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draft2.html
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<!doctype>
<html>
<head>
<style>
body{
margin:0;
background: #eee;
}
#canvas{
width:640px;
height:360px;
background: #fff;
}
</style>
</head>
<body>
<canvas id="canvas" width="640" height="360"></canvas>
</body>
</html>
<script>
// Find intersection of RAY & SEGMENT
function getIntersection(ray,segment){
// RAY in parametric: Point + Delta*T1
var r_px = ray.a.x;
var r_py = ray.a.y;
var r_dx = ray.b.x-ray.a.x;
var r_dy = ray.b.y-ray.a.y;
// SEGMENT in parametric: Point + Delta*T2
var s_px = segment.a.x;
var s_py = segment.a.y;
var s_dx = segment.b.x-segment.a.x;
var s_dy = segment.b.y-segment.a.y;
// Are they parallel? If so, no intersect
var r_mag = Math.sqrt(r_dx*r_dx+r_dy*r_dy);
var s_mag = Math.sqrt(s_dx*s_dx+s_dy*s_dy);
if(r_dx/r_mag==s_dx/s_mag && r_dy/r_mag==s_dy/s_mag){
// Unit vectors are the same.
return null;
}
// SOLVE FOR T1 & T2
// r_px+r_dx*T1 = s_px+s_dx*T2 && r_py+r_dy*T1 = s_py+s_dy*T2
// ==> T1 = (s_px+s_dx*T2-r_px)/r_dx = (s_py+s_dy*T2-r_py)/r_dy
// ==> s_px*r_dy + s_dx*T2*r_dy - r_px*r_dy = s_py*r_dx + s_dy*T2*r_dx - r_py*r_dx
// ==> T2 = (r_dx*(s_py-r_py) + r_dy*(r_px-s_px))/(s_dx*r_dy - s_dy*r_dx)
var T2 = (r_dx*(s_py-r_py) + r_dy*(r_px-s_px))/(s_dx*r_dy - s_dy*r_dx);
var T1 = (s_px+s_dx*T2-r_px)/r_dx;
// Must be within parametic whatevers for RAY/SEGMENT
if(T1<0) return null;
if(T2<0 || T2>1) return null;
// Return the POINT OF INTERSECTION
return {
x: r_px+r_dx*T1,
y: r_py+r_dy*T1,
param: T1
};
}
///////////////////////////////////////////////////////
// DRAWING
var canvas = document.getElementById("canvas");
var ctx = canvas.getContext("2d");
function draw(){
// Clear canvas
ctx.clearRect(0,0,canvas.width,canvas.height);
// Draw segments
ctx.strokeStyle = "#999";
for(var i=0;i<segments.length;i++){
var seg = segments[i];
ctx.beginPath();
ctx.moveTo(seg.a.x,seg.a.y);
ctx.lineTo(seg.b.x,seg.b.y);
ctx.stroke();
}
// 50 RAYS IN ALL DIRECTIONS
var intersects = [];
for(var angle=0;angle<Math.PI*2;angle+=(Math.PI*2)/50){
// Calculate dx & dy from angle
var dx = Math.cos(angle);
var dy = Math.sin(angle);
// Ray from center of screen to mouse
var ray = {
a:{x:Mouse.x,y:Mouse.y},
b:{x:Mouse.x+dx,y:Mouse.y+dy}
};
// Find CLOSEST intersection
var closestIntersect = null;
for(var i=0;i<segments.length;i++){
var intersect = getIntersection(ray,segments[i]);
if(!intersect) continue;
if(!closestIntersect || intersect.param<closestIntersect.param){
closestIntersect=intersect;
}
}
// Add to list of intersects
intersects.push(closestIntersect);
}
// DRAW ALL RAYS
ctx.strokeStyle = "#dd3838";
ctx.fillStyle = "#dd3838";
for(var i=0;i<intersects.length;i++){
var intersect = intersects[i];
// Draw red laser
ctx.beginPath();
ctx.moveTo(Mouse.x,Mouse.y);
ctx.lineTo(intersect.x,intersect.y);
ctx.stroke();
// Draw red dot
ctx.beginPath();
ctx.arc(intersect.x, intersect.y, 4, 0, 2*Math.PI, false);
ctx.fill();
}
}
// LINE SEGMENTS
var segments = [
// Border
{a:{x:0,y:0}, b:{x:640,y:0}},
{a:{x:640,y:0}, b:{x:640,y:360}},
{a:{x:640,y:360}, b:{x:0,y:360}},
{a:{x:0,y:360}, b:{x:0,y:0}},
// Polygon #1
{a:{x:100,y:150}, b:{x:120,y:50}},
{a:{x:120,y:50}, b:{x:200,y:80}},
{a:{x:200,y:80}, b:{x:140,y:210}},
{a:{x:140,y:210}, b:{x:100,y:150}},
// Polygon #2
{a:{x:100,y:200}, b:{x:120,y:250}},
{a:{x:120,y:250}, b:{x:60,y:300}},
{a:{x:60,y:300}, b:{x:100,y:200}},
// Polygon #3
{a:{x:200,y:260}, b:{x:220,y:150}},
{a:{x:220,y:150}, b:{x:300,y:200}},
{a:{x:300,y:200}, b:{x:350,y:320}},
{a:{x:350,y:320}, b:{x:200,y:260}},
// Polygon #4
{a:{x:340,y:60}, b:{x:360,y:40}},
{a:{x:360,y:40}, b:{x:370,y:70}},
{a:{x:370,y:70}, b:{x:340,y:60}},
// Polygon #5
{a:{x:450,y:190}, b:{x:560,y:170}},
{a:{x:560,y:170}, b:{x:540,y:270}},
{a:{x:540,y:270}, b:{x:430,y:290}},
{a:{x:430,y:290}, b:{x:450,y:190}},
// Polygon #6
{a:{x:400,y:95}, b:{x:580,y:50}},
{a:{x:580,y:50}, b:{x:480,y:150}},
{a:{x:480,y:150}, b:{x:400,y:95}}
];
// DRAW LOOP
window.requestAnimationFrame = window.requestAnimationFrame || window.webkitRequestAnimationFrame || window.mozRequestAnimationFrame || window.msRequestAnimationFrame;
var updateCanvas = true;
function drawLoop(){
requestAnimationFrame(drawLoop);
if(updateCanvas){
draw();
updateCanvas = false;
}
}
window.onload = function(){
drawLoop();
};
// MOUSE
var Mouse = {
x: canvas.width/2,
y: canvas.height/2
};
canvas.onmousemove = function(event){
Mouse.x = event.clientX;
Mouse.y = event.clientY;
updateCanvas = true;
};
</script>