WebGL 1.0. Pass vertex colors to a shader program using VBO

by Ivan Enzhaev

HTML

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

CSS

#renderCanvas {
    border: 1px solid #aaaafa;
}

JavaScript

var vertexShaderSource =
    `
    attribute vec2 a_Position;
    attribute vec3 a_Color;
    varying vec3 v_Color;
    
    void main()
    {
        gl_Position = vec4(a_Position, 0.0, 1.0);
        gl_PointSize = 10.0;
        v_Color = a_Color;
    }`;

var fragmentShaderSource =
    `precision mediump float;
    
    varying vec3 v_Color;

    void main()
    {
        gl_FragColor = vec4(v_Color, 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);

gl.clearColor(0.9, 0.9, 1.0, 1.0);
gl.clear(gl.COLOR_BUFFER_BIT);

var verticesAndColors = new Float32Array([
    0.0, 0.7,       // Coordinate
    1.0, 0.0, 0.0,  // Color
    -0.7, -0.7,
    0.0, 1.0, 0.0,
    0.7, -0.7,
    0.0, 0.0, 1.0
]);

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

var FSIZE = verticesAndColors.BYTES_PER_ELEMENT;

var a_Position = gl.getAttribLocation(program, "a_Position");
gl.vertexAttribPointer(a_Position, 2, gl.FLOAT, false, FSIZE * 5, 0);
gl.enableVertexAttribArray(a_Position);

var a_Color = gl.getAttribLocation(program, "a_Color");
gl.vertexAttribPointer(a_Color, 3, gl.FLOAT, false, FSIZE * 5, FSIZE * 2);
gl.enableVertexAttribArray(a_Color);

gl.drawArrays(gl.TRIANGLES, 0, 3);