Textures from code

This WebGL example provides a simple demonstration of procedural texturing with fragment shaders. That is, using code to generate textures for use in shading WebGL objects.

Drawing textures with code

Texturing a point sprite with calculations done per-pixel in the fragment shader.

<script type="x-shader/x-vertex" id="vertex-shader">
  #version 100
  precision highp float;

  attribute vec2 position;

  void main() {
    gl_Position = vec4(position, 0.0, 1.0);
    gl_PointSize = 128.0;
  }
</script>
<script type="x-shader/x-fragment" id="fragment-shader">
  #version 100
  precision mediump float;
  void main() {
    vec2 fragmentPosition = 2.0*gl_PointCoord - 1.0;
    float distance = length(fragmentPosition);
    float distanceSqrd = distance * distance;
    gl_FragColor = vec4(
      0.2/distanceSqrd,
      0.1/distanceSqrd,
      0.0, 1.0 );
  }
</script>
window.addEventListener("load", setupWebGL, false);

let gl;
let program;

function setupWebGL (evt) {
  window.removeEventListener(evt.type, setupWebGL, false);
  if (!(gl = getRenderingContext())) return;

  let source = document.querySelector("#vertex-shader").innerHTML;
  const vertexShader = gl.createShader(gl.VERTEX_SHADER);
  gl.shaderSource(vertexShader, source);
  gl.compileShader(vertexShader);

  source = document.querySelector("#fragment-shader").innerHTML
  const fragmentShader = gl.createShader(gl.FRAGMENT_SHADER);
  gl.shaderSource(fragmentShader, source);
  gl.compileShader(fragmentShader);

  program = gl.createProgram();
  gl.attachShader(program, vertexShader);
  gl.attachShader(program, fragmentShader);
  gl.linkProgram(program);
  gl.detachShader(program, vertexShader);
  gl.detachShader(program, fragmentShader);
  gl.deleteShader(vertexShader);
  gl.deleteShader(fragmentShader);
  if (!gl.getProgramParameter(program, gl.LINK_STATUS)) {
    const linkErrLog = gl.getProgramInfoLog(program);
    cleanup();
    document.querySelector("p").textContent = `Shader program did not link successfully. Error log: ${linkErrLog}`;
    return;
  }
  initializeAttributes();
  gl.useProgram(program);
  gl.drawArrays(gl.POINTS, 0, 1);
  cleanup();
}

let buffer;
function initializeAttributes() {
  gl.enableVertexAttribArray(0);
  buffer = gl.createBuffer();
  gl.bindBuffer(gl.ARRAY_BUFFER, buffer);
  gl.bufferData(gl.ARRAY_BUFFER, new Float32Array([0.0, 0.0]), gl.STATIC_DRAW);
  gl.vertexAttribPointer(0, 2, gl.FLOAT, false, 0, 0);
}

function cleanup() {
  gl.useProgram(null);
  if (buffer) {
    gl.deleteBuffer(buffer);
  }
  if (program) {
    gl.deleteProgram(program);
  }
}

The source code of this example is also available on GitHub.