Hello vertex attributes

This WebGL example demonstrates how to combine shader programming and user interaction by sending user input to the shader using vertex attributes.

Hello World program in GLSL

How to send input to a shader program by saving data in GPU memory.

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

  attribute float position;

  void main() {
    gl_Position = vec4(position, 0.0, 0.0, 1.0);
    gl_PointSize = 64.0;
  }
</script>
<script type="x-shader/x-fragment" id="fragment-shader">
  #version 100
  precision mediump float;
  void main() {
    gl_FragColor = vec4(0.18, 0.54, 0.34, 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);

  document.querySelector("canvas").addEventListener("click", (evt) => {
    const clickXRelativeToCanvas = evt.pageX - evt.target.offsetLeft;
    const clickXinWebGLCoords = 2.0 * (clickXRelativeToCanvas - gl.drawingBufferWidth / 2) / gl.drawingBufferWidth;
    gl.bufferData(
      gl.ARRAY_BUFFER,
      new Float32Array([clickXinWebGLCoords]),
      gl.STATIC_DRAW,
    );
    gl.drawArrays(gl.POINTS, 0, 1);
  }, false);
}

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]), gl.STATIC_DRAW);
  gl.vertexAttribPointer(0, 1, gl.FLOAT, false, 0, 0);
}

window.addEventListener("beforeunload", cleanup, true);
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.