WebGL 1.0. Drawing multiple lines using gl.LINES

by Ivan Enzhaev

HTML

<canvas id="renderCanvas" width="250" height="250"></canvas>

CSS

#renderCanvas {
    border: 5px solid #41af66;
}

JavaScript

var vertexShaderSource =
    `
    attribute vec2 a_Position;

    void main()
    {
        gl_Position = vec4(a_Position, 0.0, 1.0);
    }`;

var fragmentShaderSource =
    `
    void main()
    {
        gl_FragColor = vec4(0.411, 0.372, 0.670, 1.0);
    }`;

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

var vShader = gl.createShader(gl.VERTEX_SHADER);
gl.shaderSource(vShader, vertexShaderSource);
gl.compileShader(vShader);

var fShader = gl.createShader(gl.FRAGMENT_SHADER);
gl.shaderSource(fShader, fragmentShaderSource);
gl.compileShader(fShader);

var program = gl.createProgram();
gl.attachShader(program, vShader);
gl.attachShader(program, fShader);
gl.linkProgram(program);
gl.useProgram(program);

var vertices = new Float32Array([
    -0.9, 0.3, 0.9, 0.3,
    -0.9, -0.3, 0.9, -0.3,
    -0.3, 0.9, -0.3, -0.9,
    0.3, 0.9, 0.3, -0.9
]);

var vbo = gl.createBuffer();
gl.bindBuffer(gl.ARRAY_BUFFER, vbo);
gl.bufferData(gl.ARRAY_BUFFER, vertices, gl.STATIC_DRAW);

var a_Position = gl.getAttribLocation(program, "a_Position");
gl.vertexAttribPointer(a_Position, 2, gl.FLOAT, false, 0, 0);
gl.enableVertexAttribArray(a_Position);

gl.clearColor(0.925, 0.952, 0.905, 1.0);
gl.clear(gl.COLOR_BUFFER_BIT);

gl.drawArrays(gl.LINES, 0, 8);