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Created November 25, 2020 14:40
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<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="utf-8"/>
<title>Translate a Triangle</title>
<body onload="main()">
<canvas id="webgl" width="300" height="300" style="position: absolute">
Please use a browser that supports "canvas"
</canvas>
<div>
<h1>19</h1>
<h2>Great Designs Come from Great Designers --- Not from Great Design Processes</h2>
<p>The basic premise underlying the SEI's [Software
Engineering Institute] work on software process maturity
is that the quality of a software product is largely
determined by the quality of the software development
and maintenance processes used to build it.</p>
Mark Paulk [1995], "The evolution of the SEI's capability maturity model for software"
<p>...[W]hile some may see them as the crazy ones, we see
genius, because the ones who are crazy enough to think
that they can change the world, are the ones who do.</p>
Steve Jobs, Apple commercial (1997)
</div>
</body>
<script src="https://rawgit.com/huningxin/webglbook_examples/master/lib/webgl-utils.js"></script>
<script src="https://rawgit.com/huningxin/webglbook_examples/master/lib/webgl-debug.js"></script>
<script src="https://rawgit.com/huningxin/webglbook_examples/master/lib/cuon-utils.js"></script>
<script src="https://rawgit.com/huningxin/webglbook_examples/master/lib/cuon-matrix.js"></script>
<script type="text/javascript">
// 3DoverWeb.js (c) 2012 matsuda
// Vertex shader program
var VSHADER_SOURCE =
'attribute vec4 a_Position;\n' +
'attribute vec4 a_Color;\n' +
'uniform mat4 u_MvpMatrix;\n' +
'uniform bool u_Clicked;\n' + // Mouse is pressed
'varying vec4 v_Color;\n' +
'void main() {\n' +
' gl_Position = u_MvpMatrix * a_Position;\n' +
' if (u_Clicked) {\n' + // Draw in red if mouse is pressed
' v_Color = vec4(1.0, 0.0, 0.0, 1.0);\n' +
' } else {\n' +
' v_Color = vec4(a_Color.rgb, 1.0);\n' +
' }\n' +
'}\n';
// Fragment shader program
var FSHADER_SOURCE =
'#ifdef GL_ES\n' +
'precision mediump float;\n' +
'#endif\n' +
'varying vec4 v_Color;\n' +
'void main() {\n' +
' gl_FragColor = v_Color;\n' +
'}\n';
var ANGLE_STEP = 20.0; // Rotation angle (degrees/second)
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;
}
// Initialize shaders
if (!initShaders(gl, VSHADER_SOURCE, FSHADER_SOURCE)) {
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 and enable the depth test
gl.clearColor(0.0, 0.0, 0.0, 0.0);
gl.enable(gl.DEPTH_TEST);
// Get the storage locations of uniform variables
var u_MvpMatrix = gl.getUniformLocation(gl.program, 'u_MvpMatrix');
var u_Clicked = gl.getUniformLocation(gl.program, 'u_Clicked');
if (!u_MvpMatrix || !u_Clicked) {
console.log('Failed to get the storage location');
return;
}
// Calculate the view projection matrix
var viewProjMatrix = new Matrix4();
viewProjMatrix.setPerspective(30.0, canvas.width / canvas.height, 1.0, 100.0);
viewProjMatrix.lookAt(0.0, 0.0, 7.0, 0.0, 0.0, 0.0, 0.0, 1.0, 0.0);
gl.uniform1i(u_Clicked, 0); // Pass false to u_Clicked
var currentAngle = 0.0; // Current rotation angle
// Register the event handler
canvas.onmousedown = function(ev) { // Mouse is pressed
var x = ev.clientX, y = ev.clientY;
var rect = ev.target.getBoundingClientRect();
if (rect.left <= x && x < rect.right && rect.top <= y && y < rect.bottom) {
// If pressed position is inside <canvas>, check if it is above object
var x_in_canvas = x - rect.left, y_in_canvas = rect.bottom - y;
check(gl, n, x_in_canvas, y_in_canvas, currentAngle, u_Clicked, viewProjMatrix, u_MvpMatrix);
}
}
var tick = function() { // Start drawing
currentAngle = animate(currentAngle);
draw(gl, n, currentAngle, viewProjMatrix, u_MvpMatrix);
requestAnimationFrame(tick, canvas);
};
tick();
}
function initVertexBuffers(gl) {
// Create a cube
// v6----- v5
// /| /|
// v1------v0|
// | | | |
// | |v7---|-|v4
// |/ |/
// v2------v3
var vertices = new Float32Array([ // Vertex coordinates
1.0, 1.0, 1.0, -1.0, 1.0, 1.0, -1.0,-1.0, 1.0, 1.0,-1.0, 1.0, // v0-v1-v2-v3 front
1.0, 1.0, 1.0, 1.0,-1.0, 1.0, 1.0,-1.0,-1.0, 1.0, 1.0,-1.0, // v0-v3-v4-v5 right
1.0, 1.0, 1.0, 1.0, 1.0,-1.0, -1.0, 1.0,-1.0, -1.0, 1.0, 1.0, // v0-v5-v6-v1 up
-1.0, 1.0, 1.0, -1.0, 1.0,-1.0, -1.0,-1.0,-1.0, -1.0,-1.0, 1.0, // v1-v6-v7-v2 left
-1.0,-1.0,-1.0, 1.0,-1.0,-1.0, 1.0,-1.0, 1.0, -1.0,-1.0, 1.0, // v7-v4-v3-v2 down
1.0,-1.0,-1.0, -1.0,-1.0,-1.0, -1.0, 1.0,-1.0, 1.0, 1.0,-1.0 // v4-v7-v6-v5 back
]);
var colors = new Float32Array([ // Colors
0.2, 0.58, 0.82, 0.2, 0.58, 0.82, 0.2, 0.58, 0.82, 0.2, 0.58, 0.82, // v0-v1-v2-v3 front
0.5, 0.41, 0.69, 0.5, 0.41, 0.69, 0.5, 0.41, 0.69, 0.5, 0.41, 0.69, // v0-v3-v4-v5 right
0.0, 0.32, 0.61, 0.0, 0.32, 0.61, 0.0, 0.32, 0.61, 0.0, 0.32, 0.61, // v0-v5-v6-v1 up
0.78, 0.69, 0.84, 0.78, 0.69, 0.84, 0.78, 0.69, 0.84, 0.78, 0.69, 0.84, // v1-v6-v7-v2 left
0.32, 0.18, 0.56, 0.32, 0.18, 0.56, 0.32, 0.18, 0.56, 0.32, 0.18, 0.56, // v7-v4-v3-v2 down
0.73, 0.82, 0.93, 0.73, 0.82, 0.93, 0.73, 0.82, 0.93, 0.73, 0.82, 0.93, // v4-v7-v6-v5 back
]);
// Indices of the vertices
var indices = new Uint8Array([
0, 1, 2, 0, 2, 3, // front
4, 5, 6, 4, 6, 7, // right
8, 9,10, 8,10,11, // up
12,13,14, 12,14,15, // left
16,17,18, 16,18,19, // down
20,21,22, 20,22,23 // back
]);
// Write the vertex property to buffers (coordinates and normals)
if (!initArrayBuffer(gl, vertices, gl.FLOAT, 3, 'a_Position')) return -1; // Coordinates
if (!initArrayBuffer(gl, colors, gl.FLOAT, 3, 'a_Color')) return -1; // Color Information
// Create a buffer object
var indexBuffer = gl.createBuffer();
if (!indexBuffer) {
return -1;
}
// Write the indices to the buffer object
gl.bindBuffer(gl.ELEMENT_ARRAY_BUFFER, indexBuffer);
gl.bufferData(gl.ELEMENT_ARRAY_BUFFER, indices, gl.STATIC_DRAW);
return indices.length;
}
function check(gl, n, x, y, currentAngle, u_Clicked, viewProjMatrix, u_MvpMatrix) {
var picked = false;
gl.uniform1i(u_Clicked, 1); // Pass true to u_Clicked(Draw cube with red)
draw(gl, n, currentAngle, viewProjMatrix, u_MvpMatrix);
// Read pixel at the clicked position
var pixels = new Uint8Array(4); // Array for storing the pixel value
gl.readPixels(x, y, 1, 1, gl.RGBA, gl.UNSIGNED_BYTE, pixels);
if (pixels[0] == 255) // If red = 255, clicked on cube
picked = true;
gl.uniform1i(u_Clicked, 0); // Pass false to u_Clicked(Draw cube with specified color)
draw(gl, n, currentAngle, viewProjMatrix, u_MvpMatrix);
if (picked) alert('The cube was selected! ');
}
var g_MvpMatrix = new Matrix4(); // Model view projection matrix
function draw(gl, n, currentAngle, viewProjMatrix, u_MvpMatrix) {
// Caliculate The model view projection matrix and pass it to u_MvpMatrix
g_MvpMatrix.set(viewProjMatrix);
g_MvpMatrix.rotate(currentAngle, 1.0, 0.0, 0.0); // Rotate appropriately
g_MvpMatrix.rotate(currentAngle, 0.0, 1.0, 0.0);
g_MvpMatrix.rotate(currentAngle, 0.0, 0.0, 1.0);
gl.uniformMatrix4fv(u_MvpMatrix, false, g_MvpMatrix.elements);
gl.clear(gl.COLOR_BUFFER_BIT | gl.DEPTH_BUFFER_BIT); // Clear buffers (color and depth)
gl.drawElements(gl.TRIANGLES, n, gl.UNSIGNED_BYTE, 0); // Draw
}
var last = Date.now(); // Last time that this function was called
function animate(angle) {
var now = Date.now(); // Calculate the elapsed time
var elapsed = now - last;
last = now;
// Update the current rotation angle (adjusted by the elapsed time)
var newAngle = angle + (ANGLE_STEP * elapsed) / 1000.0;
return newAngle % 360;
}
function initArrayBuffer (gl, data, type, num, attribute) {
// Create a buffer object
var buffer = gl.createBuffer();
if (!buffer) {
console.log('Failed to create the buffer object');
return false;
}
// Write date into the buffer object
gl.bindBuffer(gl.ARRAY_BUFFER, buffer);
gl.bufferData(gl.ARRAY_BUFFER, data, gl.STATIC_DRAW);
// Assign the buffer object to the attribute variable
var a_attribute = gl.getAttribLocation(gl.program, attribute);
if (a_attribute < 0) {
console.log('Failed to get the storage location of ' + attribute);
return false;
}
gl.vertexAttribPointer(a_attribute, num, type, false, 0, 0);
// Enable the assignment of the buffer object to the attribute variable
gl.enableVertexAttribArray(a_attribute);
// Unbind the buffer object
gl.bindBuffer(gl.ARRAY_BUFFER, null);
return true;
}
</script>
</head>
</html>
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