JavaScript: initialize different image if an error occurs - javascript

I have a folder with the contents like the following (giving a minimal example)
ex1_1.png
ex1_2.png
ex2_1.png
page.html
and I've written the following JavaScript code. The HTML file has two canvas elements that are designed to draw ex1_1.png and ex2_1.png and each canvas element has an associated "Next" button. If the first one is clicked it erases the first canvas element and draws ex_2.png. What I want is for the Next button to cycle through all my images, going back to the start when the last image is exceeded. The following JavaScript accomplishes this, except for the part where it cycles back. When it reaches the image with source ex1_3.png (which doesn't exist in the folder), I get a crash, but on the draw() command--which tells me that for whatever reason, it's not cycling the source back to ex1_1.png before attempting to draw.
To the best of my ability to debug this, something is going wrong with the img.onerror part, or how its implemented with the global variable window.indicator. When I cycle through using the next button, the indicator shows true then false if I print the value from within the img.onerror function. But if I print from within the next() function, it never shows false. This sounds like some kind of an issue with the window.indicator keeping its value globally.
// Variable to indicate whether the most recently generated image
// was valid.
window.indicator = true;
// Give the file base-name and index as stored in the local address.
// Return the corresponding Image() object.
function initImg(name, ind) {
var img = new Image();
// The file is local, the image is always of the form
// baseName_i.png
window.indicator = true;
img.src = name + "_" + ind + ".png";
img.onerror = function() {
// Find the appropriate canvas state element, and
// update its state back to 1.
for (i = 0; i < canStates.length; i++) {
var n = canStates[i][0].getAttribute("id");
n = n.split("_")[1];
if (name == canStates[i][0].getAttribute("id")) {
canStates[i][1] = 1;
}
window.indicator = false;
}
};
return img;
}
// Give the canvas context and image objects. Draw the image to
// the context, no return value.
function draw(ctx, img) {
// Check that the image is loaded before writing. Keep
// checking every 50 milliseconds.
if (!img.complete) {
setTimeout( function() {
draw(ctx, img);
}, 50);
}
// Clear the current image and draw the new.
ctx.clearRect(0,0, 200,200);
ctx.drawImage(img, 0,0, 200,200);
}
// Give the string canvas id and string base-name, create the
// canvas object and draw the first image to the canvas.
function slideShow(canId, name) {
var can = document.getElementById(canId);
can.width = 300;
can.height = 300;
var ctx = can.getContext('2d');
var img = initImg(name, 1);
draw(ctx, img);
}
// Next button function. Give the name of the canvas, draw the
// next image or cycle to the start.
function next(button) {
var name = button.getAttribute("name");
// Find the appropriate canvas element.
for (i = 0; i < canStates.length; i++) {
var id = canStates[i][0].getAttribute("id");
id = id.split("_")[1];
if (id == name) {
// Use the states to produce an image, and update the
// states.
canStates[i][1] += 1;
var img = initImg(name, canStates[i][1]);
if (!window.indicator) {
img = initImg(name, 1);
}
// Draw to the canvas.
draw(canStates[i][0].getContext('2d'),img);
}
}
}
// Create a global variable tracking all states of "Next" buttons.
// Stored as a list, each element is a list, the left coordinate is
// a canvas and the right coordinate is its state (image index).
// Also initialize all slide shows.
// The variable r stores the canvases and states, initialized
// outside the function in order to pass-by-reference so as to act
// as a global variable.
var canStates = new Array();
window.onload = function() {
var cans = document.getElementsByTagName("canvas");
for (i=0; i < cans.length; i++) {
var c = cans[i];
var n = c.getAttribute("id").split("_")[1];
slideShow("can_"+n, n);
}
for (i = 0; i < cans.length; i++) {
canStates[i] = [cans[i],1];
}
}
I could switch strategies completely here. I've heard that PHP is a decent way to server-side look at the files in a directory, and I could use that, but I don't know how to make a PHP script execute when a browser is loaded, or how to take its results and hand them over to the JavaScript file.

Related

Image array not being read

The code below is intended to display a set of images numbered x.jpg (where x is a number starting at 0 and going up to n) in normal order, then in reverse order. The final product is meant to do it only in reverse order but the normal order part was put in for testing purposes. It currently displays the images in normal order correctly, but does not display them in reverse order. I understand that this sort of functionality was not really intended to be done in normal javascript alone but it would be helpful to know why this does not work.
<script>
var counter = 0;
var imageArray = [];
function getImg(){
var imgURL = "images/" + counter + ".jpg";
var img = new Image();
img.src=imgURL;
imageArray.push(img)
document.getElementById('imageList').appendChild(img);
counter++;
img.onload = function(){
//alert(this.width);
if(this.width!=0){
getImg();
}
else{
var popped = imageArray.pop()
}
}
}
function reverseImg() {
imageArray.reverse();
for (i=1; i<imageArray.length; i++) {
image = imageArray[i]
document.getElementById('reversedList').appendChild(image);
}
}
getImg();
reverseImg();
</script>
It doesn't work because when you call reverseImg, imageArray has only one image in it, and you're skipping that in your for loop by starting with 1. The code in the onload callbacks in getImg doesn't run until later, when the first image loads.
If you want the images displayed in reverse order with a time delay in-between, you need to do something like getImg with its onload behavior (but I'd handle error as well), but starting by reversing the array first. Or actually, there's no need for the array at all, just start with n (the last image) and count backward, creating the Image elements within the callbacks.
For example:
function reverseImg() {
var n = 9;
tick();
function tick() {
var img = document.createElement("img");
if (n > 0) {
// When this image loads/fails, load the next
img.addEventListener("load", tick);
img.addEventListener("error", tick);
}
// Show this image
img.src = "https://via.placeholder.com/100/000080/FFFFFF?text=Image%20" + n;
document.body.appendChild(img);
--n;
}
}
reverseImg();
img {
padding: 2px;
}

Javascript - retrieve random image from array

I'm trying to write a program using Javascript and the p5.js library to trigger a random image from an array whenever a peak in an audio file is detected. p5's sound library can detect the audio peak for me and then trigger a function upon that audio peak. However, I don't have much experience in Javascript so I'm not sure where to go from here. I've created an array of images and am planning on creating a function using math.Random to grab one of these images. Can I then call that function within my triggerBeat function?
Also, I've set the image as the background so that it's not within p5's draw function, so I'm trying to change the bg variable. I've preloaded the background image, and I've also got code within the preload function to allow the user to upload an audio file.
Sorry if this doesn't make a ton of sense. I'm pretty new to Javascript and I've spent most of today trying to wrap my head around it.
EDIT: updated code
var cnv, song, fft, peakDetect, img, bg;
var imageset = new Array("1.png","2.png","3.png");
function preload(){
img = loadImage("1.png");
var loader = document.querySelector(".loader");
document.getElementById("audiofile").onchange = function(event) {
if(event.target.files[0]) {
if(typeof song != "undefined") {
song.disconnect();
song.stop();
}
song = loadSound(URL.createObjectURL(event.target.files[0]));
loader.classList.add("loading");
}
}
}
function setup() {
cnv = createCanvas(900,900);
drawImage(imageset[0]);
fft = new p5.FFT();
peakDetect = new p5.PeakDetect();
setupSound();
peakDetect.onPeak(drawImage(imageset));
}
function draw() {
drawImage();
}
function drawImage(arr) {
var bg = loadImage(random(arr));
background(bg);
fill(0);
text('play', width/2, height/2);
fft.analyze();
peakDetect.update(fft);
}
function setupSound() {
cnv.mouseClicked( function() {
if (song.isPlaying() ) {
song.stop();
} else {
song.play();
}
});
}
p5 has math functions, one of which is random.
If one argument is given and it is an array, returns a random element from that array.
EDIT
As the result was more messy after answering the initial question, I updated the whole code.
var cnv, song, fft, peakDetect, img, bg;
var imageset = new Array("pic1.png","pic2.png","pic3.png", "pic4.png");
var imagesArr = [];
//next line will make p5 global. Otherwise would the p5 functions be
//accessable from p5 struct functions only.
new p5();
/*******************************************************************
* PRELOAD
* we are using for loading images/audios only
********************************************************************/
function preload(){
//load all images from 'imageset' into 'imagesArr'
for(var i=0; i<imageset.length; i++){
loadImage('../img/'+imageset[i], function(img) {
imagesArr.push(img);
});
}
// next lets load soundfile(s).
//song = loadSound("../snd/test.mp3");
// I used testfile, didn't touch nor tested your code here,
// BUT, again:
// you should only (pre)load you sounds here, setting event should go
// to the setup()
var loader = document.querySelector(".loader");
document.getElementById("audiofile").onchange = function(event) {
if(event.target.files[0]) {
if(typeof song != "undefined") {
song.disconnect();
song.stop();
}
song = loadSound(URL.createObjectURL(event.target.files[0]));
loader.classList.add("loading");
}
}
}
/*******************************************************************
* SETUP
* run once, use for initialisation.
********************************************************************/
function setup() {
//create canvas, draw initial background and text
cnv = createCanvas(900,900);
drawBackground();
text('play', width/2, height/2);
//initiate fft, peakdetect. Set event (onpeak)
fft = new p5.FFT();
peakDetect = new p5.PeakDetect();
setupSound();
peakDetect.onPeak(drawBackground);
}
/*******************************************************************
* DRAW
* endless loop. Here happens all the action.
* But you cannot draw your background here, as it is done by event.
********************************************************************/
function draw(){
//fft and peakdetecting are in use.
fft.analyze();
peakDetect.update(fft);
}
function drawBackground() {
background(255);
background(random(imagesArr));
}
function setupSound() {
cnv.mouseClicked( function() {
if (song.isPlaying() ) {
song.stop();
} else {
song.play();
}
});
}
Have yourArray[Math.floor(Math.random() * yourArray.length)] to get a random img by calling it in your triggerBeat function

ExtJS how to set icon of button to image in memory (not on disk)?

Long story short in another portion of the program I make canvases, convert them to DataURLs, then pass them over to the following portion to use as the icon image of the buttons. Whenever I set this.icon = "/path/to/image.jpg", it pulls it correctly, but since these images are not on disk, I am unsure how to
arrowHandler: function (arrow) {
var list = [];
var library = Ext.getCmp("library");
var buttons = Ext.getCmp("numbered").menu.buttons; //where the dataURLs are pushed in another portion of the program
function btn(num) {
var image = new Image;
image.src = buttons[num].dataURL;
this.xtype = "button";
this.height = 50;
this.width = 50;
this.icon = image; //where putting an actual path works correctly, but this code doesn't
this.num = num;
this.handler = function (btn) {
btn.up("button").menu.Style = this.num;
btn.up("button").fireEvent("selected", this.num);
};
}
for (var i = 0; i <= 0; i++)
library.items.items.push(new btn(i));
},
I am aware the loop is only going thru index 0 - it's like that purposefully for testing.
SOLUTION
The selected correct answer did provide the right way to set the icon with a DataURI, but it wasn't the fix to my issue. Turns out instead of doing
library.items.items.push(new btn(i));
I needed to be doing
library.add(new btn(i));
The error I kept encountering with pushing was "c.render() is not a function". I mention that solely to make it hopefully searchable for anyone else who encounters that error.
Should be the same as data uri, you'll have to convert it first.
https://developer.mozilla.org/en-US/docs/Web/API/HTMLCanvasElement/toDataURL
var dataURL = canvas.toDataURL();
Here is a button fiddle:
https://fiddle.sencha.com/#view/editor&fiddle/1og6

Problems getting context while using a javascript library to handle image sizing

I'm using a good library on here to handle some large images coming in through the iphone camera in order to avoid the whole subsampling drama here.
My draw code:
function imageLoaded(img, frontCamera) {
element = document.getElementById("canvas1");
var mpImg= new MegaPixImage(img);
// read the width and height of the canvas- scaled down
width = element.width; //188 94x2
height = element.height; //125
//used for side by side comparison of images
w2 = width / 2;
// stamp the image on the left of the canvas
if (frontCamera) {
mpImg.render(element, {maxWidth:94, maxHeight:125});} else{
mpImg.render(element, {maxWidth:94, maxHeight:125});}
//at this point, i want to grab the imageData drawn to the canvas using
//MegaPixImage and continue to do some more image processing, which normally
//would happen by declaring ctx=element.getContext("2d");
//more stuff here
}
The image is drawing fine,...but I cannot seem to find a way of then doing image processing on that image subsequently. How would I get a new context after having drawn that image on the canvas?
Maybe I would either have to run further image processing from within that library so I have context access or strip the context drawing out of the library.
Thanks for the help!
I had a similar issue, and actually found a helpful function to detect subsampling and only use MegaPixImage when subsampling was found.
In my case, for local file reading (iPhone camera, in your case), I called a handleFileSelect function when a <input type="file"> value is changed (i.e. when a file is selected to populate this input). Inside this function, I called a general populateImage JS function that draws the image data to the canvas.
Here's the handleFileSelect function and input binding:
$("#my_file_input").bind('change', function (event) {
handleFileSelect(event);
});
function handleFileSelect(event) {
var reader,
tmp,
file = event.target.files[0];
try {
reader = new FileReader();
reader.onload = function (e) {
tmp = e.target.result.toString();
// In my case, some image data (from Androids, mostly) didn't contain necessary image data, so I added it in
if (tmp.search("image/jpeg") === -1 && tmp.search("data:base64") !== -1) {
tmp = tmp.replace("data:", "data:image/jpeg;");
}
populateImage(tmp);
};
reader.onerror = function (err) {
// Handle error as you need
};
reader.readAsDataURL(file);
} catch (error) {
// Handle error as you need
}
}
Then, my populateImage function (called in the reader.onload function above):
function populateImage(imageURL) {
var tmpImage = new Image();
$(tmpImage).load(function () {
var mpImg, mpImgData;
// If subsampling found, render using MegaPixImage fix, grab image data, and re-populate so we can use non-subsampled image.
// Note: imageCanvas is my canvas element.
if (detectSubsampling(this)) {
mpImg = new MegaPixImage(this);
mpImg.render(imageCanvas, {maxWidth: 94, maxHeight: 125});
mpImgData = imageCanvas.toDataURL("image/jpg");
populateImage(mpImgData);
return;
}
// Insert regular code to draw image to the canvas
// Note: ctx is my canvas element's context
ctx.drawImage(tmpImage, 0, 0, 94, 125); // Or whatever x/y/width/height values you need
});
$(tmpImage).error(function (event) {
// Handle error as you need
});
tmpImage.src = imageURL;
}
And last but not least, the detectSubsampling function. Note that this method was found from another source and isn't my own.
function detectSubsampling(img) {
var iw = img.naturalWidth,
ih = img.naturalHeight,
ssCanvas,
ssCTX;
if (iw * ih > 1024 * 1024) { // Subsampling may happen over megapixel image
ssCanvas = document.createElement('canvas');
ssCanvas.width = ssCanvas.height = 1;
ssCTX = ssCanvas.getContext('2d');
ssCTX.drawImage(img, -iw + 1, 0);
// Subsampled image becomes half smaller in rendering size.
// Check alpha channel value to confirm image is covering edge pixel or not.
// If alpha value is 0 image is not covering, hence subsampled.
return ssCTX.getImageData(0, 0, 1, 1).data[3] === 0;
}
return false;
}
This may be more than you bargained for, but like I said, I ran into a similar issue and this solution proved to work across all browsers/devices that were canvas supported.
Hope it helps!

image loading loop IE7 Stack Overflow at line 0

Im trying to load in jpeg images, frame by frame to create an sequence animation of jpeg images. I'm attempting to load them in a recursive loop using javascript. I need to load images in linearly to achieve progressive playback of the animation. (start playback before all frames are loaded) I get a Stack overflow at line: 0 error from IE due to the natural recursion of the function. (My real code loads in over 60+ frames)
Here is a basic example of how I'm doing this:
var paths = ['image1.jpg', 'image2.jpg', 'image3.jpg']; //real code has 60+ frames
var images = [];
var load_index = 0;
var load = function(){
var img = new Image();
img.onload = function(){
if(load_index<=paths.length){
load_index++;
load();
}else{
alert('done loading');
}
}
img.src = paths[load_index];
images.push(img);
}
It seems I can avoid this error by using a setTimeout with an interval of 1 when calling the next step of the load. This seems to let IE "breathe" before loading the next image, but decreases the speed at which the images load dramatically.
Any one know how to avoid this stack overflow error?
http://cappuccino.org/discuss/2010/03/01/internet-explorer-global-variables-and-stack-overflows/
The above link suggests that wrapping the function to remove it from the window object will help avoid stack overflow errors. But I then see strangeness with it only getting about 15 frames through the sequence and just dies.
Put simply, don't use a recursive function for this situation, there isn't any need:
var paths = ['image1.jpg', 'image2.jpg', 'image3.jpg'];
var images = [];
var loads = [];
/// all complete function, probably should be renamed to something with a
/// unique namespace unless you are working within your own function scope.
var done = function(){
alert('all loaded');
}
var loaded = function(e,t){
/// fallbacks for old IE
e = e||Event; t = e.target||e.srcElement;
/// keep a list of the loaded images, you can delete this later if wanted
loads.push( t.src );
if ( loads.length >= paths.length ) {
done();
}
}
var load = function(){
var i, l = paths.length, img;
for( i=0; i<l; i++ ){
images.push(img = new Image());
img.onload = loaded;
img.src = paths[i];
}
}
In fact, as you are finding, the method you are using currently is quite intensive. Instead, the above version doesn't create a new function for each onload listener (saves memory) and will trigger off as many concurrent loads as your browser will allow (rather than waiting for each image load).
(the above has been manually typed and not tested, as of yet)
update
Ah, then it makes more sense as to why you are doing things this way :) In that case then your first approach using the setTimeout would probably be the best solution (you should be able to use a timeout of 0). There is still room for rearranging things to see if you can avoid that though. The following may get around the problem...
var paths = ['image1.jpg', 'image2.jpg', 'image3.jpg'];
var images = []; /// will contain the image objects
var loads = []; /// will contain loaded paths
var buffer = []; /// temporary buffer
var done = function(){ alert('all loaded'); }
var loaded = function(e,t){
e = e||Event; t = e.target||e.srcElement; loads.push( t.src );
/// you can do your "timing/start animation" calculation here...
/// check to see if we are complete
if ( loads.length >= paths.length ) { done(); }
/// if not fire off the next image load
else { next(); }
}
var next = function(){
/// current will be the next image
var current = buffer.shift();
/// set the load going for the current image
if ( current ) { current.img.src = current.path; }
}
var load = function(){
var i, l = paths.length, img;
for( i=0; i<l; i++ ){
img = new Image();
img.onload = loaded;
/// build up a list of images and paths to load
buffer.push({ img: img, path: paths[i] });
}
/// set everything going
next();
}
If the above doesn't do it, another way of getting around the issue would be to step through your list of paths, one at a time, and append a string of image markup (that would render off-screen) to the DOM with it's own onload="next()" handler... next() would be responsible for inserting the next image. By doing this it would hand off the triggering of the load and the subsequent load event to outside of your code, and should get around stacking calls.

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