WebGL 1.0. Pass a point coordinate to a shader

by Ivan Enzhaev

HTML

<canvas id="renderCanvas" width="200" height="200" style="border: 1px solid #aaaafa;"></canvas>

JavaScript

var vertexShaderSource =
    `attribute vec2 a_Position;

    void main()
    {
        gl_Position = vec4(a_Position, 0.0, 1.0);
        gl_PointSize = 10.0;
    }`;

var fragmentShaderSource =
    `void main()
    {
        gl_FragColor = vec4(1.0, 0.0, 0.0, 1.0);
    }`;

function main()
{
    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 a_Position = gl.getAttribLocation(program, "a_Position");
    gl.vertexAttrib2f(a_Position, -0.7, 0.2);

    gl.drawArrays(gl.POINTS, 0, 1);
}
main();