examples/example2.html

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	Copyright 2006 Google Inc.

	Licensed under the Apache License, Version 2.0 (the "License");
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<html>
<head>
	<title>ExplorerCanvas Example 1</title>
	<!--[if IE]><script type="text/javascript" src="../excanvas.js"></script><![endif]-->
	<script type="text/javascript">
		/* -------------------------------------------------------------------- */

		var canvas, ctx;
		var canvasWidth, halfCanvasWidth;
		var canvasHeight, halfCanvasHeight;

		var space;  // 3D Engine
		var scene;  // 3D Scene

		/* -------------------------------------------------------------------- */

		/**
		 * Space is a simple 3D system.
		 *
		 * Y+ = up
		 * Z+ = into screen
		 * X+ = right
		 */
		function Space() {
			this.m = this.createMatrixIdentity();
			this.mStack = [];
		}

		Space.prototype.createMatrixIdentity = function() {
			return [
				[1, 0, 0, 0],
				[0, 1, 0, 0],
				[0, 0, 1, 0],
				[0, 0, 0, 1]
			];
		}

		/**
		 * Multiplies two 4x4 matricies together.
		 */
		Space.prototype.matrixMultiply = function(m1, m2) {
			var result = this.createMatrixIdentity();

			var width = m1[0].length;
			var height = m1.length;

			if (width != m2.length) {
				// error
			}

			for (var x = 0; x < width; x++) {
				for (var y = 0; y < height; y++) {
					var sum = 0;

					for (var z = 0; z < width; z++) {
						sum += m1[y][z] * m2[z][x];
					}

					result[y][x] = sum;
				}
			}

			return result;
		}

		/**
		 * Transforms a coordinate using the current transformation
		 * matrix, then flattens it using the projection matrix.
		 */
		Space.prototype.flatten = function(point) {
			var p = [[point.x, point.y, point.z, 1]];
			var pm = this.matrixMultiply(p, this.m);

			point.tx = pm[0][0];
			point.ty = pm[0][1];
			point.tz = pm[0][2];

			// lazy projection
			point.fx = halfCanvasWidth + (canvasWidth * point.tx / point.tz);
			point.fy = halfCanvasHeight -(canvasWidth * point.ty / point.tz);
		}

		/**
		 * Translate (move) the current transformation matrix
		 */
		Space.prototype.translate = function(x, y, z) {
			var m = [
				[1, 0, 0, 0],
				[0, 1, 0, 0],
				[0, 0, 1, 0],
				[x, y, z, 1]
			];

			this.m = this.matrixMultiply(m, this.m);
		}

		/**
		 * Rotate the current transformation matrix. Rotations are
		 * world-oriented, and occur in y,x,z order.
		 */
		Space.prototype.rotate = function(x, y, z) {
			if (y) {
				var cosY = Math.cos(y);
				var sinY = Math.sin(y);
				var rotY = [
					[cosY, 0, sinY, 0],
					[0, 1, 0, 0],
					[-sinY, 0, cosY, 0],
					[0, 0, 0, 1]
				];

				this.m = this.matrixMultiply(this.m, rotY);
			}

			if (x) {
				var cosX = Math.cos(x);
				var sinX = Math.sin(x);
				var rotX = [
					[1, 0, 0, 0],
					[0, cosX, -sinX, 0],
					[0, sinX, cosX,0],
					[0, 0, 0, 1]
				];
				this.m = this.matrixMultiply(this.m, rotX);
			}

			if (z) {
				var cosZ = Math.cos(z);
				var sinZ = Math.sin(z);
				var rotZ = [
					[cosZ, -sinZ, 0, 0],
					[sinZ, cosZ, 0, 0],
					[0, 0, 1, 0],
					[0, 0, 0, 1]
				];

				this.m = this.matrixMultiply(this.m, rotZ);
			}
		}

		/**
		 * Pushes the current transformation onto the stack
		 */
		Space.prototype.push = function() {
			this.mStack.push(this.m);
			this.m = [
				[this.m[0][0], this.m[0][1], this.m[0][2], this.m[0][3]],
				[this.m[1][0], this.m[1][1], this.m[1][2], this.m[1][3]],
				[this.m[2][0], this.m[2][1], this.m[2][2], this.m[2][3]],
				[this.m[3][0], this.m[3][1], this.m[3][2], this.m[3][3]]
			];
		}

		/**
		 * Pops the end off the transformation stack
		 */
		Space.prototype.pop = function() {
			this.m = this.mStack.pop();
		}

		/* -------------------------------------------------------------------- */

		/**
		 * A 3d coordinate
		 */
		function Point(x, y, z) {
			this.x = x;
			this.y = y;
			this.z = z;

			// Relative to camera coordinates
			this.tx;
			this.ty;
			this.tz;

			// Flattened coordinates
			this.fx;
			this.fy;
		}

		/**
		 * A Shape is made up of polygons
		 */
		function Shape() {
			this.points = [];
			this.polygons = [];
		}

		/**
		 * Draws the shape
		 */
		Shape.prototype.draw = function(drawlist) {
			for (var i = 0; i< this.points.length; i++) {
				space.flatten(this.points[i]);
			}

			for (var i = 0; i< this.polygons.length; i++) {
				var poly = this.polygons[i]; // convenience

				space.flatten(poly.origin);

				// lazy backface culling
				if (poly.normal && this.backface) {
					space.flatten(poly.normal);

					var originDist = Math.pow(poly.origin.tx, 2)
												 + Math.pow(poly.origin.ty, 2)
												 + Math.pow(poly.origin.tz, 2);

					var normalDist = Math.pow(poly.normal.tx, 2)
												 + Math.pow(poly.normal.ty, 2)
												 + Math.pow(poly.normal.tz, 2);

					if(originDist > normalDist) {
						drawlist.push(poly);
					}
				} else {
					drawlist.push(poly);
				}
			}
		}

		/**
		 * A polygon is a connection of points in the shape object. You
		 * should probably try to make them coplanar.
		 */
		function Polygon(points, normal, backface, type, color) {
			this.points = points;

			this.origin = new Point(0, 0, 0);
			for(var i = 0; i < this.points.length; i++) {
				this.origin.x += this.points[i].x;
				this.origin.y += this.points[i].y;
				this.origin.z += this.points[i].z;
			}

			this.origin.x /= this.points.length;
			this.origin.y /= this.points.length;
			this.origin.z /= this.points.length;

			if (normal) {
				this.normal = new Point(this.origin.x + normal.x,
																this.origin.y + normal.y,
																this.origin.z + normal.z);
			} else {
				this.normal = null;
			}

			this.backface = backface;
			this.type = type;
			this.color = color;
		}

		Polygon.SOLID = 0;
		Polygon.WIRE = 1;

		/**
		 * Draws the polygon. Assumes that the points have already been
		 * flattened.
		 */
		Polygon.prototype.draw = function() {
			ctx.beginPath();
			ctx.moveTo(this.points[0].fx, this.points[0].fy);

			for(var i = 0; i < this.points.length; i++) {
				ctx.lineTo(this.points[i].fx, this.points[i].fy);
			}

			ctx.closePath();

			var color = this.color;

			/*
			// Do lighting here
			lightvector = Math.abs(this.normal.x + this.normal.y);
			if(lightvector > 1) {
				lightvector = 1;
			}

			color[0] = (color[0] * lightvector).toString();
			color[1] = (color[1] * lightvector).toString();
			color[2] = (color[2] * lightvector).toString();
			*/

			if (color.length > 3) {
				var style = ["rgba(",
				             color[0], ",",
				             color[1], ",",
				             color[2], ",",
				             color[3], ")"].join("");
			} else {
				var style = ["rgb(",
				             color[0], ",",
				             color[1], ",",
				             color[2], ")"].join("");
			}

			if (this.type == Polygon.SOLID) {
				ctx.fillStyle = style;
				ctx.fill();
			} else if (this.type == Polygon.WIRE) {
				ctx.strokeStyle = style;
				ctx.stroke();
			}
		}

		/* -------------------------------------------------------------------- */

		/**
		 * Scene describes the 3D environment
		 */
		function Scene() {
			this.shapes = {};
			this.camera = new Point(0, 0, 0);
			this.cameraTarget = new Point(0, 0, 0);
			this.cameraRotation = 0;

			this.drawlist = [];
		}

		/**
		 * Draw the world
		 */
		Scene.prototype.draw = function() {
			space.push();

			// Camera transformation
			space.translate(
				-this.camera.x,
				-this.camera.y,
				-this.camera.z
			);

			// Camera rotation
			var xdiff = this.cameraTarget.x - this.camera.x;
			var ydiff = this.cameraTarget.y - this.camera.y;
			var zdiff = this.cameraTarget.z - this.camera.z;

			var xzdist = Math.sqrt(Math.pow(xdiff, 2) + Math.pow(zdiff, 2));

			var xrot = -Math.atan2(ydiff, xzdist); // up/down rotation
			var yrot =  Math.atan2(xdiff, zdiff);  // left/right rotation

			space.rotate(xrot, yrot, this.cameraRotation);

			// Drawing
			this.drawlist = [];

			for(var i in this.shapes) {
				this.shapes[i].draw(this.drawlist);
			}

			// Depth sorting (warning: this is only enough to drive this demo - feel
			// free to contribute a better system).
			this.drawlist.sort(function (poly1, poly2) {
				return poly2.origin.tz - poly1.origin.tz;
			});

			for (var i = 0; i < this.drawlist.length; i++) {
				this.drawlist[i].draw();
			}

			space.pop();
		}

		/* -------------------------------------------------------------------- */

		var count = 0;

		function loop() {
			ctx.clearRect(0, 0, canvasWidth, canvasHeight);

			scene.camera.x = 70*Math.sin(count);
			scene.camera.y = 70;
			scene.camera.z = 70*Math.cos(count);
			scene.cameraRotation = count / 10;

			count += 0.01;
			scene.draw();
		}

		function load() {
			// Init drawing system
			canvas = document.getElementById("cv");
			ctx = canvas.getContext("2d");

			canvasWidth = canvas.width;
			canvasHeight = canvas.height;
			halfCanvasWidth = canvasWidth * 0.5;
			halfCanvasHeight = canvasHeight * 0.5;

			// Init 3D components
			space = new Space();
			scene = new Scene();

			// Create a box shape and add it to the scene
			scene.shapes['box'] = new Shape();
			var p = scene.shapes['box'].points; // for convenience

			p[0] = new Point(-10, -10, -10); // left  bottom front
			p[1] = new Point(10, -10, -10);  // right bottom front
			p[2] = new Point(10, 10, -10);   // right top    front
			p[3] = new Point(-10, 10, -10);  // left  top    front

			p[4] = new Point(-10, -10, 10);  // left  bottom back
			p[5] = new Point(10, -10, 10);   // right bottom back
			p[6] = new Point(10, 10, 10);    // right top    back
			p[7] = new Point(-10, 10, 10);   // left  top    back

			// Back
			scene.shapes['box'].polygons.push(new Polygon(
				[ p[0], p[1], p[2], p[3] ],
				new Point(0, 0, -1),
				true /* double-sided */,
				Polygon.SOLID,
				[255, 0, 0]
			));

			// Front
			scene.shapes['box'].polygons.push(new Polygon(
				[ p[4], p[5], p[6], p[7] ],
				new Point(0, 0, 1),
				true /* double-sided */,
				Polygon.SOLID,
				[0, 0, 255]
			));

			// Top
			scene.shapes['box'].polygons.push(new Polygon(
				[ p[2], p[3], p[7], p[6] ],
				new Point(0, 1, 0),
				false /* single-sided */,
				Polygon.WIRE,
				[0, 255, 0]
			));

			// Transparent Top
			scene.shapes['box'].polygons.push(new Polygon(
				[ p[2], p[3], p[7], p[6] ],
				new Point(0, 1, 0),
				false /* single-sided */,
				Polygon.SOLID,
				[0, 255, 0, 0.4]
			));

			// Left
			scene.shapes['box'].polygons.push(new Polygon(
				[ p[0], p[4], p[7], p[3] ],
				new Point(-1, 0, 0),
				true /* double-sided */,
				Polygon.SOLID,
				[255, 255, 0]
			));

			// Right
			scene.shapes['box'].polygons.push(new Polygon(
				[ p[1], p[5], p[6], p[2] ],
				new Point(1, 0, 0),
				true /* double-sided */,
				Polygon.SOLID,
				[0, 255, 255]
			));

			// Create a floor shape and add it to the scene
			scene.shapes['floor'] = new Shape();
			var p = scene.shapes['floor'].points; // for convenience

			p[0]  = new Point(-40, -10, -40);
			p[1]  = new Point(-40, -10,  40);
			p[2] = new Point( 40, -10,  40);
			p[3] = new Point( 40, -10, -40);

			// Floor
			scene.shapes['floor'].polygons.push(new Polygon(
				[ p[0], p[1], p[2], p[3] ],
				new Point(0, 1, 0),
				false /* single-sided */,
				Polygon.SOLID,
				[45, 45, 45]
			));

			setInterval('loop()', 20);
		}

		/* -------------------------------------------------------------------- */
	</script>
	<style>
	body {
		background-color:black;
		margin:50px;
		text-align:center;
	}
	</style>
</head>
<body onload="load();">
  <canvas id="cv" width="400" height="300"></canvas>
</body>
</html>