我尝试使用javascript在画布上创建一个游戏，你可以控制太空飞船并让它进行平移和旋转，使其看起来就像宇宙飞船保持静止而不是旋转。
非常感谢任何帮助。
window.addEventListener("load",eventWindowLoaded, false);
function eventWindowLoaded() {
canvasApp();
}
function canvasSupport() {
return Modernizr.canvas;
}
function canvasApp() {
if (!canvasSupport()) {
return;
}
var theCanvas = document.getElementById("myCanvas");
var height = theCanvas.height; //get the heigth of the canvas
var width = theCanvas.width; //get the width of the canvas
var context = theCanvas.getContext("2d"); //get the context
var then = Date.now();
var bgImage = new Image();
var stars = new Array;
bgImage.onload = function() {
context.translate(width/2,height/2);
main();
}
var rocket = {
xLoc: 0,
yLoc: 0,
score : 0,
damage : 0,
speed : 20,
angle : 0,
rotSpeed : 1,
rotChange: 0,
pointX: 0,
pointY: 0,
setScore : function(newScore){
this.score = newScore;
}
}
function Star(){
var dLoc = 100;
this.xLoc = rocket.pointX+ dLoc - Math.random()*2*dLoc;
this.yLoc = rocket.pointY + dLoc - Math.random()*2*dLoc;
//console.log(rocket.xLoc+" "+rocket.yLoc);
this.draw = function(){
drawStar(this.xLoc,this.yLoc,20,5,.5);
}
}
//var stars = new Array;
var drawStars = function(){
context.fillStyle = "yellow";
if (typeof stars !== 'undefined'){
//console.log("working");
for(var i=0;i< stars.length ;i++){
stars[i].draw();
}
}
}
var getDistance = function(x1,y1,x2,y2){
var distance = Math.sqrt(Math.pow((x2-x1),2)+Math.pow((y2-y1),2));
return distance;
}
var updateStars = function(){
var numStars = 10;
while(stars.length<numStars){
stars[stars.length] = new Star();
}
for(var i=0; i<stars.length; i++){
var tempDist = getDistance(rocket.pointX,rocket.pointY,stars[i].xLoc,stars[i].yLoc);
if(i == 0){
//console.log(tempDist);
}
if(tempDist > 100){
stars[i] = new Star();
}
}
}
function drawRocket(xLoc,yLoc, rWidth, rHeight){
var angle = rocket.angle;
var xVals = [xLoc,xLoc+(rWidth/2),xLoc+(rWidth/2),xLoc-(rWidth/2),xLoc-(rWidth/2),xLoc];
var yVals = [yLoc,yLoc+(rHeight/3),yLoc+rHeight,yLoc+rHeight,yLoc+(rHeight/3),yLoc];
for(var i = 0; i < xVals.length; i++){
xVals[i] -= xLoc;
yVals[i] -= yLoc+rHeight;
if(i == 0){
console.log(yVals[i]);
}
var tempXVal = xVals[i]*Math.cos(angle) - yVals[i]*Math.sin(angle);
var tempYVal = xVals[i]*Math.sin(angle) + yVals[i]*Math.cos(angle);
xVals[i] = tempXVal + xLoc;
yVals[i] = tempYVal+(yLoc+rHeight);
}
rocket.pointX = xVals[0];
rocket.pointY = yVals[0];
//rocket.yLoc = yVals[0];
//next rotate
context.beginPath();
context.moveTo(xVals[0],yVals[0])
for(var i = 1; i < xVals.length; i++){
context.lineTo(xVals[i],yVals[i]);
}
context.closePath();
context.lineWidth = 5;
context.strokeStyle = 'blue';
context.stroke();
}
var world = {
//pixels per second
startTime: Date.now(),
speed: 50,
startX:width/2,
startY:height/2,
originX: 0,
originY: 0,
xDist: 0,
yDist: 0,
rotationSpeed: 20,
angle: 0,
distance: 0,
calcOrigins : function(){
world.originX = -world.distance*Math.sin(world.angle*Math.PI/180);
world.originY = -world.distance*Math.cos(world.angle*Math.PI/180);
}
};
var keysDown = {};
addEventListener("keydown", function (e) {
keysDown[e.keyCode] = true;
}, false);
addEventListener("keyup", function (e) {
delete keysDown[e.keyCode];
}, false);
var update = function(modifier) {
if (37 in keysDown) { // Player holding left
rocket.angle -= rocket.rotSpeed* modifier;
rocket.rotChange = - rocket.rotSpeed* modifier;
//console.log("left");
}
if (39 in keysDown) { // Player holding right
rocket.angle += rocket.rotSpeed* modifier;
rocket.rotChange = rocket.rotSpeed* modifier;
//console.log("right");
}
};
var render = function (modifier) {
context.clearRect(-width*10,-height*10,width*20,height*20);
var dX = (rocket.speed*modifier)*Math.sin(rocket.angle);
var dY = (rocket.speed*modifier)*Math.cos(rocket.angle);
rocket.xLoc += dX;
rocket.yLoc -= dY;
updateStars();
drawStars();
context.translate(-dX,dY);
context.save();
context.translate(-rocket.pointX,-rocket.pointY);
context.translate(rocket.pointX,rocket.pointY);
drawRocket(rocket.xLoc,rocket.yLoc,50,200);
context.fillStyle = "red";
context.fillRect(rocket.pointX,rocket.pointY,15,5);
//context.restore(); // restores the coordinate system back to (0,0)
context.fillStyle = "green";
context.fillRect(0,0,10,10);
context.rotate(rocket.angle);
context.restore();
};
function drawStar(x, y, r, p, m)
{
context.save();
context.beginPath();
context.translate(x, y);
context.moveTo(0,0-r);
for (var i = 0; i < p; i++)
{
context.rotate(Math.PI / p);
context.lineTo(0, 0 - (r*m));
context.rotate(Math.PI / p);
context.lineTo(0, 0 - r);
}
context.fill();
context.restore();
}
// the game loop
function main(){
requestAnimationFrame(main);
var now = Date.now();
var delta = now - then;
update(delta / 1000);
//now = Date.now();
//delta = now - then;
render(delta / 1000);
then = now;
// Request to do this again ASAP
}
var w = window;
var requestAnimationFrame = w.requestAnimationFrame || w.webkitRequestAnimationFrame || w.msRequestAnimationFrame || w.mozRequestAnimationFrame;
//start the game loop
//gameLoop();
//event listenters
bgImage.src = "images/background.jpg";
} //canvasApp()
答案 0 :(得分：1)
如果您需要在画布上旋转某些内容，它将始终围绕原点旋转，或者如果您喜欢x和y轴交叉的位置，则会围绕网格旋转。
您可能会发现 answer here 也很有用
默认情况下，原点位于位图的（0,0）左上角。
因此，为了围绕（x，y）点旋转内容，必须首先将原点转换为该点，然后旋转并最终（通常）平移回原点。现在可以按正常顺序绘制事物，并且它们都将相对于该旋转点旋转绘制：
ctx.translate(rotateCenterX, rotateCenterY);
ctx.rotate(angleInRadians);
ctx.translate(-rotateCenterX, -rotateCenterY);
绝对角度和位置
如果使用绝对角度而不是使用随时间积累的角度，有时更容易跟踪。
translate()，transform()，rotate()等是累积方法;他们添加到以前的转换。我们可以使用setTransform()设置绝对变换（最后两个参数用于翻译）：
ctx.setTransform(1, 0, 0, 1, rotateCenterX, rotateCenterY); // absolute
ctx.rotate(absoluteAngleInRadians);
ctx.translate(-rotateCenterX, -rotateCenterY);
rotateCenterX / Y将表示未转换绘制的船舶位置。此外，绝对变换可以是更好的选择，因为您可以使用绝对角度进行旋转，绘制背景，重置变换，然后在rotateCenterX / Y处在船上绘制：
ctx.setTransform(1, 0, 0, 1, rotateCenterX, rotateCenterY);
ctx.rotate(absoluteAngleInRadians);
ctx.translate(-rotateCenterX, -rotateCenterY);
// update scene/background etc.
ctx.setTransform(1, 0, 0, 1, 0, 0); // reset transforms
ctx.drawImage(ship, rotateCenterX, rotateCenterY);
（根据事物的顺序，你可以用translate()代替第一行，因为稍后会重置变换，例如见demo。）
这使您可以在不需要担心当前变换的情况下移动船只，当需要旋转时，使用船舶的当前位置作为平移和旋转的中心。
最后一点：你用来旋转的角度当然应该是应该表示的反角（即ctx.rotate(-angle);）。
红色“流星”在一个方向（从顶部）下降，但随着船“导航”，它们将相对于我们的顶视角改变方向。相机将固定在船的位置上。
（忽略凌乱的部分 - 它只是用于演示设置，我讨厌滚动条......专注于中心部分:)）
var img = new Image();
img.onload = function() {
var ctx = document.querySelector("canvas").getContext("2d"),
w = 600, h = 400, meteors = [], count = 35, i = 0, x = w * 0.5, y, a = 0, a2 = 0;
ctx.canvas.width = w; ctx.canvas.height = h; ctx.fillStyle = "#555";
while(i++ < count) meteors.push(new Meteor());
(function loop() {
ctx.clearRect(0, 0, w, h);
y = h * 0.5 + 30 + Math.sin((a+=0.01) % Math.PI*2) * 60; // ship's y and origin's y
// translate to center of ship, rotate, translate back, render bg, reset, draw ship
ctx.translate(x, y); // translate to origin
ctx.rotate(Math.sin((a2+=0.005) % Math.PI) - Math.PI*0.25); // rotate some angle
ctx.translate(-x, -y); // translate back
ctx.beginPath(); // render some moving meteors for the demo
for(var i = 0; i < count; i++) meteors[i].update(ctx); ctx.fill();
ctx.setTransform(1, 0, 0, 1, 0, 0); // reset transforms
ctx.drawImage(img, x - 32, y); // draw ship as normal
requestAnimationFrame(loop); // loop animation
})();
};
function Meteor() { // just some moving object..
var size = 5 + 35 * Math.random(), x = Math.random() * 600, y = -200;
this.update = function(ctx) {
ctx.moveTo(x + size, y); ctx.arc(x, y, size, 0, 6.28);
y += size * 0.5; if (y > 600) y = -200;
};
}
img.src = "http://i.imgur.com/67KQykW.png?1";body {background:#333} canvas {background:#000}<canvas></canvas>