我知道在stackoverflow上已经有很多类似的问题,但是,我仍然无法弄清楚如何去做。我想只旋转球纹理。用计时器调用draw:
var canvas;
var ctx;
var width;
var height;
var ready;
var textures;
var loadIndex;
var loadCount;
var keyCodes;
var mouseLoc;
var playerX;
var playerY;
var playerVelocity;
function init() {
canvas = document.getElementById('game');
ctx = canvas.getContext("2d");
width = canvas.width;
height = canvas.height;
textures = [];
loadingCount = 0;
keyCodes = [];
mouseLoc = {};
playerX = 0;
playerY = 0;
playerVelocity = 6;
textures['Background'] = loadTexture('./textures/Background.png');
textures['Ball'] = loadTexture('./textures/Ball.png');
setInterval(function(){
if(loadingCount == 0) {
update();
draw();
}
}, 50);
}
function update(){
if(keyCodes[37])
playerX -= playerVelocity;
if(keyCodes[38])
playerY -= playerVelocity;
if(keyCodes[39])
playerX += playerVelocity;
if(keyCodes[40])
playerY += playerVelocity;
}
function draw() {
//ctx.clearRect(0, 0, width, height);
//ctx.beginPath();
drawBackground();
drawPlayer();
//ctx.closePath();
//ctx.fill();
}
function drawBackground(){
ctx.drawImage(textures['Background'], 0, 0, width, height);
}
function drawPlayer(){
ctx.save();
ctx.rotate(0.17);
ctx.drawImage(textures['Ball'], playerX, playerY, 100, 100);
ctx.restore();
}
function loadTexture(src){
var image = new Image();
image.src = src;
loadingCount++;
image.onload = function(){
loadingCount--;
};
return image;
}
document.onkeydown = function(evt){
keyCodes[evt.keyCode] = true;
evt.returnValue = false;
}
document.onkeyup = function(evt){
keyCodes[evt.keyCode] = false;
}
document.onmousemove = function(evt){
mouseLoc.x = evt.layerX;
mouseLoc.y = evt.layerY;
}
document.onmousedown = function(evt){
mouseLoc.down = true;
}
document.onmouseup = function(evt){
mouseLoc.down = false;
}
init();
答案 0 :(得分:1)
您只需要保存并恢复画布的状态(状态机)
function drawPlayer(){
ctx.save();
ctx.rotate(0.17);
ctx.drawImage(textures['Ball'], playerX, playerY, 100, 100);
ctx.restore();
}
答案 1 :(得分:1)
假设你想让球继续的幻觉旋转,你应该增加每个画框的旋转角度。
如上所述,您的代码会在每帧上为球提供0.17弧度的固定旋转。
var frame = 0;
function drawPlayer() {
ctx.save();
ctx.rotate(0.17 * frame);
...
ctx.restore();
}
function draw() {
++frame;
drawPlayer();
...
}
答案 2 :(得分:1)
您希望使用增量时间来计算旋转距离。也就是说,从最后一帧开始经过的时间。如果您的浏览器打嗝并在这里或那里丢失一个框架,这将使您的旋转更顺畅。
因此,存储每帧的时间,以便您可以在帧之间进行比较,并将旋转速度设置为每秒弧度。