<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<title>01_simple-shape</title>
<style>
.test {
background-color: gray;
}
canvas {
background-color: gray;
width: 100%;
height: 100%;
display: block;
}
</style>
</head>
<body>
<!-- Simple example of shader source code (WebGL Fundamentals) -->
<script id="vertex-simple-shader" type="x-shader/x-vertex">
attribute vec2 a_position;
uniform vec2 u_resolution;
void main() {
// Convert pixel coordinates to a float randing from 0.0 -> 1.0
vec2 zeroToOne = a_position / u_resolution;
// Convert from 0->1 to 0->2
vec2 zeroToTwo = zeroToOne * 2.0;
// Convert from 0->2 to -1.0->1.0
vec2 clipSpace = zeroToTwo - 1.0;
gl_Position = vec4(clipSpace * vec2(1, -1), 0, 1);
}
</script>
<script id="fragment-simple-shader" type="x-shader/x-vertex">
precision mediump float;
uniform vec4 u_color;
void main() {
gl_FragColor = u_color;
}
</script>
<!-- HTML document -->
<p class="test">This is test HTML with some CSS. Logging with JS...<br>The following block is an OpenGL canvas</p>
<canvas id="canvas"></canvas>
<!-- WebGL -->
<script>
function main() {
//
// Boilerplate OpenGL helper functions
function createShader(gl, type, source) {
let shader = gl.createShader(type);
gl.shaderSource(shader, source);
gl.compileShader(shader);
let success = gl.getShaderParameter(shader, gl.COMPILE_STATUS);
if (success) {
return shader;
}
console.log(gl.getShaderInfoLog(shader));
gl.deleteShader(shader);
}
function createProgram(gl, vertexShader, fragmentShader) {
// Add check to automatically compile shaders if Strings are provided
// + Strings should be equal to HTML script id attribute value for vertex and fragment shaders
if (typeof vertexShader == 'string') {
let vertexShaderSource = document.querySelector(vertexShader).text;
vertexShader = createShader(gl, gl.VERTEX_SHADER, vertexShaderSource);
}
if (typeof fragmentShader == 'string') {
let fragmentShaderSource = document.querySelector(fragmentShader).text;
fragmentShader = createShader(gl, gl.FRAGMENT_SHADER, fragmentShaderSource);
}
let program = gl.createProgram();
gl.attachShader(program, vertexShader);
gl.attachShader(program, fragmentShader);
gl.linkProgram(program);
let success = gl.getProgramParameter(program, gl.LINK_STATUS);
if (success) {
return program;
}
console.log(gl.getProgramInfoLog(program));
gl.deleteProgram(program);
}
let canvas = document.querySelector("#canvas");
let gl = canvas.getContext('webgl');
if (!gl) {
console.log("ERROR: Unable to get OpenGL context");
return;
}
else {
console.log("Created OpenGL context on HTML canvas")
}
// Creating shader program and compiling shader source code
let program = createProgram(gl, "#vertex-simple-shader", "#fragment-simple-shader");
// look up where the vertex data needs to go.
let positionAttributeLocation = gl.getAttribLocation(program, "a_position");
// look up uniform locations
let resolutionUniformLocation = gl.getUniformLocation(program, "u_resolution");
let colorUniformLocation = gl.getUniformLocation(program, "u_color");
// Create a buffer to put three 2d clip space points in
let positionBuffer = gl.createBuffer();
// Bind it to ARRAY_BUFFER (think of it as ARRAY_BUFFER = positionBuffer)
gl.bindBuffer(gl.ARRAY_BUFFER, positionBuffer);
// Canvas setup
// Resize canvas to match client size
const width = canvas.clientWidth;
const height = canvas.clientHeight;
canvas.width = width;
canvas.height = height;
gl.viewport(0, 0, gl.canvas.width, gl.canvas.height);
// Clear the canvas
gl.clearColor(0, 0, 0, 0);
gl.clear(gl.COLOR_BUFFER_BIT);
// Tell OpenGL to use our shader program
gl.useProgram(program);
// Enable attribute; Bind gl.ARRAY_BUFFER for use with this attribute
gl.enableVertexAttribArray(positionAttributeLocation);
gl.bindBuffer(gl.ARRAY_BUFFER, positionBuffer);
// Tell the attribute how to get data out of positionBuffer (ARRAY_BUFFER)
let size = 2; // 2 components per iteration (X and Y value for each vertex position)
let type = gl.FLOAT; // Each X and Y value is a 32bit float
let normalize = false; // don't normalize the data
let stride = 0; // 0 = move forward size * sizeof(type) each iteration to get the next position
let offset = 0; // start at the beginning of the buffer
gl.vertexAttribPointer(positionAttributeLocation, size, type, normalize, stride, offset);
// Initialize geometry data for a 2D triangle with 3 vertices
let triangle = new Float32Array([
350, 100,
500, 300,
200, 300,
]);
// Write geometry data to positions array buffer
gl.bufferData(gl.ARRAY_BUFFER, triangle, gl.STATIC_DRAW);
// Set a random color
gl.uniform4f(colorUniformLocation, Math.random(), Math.random(), Math.random(), 1);
// set the resolution
gl.uniform2f(resolutionUniformLocation, gl.canvas.width, gl.canvas.height);
// Draw the triangle with 0 offset and 3 total vertices
gl.drawArrays(gl.TRIANGLES, 0, 3);
}
main();
</script>
</body>
</html>