Kevin Powell - Community•7mo ago

Canvas in flexbox not resizing properly

Any idea why the canvas in this example code takes the full width of the viewport? https://codepen.io/codecab/pen/abXaKJr?editors=1100 When I replace the canvas with a div it works as expected. I put the canvas in a wrapper element for now, which works, but I'd like to understand why its behaving as it does. Am I missing something?

29 Replies

MarkBoots•7mo ago

your body has a height of 100vh and has display: flex; the canvas has flex-grow: 1 which allows it to grow to the full available space of the flex container (the body)

ccabd•7mo ago

but why does it behave differently when i replace the canvas with a div ?

MarkBoots•7mo ago

because your div probably is not a flex-container

ccabd•7mo ago

try it out for yourself in the pen, just change canvas to div

MarkBoots•7mo ago

flex-grow works only when its parent has display flex so if you put a div in between, it has no effect, and it wont grow

ccabd•7mo ago

not in between

MarkBoots•7mo ago

i mean around

ccabd•7mo ago

<div id="canvas"></div>

<aside id="config">
    <button id="regenerate">regenerate</button>
</aside>

<div id="canvas"></div>

<aside id="config">
    <button id="regenerate">regenerate</button>
</aside>

instead of

<canvas id="canvas"></canvas>

<aside id="config">
    <button id="regenerate">regenerate</button>
</aside>

<canvas id="canvas"></canvas>

<aside id="config">
    <button id="regenerate">regenerate</button>
</aside>

with same css, behaves differently, thats what is confusing to me

MarkBoots•7mo ago

ah okay, now i see what you mean.

ccabd•7mo ago

thank you 😄

MarkBoots•7mo ago

haha, that indeed is strange. never noticed that with canvas. really weird. have to dive into that somehow it grows respecting the aspect-ratio and gets to wide

ccabd•7mo ago

yeah that what i was thinking too, but object-fit: none didn't have any effect either

MarkBoots•7mo ago

have never seen that behaviour before. even with unset: all as the first line in canvas, it still does it

ccabd•7mo ago

first time in years i have to actually wrap an element for it to behave

MarkBoots•7mo ago

i always had canvas within a wrapper, so never noticed this

ccabd•7mo ago

i guess its an acceptable workaround, but im still curious so if you happen to have an idea, lmk 🙂

MarkBoots•7mo ago

when you set width: 0 it works there must be a logical reason why it behaves like this (which I can not think of).

ccabd•7mo ago

huh, indeed min-width: 0 works as well

MarkBoots•7mo ago

i do think you would like to respect the dimensions. what you draw on to it wont be responsive. the ctx needs to know the size it will stretch what you draw

ccabd•7mo ago

i'm playing around with creating a minigame, so as part of my render loop i resize the canvas like this

function resizeCanvas() {
    const height = canvas.clientHeight;
    const width = canvas.clientWidth;

    if ( canvas.height !== height || canvas.width !== width ) {
        canvas.height = height;
        canvas.width = width;
    }
}

function resizeCanvas() {
    const height = canvas.clientHeight;
    const width = canvas.clientWidth;

    if ( canvas.height !== height || canvas.width !== width ) {
        canvas.height = height;
        canvas.width = width;
    }
}

MarkBoots•7mo ago

ah ok.. yea, might work for you

ccabd•7mo ago

for now it does. first time really diving into canvas so i'll probably make a lot of mistakes along the way, but that's the fun part, isnt it anyways, i removed the wrapper and added min-width, thanks for helping out 🙂

MarkBoots•7mo ago

if you want to do it all in vanilla js. i'd recommend watching franks labarotory on youtube. he makes great things on canvas ans explains it really well

ccabd•7mo ago

i faintly remember something about some elements in some circumstances needing an explicit width set, but for the love of god i can't remember any specifics alright, might check it out 🙂

MarkBoots•7mo ago

was a long time ago i did something on canvas. i made some easy clocks and small tic tac toe like games, but that's about it.

MarkBoots•7mo ago

here some older pens https://codepen.io/collection/waQVVW

CodePen

canvas - a Collection by Mark Boots on CodePen

ccabd•7mo ago

nice, the bubbly beer is a neat effect

ccabd•7mo ago

did you use a tool to generate the transforms applied here?

ccabd•7mo ago

ah nvm its svg code

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Canvas in flexbox not resizing properly