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Misha’s Tech Playground
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Animating with Scroll Properties, A view on Performance
Having had some time to polish up the AnimSprite Object of the game engine I had a chance to make a small performance test. I decided to give some insights on ow this style of animation works and to post the code that goes along with it for your personal joy.
The following html is generated by the script for each sprite that is placed on the stage.
Of course there is a stylesheet having defined the sprite class:
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.CGE_sprite {
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overflow: hidden;
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position: absolute;
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}
Utilizing the ScrollTop and ScrollLeft properties of the sprite box (the surrounding div) I can display 50 animated sprites @ 25fps on a page using Firefox 3 Beta 4 with a processor load of about 98% on my MBP 2.16GHz Core Duo.
Safari on the other hand is quite fast and has only 19% processor load for 50 sprites.
Having 100 sprites lets Firefox peak out at 100.9% load and slows down the animation to about 50% speed.
I'd say this is still not optimum, but it's quite a good start.
Here's my JS code for the sprites.
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var CGE = {
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// globals attributes
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LEFT: 3,
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TOP: 0,
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RIGHT: 1,
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BOTTOM: 2,
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HEIGHT: 1,
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WIDTH: 0,
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X: 0,
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Y: 1,
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Z: 2,
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STYLE_SPRITE: "CGE_sprite",
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// the game instance if needed
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game: null,
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};
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CGE.Game = new AJS.Class({
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animSprites: [],
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init: function (keys) {
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for (var i=0; i <50; i++) {
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this.animSprites[i] = new CGE.MirroredAnimSprite("_img/jumping_shadow.png", [Math.random()*300,Math.random()*250], [32,32], AJS.$("map"), true);
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};
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this.run(this);
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},
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run: function (game) {
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game.hero.move(CGE.moveDir);
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for(var i = 0; i <game.animSprites.length; ++i) {
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game.animSprites[i].next();
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}
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game.mainLoop = window.setTimeout(function(){game.run(game)}, 40); //25fps
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}
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});
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CGE.Sprite = new AJS.Class({
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box: null, // for tiles this is the tile container, pos is relative to it
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img: null,
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spriteH: 0,
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spriteW: 0,
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// get x and y directly from object, faster for anim
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z: 0,
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frames: null,
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init: function(url, pos, size, parent, useBox) {
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this.img = AJS.IMG({src: url});
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if(useBox)
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this.box = AJS.DIV({className: CGE.STYLE_SPRITE}, this.img);
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if(pos)
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this.setPos(pos);
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if(size)
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this.setSize(size);
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if(parent)
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AJS.ACN(parent, this.box);
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},
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get: function() {
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return this.img.src;
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},
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set: function(url, size) {
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this.img.src = url;
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},
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getPos: function() {
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return [this.box.offsetLeft, this.box.offsetTop];
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},
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setFrame: function(name, n) {
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this.box.scrollTop = this.frames[name][n][CGE.Y];
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this.box.scrollLeft = this.frames[name][n][CGE.X];
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},
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setPos: function(pos) {
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AJS.setLeft(this.box, pos[CGE.X]);
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AJS.setTop(this.box, pos[CGE.Y]);
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},
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setSize: function(size) {
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this.spriteH = size[CGE.HEIGHT];
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this.spriteW = size[CGE.WIDTH];
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AJS.setHeight(this.box, this.spriteH);
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AJS.setWidth(this.box, this.spriteW);
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}
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});
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CGE.AnimSprite = CGE.Sprite.extend({
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isPlaying: false,
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isMirrored: true,
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sign: true, // true=add, false = substract
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frames: null,
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key: null,
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init: function(url, pos, size, parent, isPlaying) {
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this.parent(url, pos, size, parent, true);
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this.key = {name: "base",num: 0}
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this.isPlaying = (isPlaying);
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this.frames = {base: [[0,0],[32,0],[64,0],[96,0],[128,0],[160,0]]};
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},
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getFrame: function() {
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return this.key;
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},
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setFrame: function(name, n) {
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if(n>= this.frames[name].length)
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n = 0;
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this.parent(name, n)
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this.key = {name: name, num: n};
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},
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next: function() {
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if(this.isPlaying)
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this.setFrame(this.key.name, ++this.key.num);
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},
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pause: function() {
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this.isPlaying = false;
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},
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play: function(name) {
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if(name)
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this.key.name = name;
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this.isPlaying = true;
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},
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stop: function() {
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this.pause();
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this.setFrame("base", 0);
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}
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});
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CGE.MirroredAnimSprite = CGE.AnimSprite.extend({
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sign: true, // true=add, false = substract
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setFrame: function(name, n) {
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switch(n) {
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case this.frames[name].length-1:
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this.sign = false;
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break;
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case 0:
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this.sign = true;
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};
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(this.sign) ? ++n : --n;
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this.parent(name, n);
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},
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next: function() {
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if(this.isPlaying)
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this.setFrame(this.key.name, this.key.num);
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},
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});
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function init() {
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CGE.game = new CGE.Game();
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}
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AJS.AEV(window, 'load', init);
As you can see, I make extensive use of AJS. You can get the stock version of it at the official website: AJS JavaScript Library.
The code shown here should be fully functional. I just removed the methods and members which aren't used in this example. And as a little caveat, there is no depth management as of yet.
The image I used in my code is the same as in the Javascript Sprite Animation post.
The classes to use would be:
- CGE.Sprite - which is a single not animated sprite
- CGE.AnimSprite - which is an animated sprite running in a loop
- CGE.MirroredAnimSprite - which is an animated sprite that plays in reverse when it's last/first frame is reached
- CGE.Game - which coordinates the loop in which all animations are run
Have fun 
Tags: code performance, Firefox, Games, JavaScript Library, pbbg, Safari, tile graphics
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