[英]Rotate an objects coordinates around a center point
编辑:工作jsfiddle: https://jsfiddle.net/Harry999/xy9uq7ed/56/
我正在制作 HTML canvas 游戏。
https://jsfiddle.net/Harry999/xy9uq7ed/53/
我的目标是围绕一个中心点旋转多个形状。
形状的 x 和 y 坐标必须随着形状的旋转而改变,以进行碰撞检测。
如何使形状围绕中心点旋转? (中心X,中心Y)
如何设置形状旋转的速度? (速度)
如何从形状旋转的中心点设置半径? (半径)
var rotationAmount = 10;
var rect = new rectangle(20, 20, 200, 200, 10, 2);
var gameArea = {
canvas: document.createElement("canvas"),
create: function() {
this.canvas.width = 400;
this.canvas.height = 400;
this.context = this.canvas.getContext("2d");
document.body.insertBefore(this.canvas, document.body.childNodes[0]);
},
start: function() {
this.interval = setInterval(redraw, 20);
},
clear: function() {
this.context.clearRect(0, 0, this.canvas.width, this.canvas.height);
}
}
// runs every 20ms
function redraw() {
gameArea.clear();
rect.update();
}
function rectangle(width, height, x, y, radius, speed) {
this.gamearea = gameArea;
this.width = width;
this.height = height;
this.x = x;
this.y = y;
this.radians = Math.PI;
// I want these to be the center points of the rotation
this.centerX = x;
this.centerY = y;
// I want this to be the distance at which the rect rotates from the center
this.radius = radius;
// I want this to be the speed at which the rect rotates
this.speed = speed;
this.update = function() {
// iterate rotation amount through 10 - 360 degrees
if (rotationAmount < 360) {
rotationAmount += 10;
} else {
rotationAmount = 10;
}
// update radians
this.radians = rotationAmount * (Math.PI / 180);
// adjust x and y coordinates
this.x = this.x + this.width * Math.sin(this.radians);
this.y = this.y + this.width * Math.cos(this.radians);
// draw rectangle
gameArea.context.fillStyle = "red";
gameArea.context.fillRect(this.x-this.width/2, this.y-this.height/2, this.width, this.height);
// draw center point
gameArea.context.fillStyle = "black";
gameArea.context.fillRect(this.centerX-2, this.centerY-2, 4, 4);
}
}
// run game
gameArea.create();
gameArea.start();
class Point
{
constructor(x, y, pos=false)
{
if(pos==false)
{
this.pos=[x, y];
}
else
{
this.pos=pos;
}
}
rotate(angle, cx, cy)
{
angle=angle*3.14/180;
let newX = Math.cos(angle)*this.pos[0]-Math.sin(angle)*this.pos[1]+cx;
let newY = Math.sin(angle)*this.pos[0]+Math.cos(angle)*this.pos[1]+cy;
this.pos=[newX, newY];
}
size(x, y)
{
this.pos=[this.pos[0]*x, this.pos[1]*y];
}
draw(x, y)
{
window.ctx.fillRect(this.pos[0]+x, this.pos[1]+y, 1, 1);
}
}```
cx, cy - point of rotating
more angle you use - faster it rotates
distance from point to center is radius, if you want to make it lower than just edit coords
我想到了。 工作示例jsfiddle:
https://jsfiddle.net/Harry999/xy9uq7ed/56/
var rect = new rectangle(20, 20, 200, 200, 40, 10);
var rect2 = new rectangle(20, 20, 200, 200, 10, 20);
var gameArea = {
canvas: document.createElement("canvas"),
create: function() {
this.canvas.width = 400;
this.canvas.height = 400;
this.context = this.canvas.getContext("2d");
document.body.insertBefore(this.canvas, document.body.childNodes[0]);
},
// start interval that redraws canvas once every 20 ms
start: function() {
this.interval = setInterval(redraw, 20);
},
clear: function() {
this.context.clearRect(0, 0, this.canvas.width, this.canvas.height);
}
}
// runs every 20ms
function redraw() {
gameArea.clear();
rect.update();
rect2.update();
}
function rectangle(width, height, centerX, centerY, radius, speed) {
this.gamearea = gameArea;
this.width = width;
this.height = height;
// Center points of the rotation
this.centerX = centerX;
this.centerY = centerY;
// The distance at which the rect rotates from the center
this.radius = radius;
// The coordinates of the shape
this.x = this.centerX + this.radius;
this.y = this.centerY + this.radius;
// The speed at which the shape rotates
this.speed = speed;
// this.angle is calculated in radians
this.angle = this.speed * (Math.PI / 180);
this.update = function() {
// adjust x and y coordinates
var x2 = this.centerX + (this.x - this.centerX) * Math.cos(this.angle) - (this.y - this.centerY) * Math.sin(this.angle);
var y2 = this.centerY + (this.x - this.centerX) * Math.sin(this.angle) + (this.y - this.centerY) * Math.cos(this.angle);
// update x and y coordinates
this.x = x2;
this.y = y2;
// draw rectangle
gameArea.context.fillStyle = "red";
gameArea.context.fillRect(this.x - this.width / 2, this.y - this.height / 2, this.width, this.height);
// draw center point
gameArea.context.fillStyle = "black";
gameArea.context.fillRect(this.centerX - 2, this.centerY - 2, 4, 4);
}
}
// run game
gameArea.create();
gameArea.start();
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