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 获得了这个代码示例，我想知道我应该做哪些修改，以便可以为每个立方体面设置不同的纹理。我已阅读有关更改活动纹理的信息，但我不知道如何操作，以免影响整个立方体。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入一个纹理中，并使用 UV 坐标为立方体的每个面选择纹理的不同部分。

See example on this page with lots of explanation

或者这里

"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>

它可以说是最好的方法有很多原因。作为一个简单的例子，如果您实际上制作了一个使用 6 个纹理的着色器，那么您需要一个不同的着色器用于金字塔（3-4 个面），另一个用于二十面体（12 个面），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，则它只适用于相同的着色器。

即使您想分别加载 6 张图像，最好还是制作一个 2d 画布，使用 drawImage 将所有 6 张图像复制到该画布中，然后将该画布复制到单个纹理中。

"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>

如果您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 个平面并将它们定位，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，每个平面调用一次。

"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>