this post was submitted on 22 Mar 2025
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Programming

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Hi all, 

I'm working on my personal website, my first forway into javascript and web development.

I wanted to create a flip dot style display which has since morphed into more of a CRT look. 

You can take a look here if you like:  https://343f-66-113-2-158.ngrok-free.app/main.html

However, I've recently, when sending it to a friend, we found it only seems to work with any performance on Safari, sometimes in fact failing entirely on Chrome and Firefox.

I'm wondering if anyone has any ideas on how I might change my design to migigate this or whether there is some way to give myself more resources on firefox and chrome.

A cursary look into fixing this seems to suggest I should use RequestAnimationFrame, however, this drawing of all elements smoothly at once, while efficent, destroyes the organic effect that the timeouts gave both on the individual dot level and when refreshing line by line.

My general design is outlined here: 

I'm using HTML5 canvas; each dot is a class which redraws its section of the canvas with a 50-300 ms delay to emulate the per dot lag of a given hinge on a flip dot display. The display class again using setTimeOut(), schedules each line of the display, consisting of dots, to update at a slight offset so that you can see the display refresh from left to right. Then the rest of the program modifies the "next frame" array with text or images which I wish to be displayed. 

 

Thank you!

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[–] bleistift2@sopuli.xyz 13 points 1 day ago (1 children)

script.js, ll. 57ff.

    fillRect() {
        var sideColor = this.on_side_one ? this.c_side_1 : this.c_side_2;
        ctx.fillStyle = sideColor;
        ctx.fillRect(g_pixelOffset + (g_pixelOffset * this.x), g_pixelOffset + (g_pixelOffset * this.y), this.radius, this.radius);
    }

All these computations don’t have to be delayed until you’re actually drawing the dot. If you’d compute them when you’re creating the dot, the rendering might become smoother.

[–] crimsonpoodle@pawb.social 5 points 1 day ago

oh jeez! yeah that makes sense will add them to constructor thank you!

[–] simbico@lemmy.zip 7 points 2 days ago

Use requestAnimationFrame for the drawing loop. Dont instantiate new objects unless needed

[–] bleistift2@sopuli.xyz 6 points 1 day ago (1 children)

You’re mixing spaces and tabs for indentation. This makes it hard to read for anyone whose tab settings aren’t the same as yours.

[–] crimsonpoodle@pawb.social 6 points 1 day ago

Ah good to know just using tabs in vim but in two different machines so might be the issue— thanks!

[–] bleistift2@sopuli.xyz 5 points 1 day ago

With all these comments said, I experience no problems in Firefox on Linux, and I really like the art style. If one browser is troublesome to you, check which function(s) really are the culprit. (This is actually true for any optimization: Only optimize the stuff that’s slow (duh)).

[–] bleistift2@sopuli.xyz 5 points 1 day ago

First: For every performance optimization you do, you must actually measure if it improves things. It could be that you’re doing a perfectly sensible optimization, which turns out to work against the compiler (yes, even JavaScript is compiled) and thus decreases performance.

[–] bleistift2@sopuli.xyz 5 points 1 day ago* (last edited 1 day ago) (1 children)

In script.js, l.149ff:

	drawImage(Image, topLeftX, topLeftY) {
		for (let row = 0; row < Image.length; row++) {
			for(let column = 0; column < Image[row].length; column++) {
				this.nextFrame[(topLeftX + column)*this.height + (topLeftY+row)] = Image[row][column];
			}
		}
	}

The term topLeftX + column * this.height can be rewritten as topLeftX * this.height + column * this.height. The first term of this is a constant and can be extracted into a variable const verticalOffset = topLeftX * this.height.

Similarly, topLeftY + row doesn’t need to be recomputed in every iteration of the inner for loop. Move it out into the outer for loop.

Also notice that the variable part, column * this.height is all the integer multiples of this.height. Therefore, instead of a multiplication, you can simply add this.height to a running total. Sums should be faster than multiplications.

With these three changes you get [Edit: I think I made mistakes during the replacements.]

drawImage(Image, topLeftX, topLeftY) {
	const TODO_NAME_THIS = topLeftX * this.height
	let TODO_NAME_THIS_ALSO = topLeftY
	for (let row = 0; row < Image.length; row++) {
		let TODO_NAME_THIS_TOO = 0
		for(let column = 0; column < Image[row].length; column++) {
			this.nextFrame[TODO_NAME_THIS + TODO_NAME_THIS_TOO + TODO_NAMES_THIS_ALSO] = Image[row][column];
			TODO_NAME_THIS_TOO += this.height
		}
		TODO_NAME_THIS_ALSO += row
	}
}
[–] crimsonpoodle@pawb.social 2 points 1 day ago

Ah yes I see! That should offer some improvement given the number of times it’s called— also see I’m used to swift so I keep using let when I should probably use const— thanks I’ll give it a try and let you know what happens!

[–] bleistift2@sopuli.xyz 4 points 1 day ago* (last edited 1 day ago)

script.js, ll. 788ff.

for (var i = 0; i < elements.length; i++)

If you’re not using the index of an iteration, you might as well use the array iterator. This is more of a legibility improvement rather than a performance improvement.

for (const element of elements)
[–] TheMightyCat@lemm.ee 1 points 2 days ago* (last edited 1 day ago) (1 children)

A random suggestion would be to draw to multiple canvases, and use a CSS animation for the delay.

Also not sure if you are already doing this but it might be more peformant to use the raw buffer instead of draw functions.

Alternatively you could look into webgpu, it is ment for these kind of things.

[–] bleistift2@sopuli.xyz 1 points 1 day ago (1 children)

I’ve thought about setting whole ‘images’ inside the canvas at once, but that would probably ruin the pixel-by-pixel style OP was going for. Do you have a suggestion how that could be maintained while not drawing every pixel individually?

[–] TheMightyCat@lemm.ee 2 points 1 day ago* (last edited 1 day ago)

All the calculations could be done before hand and stored and then the only thing left in the delayed draw is to set the buffer.

I haven't looked at the code yet so not sure how much if any it will save though.

Could also group pixels that are far away from eachother into a single call, while a compromise i think it will maintain the effect.