webgl 21.画带颜色的正方体

colored cube.png

上一节中我们每个顶点给了一个颜色，颜色在各个顶点之间进行了插值。现在我们要每一个面都有一个不同的颜色怎么办呢？

每个面一个颜色要求每个面上的 4 个顶点的颜色相同，但每个顶点都是被 3 个面所共用，所以 8 个顶点已经不行了，现在每个面需要 4 个顶点，总共需要 24 个顶点。

每个面用 4 个顶点

//    v6----- v5
//   /|      /|
//  v1------v0|
//  | |     | |
//  | |v7---|-|v4
//  |/      |/
//  v2------v3

var vertices = new Float32Array([
   1.0, 1.0, 1.0, -1.0, 1.0, 1.0, -1.0, -1.0, 1.0, 1.0, -1.0, 1.0,  // v0-v1-v2-v3 front
   1.0, 1.0, 1.0, 1.0, -1.0, 1.0, 1.0, -1.0, -1.0, 1.0, 1.0, -1.0,  // v0-v3-v4-v5 right
   1.0, 1.0, 1.0, 1.0, 1.0, -1.0, -1.0, 1.0, -1.0, -1.0, 1.0, 1.0,  // v0-v5-v6-v1 up
   -1.0, 1.0, 1.0, -1.0, 1.0, -1.0, -1.0, -1.0, -1.0, -1.0, -1.0, 1.0,  // v1-v6-v7-v2 left
   -1.0, -1.0, -1.0, 1.0, -1.0, -1.0, 1.0, -1.0, 1.0, -1.0, -1.0, 1.0,  // v7-v4-v3-v2 down
   1.0, -1.0, -1.0, -1.0, -1.0, -1.0, -1.0, 1.0, -1.0, 1.0, 1.0, -1.0   // v4-v7-v6-v5 back
]);

每个面 4个顶点指定一个颜色

var colors = new Float32Array([     // Colors
   0.4, 0.4, 1.0, 0.4, 0.4, 1.0, 0.4, 0.4, 1.0, 0.4, 0.4, 1.0,  // v0-v1-v2-v3 front(blue)
   0.4, 1.0, 0.4, 0.4, 1.0, 0.4, 0.4, 1.0, 0.4, 0.4, 1.0, 0.4,  // v0-v3-v4-v5 right(green)
   1.0, 0.4, 0.4, 1.0, 0.4, 0.4, 1.0, 0.4, 0.4, 1.0, 0.4, 0.4,  // v0-v5-v6-v1 up(red)
   1.0, 1.0, 0.4, 1.0, 1.0, 0.4, 1.0, 1.0, 0.4, 1.0, 1.0, 0.4,  // v1-v6-v7-v2 left
   1.0, 1.0, 1.0, 1.0, 1.0, 1.0, 1.0, 1.0, 1.0, 1.0, 1.0, 1.0,  // v7-v4-v3-v2 down
   0.4, 1.0, 1.0, 0.4, 1.0, 1.0, 0.4, 1.0, 1.0, 0.4, 1.0, 1.0   // v4-v7-v6-v5 back
]);

索引值需要相应的改变

var indices = new Uint8Array([   
    0, 1, 2, 0, 2, 3,    // front
    4, 5, 6, 4, 6, 7,    // right
    8, 9, 10, 8, 10, 11,    // up
    12, 13, 14, 12, 14, 15,    // left
    16, 17, 18, 16, 18, 19,    // down
    20, 21, 22, 20, 22, 23     // back
]);

完整代码

<script id="vertex-shader" type="glsl">
    attribute vec4 a_Position;
    attribute vec4 a_Color;
    uniform mat4 u_mvpMatrix;
    varying vec4 v_Color;

    void main() {
        gl_Position = u_mvpMatrix * a_Position;
        v_Color = a_Color;
    }
</script>

<script id="fragment-shader" type="glsl">
    precision mediump float;
    varying vec4 v_Color;
    void main() {
       gl_FragColor = v_Color;
    }
</script>

<script src="lib/cuon-matrix.js"></script>
<script src="lib/myutils.js"></script>

<script>
    var VERTEX_SHADER_SOURCE = document.getElementById('vertex-shader').text;
    var FRAGMENT_SHADER_SOURCE = document.getElementById('fragment-shader').text;

    var canvas = document.getElementById("canvas");
    var gl = canvas.getContext('webgl');

    if (!initShaders(gl, VERTEX_SHADER_SOURCE, FRAGMENT_SHADER_SOURCE)) {
        alert('Failed to init shaders');
    }

    var n = initVertexBuffers(gl);

    var u_mvpMatrix = gl.getUniformLocation(gl.program, 'u_mvpMatrix');
    // <projection matrix> * <view matrix>
    var mvpMatrix = new Matrix4();
    mvpMatrix.setPerspective(30, 1, 1, 100);
    mvpMatrix.lookAt(3, 3, 7, 0, 0, 0, 0, 1, 0);

    gl.uniformMatrix4fv(u_mvpMatrix, false, mvpMatrix.elements);

    gl.enable(gl.DEPTH_TEST);
    gl.clearColor(0.0, 0.0, 0.0, 1.0);
    gl.clear(gl.COLOR_BUFFER_BIT | gl.DEPTH_BUFFER_BIT);
    gl.drawElements(gl.TRIANGLES, n, gl.UNSIGNED_BYTE, 0);

    function initVertexBuffers(gl) {
        // Create a cube
        //    v6----- v5
        //   /|      /|
        //  v1------v0|
        //  | |     | |
        //  | |v7---|-|v4
        //  |/      |/
        //  v2------v3

        var vertices = new Float32Array([
            1.0, 1.0, 1.0, -1.0, 1.0, 1.0, -1.0, -1.0, 1.0, 1.0, -1.0, 1.0,  // v0-v1-v2-v3 front
            1.0, 1.0, 1.0, 1.0, -1.0, 1.0, 1.0, -1.0, -1.0, 1.0, 1.0, -1.0,  // v0-v3-v4-v5 right
            1.0, 1.0, 1.0, 1.0, 1.0, -1.0, -1.0, 1.0, -1.0, -1.0, 1.0, 1.0,  // v0-v5-v6-v1 up
            -1.0, 1.0, 1.0, -1.0, 1.0, -1.0, -1.0, -1.0, -1.0, -1.0, -1.0, 1.0,  // v1-v6-v7-v2 left
            -1.0, -1.0, -1.0, 1.0, -1.0, -1.0, 1.0, -1.0, 1.0, -1.0, -1.0, 1.0,  // v7-v4-v3-v2 down
            1.0, -1.0, -1.0, -1.0, -1.0, -1.0, -1.0, 1.0, -1.0, 1.0, 1.0, -1.0   // v4-v7-v6-v5 back
        ]);

        var colors = new Float32Array([     // Colors
            0.4, 0.4, 1.0, 0.4, 0.4, 1.0, 0.4, 0.4, 1.0, 0.4, 0.4, 1.0,  // v0-v1-v2-v3 front(blue)
            0.4, 1.0, 0.4, 0.4, 1.0, 0.4, 0.4, 1.0, 0.4, 0.4, 1.0, 0.4,  // v0-v3-v4-v5 right(green)
            1.0, 0.4, 0.4, 1.0, 0.4, 0.4, 1.0, 0.4, 0.4, 1.0, 0.4, 0.4,  // v0-v5-v6-v1 up(red)
            1.0, 1.0, 0.4, 1.0, 1.0, 0.4, 1.0, 1.0, 0.4, 1.0, 1.0, 0.4,  // v1-v6-v7-v2 left
            1.0, 1.0, 1.0, 1.0, 1.0, 1.0, 1.0, 1.0, 1.0, 1.0, 1.0, 1.0,  // v7-v4-v3-v2 down
            0.4, 1.0, 1.0, 0.4, 1.0, 1.0, 0.4, 1.0, 1.0, 0.4, 1.0, 1.0   // v4-v7-v6-v5 back
        ]);

        var indices = new Uint8Array([       // Indices of the vertices
            0, 1, 2, 0, 2, 3,    // front
            4, 5, 6, 4, 6, 7,    // right
            8, 9, 10, 8, 10, 11,    // up
            12, 13, 14, 12, 14, 15,    // left
            16, 17, 18, 16, 18, 19,    // down
            20, 21, 22, 20, 22, 23     // back
        ]);

        if (!initArrayBuffer(gl, vertices, 3, gl.FLOAT, 'a_Position')) {
            return -1;
        }
        if (!initArrayBuffer(gl, colors, 3, gl.FLOAT, 'a_Color')) {
            return -1;
        }

        var indexBuffer = gl.createBuffer();
        if (!indexBuffer) {
            console.log('Failed to create index buffer');
            return -1;
        }
        gl.bindBuffer(gl.ELEMENT_ARRAY_BUFFER, indexBuffer);
        gl.bufferData(gl.ELEMENT_ARRAY_BUFFER, indices, gl.STATIC_DRAW);

        return indices.length;
    }

    function initArrayBuffer(gl, data, numOfComponents, dataType, attributeName) {
        var buffer = gl.createBuffer();
        if (!buffer) {
            console.log('Failed to create buffer object');
            return false;
        }

        gl.bindBuffer(gl.ARRAY_BUFFER, buffer);
        gl.bufferData(gl.ARRAY_BUFFER, data, gl.STATIC_DRAW);

        var attribute = gl.getAttribLocation(gl.program, attributeName);
        gl.vertexAttribPointer(attribute, numOfComponents, dataType, false, 0, 0);
        gl.enableVertexAttribArray(attribute);

        return true;
    }
</script>

查看源码