webgl_19_DepthTest.html

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="utf-8"/>
    <title>Hidden Surface Removal & Depth Test</title>
</head>
<body>

<canvas id="canvas" width="400" height="400">
    Please use a browser that supports "canvas"
</canvas>

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

    void main() {
        gl_Position = u_ProjMatrix * u_ViewMatrix * 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 vertices = new Float32Array([
        // Three triangles on the right side
        0.75, 1.0, 0.0, 0.4, 0.4, 1.0,  // 前面的蓝色三角形
        0.25, -1.0, 0.0, 0.4, 0.4, 1.0,
        1.25, -1.0, 0.0, 1.0, 0.4, 0.4,

        0.75, 1.0, -2.0, 1.0, 1.0, 0.4, // 中间的黄色三角形
        0.25, -1.0, -2.0, 1.0, 1.0, 0.4,
        1.25, -1.0, -2.0, 1.0, 0.4, 0.4,

        0.75, 1.0, -4.0, 0.4, 1.0, 0.4, // 后面的绿色三角形
        0.25, -1.0, -4.0, 0.4, 1.0, 0.4,
        1.25, -1.0, -4.0, 1.0, 0.4, 0.4,

        // Three triangles on the left side
        -0.75, 1.0, 0.0, 0.4, 0.4, 1.0,  // 前面的蓝色三角形
        -1.25, -1.0, 0.0, 0.4, 0.4, 1.0,
        -0.25, -1.0, 0.0, 1.0, 0.4, 0.4,

        -0.75, 1.0, -2.0, 1.0, 1.0, 0.4, // 中间的黄色三角形
        -1.25, -1.0, -2.0, 1.0, 1.0, 0.4,
        -0.25, -1.0, -2.0, 1.0, 0.4, 0.4,

        -0.75, 1.0, -4.0, 0.4, 1.0, 0.4, // 后面的绿色三角形
        -1.25, -1.0, -4.0, 0.4, 1.0, 0.4,
        -0.25, -1.0, -4.0, 1.0, 0.4, 0.4
    ]);

    initVertexBuffers(gl, vertices);

    var u_ViewMatrix = gl.getUniformLocation(gl.program, 'u_ViewMatrix');
    var u_ProjMatrix = gl.getUniformLocation(gl.program, 'u_ProjMatrix');

    var viewMatrix = new Matrix4();
    viewMatrix.setLookAt(0, 0, 5, 0, 0, -100, 0, 1, 0);

    var projMatrix = new Matrix4();
    projMatrix.setPerspective(30, canvas.width / canvas.height, 1, 100);

    gl.uniformMatrix4fv(u_ViewMatrix, false, viewMatrix.elements);
    gl.uniformMatrix4fv(u_ProjMatrix, false, projMatrix.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.drawArrays(gl.TRIANGLES, 0, 18);

    function initVertexBuffers(gl, vertices) {
        var vertexBuffer = gl.createBuffer();
        if (!vertexBuffer) {
            console.log('Failed to create buffer object');
            return -1;
        }

        gl.bindBuffer(gl.ARRAY_BUFFER, vertexBuffer);
        gl.bufferData(gl.ARRAY_BUFFER, vertices, gl.STATIC_DRAW);

        var FSIZE = vertices.BYTES_PER_ELEMENT;

        var a_Position = gl.getAttribLocation(gl.program, 'a_Position');
        gl.vertexAttribPointer(a_Position, 3, gl.FLOAT, false, 6 * FSIZE, 0);
        gl.enableVertexAttribArray(a_Position);

        var a_Color = gl.getAttribLocation(gl.program, 'a_Color');
        gl.vertexAttribPointer(a_Color, 3, gl.FLOAT, false, 6 * FSIZE, 3 * FSIZE);
        gl.enableVertexAttribArray(a_Color);
    }
</script>
</body>
</html>