GCanvas/node/examples/webgl/glrectangle.js

const { createCanvas, Image } = require('../../export')
const fs = require('fs')
const path = require('path');
const out = fs.createWriteStream(path.join(__dirname, "..","..")+ '/rectangle.png');

const canvas = createCanvas(1200, 700);
var gl = canvas.getContext("webgl");

var vertexSource = `
attribute vec2 a_position;
uniform vec2 u_resolution;
void main() {
    // convert the rectangle from pixels to 0.0 to 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->+1 (clipspace)
    vec2 clipSpace = zeroToTwo - 1.0;
    gl_Position = vec4(clipSpace * vec2(1, -1), 0, 1);
}
`;
var fragmentSource = `
precision mediump float;
uniform vec4 u_color;
void main() {
    gl_FragColor = u_color;
}
`;

// setup program
var vertexShader = gl.createShader(gl.VERTEX_SHADER);
gl.shaderSource(vertexShader, vertexSource);
gl.compileShader(vertexShader);
if (!gl.getShaderParameter(vertexShader, gl.COMPILE_STATUS)) {
    console.log("failed to load shader", " ", gl.getShaderInfoLog(vertexShader));
}
var fragmentShader = gl.createShader(gl.FRAGMENT_SHADER);
gl.shaderSource(fragmentShader, fragmentSource);
gl.compileShader(fragmentShader);
if (!gl.getShaderParameter(fragmentShader, gl.COMPILE_STATUS)) {
    console.log("failed to load shader", " ", gl.getShaderInfoLog(fragmentShader));
}
var program = gl.createProgram();
gl.attachShader(program, vertexShader);
gl.attachShader(program, fragmentShader);
gl.linkProgram(program);

if (!gl.getProgramParameter(program, gl.LINK_STATUS)) {
    console.log("linker failed", " ", gl.getProgramInfoLog(program));
}

// look up where the vertex data needs to go.
var positionAttributeLocation = gl.getAttribLocation(program, "a_position");
// look up uniform locations
var resolutionUniformLocation = gl.getUniformLocation(program, "u_resolution");
var colorUniformLocation = gl.getUniformLocation(program, "u_color");
// Create a buffer to put three 2d clip space points in
var positionBuffer = gl.createBuffer();
// Bind it to ARRAY_BUFFER (think of it as ARRAY_BUFFER = positionBuffer)
gl.bindBuffer(gl.ARRAY_BUFFER, positionBuffer);

// Tell WebGL how to convert from clip space to pixels
gl.viewport(0, 0, canvas.width, canvas.height);
// Clear the canvas
gl.clearColor(0, 0, 0, 0);
gl.clear(gl.COLOR_BUFFER_BIT);
// Tell it to use our program (pair of shaders)
gl.useProgram(program);
// Turn on the attribute
gl.enableVertexAttribArray(positionAttributeLocation);
// Bind the position buffer.
gl.bindBuffer(gl.ARRAY_BUFFER, positionBuffer);
// Tell the attribute how to get data out of positionBuffer (ARRAY_BUFFER)
var size = 2;          // 2 components per iteration
var type = gl.FLOAT;   // the data is 32bit floats
var normalize = false; // don't normalize the data
var stride = 0;        // 0 = move forward size * sizeof(type) each iteration to get the next position
var offset = 0;        // start at the beginning of the buffer
gl.vertexAttribPointer(positionAttributeLocation, size, type, normalize, stride, offset)
// set the resolution
gl.uniform2f(resolutionUniformLocation, gl.canvas.width, gl.canvas.height);
// draw 50 random rectangles in random colors
for (var ii = 0; ii < 50; ++ii) {
    // Setup a random rectangle
    // This will write to positionBuffer because
    // its the last thing we bound on the ARRAY_BUFFER
    // bind point
//    setRectangle(gl, randomInt(300), randomInt(300), randomInt(300), randomInt(300));
    setRectangle(gl, ii%10*100+10, ii/10*100+10, 100, 100);
    // Set a random color.
//    gl.uniform4f(colorUniformLocation, Math.random(), Math.random(), Math.random(), 1);
    gl.uniform4f(colorUniformLocation, (ii/10)*0.1+(ii%10)*0.01, (ii/10)*0.1+(ii%10)*0.2, (ii%10)*0.1, 1);
    // Draw the rectangle.
    var primitiveType = gl.TRIANGLES;
    var offset = 0;
    var count = 6;
    gl.drawArrays(primitiveType, offset, count);
}

// Returns a random integer from 0 to range - 1.
function randomInt(range) {
    return Math.floor(Math.random() * range);
}
// Fill the buffer with the values that define a rectangle.
function setRectangle(gl, x, y, width, height) {
    var x1 = x;
    var x2 = x + width;
    var y1 = y;
    var y2 = y + height;
    gl.bufferData(gl.ARRAY_BUFFER, new Float32Array([
                                                     x1, y1,
                                                     x2, y1,
                                                     x1, y2,
                                                     x1, y2,
                                                     x2, y1,
                                                     x2, y2,
                                                     ]), gl.STATIC_DRAW);
 }


var stream = canvas.createPNGStream();
stream.on('data', function (chunk) {
    out.write(chunk);
});