reasons why it's arguably the best way. As a simple example of why this is the way if you actually made a shader that uses 6 textures you'd need a different shader for a pyramid (3-4 faces) and another for an icosahedron (12 faces) and yet another for a dodecahedron (20 faces) whereas if you put the images in one texture it just works with the same shader.

Even if you want to load the 6 images separately it would arguably be best to make a 2d canvas, use drawImage to copy all 6 images into that canvas and then copy that canvas to a single texture.

"use strict";
var m4 = twgl.m4;
var gl = document.getElementById("c").getContext("webgl");
// compiles shader, links and looks up locations
var programInfo = twgl.createProgramInfo(gl, ["vs", "fs"]);

var arrays = {
  position: [1, 1, -1, 1, 1, 1, 1, -1, 1, 1, -1, -1, -1, 1, 1, -1, 1, -1, -1, -1, -1, -1, -1, 1, -1, 1, 1, 1, 1, 1, 1, 1, -1, -1, 1, -1, -1, -1, -1, 1, -1, -1, 1, -1, 1, -1, -1, 1, 1, 1, 1, -1, 1, 1, -1, -1, 1, 1, -1, 1, -1, 1, -1, 1, 1, -1, 1, -1, -1, -1, -1, -1],
  texcoord: [
 // select the bottom left image
    0   , 0  ,
    0   , 0.5,
    0.25, 0.5,
    0.25, 0  ,
    // select the bottom middle image
    0.25, 0  ,
    0.5 , 0  ,
    0.5 , 0.5,
    0.25, 0.5,
    // select to bottom right image
    0.5 , 0  ,
    0.5 , 0.5,
    0.75, 0.5,
    0.75, 0  ,
    // select the top left image
    0   , 0.5,
    0.25, 0.5,
    0.25, 1  ,
    0   , 1  ,
    // select the top middle image
    0.25, 0.5,
    0.25, 1  ,
    0.5 , 1  ,
    0.5 , 0.5,
    // select the top right image
    0.5 , 0.5,
    0.75, 0.5,
    0.75, 1  ,  
    0.5 , 1  ,
  ],
  indices:  [0, 1, 2, 0, 2, 3, 4, 5, 6, 4, 6, 7, 8, 9, 10, 8, 10, 11, 12, 13, 14, 12, 14, 15, 16, 17, 18, 16, 18, 19, 20, 21, 22, 20, 22, 23],
};
// calls gl.createBuffer, gl.bindBuffer, gl.bufferData for each array
var bufferInfo = twgl.createBufferInfoFromArrays(gl, arrays);


var ctx = document.createElement("canvas").getContext("2d");
ctx.canvas.width = 512;
ctx.canvas.height = 256;
ctx.fillRect(0, 0, 512, 256);  // black to start

var tex = gl.createTexture();
uploadCanvasToTexture();

[
  "https://i.imgur.com/weklTat.gif",
  "https://i.imgur.com/6AvnLa3.jpg",
  "https://i.imgur.com/HkzeCU2.jpg",
  "https://i.imgur.com/D9HVm6n.png",
  "https://i.imgur.com/7MlmkJr.jpg",
  "https://i.imgur.com/v38pV.jpg",
].forEach(function(url, ndx) {
  var img = new Image();
  img.onload = function() {
    addFaceToCanvasAndUploadToTexture(img, ndx);
  };
  img.crossOrigin = "";
  img.src = url;
});
  
function addFaceToCanvasAndUploadToTexture(img, ndx) {
  var x = ndx % 3;
  var y = ndx / 3 | 0;
  ctx.drawImage(img, 0, 0, img.width, img.height, x * 128, y * 128, 128, 128);
  uploadCanvasToTexture();
}
  
function uploadCanvasToTexture() {
  gl.bindTexture(gl.TEXTURE_2D, tex);
  gl.texImage2D(gl.TEXTURE_2D, 0, gl.RGBA, gl.RGBA, gl.UNSIGNED_BYTE, ctx.canvas);
  gl.generateMipmap(gl.TEXTURE_2D);
}    
    
var uniforms = {
  u_texture: tex,
};

function render(time) {
  time *= 0.001;
  twgl.resizeCanvasToDisplaySize(gl.canvas);
  gl.viewport(0, 0, gl.canvas.width, gl.canvas.height);

  gl.enable(gl.DEPTH_TEST);
  gl.enable(gl.CULL_FACE);
  gl.clear(gl.COLOR_BUFFER_BIT | gl.DEPTH_BUFFER_BIT);

  var projection = m4.perspective(30 * Math.PI / 180, gl.canvas.clientWidth / gl.canvas.clientHeight, 0.5, 10);
  var eye = [1, 4, -6];
  var target = [0, 0, 0];
  var up = [0, 1, 0];

  var camera = m4.lookAt(eye, target, up);
  var view = m4.inverse(camera);
  var viewProjection = m4.multiply(view, projection);
  var world = m4.rotationY(time);

  uniforms.u_worldViewProjection = m4.multiply(world, viewProjection);

  gl.useProgram(programInfo.program);
  // calls gl.bindBuffer, gl.enableVertexAttribArray, gl.vertexAttribPointer
  twgl.setBuffersAndAttributes(gl, programInfo, bufferInfo);
  // calls gl.uniformXXX, gl.activeTexture, gl.bindTexture
  twgl.setUniforms(programInfo, uniforms);
  // calls gl.drawArray or gl.drawElements
  twgl.drawBufferInfo(gl, gl.TRIANGLES, bufferInfo);

  requestAnimationFrame(render);
}
requestAnimationFrame(render);

body { margin: 0px; }
canvas { width: 100vw; height: 100vh; display: block; }

<script id="vs" type="notjs">
uniform mat4 u_worldViewProjection;

attribute vec4 position;
attribute vec2 texcoord;

varying vec2 v_texCoord;

void main() {
  v_texCoord = texcoord;
  gl_Position = u_worldViewProjection * position;
}
  </script>
  <script id="fs" type="notjs">
precision mediump float;

varying vec2 v_texCoord;

uniform sampler2D u_texture;
void main() {
  gl_FragColor = texture2D(u_texture, v_texCoord);
}
  </script>
<script src="https://twgljs.org/dist/twgl-full.min.js"></script>
<canvas id="c"></canvas>

If you really need the resolution for each face then the 2nd most common way would be to make 6 planes and just position them so they form a cube. Put a single texture on each plane. Draw with 6 draw calls, one for each plane.

"use strict";
var m4 = twgl.m4;
var gl = document.getElementById("c").getContext("webgl");
// compiles shader, links and looks up locations
var programInfo = twgl.createProgramInfo(gl, ["vs", "fs"]);

var arrays = {
  position: [
    -1, -1, 0,
     1, -1, 0,
    -1,  1, 0,
     1,  1, 0,
  ],
  texcoord: [
    0, 0,
    1, 0,
    0, 1,
    1, 1,
  ],
  indices:  [
    0, 1, 2, 2, 1, 3,
  ],
};
// calls gl.createBuffer, gl.bindBuffer, gl.bufferData for each array
var bufferInfo = twgl.createBufferInfoFromArrays(gl, arrays);
    
// calls gl.createTexture, gl.bindTexture, gl.texImage2D, gl.texParameteri
var textures = twgl.createTextures(gl, {
  face0: { src:"https://i.imgur.com/weklTat.gif", crossOrigin: "", },
  face1: { src:"https://i.imgur.com/6AvnLa3.jpg", crossOrigin: "", },
  face2: { src:"https://i.imgur.com/HkzeCU2.jpg", crossOrigin: "", },
  face3: { src:"https://i.imgur.com/D9HVm6n.png", crossOrigin: "", },
  face4: { src:"https://i.imgur.com/7MlmkJr.jpg", crossOrigin: "", },
  face5: { src:"https://i.imgur.com/v38pV.jpg", crossOrigin: "", },
});
    
var models = [
  { tex: textures.face0, local: m4.translate(m4.rotationY(Math.PI * 0.0), [0, 0, 1]), },
  { tex: textures.face1, local: m4.translate(m4.rotationY(Math.PI * 0.5), [0, 0, 1]), }, 
  { tex: textures.face2, local: m4.translate(m4.rotationY(Math.PI * 1.0), [0, 0, 1]), }, 
  { tex: textures.face3, local: m4.translate(m4.rotationY(Math.PI * 1.5), [0, 0, 1]), }, 
  { tex: textures.face4, local: m4.translate(m4.rotationX(Math.PI * 0.5), [0, 0, 1]), }, 
  { tex: textures.face5, local: m4.translate(m4.rotationX(Math.PI * 1.5), [0, 0, 1]), }, 
];

var uniforms = {
};

function render(time) {
  time *= 0.001;
  twgl.resizeCanvasToDisplaySize(gl.canvas);
  gl.viewport(0, 0, gl.canvas.width, gl.canvas.height);

  gl.enable(gl.DEPTH_TEST);
  gl.enable(gl.CULL_FACE);
  gl.clear(gl.COLOR_BUFFER_BIT | gl.DEPTH_BUFFER_BIT);

  var projection = m4.perspective(30 * Math.PI / 180, gl.canvas.clientWidth / gl.canvas.clientHeight, 0.5, 10);
  var eye = [1, 4, -6];
  var target = [0, 0, 0];
  var up = [0, 1, 0];

  var camera = m4.lookAt(eye, target, up);
  var view = m4.inverse(camera);
  var viewProjection = m4.multiply(view, projection);

  gl.useProgram(programInfo.program);
  // calls gl.bindBuffer, gl.enableVertexAttribArray, gl.vertexAttribPointer
  twgl.setBuffersAndAttributes(gl, programInfo, bufferInfo);
  
  models.forEach(function(model) {
    var world = m4.rotationY(time);
    m4.multiply(model.local, world, world);
    uniforms.u_texture = model.tex;
    uniforms.u_worldViewProjection = m4.multiply(world, viewProjection);

    // calls gl.uniformXXX, gl.activeTexture, gl.bindTexture
    twgl.setUniforms(programInfo, uniforms);
    // calls gl.drawArray or gl.drawElements
    twgl.drawBufferInfo(gl, gl.TRIANGLES, bufferInfo);
  });

  requestAnimationFrame(render);
}
requestAnimationFrame(render);

body { margin: 0px; }
canvas { width: 100vw; height: 100vh; display: block; }

<script id="vs" type="notjs">
uniform mat4 u_worldViewProjection;

attribute vec4 position;
attribute vec2 texcoord;

varying vec2 v_texCoord;

void main() {
  v_texCoord = texcoord;
  gl_Position = u_worldViewProjection * position;
}
  </script>
  <script id="fs" type="notjs">
precision mediump float;

varying vec2 v_texCoord;

uniform sampler2D u_texture;
void main() {
  gl_FragColor = texture2D(u_texture, v_texCoord);
}
  </script>
<script src="https://twgljs.org/dist/twgl-full.min.js"></script>
<canvas id="c"></canvas>