gifts/Printf

This is an example from the book "WebGL Programming Guide" by Kouichi Matsuda and Rodger Lea

by Ivan Enzhaev

HTML

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

    <script type="x-shader/x-vertex" id="VertexShader">
        attribute vec4 a_Position;
        attribute vec2 a_TexCoord;
        varying vec2 v_TexCoord;

        void main()
        {
            gl_Position = a_Position;
            v_TexCoord = a_TexCoord;
        }
    </script>

    <script type="x-shader/x-fragment" id="FragmentShader">
        precision mediump float;

        uniform sampler2D u_Sampler;
        varying vec2 v_TexCoord;

        // Get the number at the specified digit
        float getNumber(float value, float digit)
        {
            int thisDigit = int(value / digit);
            int upperDigit = int(thisDigit / 10) * 10;
            return float(thisDigit - upperDigit);
        }

        void main()
        {
            float testValue = 57.2957; // The value to be displayed
        
            vec2 texCoord = v_TexCoord;
        
            if (texCoord.x < (1.0/16.0)) // 10
            {
                if (testValue >= 10.0)
                {
                    float xOffset = mod(texCoord.x, 1.0/16.0);
                    texCoord.x = getNumber(testValue, 10.0) / 16.0 + xOffset;
                }
                else
                {
                    texCoord.x = 12.0/16.0;
                }
            }
            else if (texCoord.x < (2.0/16.0)) // 1
            {
                float xOffset = mod(texCoord.x, 1.0/16.0);
                texCoord.x = getNumber(testValue, 1.0) / 16.0 + xOffset;
            }
            else if (texCoord.x < (3.0/16.0)) // Decimal point
            {
                float xOffset = mod(texCoord.x, 1.0/16.0);
                texCoord.x = (10.0/16.0) + xOffset; // Decimal point is located at 10/16
            }
            else if (texCoord.x < (4.0/16.0)) // 0.1
            {
                float xOffset = mod(texCoord.x, 1.0/16.0);
                texCoord.x =...

JavaScript

// Printf.js 2012 (c) itami & matsuda
// This is an example from the book "WebGL Programming Guide"
// by Kouichi Matsuda and Rodger Lea

main();
//window.onload = main;

function main()
{
    // Retrieve <canvas> element
    var canvas = document.getElementById('webgl');

    // Get the rendering context for WebGL
    var gl = getWebGLContext(canvas);
    if (!gl)
    {
        console.log('Failed to get the rendering context for WebGL');
        return;
    }

    // Get shader elements
    var vShaderElement = document.getElementById("VertexShader");
    var fShaderElement = document.getElementById("FragmentShader");
    if (vShaderElement == null)
    {
        console.log("Failed to get the vertex shader element");
        return;
    }
    if (fShaderElement == null)
    {
        console.log("Failed to get the fragment shader element");
        return;
    }

    // Get shader sources
    var vShaderSource = vShaderElement.firstChild.textContent;
    var fShaderSource = fShaderElement.firstChild.textContent;

    // Initialize shaders
    if (!initShaders(gl, vShaderSource, fShaderSource))
    {
        console.log('Failed to intialize shaders.');
        return;
    }

    // Set the vertex information
    var n = initVertexBuffers(gl);
    if (n < 0)
    {
        console.log('Failed to set the vertex information');
        return;
    }

    // Set the clear color
    gl.clearColor(0, 0, 0, 1);

    // Set texture
    if (!initTextures(gl, n))
    {
        console.log('Failed to intialize the texture.');
        return;
    }
}

function initVertexBuffers(gl)
{
    var verticesTexCoords = new Float32Array([
      -0.8, 0.05, 0.0, 1.0,
      -0.8, -0.05, 0.0, 0.0,
       0.8, 0.05, 1.0, 1.0,
       0.8, -0.05, 1.0, 0.0,
    ]);
    var n = 4; // The number of vertices

    // Create a buffer object
    var vertexTexCoordBuffer = gl.createBuffer();
    if (!vertexTexCoordBuffer)
    {
        console.log('Failed to create a buffer object');
       ...