我想在 HTML5 画布上做一个简单的 javascript 动画。现在我的画布是分层的,所以当我收到鼠标事件时,背景层不会改变,但带有头像的顶层会移动。如果我使用 requestAnimationFrame 并且不清除屏幕,我会看到我漂亮的小玩家在多个帧中在屏幕上移动,角色的尾巴很长。但是,如果我尝试在每个动画帧之后执行 clearRect,那么我的角色永远不会出现,我不确定是什么原因造成的。
我使用这些链接作为我的代码的基础:http:
//www.html5canvastutorials.com/advanced/html5-canvas-start-and-stop-an-animation/
http://paulirish.com/2011/requestanimationframe-智能动画/
http://www.nczonline.net/blog/2011/05/03/better-javascript-animations-with-requestanimationframe/
很多示例都是绘制动画形状,而我使用的是图像,不确定这是否重要以及我是否应该只使用画布变换函数而不是 clearRect,但认为这不应该一个区别。另外,为了可读性,我删除了一堆代码,所以括号可能是关闭的,但代码是正常的,我只是为了可读性而这样做,所以你可以看到一个方向的动画。我的代码看起来像:
// what is this function for? See here - http://stackoverflow.com/questions/10237471/please-explain-this-requestanimationframe-idiom
window.requestAnimFrame = function(callback){
// add in this parentheses - http://stackoverflow.com/questions/5605588/how-to-use- requestanimationframe
return ( window.requestAnimationFrame ||
window.webkitRequestAnimationFrame ||
window.mozRequestAnimationFrame ||
window.oRequestAnimationFrame ||
window.msRequestAnimationFrame ||
function(callback){
window.setTimeout(callback, 1000 / 60);
}
);
}();
function stopAnimatingPlayer(currentAvatarAnimating, destinationCellX, destinationCellY) {
gIsAnimating = false;
//Did this final draw because I wasn't sure if the avatar would end on the exact pixel position, so this should snap him back into place
drawAvatar(currentAvatarAnimating, destinationCellX, destinationCellY, false,0,0);
}
function movePlayer(lastTime, playerPixelX, playerPixelY, destinationCellX, destinationCellY) {
if (gIsAnimating) {
// the canvas is already globally held as gAvatarCanvasElement & gAvatarDrawingContext;
// update
var date = new Date();
var time = date.getTime();
var timeDiff = time - lastTime;
var linearSpeed = 100;
// pixels / second
var linearDistEachFrame = linearSpeed * timeDiff / 1000;
var horizontal = false;
var newX, newY;
// gets the new coordinate of the player
if (gTowerCurrentPlayer == 1) {
//fill in later - just trying to get one horizontal animation working
} else if (destinationCellY == gPlayer1Cell.y) { // we're moving horizontally
var currentX = playerPixelX;
var diffX = destinationCellX - gPlayer1Cell.x;
horizontal = true;
if (diffX > 0) { // player is moving right - just get one direction going for now
if (currentX < getPixelFromRow(destinationCellX)) {
newX = currentX + linearDistEachFrame;
} else {
stopAnimatingPlayer(gTowerCurrentPlayer, destinationCellX, destinationCellY);
}
} //fill in rest later - get one direction working
lastTime = time;
// clear - this is where the problem is
gAvatarDrawingContext.clearRect(playerPixelX, playerPixelY, kPieceWidth, kPieceHeight);
//gAvatarDrawingContext.clearRect(0,0, gAvatarCanvasElement.width, gAvatarCanvasElement.height);
if (horizontal) {
drawAvatar(gTowerCurrentPlayer, 0, 0, true, newX, playerPixelY);
// request new frame
requestAnimFrame(function(){
movePlayer(lastTime, newX, playerPixelY, destinationCellX, destinationCellY);
});
}
}
}
function animatePlayer(playerPixelX, playerPixelY, destinationCellX, destinationCellY) {
gIsAnimating = true; // global var here
var date = new Date();
var time = date.getTime();
movePlayer(time, playerPixelX, playerPixelY, destinationCellX, destinationCellY);
}
如果有人可以提供任何帮助,我将不胜感激,我只是不明白为什么这不起作用。我不需要超级华丽的动画,这就是为什么我没有使用 kineticjs 或任何其他库。
谢谢。