如何在 WebGL 中将不同的纹理映射到立方体的不同面？

Question

我有以下立方体坐标：

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,  1.0,

    // Back face
    -1.0, -1.0, -1.0,
    -1.0,  1.0, -1.0,
     1.0,  1.0, -1.0,
     1.0, -1.0, -1.0,

    // Top face
    -1.0,  1.0, -1.0,
    -1.0,  1.0,  1.0,
     1.0,  1.0,  1.0,
     1.0,  1.0, -1.0,

    // Bottom face
    -1.0, -1.0, -1.0,
     1.0, -1.0, -1.0,
     1.0, -1.0,  1.0,
    -1.0, -1.0,  1.0,

    // Right face
     1.0, -1.0, -1.0,
     1.0,  1.0, -1.0,
     1.0,  1.0,  1.0,
     1.0, -1.0,  1.0,

    // Left face
    -1.0, -1.0, -1.0,
    -1.0, -1.0,  1.0,
    -1.0,  1.0,  1.0,
    -1.0,  1.0, -1.0
];

这些是纹理坐标：

var textureCoordinates = [
    // Front
    0.0,  0.0,
    1.0,  0.0,
    1.0,  1.0,
    0.0,  1.0,

    // Back
    0.0,  0.0,
    1.0,  0.0,
    1.0,  1.0,
    0.0,  1.0,

    // Top
    0.0,  0.0,
    1.0,  0.0,
    1.0,  1.0,
    0.0,  1.0,

    // Bottom
    0.0,  0.0,
    1.0,  0.0,
    1.0,  1.0,
    0.0,  1.0,

    // Right
    0.0,  0.0,
    1.0,  0.0,
    1.0,  1.0,
    0.0,  1.0,

    // Left
    0.0,  0.0,
    1.0,  0.0,
    1.0,  1.0,
    0.0,  1.0
];

现在，通过下面的代码，它只加载一张纹理图像。

gl.activeTexture(gl.TEXTURE0);
gl.bindTexture(gl.TEXTURE_2D, cubeTexture);
gl.uniform1i(gl.getUniformLocation(shaderProgram, "uSampler"), 0);

我从 MDN web docs 那里得到了这个代码示例，我想知道我应该做些什么修改才能让每个立方体面都可以设置不同的纹理。我已经阅读过有关更改活动纹理的信息，但我不知道如何进行更改以使其不会影响整个立方体。我是 WebGL 的新手，希望有人能帮助我理解这一点。

Answer 1

可以说，将不同图像放在立方体上的最佳方法是将所有图像放在一个纹理中，并使用 UV 坐标 select 立方体每个面的纹理的不同部分。

See example on this page with lots of explanation

或在这里

"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>

它被认为是最佳方式的原因有很多。作为一个简单的例子来说明为什么如果你真的制作了一个使用 6 个纹理的着色器，你需要一个不同的着色器用于金字塔（3-4 个面）和另一个用于二十面体（12 个面）和另一个用于十二面体（20 个面），而如果将图像放在一个纹理中，它只适用于相同的着色器。

即使您想分别加载 6 张图像，也可以说最好制作一个 2d canvas，使用 drawImage 将所有 6 张图像复制到 canvas 中，然后将 canvas 复制到单个纹理。

"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>

如果你真的需要每个面的分辨率，那么第二种最常见的方法是制作 6 个平面，然后将它们定位，使它们形成一个立方体。在每个平面上放置一个纹理。使用 6 个绘制调用进行绘制，每个平面一个。

"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>

如何在 WebGL 中将不同的纹理映射到立方体的不同面？

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

textures

webgl