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<!-- 代码参考自 《HTML5 核心技术》 -->
<canvas id="canvas" width="600" height="280"></canvas>
* {
margin: 0;
padding: 0;
}
canvas {
border: 1px solid orange;
margin: 20px auto 0;
display: block;
}
// S vector.js
var Vector = function(point) {
if (point === undefined) {
this.x = 0;
this.y = 0;
}
else {
this.x = point.x;
this.y = point.y;
}
}
Vector.prototype = {
// 获取向量大小
getMagnitude: function() {
return Math.sqrt(Math.pow(this.x, 2) + Math.pow(this.y, 2))
},
add: function(vector) {
var v = new Vector()
v.x = this.x + vector.x
v.y = this.y + vector.y
return v
},
subtract: function(vector) {
var v = new Vector()
v.x = this.x - vector.x
v.y = this.y - vector.y
return v
},
dotProduct: function(vector) {
return this.x * vector.x + this.y * vector.y
},
// 由两点生成边
edge: function(vector) {
return this.subtract(vector)
},
// 垂直,即投影轴
perpendicular: function() {
var v = new Vector()
v.x = this.y
v.y = 0 - this.x
return v
},
normalize: function() {
var v = new Vector(0, 0),
m = this.getMagnitude()
if(m !== 0) {
v.x = this.x / m
v.y = this.y /m
}
return v
},
// 投影轴的单位向量
normal: function() {
var p = this.perpendicular()
return p.normalize()
}
}
// E vector.js
// S projection.js
var Projection = function(min, max) {
this.min = min
this.max = max
}
Projection.prototype = {
overlaps: function(projection) {
return this.max > projection.min && projection.max > this.min
}
}
// E projection.js
// S shape.js
var Shape = function() {
this.x = undefined
this.y = undefined
this.strokeStyle = 'rgba(255, 253, 208, 0.9)'
this.fillStyle = 'rgba(147, 147, 147, .8)'
}
Shape.prototype = {
collidesWith: function(shape) {
var axes = this.getAxes().concat(shape.getAxes())
return !this.separationOnAxes(axes, shape)
},
separationOnAxes: function(axes, shape) {
for(var i = 0, len = axes.length; i < len; i++) {
axis = axes[i]
projection1 = shape.project(axis)
projection2 = this.project(axis)
if(!projection1.overlaps(projection2)) {
return true
}
}
return false
},
project: function(axis) {
throw 'project(axis) not implemented'
},
getAxes: function() {
throw 'getAxes() not implemented'
},
move: function(dx, dy) {
throw 'move(dx, dy) not implemented'
},
// Drawing methods................................
createPath: function(context) {
throw 'createPath(context) not implemented'
},
fill: function(context) {
context.save()
context.fillStyle = this.fillStyle
this.createPath(context)
context.fill()
context.restore()
},
stroke: function(context) {
context.save()
context.strokeStyle = this.strokeStyle
this.createPath(context)
context.stroke()
context.restore()
},
isPointInPath: function(context, x, y) {
this.createPath(context)
return context.isPointInPath(x, y)
}
}
// E shape.js
// S polygon.js
var Point = function(x, y) {
this.x = x
this.y = y
}
var Polygon = function() {
this.points = []
this.strokeStyle = 'blue'
this.fillStyle = 'white'
}
Polygon.prototype = new Shape()
Polygon.prototype.getAxes = function() {
var v1 = new Vector(),
v2 = new Vector(),
axes = []
for(var i = 0, len = this.points.length - 1; i < len; i++) {
v1.x = this.points[i].x
v1.y = this.points[i].y
v2.x = this.points[i + 1].x
v2.y = this.points[i + 1].y
axes.push(v1.edge(v2).normal())
}
v1.x = this.points[this.points.length - 1].x
v1.y = this.points[this.points.length - 1].y
v2.x = this.points[0].x
v2.y = this.points[0].y
axes.push(v1.edge(v2).normal())
return axes
}
Polygon.prototype.project = function(axis) {
var scalars = [],
v = new Vector()
this.points.forEach(function(point) {
v.x = point.x
v.y = point.y
scalars.push(v.dotProduct(axis))
})
return new Projection(Math.min.apply(Math, scalars),
Math.max.apply(Math, scalars))
}
Polygon.prototype.addPoint = function(x, y) {
this.points.push(new Point(x, y))
}
Polygon.prototype.createPath = function(context) {
if(this.points.length === 0) {
return
}
context.beginPath()
context.moveTo(this.points[0].x,
this.points[0].y)
for(var i = 0, len = this.points.length; i < len; i++) {
context.lineTo(this.points[i].x,
this.points[i].y)
}
context.closePath()
}
Polygon.prototype.move = function(dx, dy) {
for(var i = 0, point, len = this.points.length; i < len; i++) {
point = this.points[i]
point.x += dx
point.y += dy
}
}
Polygon.prototype.collidesWith = function(shape) {
var axes = shape.getAxes()
if(axes === undefined) {
return polygonCollidesWithCircle(this, shape)
} else {
axes = axes.concat(this.getAxes())
return !this.separationOnAxes(axes, shape)
}
}
// E polygon.js
// S circle.js
var Circle = function(x, y, radius) {
this.x = x
this.y = y
this.radius = radius
this.strokeStyle = 'rgba(255, 253, 208, .9)'
this.fillStyle = 'rgba(147, 197, 114, .8)'
}
Circle.prototype = new Shape()
Circle.prototype.collidesWith = function(shape) {
var point, length, min = 10000, v1, v2,
edge, perpendicular, normal,
axes = shape.getAxes(), distance
if(axes === undefined) {
distance = Math.sqrt(Math.pow(shape.x - this.x, 2) +
Math.pow(shape.y - this.y, 2))
return distance < Math.abs(this.radius + shape.radius)
} else {
return polygonCollidesWithCircle(shape, this)
}
}
Circle.prototype.getAxes = function() {
return undefined
}
Circle.prototype.project = function(axis) {
var scalars = [],
point = new Point(this.x, this.y),
dotProduct = new Vector(point).dotProduct(axis)
scalars.push(dotProduct)
scalars.push(dotProduct + this.radius)
scalars.push(dotProduct - this.radius)
return new Projection(Math.min.apply(Math, scalars),
Math.max.apply(Math, scalars))
}
Circle.prototype.move = function(dx, dy) {
this.x += dx
this.y += dy
}
Circle.prototype.createPath = function(context) {
context.beginPath()
context.arc(this.x, this.y, this.radius, 0, Math.PI * 2, false)
}
function getPolygonPointClosestToCircle(polygon, circle) {
var min = 10000,
length, testPoint, closestPoint
for(var i = 0, len = polygon.points.length; i < len; i++) {
testPoint = polygon.points[i]
length = Math.sqrt(Math.pow(testPoint.x - circle.x, 2),
Math.pow(testPoint.y - circle.y, 2))
if(length < min) {
min = length
closestPoint = testPoint
}
}
return closestPoint
}
function polygonCollidesWithCircle(polygon, circle) {
var min = 10000, v1, v2,
edge, perpendicular,
axes = polygon.getAxes(),
closestPoint = getPolygonPointClosestToCircle(polygon, circle)
v1 = new Vector(new Point(circle.x, circle.y))
v2 = new Vector(new Point(closestPoint.x, closestPoint.y))
axes.push(v1.subtract(v2).normalize())
return !polygon.separationOnAxes(axes, circle)
}
// E circle.js
// S index.js
var canvas = document.getElementById('canvas'),
context = canvas.getContext('2d'),
shapes = [],
polygonPoints = [
[ new Point(250, 150), new Point(250, 250),
new Point(350, 250) ],
[ new Point(100, 100), new Point(100, 150),
new Point(150, 150), new Point(150, 100) ],
[ new Point(400, 100), new Point(380, 150),
new Point(500, 150), new Point(520, 100) ]
],
polygonStrokeStyles = [ 'blue', 'yellow', 'red'],
polygonFillStyles = [ 'rgba(255,255,0,0.7)',
'rgba(100,140,230,0.6)',
'rgba(255,255,255,0.8)' ],
circle1 = new Circle(150, 75, 20),
circle2 = new Circle(350, 45, 30),
mousedown = { x: 0, y: 0 },
lastdrag = { x: 0, y: 0 },
shapeBeingDragged = undefined;
// Functions.....................................................
function windowToCanvas(e) {
var x = e.x || e.clientX,
y = e.y || e.clientY,
bbox = canvas.getBoundingClientRect();
return { x: x - bbox.left * (canvas.width / bbox.width),
y: y - bbox.top * (canvas.height / bbox.height)
};
};
function drawShapes() {
shapes.forEach( function (shape) {
shape.stroke(context);
shape.fill(context);
});
}
function detectCollisions() {
var textY = 30,
numShapes = shapes.length,
shape,
i;
if (shapeBeingDragged) {
for(i = 0; i < numShapes; ++i) {
shape = shapes[i];
if (shape !== shapeBeingDragged) {
if (shapeBeingDragged.collidesWith(shape)) {
context.fillStyle = shape.fillStyle;
context.fillText('collision', 20, textY);
textY += 40;
}
}
}
}
}
// Event handlers................................................
canvas.onmousedown = function (e) {
var location = windowToCanvas(e);
shapes.forEach( function (shape) {
if (shape.isPointInPath(context, location.x, location.y)) {
shapeBeingDragged = shape;
mousedown.x = location.x;
mousedown.y = location.y;
lastdrag.x = location.x;
lastdrag.y = location.y;
}
});
}
canvas.onmousemove = function (e) {
var location,
dragVector;
if (shapeBeingDragged !== undefined) {
location = windowToCanvas(e);
dragVector = { x: location.x - lastdrag.x,
y: location.y - lastdrag.y
};
shapeBeingDragged.move(dragVector.x, dragVector.y);
lastdrag.x = location.x;
lastdrag.y = location.y;
context.clearRect(0,0,canvas.width,canvas.height);
drawShapes();
detectCollisions();
}
}
canvas.onmouseup = function (e) {
shapeBeingDragged = undefined;
}
for (var i=0; i < polygonPoints.length; ++i) {
var polygon = new Polygon(),
points = polygonPoints[i];
polygon.strokeStyle = polygonStrokeStyles[i];
polygon.fillStyle = polygonFillStyles[i];
points.forEach( function (point) {
polygon.addPoint(point.x, point.y);
});
shapes.push(polygon);
}
// Initialization................................................
shapes.push(circle1)
shapes.push(circle2)
context.shadowColor = 'rgba(100,140,255,0.5)';
context.shadowBlur = 4;
context.shadowOffsetX = 2;
context.shadowOffsetY = 2;
context.font = '38px Arial';
drawShapes();
context.save();
context.fillStyle = 'cornflowerblue';
context.font = '24px Arial';
context.fillText('拖拽物体', 10, 25);
context.restore();
// E index.js
Also see: Tab Triggers