How to put a gif with Canvas
I'm creating a game, and in my game, when the HERO stay near the MONSTER, a gif will be showed, to scare the player. But I have no idea how to do this. I tried to put PHP or HTML code, but it doesn't works... The function is AtualizaTela2(). This is my main code:
<!DOCTYPE HTML>
<html>
<head>
<title>Hero's Escape Game</title>
<script language="JavaScript" type="text/javascript">
var objCanvas=null; // object that represents the canvas
var objContexto=null;
// Hero positioning control
var xHero=300;
var yHero=100;
// Monster positioning control
var xMonster=620;
var yMonster=0;
var imgFundo2 = new Image();
imgFundo2.src = "Images/Pista2.png";
var imgMonster = new Image();
imgMonster.src = "Images/Monster.png";
var imgHero = new Image();
imgHero.src = "Images/Hero.png";
function AtualizaTela2(){
if((xHero >= xMonster-10)&&(xHero <= xMonster + 10))
{
/*gif here*/
}
objContexto.drawImage(imgFundo2,0,0);
objContexto.drawImage(imgHero, xHero, yHero);
objContexto.drawImage(imgMonster, xMonster, yMonster);
function Iniciar(){
objCanvas = document.getElementById("meuCanvas");
objContexto = objCanvas.getContext("2d");
AtualizaTela2();
}
/* the function HeroMovement() and MonsterMovement() are not here */
}
</script>
</head>
<body onLoad="Iniciar();" onkeydown="HeroMovement(event);">
<canvas id="meuCanvas" width="1233"
height="507"
style="border:1px solid #000000;">
Seu browser não suporta o elemento CANVAS, atualize-se!!!
</canvas><BR>
</body>
</html>
This is the simplified code, because the real code is very big!
Thanks for the help! :)
Answer
Loading and playing GIF image to canvas.
Sorry answer exceeded size limit, had to remove much of the detailed code comments.
I am not going to go into details as the whole process is rather complicated.
The only way to get a GIF animated in canvas is to decode the GIF image in javascript. Luckily the format is not too complicated with data arranged in blocks that contain image size, color pallets, timing information, a comment field, and how frames are drawn.
Custom GIF load and player.
The example below contains an object called GIF that will create custom format GIF images from URLs that can play a GIF similar to how a video is played. You can also randomly access all GIF frames in any order.
There are many callbacks and options. There is basic usage information in comments and the code shows how to load the gif. There are functions to pause and play, seek(timeInSeconds) and seekFrame(frameNumber), properties to control playSpeed and much more. There are no shuttling events as access is immediate.
var myGif = GIF();
myGif.load("GIFurl.gif");
Once loaded
ctx.drawImage(myGif.image,0,0); // will draw the playing gif image
Or access the frames via the frames buffer
ctx.drawImage(myGif.frames[0].image,0,0); // draw frame 0 only.
Go to the bottom of the GIF object to see all the options with comments.
The GIF must be same domain or have CORS header
The gif in he demo is from wiki commons and contains 250+ frames, some low end devices will have trouble with this as each frame is converted to a full RGBA image making the loaded GIF significantly larger than the gif file size.
The demo
Loads the gif displaying the frames and frame count as loaded. When loaded 100 particles each with random access frames playing at independent speeds and independent directions are displayed in the background.
The foreground image is the gif playing at the frame rate embedded in the file.
Code is as is, as an example only and NOT for commercial use.
const ctx = canvas.getContext("2d");
var myGif;
// Can not load gif cross domain unless it has CORS header
const gifURL = "https://upload.wikimedia.org/wikipedia/commons/a/a2/Wax_fire.gif";
// timeout just waits till script has been parsed and executed
// then starts loading a gif
setTimeout(()=>{
myGif = GIF(); // creates a new gif
myGif.onerror = function(e){
console.log("Gif loading error " + e.type);
}
myGif.load(gifURL);
},0);
// Function draws an image
function drawImage(image,x,y,scale,rot){
ctx.setTransform(scale,0,0,scale,x,y);
ctx.rotate(rot);
ctx.drawImage(image,-image.width / 2, -image.height / 2);
}
// helper functions
const rand = (min = 1, max = min + (min = 0)) => Math.random() * (max - min) + min;
const setOf =(c,C)=>{var a=[],i=0;while(i<c){a.push(C(i++))}return a};
const eachOf =(a,C)=>{var i=0;const l=a.length;while(i<l && C(a[i],i++,l)!==true);return i};
const mod = (v,m) => ((v % m) + m) % m;
// create 100 particles
const particles = setOf(100,() => {
return {
x : rand(innerWidth),
y : rand(innerHeight),
scale : rand(0.15, 0.5),
rot : rand(Math.PI * 2),
frame : 0,
frameRate : rand(-2,2),
dr : rand(-0.1,0.1),
dx : rand(-4,4),
dy : rand(-4,4),
};
});
// Animate and draw 100 particles
function drawParticles(){
eachOf(particles, part => {
part.x += part.dx;
part.y += part.dy;
part.rot += part.dr;
part.frame += part.frameRate;
part.x = mod(part.x,innerWidth);
part.y = mod(part.y,innerHeight);
var frame = mod(part.frame ,myGif.frames.length) | 0;
drawImage(myGif.frames[frame].image,part.x,part.y,part.scale,part.rot);
});
}
var w = canvas.width;
var h = canvas.height;
var cw = w / 2; // center
var ch = h / 2;
// main update function
function update(timer) {
ctx.setTransform(1, 0, 0, 1, 0, 0); // reset transform
if (w !== innerWidth || h !== innerHeight) {
cw = (w = canvas.width = innerWidth) / 2;
ch = (h = canvas.height = innerHeight) / 2;
} else {
ctx.clearRect(0, 0, w, h);
}
if(myGif) { // If gif object defined
if(!myGif.loading){ // if loaded
// draw random access to gif frames
drawParticles();
drawImage(myGif.image,cw,ch,1,0); // displays the current frame.
}else if(myGif.lastFrame !== null){ // Shows frames as they load
ctx.drawImage(myGif.lastFrame.image,0,0);
ctx.fillStyle = "white";
ctx.fillText("GIF loading frame " + myGif.frames.length ,10,21);
ctx.fillText("GIF loading frame " + myGif.frames.length,10,19);
ctx.fillText("GIF loading frame " + myGif.frames.length,9,20);
ctx.fillText("GIF loading frame " + myGif.frames.length,11,20);
ctx.fillStyle = "black";
ctx.fillText("GIF loading frame " + myGif.frames.length,10,20);
}
}else{
ctx.fillText("Waiting for GIF image ",10,20);
}
requestAnimationFrame(update);
}
requestAnimationFrame(update);
/*============================================================================
Gif Decoder and player for use with Canvas API's
**NOT** for commercial use.
To use
var myGif = GIF(); // creates a new gif
var myGif = new GIF(); // will work as well but not needed as GIF() returns the correct reference already.
myGif.load("myGif.gif"); // set URL and load
myGif.onload = function(event){ // fires when loading is complete
//event.type = "load"
//event.path array containing a reference to the gif
}
myGif.onprogress = function(event){ // Note this function is not bound to myGif
//event.bytesRead bytes decoded
//event.totalBytes total bytes
//event.frame index of last frame decoded
}
myGif.onerror = function(event){ // fires if there is a problem loading. this = myGif
//event.type a description of the error
//event.path array containing a reference to the gif
}
Once loaded the gif can be displayed
if(!myGif.loading){
ctx.drawImage(myGif.image,0,0);
}
You can display the last frame loaded during loading
if(myGif.lastFrame !== null){
ctx.drawImage(myGif.lastFrame.image,0,0);
}
To access all the frames
var gifFrames = myGif.frames; // an array of frames.
A frame holds various frame associated items.
myGif.frame[0].image; // the first frames image
myGif.frame[0].delay; // time in milliseconds frame is displayed for
Gifs use various methods to reduce the file size. The loaded frames do not maintain the optimisations and hold the full resolution frames as DOM images. This mean the memory footprint of a decode gif will be many time larger than the Gif file.
*/
const GIF = function () {
// **NOT** for commercial use.
var timerID; // timer handle for set time out usage
var st; // holds the stream object when loading.
var interlaceOffsets = [0, 4, 2, 1]; // used in de-interlacing.
var interlaceSteps = [8, 8, 4, 2];
var interlacedBufSize; // this holds a buffer to de interlace. Created on the first frame and when size changed
var deinterlaceBuf;
var pixelBufSize; // this holds a buffer for pixels. Created on the first frame and when size changed
var pixelBuf;
const GIF_FILE = { // gif file data headers
GCExt : 0xF9,
COMMENT : 0xFE,
APPExt : 0xFF,
UNKNOWN : 0x01, // not sure what this is but need to skip it in parser
IMAGE : 0x2C,
EOF : 59, // This is entered as decimal
EXT : 0x21,
};
// simple buffered stream used to read from the file
var Stream = function (data) {
this.data = new Uint8ClampedArray(data);
this.pos = 0;
var len = this.data.length;
this.getString = function (count) { // returns a string from current pos of len count
var s = "";
while (count--) { s += String.fromCharCode(this.data[this.pos++]) }
return s;
};
this.readSubBlocks = function () { // reads a set of blocks as a string
var size, count, data = "";
do {
count = size = this.data[this.pos++];
while (count--) { data += String.fromCharCode(this.data[this.pos++]) }
} while (size !== 0 && this.pos < len);
return data;
}
this.readSubBlocksB = function () { // reads a set of blocks as binary
var size, count, data = [];
do {
count = size = this.data[this.pos++];
while (count--) { data.push(this.data[this.pos++]);}
} while (size !== 0 && this.pos < len);
return data;
}
};
// LZW decoder uncompressed each frames pixels
// this needs to be optimised.
// minSize is the min dictionary as powers of two
// size and data is the compressed pixels
function lzwDecode(minSize, data) {
var i, pixelPos, pos, clear, eod, size, done, dic, code, last, d, len;
pos = pixelPos = 0;
dic = [];
clear = 1 << minSize;
eod = clear + 1;
size = minSize + 1;
done = false;
while (!done) { // JavaScript optimisers like a clear exit though I never use 'done' apart from fooling the optimiser
last = code;
code = 0;
for (i = 0; i < size; i++) {
if (data[pos >> 3] & (1 << (pos & 7))) { code |= 1 << i }
pos++;
}
if (code === clear) { // clear and reset the dictionary
dic = [];
size = minSize + 1;
for (i = 0; i < clear; i++) { dic[i] = [i] }
dic[clear] = [];
dic[eod] = null;
} else {
if (code === eod) { done = true; return }
if (code >= dic.length) { dic.push(dic[last].concat(dic[last][0])) }
else if (last !== clear) { dic.push(dic[last].concat(dic[code][0])) }
d = dic[code];
len = d.length;
for (i = 0; i < len; i++) { pixelBuf[pixelPos++] = d[i] }
if (dic.length === (1 << size) && size < 12) { size++ }
}
}
};
function parseColourTable(count) { // get a colour table of length count Each entry is 3 bytes, for RGB.
var colours = [];
for (var i = 0; i < count; i++) { colours.push([st.data[st.pos++], st.data[st.pos++], st.data[st.pos++]]) }
return colours;
}
function parse (){ // read the header. This is the starting point of the decode and async calls parseBlock
var bitField;
st.pos += 6;
gif.width = (st.data[st.pos++]) + ((st.data[st.pos++]) << 8);
gif.height = (st.data[st.pos++]) + ((st.data[st.pos++]) << 8);
bitField = st.data[st.pos++];
gif.colorRes = (bitField & 0b1110000) >> 4;
gif.globalColourCount = 1 << ((bitField & 0b111) + 1);
gif.bgColourIndex = st.data[st.pos++];
st.pos++; // ignoring pixel aspect ratio. if not 0, aspectRatio = (pixelAspectRatio + 15) / 64
if (bitField & 0b10000000) { gif.globalColourTable = parseColourTable(gif.globalColourCount) } // global colour flag
setTimeout(parseBlock, 0);
}
function parseAppExt() { // get application specific data. Netscape added iterations and terminator. Ignoring that
st.pos += 1;
if ('NETSCAPE' === st.getString(8)) { st.pos += 8 } // ignoring this data. iterations (word) and terminator (byte)
else {
st.pos += 3; // 3 bytes of string usually "2.0" when identifier is NETSCAPE
st.readSubBlocks(); // unknown app extension
}
};
function parseGCExt() { // get GC data
var bitField;
st.pos++;
bitField = st.data[st.pos++];
gif.disposalMethod = (bitField & 0b11100) >> 2;
gif.transparencyGiven = bitField & 0b1 ? true : false; // ignoring bit two that is marked as userInput???
gif.delayTime = (st.data[st.pos++]) + ((st.data[st.pos++]) << 8);
gif.transparencyIndex = st.data[st.pos++];
st.pos++;
};
function parseImg() { // decodes image data to create the indexed pixel image
var deinterlace, frame, bitField;
deinterlace = function (width) { // de interlace pixel data if needed
var lines, fromLine, pass, toline;
lines = pixelBufSize / width;
fromLine = 0;
if (interlacedBufSize !== pixelBufSize) { // create the buffer if size changed or undefined.
deinterlaceBuf = new Uint8Array(pixelBufSize);
interlacedBufSize = pixelBufSize;
}
for (pass = 0; pass < 4; pass++) {
for (toLine = interlaceOffsets[pass]; toLine < lines; toLine += interlaceSteps[pass]) {
deinterlaceBuf.set(pixelBuf.subArray(fromLine, fromLine + width), toLine * width);
fromLine += width;
}
}
};
frame = {}
gif.frames.push(frame);
frame.disposalMethod = gif.disposalMethod;
frame.time = gif.length;
frame.delay = gif.delayTime * 10;
gif.length += frame.delay;
if (gif.transparencyGiven) { frame.transparencyIndex = gif.transparencyIndex }
else { frame.transparencyIndex = undefined }
frame.leftPos = (st.data[st.pos++]) + ((st.data[st.pos++]) << 8);
frame.topPos = (st.data[st.pos++]) + ((st.data[st.pos++]) << 8);
frame.width = (st.data[st.pos++]) + ((st.data[st.pos++]) << 8);
frame.height = (st.data[st.pos++]) + ((st.data[st.pos++]) << 8);
bitField = st.data[st.pos++];
frame.localColourTableFlag = bitField & 0b10000000 ? true : false;
if (frame.localColourTableFlag) { frame.localColourTable = parseColourTable(1 << ((bitField & 0b111) + 1)) }
if (pixelBufSize !== frame.width * frame.height) { // create a pixel buffer if not yet created or if current frame size is different from previous
pixelBuf = new Uint8Array(frame.width * frame.height);
pixelBufSize = frame.width * frame.height;
}
lzwDecode(st.data[st.pos++], st.readSubBlocksB()); // decode the pixels
if (bitField & 0b1000000) { // de interlace if needed
frame.interlaced = true;
deinterlace(frame.width);
} else { frame.interlaced = false }
processFrame(frame); // convert to canvas image
};
function processFrame(frame) { // creates a RGBA canvas image from the indexed pixel data.
var ct, cData, dat, pixCount, ind, useT, i, pixel, pDat, col, frame, ti;
frame.image = document.createElement('canvas');
frame.image.width = gif.width;
frame.image.height = gif.height;
frame.image.ctx = frame.image.getContext("2d");
ct = frame.localColourTableFlag ? frame.localColourTable : gif.globalColourTable;
if (gif.lastFrame === null) { gif.lastFrame = frame }
useT = (gif.lastFrame.disposalMethod === 2 || gif.lastFrame.disposalMethod === 3) ? true : false;
if (!useT) { frame.image.ctx.drawImage(gif.lastFrame.image, 0, 0, gif.width, gif.height) }
cData = frame.image.ctx.getImageData(frame.leftPos, frame.topPos, frame.width, frame.height);
ti = frame.transparencyIndex;
dat = cData.data;
if (frame.interlaced) { pDat = deinterlaceBuf }
else { pDat = pixelBuf }
pixCount = pDat.length;
ind = 0;
for (i = 0; i < pixCount; i++) {
pixel = pDat[i];
col = ct[pixel];
if (ti !== pixel) {
dat[ind++] = col[0];
dat[ind++] = col[1];
dat[ind++] = col[2];
dat[ind++] = 255; // Opaque.
} else
if (useT) {
dat[ind + 3] = 0; // Transparent.
ind += 4;
} else { ind += 4 }
}
frame.image.ctx.putImageData(cData, frame.leftPos, frame.topPos);
gif.lastFrame = frame;
if (!gif.waitTillDone && typeof gif.onload === "function") { doOnloadEvent() }// if !waitTillDone the call onload now after first frame is loaded
};
// **NOT** for commercial use.
function finnished() { // called when the load has completed
gif.loading = false;
gif.frameCount = gif.frames.length;
gif.lastFrame = null;
st = undefined;
gif.complete = true;
gif.disposalMethod = undefined;
gif.transparencyGiven = undefined;
gif.delayTime = undefined;
gif.transparencyIndex = undefined;
gif.waitTillDone = undefined;
pixelBuf = undefined; // dereference pixel buffer
deinterlaceBuf = undefined; // dereference interlace buff (may or may not be used);
pixelBufSize = undefined;
deinterlaceBuf = undefined;
gif.currentFrame = 0;
if (gif.frames.length > 0) { gif.image = gif.frames[0].image }
doOnloadEvent();
if (typeof gif.onloadall === "function") {
(gif.onloadall.bind(gif))({ type : 'loadall', path : [gif] });
}
if (gif.playOnLoad) { gif.play() }
}
function canceled () { // called if the load has been cancelled
finnished();
if (typeof gif.cancelCallback === "function") { (gif.cancelCallback.bind(gif))({ type : 'canceled', path : [gif] }) }
}
function parseExt() { // parse extended blocks
const blockID = st.data[st.pos++];
if(blockID === GIF_FILE.GCExt) { parseGCExt() }
else if(blockID === GIF_FILE.COMMENT) { gif.comment += st.readSubBlocks() }
else if(blockID === GIF_FILE.APPExt) { parseAppExt() }
else {
if(blockID === GIF_FILE.UNKNOWN) { st.pos += 13; } // skip unknow block
st.readSubBlocks();
}
}
function parseBlock() { // parsing the blocks
if (gif.cancel !== undefined && gif.cancel === true) { canceled(); return }
const blockId = st.data[st.pos++];
if(blockId === GIF_FILE.IMAGE ){ // image block
parseImg();
if (gif.firstFrameOnly) { finnished(); return }
}else if(blockId === GIF_FILE.EOF) { finnished(); return }
else { parseExt() }
if (typeof gif.onprogress === "function") {
gif.onprogress({ bytesRead : st.pos, totalBytes : st.data.length, frame : gif.frames.length });
}
setTimeout(parseBlock, 0); // parsing frame async so processes can get some time in.
};
function cancelLoad(callback) { // cancels the loading. This will cancel the load before the next frame is decoded
if (gif.complete) { return false }
gif.cancelCallback = callback;
gif.cancel = true;
return true;
}
function error(type) {
if (typeof gif.onerror === "function") { (gif.onerror.bind(this))({ type : type, path : [this] }) }
gif.onload = gif.onerror = undefined;
gif.loading = false;
}
function doOnloadEvent() { // fire onload event if set
gif.currentFrame = 0;
gif.nextFrameAt = gif.lastFrameAt = new Date().valueOf(); // just sets the time now
if (typeof gif.onload === "function") { (gif.onload.bind(gif))({ type : 'load', path : [gif] }) }
gif.onerror = gif.onload = undefined;
}
function dataLoaded(data) { // Data loaded create stream and parse
st = new Stream(data);
parse();
}
function loadGif(filename) { // starts the load
var ajax = new XMLHttpRequest();
ajax.responseType = "arraybuffer";
ajax.onload = function (e) {
if (e.target.status === 404) { error("File not found") }
else if(e.target.status >= 200 && e.target.status < 300 ) { dataLoaded(ajax.response) }
else { error("Loading error : " + e.target.status) }
};
ajax.open('GET', filename, true);
ajax.send();
ajax.onerror = function (e) { error("File error") };
this.src = filename;
this.loading = true;
}
function play() { // starts play if paused
if (!gif.playing) {
gif.paused = false;
gif.playing = true;
playing();
}
}
function pause() { // stops play
gif.paused = true;
gif.playing = false;
clearTimeout(timerID);
}
function togglePlay(){
if(gif.paused || !gif.playing){ gif.play() }
else{ gif.pause() }
}
function seekFrame(frame) { // seeks to frame number.
clearTimeout(timerID);
gif.currentFrame = frame % gif.frames.length;
if (gif.playing) { playing() }
else { gif.image = gif.frames[gif.currentFrame].image }
}
function seek(time) { // time in Seconds // seek to frame that would be displayed at time
clearTimeout(timerID);
if (time < 0) { time = 0 }
time *= 1000; // in ms
time %= gif.length;
var frame = 0;
while (time > gif.frames[frame].time + gif.frames[frame].delay && frame < gif.frames.length) { frame += 1 }
gif.currentFrame = frame;
if (gif.playing) { playing() }
else { gif.image = gif.frames[gif.currentFrame].image}
}
function playing() {
var delay;
var frame;
if (gif.playSpeed === 0) {
gif.pause();
return;
} else {
if (gif.playSpeed < 0) {
gif.currentFrame -= 1;
if (gif.currentFrame < 0) {gif.currentFrame = gif.frames.length - 1 }
frame = gif.currentFrame;
frame -= 1;
if (frame < 0) { frame = gif.frames.length - 1 }
delay = -gif.frames[frame].delay * 1 / gif.playSpeed;
} else {
gif.currentFrame += 1;
gif.currentFrame %= gif.frames.length;
delay = gif.frames[gif.currentFrame].delay * 1 / gif.playSpeed;
}
gif.image = gif.frames[gif.currentFrame].image;
timerID = setTimeout(playing, delay);
}
}
var gif = { // the gif image object
onload : null, // fire on load. Use waitTillDone = true to have load fire at end or false to fire on first frame
onerror : null, // fires on error
onprogress : null, // fires a load progress event
onloadall : null, // event fires when all frames have loaded and gif is ready
paused : false, // true if paused
playing : false, // true if playing
waitTillDone : true, // If true onload will fire when all frames loaded, if false, onload will fire when first frame has loaded
loading : false, // true if still loading
firstFrameOnly : false, // if true only load the first frame
width : null, // width in pixels
height : null, // height in pixels
frames : [], // array of frames
comment : "", // comments if found in file. Note I remember that some gifs have comments per frame if so this will be all comment concatenated
length : 0, // gif length in ms (1/1000 second)
currentFrame : 0, // current frame.
frameCount : 0, // number of frames
playSpeed : 1, // play speed 1 normal, 2 twice 0.5 half, -1 reverse etc...
lastFrame : null, // temp hold last frame loaded so you can display the gif as it loads
image : null, // the current image at the currentFrame
playOnLoad : true, // if true starts playback when loaded
// functions
load : loadGif, // call this to load a file
cancel : cancelLoad, // call to stop loading
play : play, // call to start play
pause : pause, // call to pause
seek : seek, // call to seek to time
seekFrame : seekFrame, // call to seek to frame
togglePlay : togglePlay, // call to toggle play and pause state
};
return gif;
}
/*=========================================================================
End of gif reader
*/
const mouse = {
bounds: null,
x: 0,
y: 0,
button: false
};
function mouseEvents(e) {
const m = mouse;
m.bounds = canvas.getBoundingClientRect();
m.x = e.pageX - m.bounds.left - scrollX;
m.y = e.pageY - m.bounds.top - scrollY;
mouse.x = e.pageX;
m.button = e.type === "mousedown" ? true : e.type === "mouseup" ? false : m.button;
}
["down", "up", "move"].forEach(name => document.addEventListener("mouse" + name, mouseEvents));canvas {
position: absolute;
top: 0px;
left: 0px;
}<canvas id="canvas"></canvas>NOTES
This works for 99% of gifs. Occasionally you will find a gif that does not play correctly. Reason: (I never bothered to find out). Fix: re-encode gif using modern encoder.
There are some minor inconsistencies that need fixing. In time I will provide a codePen example with ES6 and improved interface. Stay tuned.