webgl-tutorial/webgl_7_draw_triangles.html at master · Paweled/webgl-tutorial · GitHub

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="utf-8"/>
    <title>draw triangles</title>
</head>
<body>

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

<script>
    // vertex shader
    var VERTEX_SHADER_SOURCE =
            'attribute vec4 a_Position;\n' +
            'attribute vec4 a_Color;\n' +
            'varying vec4 v_Color;\n' +

            'void main() {\n' +
            '   gl_Position = a_Position;\n' +
            '   gl_PointSize = 10.0;\n' +
            '   v_Color = a_Color;\n' +
            '}\n';

    // fragment shader
    var FRAGMENT_SHADER_SOURCE =
            'precision mediump float;\n' +
            'varying vec4 v_Color;\n' +

            'void main() {\n' +
            '   gl_FragColor = v_Color;\n' +
            '}\n';

    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([
        0.0, 0.5, 1.0, 0.0, 0.0, // (x,y) (r,g,b)
        -0.5, -0.5, 0.0, 1.0, 0.0,
        0.5, -0.5, 0.0, 0.0, 1.0
    ]);

    initVertexBuffers(gl, vertices);

    gl.clearColor(0.0, 0.0, 0.0, 1.0);
    gl.clear(gl.COLOR_BUFFER_BIT);
    gl.drawArrays(gl.TRIANGLES, 0, 3);

    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 a_Position = gl.getAttribLocation(gl.program, 'a_Position');
        var a_Color = gl.getAttribLocation(gl.program, 'a_Color');

        var BYTES_PER_ELEMENT = vertices.BYTES_PER_ELEMENT;

        gl.vertexAttribPointer(a_Position, 2, gl.FLOAT, false, 5 * BYTES_PER_ELEMENT, 0);
        gl.enableVertexAttribArray(a_Position);

        gl.vertexAttribPointer(a_Color, 3, gl.FLOAT, false, 5 * BYTES_PER_ELEMENT, 2 * BYTES_PER_ELEMENT);
        gl.enableVertexAttribArray(a_Color);
    }

    function initShaders(gl, vertexShaderSource, fragmentShaderSource) {
        var program = createProgram(gl, vertexShaderSource, fragmentShaderSource);
        if (!program) {
            console.log('Failed to create program');
            return false;
        }

        gl.useProgram(program);
        gl.program = program;

        return true;
    }

    function loadShader(gl, type, source) {
        // create shader object
        var shader = gl.createShader(type);
        if (shader == null) {
            console.log('unable to create shader');
            return null;
        }

        // set shader source code
        gl.shaderSource(shader, source);

        // compile the shader
        gl.compileShader(shader);

        // check compile status
        var compiled = gl.getShaderParameter(shader, gl.COMPILE_STATUS);
        if (!compiled) {
            var error = gl.getShaderInfoLog(shader);
            console.log('Failed to compile shader: ' + error);
            return null;
        }

        return shader;
    }

    function createProgram(gl, vertexShaderSource, fragmentShaderSource) {
        var vertexShader = loadShader(gl, gl.VERTEX_SHADER, vertexShaderSource);
        var fragmentShader = loadShader(gl, gl.FRAGMENT_SHADER, fragmentShaderSource);
        if (!vertexShader || !fragmentShader) {
            return null;
        }

        // create a program object
        var program = gl.createProgram();
        if (!program) {
            console.log('gl.createProgram failed');
            return null;
        }

        // attach  the shader objects
        gl.attachShader(program, vertexShader);
        gl.attachShader(program, fragmentShader);

        // link the program object
        gl.linkProgram(program);

        // check link status
        var linked = gl.getProgramParameter(program, gl.LINK_STATUS);
        if (!linked) {
            var error = gl.getProgramInfoLog(program);
            console.log('Failed to link program: ' + error);
            gl.deleteProgram(program);
            gl.deleteShader(vertexShader);
            gl.deleteShader(fragmentShader);
            return null;
        }

        return program;
    }

</script>
</body>
</html>