Can a canvas be forced to use available space in a flex column?

Basj
May 11, 2023
162 views
4 votes
4 Answers

I have a full size page, containing a top toolbar, and below, a container with 2 columns:

a right column
a left column containing a canvas (centered horizontally and vertically in this column), which has its own coordinates system (typically 4000 x 3000) and should preserve this aspect ratio. This canvas has a "+" button layered on it. (In my real code, there are several canvas for multiple layers, and multiple buttons, but not important here)

Here it nearly works, but I can’t make the canvas occupy the full available space in the left column.

With all methods that I tried (max-width: 100%, max-height: 100%), either it fails when we zoom in / out in the browser (70% 80% … 150 %), or it fails because the method used prevents the button to stay on top of the canvas, at its right corner.

TL;DR: how to make this canvas take all available space in the left column, keeping its aspect ratio, keeping the layered buttons, without overflow?

Note: I’m looking for a CSS solution, the JS is not for the positioning, but only the drawing.

ctx = document.querySelector("canvas").getContext("2d");
ctx.fillStyle = "#FF0000"; ctx.fillRect(0, 0, 1000, 1000);
ctx.fillStyle = "#00FF00"; ctx.fillRect(1000, 1000, 1000, 1000);
ctx.fillStyle = "#0000FF"; ctx.fillRect(2000, 2000, 1000, 1000);
ctx.fillStyle = "#000000"; ctx.fillRect(3000, 0, 1000, 1000);

* {
  padding: 0;
  margin: 0;
}

.page {
  display: flex;
  flex-direction: column;
  height: 100vh;
}

.toolbar {
  background-color: yellow;
  flex: 0 0 5em;
}

.container {
  background-color: orange;
  flex: 1 0 0;
  display: flex;
}

.left {
  background-color: magenta;
  flex: 1 0 0;
  display: flex;
  align-items: center;
  justify-content: center;
}

.right {
  background-color: salmon;
  flex: 0 0 10em;
}

.canvas-wrapper {
  background-color: grey;
  display: flex;
  position: relative;
}

canvas {
  height: 100px;
  background-color: white;
}

.button {
  background-color: yellow;
  position: absolute;
  top: 0;
  right: 0;
  width: 1em;
  height: 1em;
}

<div class="page">
  <div class="toolbar">
    TOOLBAR OF HEIGHT 5 EM
  </div>
  <div class="container">
    <div class="left">
      <div class="canvas-wrapper">
        <canvas width="4000" height="3000"></canvas>
        <div class="button">+</div>
      </div>
    </div>
    <div class="right">
      RIGHT OF WIDTH 10 EM
    </div>
  </div>
</div>

PS: you have to open the snippet in "Full page" to see the browser zoom in / zoom out feature (CTRL + , CTRL -).

Answers

Chosen as BEST ANSWER

Here is an answer based on RokBenko's answer which seems to work, without the secondary wrapper and the secondary flex:

ctx = document.querySelector("canvas").getContext("2d");
ctx.fillStyle = "#FF0000";
ctx.fillRect(0, 0, 1000, 1000);
ctx.fillStyle = "#00FF00";
ctx.fillRect(1000, 1000, 1000, 1000);
ctx.fillStyle = "#0000FF";
ctx.fillRect(2000, 2000, 1000, 1000);
ctx.fillStyle = "#000000";
ctx.fillRect(3000, 0, 1000, 1000);

* {
  padding: 0;
  margin: 0;
}

.page {
  display: flex;
  flex-direction: column;
  height: 100vh;
}

.toolbar {
  background-color: yellow;
  flex: 0 0 5em;
}

.container {
  background-color: orange;
  flex: 1 0 0;
  display: flex;
}

.left {
  background-color: magenta;
  flex: 1 0 0;
  display: flex;
  align-items: center;
  justify-content: center;
}

.right {
  background-color: salmon;
  flex: 0 0 10em;
}

.canvas-wrapper {
  background-color: #aaa;
  position: relative;
}

canvas {
  background-color: white;
  width: 100%;
  max-height: calc(100vh - 5em);
}

.button {
  background-color: yellow;
  position: absolute;
  top: 0;
  right: 0;
  width: 1em;
  height: 1em;
}

<div class="page">
  <div class="toolbar">
    TOOLBAR OF HEIGHT 5 EM
  </div>
  <div class="container">
    <div class="left">
      <div class="canvas-wrapper">
        <canvas width="4000" height="3000"></canvas>
        <div class="button">+</div>
      </div>
    </div>
    <div class="right">
      RIGHT OF WIDTH 10 EM
    </div>
  </div>
</div>

(Edit)

You need to change some alignments, widths, heights, flex-grows and add an HTML wrapper (i.e., <div class="canvas-wrapper-inner">).

See the snippet below.

ctx = document.querySelector("canvas").getContext("2d");
ctx.fillStyle = "#FF0000";
ctx.fillRect(0, 0, 1000, 1000);
ctx.fillStyle = "#00FF00";
ctx.fillRect(1000, 1000, 1000, 1000);
ctx.fillStyle = "#0000FF";
ctx.fillRect(2000, 2000, 1000, 1000);
ctx.fillStyle = "#000000";
ctx.fillRect(3000, 0, 1000, 1000);

* {
  padding: 0;
  margin: 0;
}

.page {
  display: flex;
  flex-direction: column;
  height: 100vh;
}

.toolbar {
  background-color: yellow;
  flex: 0 0 5em;
}

.container {
  background-color: orange;
  flex: 1 0 0;
  display: flex;
}

.left {
  background-color: magenta;
  flex: 1 0 0;
  display: flex;
  align-items: center;
  justify-content: center;
}

.right {
  background-color: salmon;
  flex: 0 0 10em;
}

.canvas-wrapper {
  background-color: grey;
  display: flex;
  position: relative;
  flex-grow: 1; /* Added */
  align-self: stretch; /* Added */
  align-items: center; /* Added */
  justify-content: center; /* Added */
}

canvas {
  width: 100%; /* Added */
  flex-grow: 1; /* Added */
  object-fit: contain; /* Added */
  max-height: calc(100vh - 5em); /* Added */
}

.button {
  background-color: yellow;
  position: absolute;
  top: 0;
  right: 0;
  width: 1em;
  height: 1em;
}

/* Added */
.canvas-wrapper-inner {
  position: relative;
}

<div class="page">
  <div class="toolbar">
    TOOLBAR OF HEIGHT 5 EM
  </div>
  <div class="container">
    <div class="left">
      <div class="canvas-wrapper">
        <div class="canvas-wrapper-inner">
          <canvas width="4000" height="3000"></canvas>
          <div class="button">+</div>
        </div>
      </div>
    </div>
    <div class="right">
      RIGHT OF WIDTH 10 EM
    </div>
  </div>
</div>

There’s a handy unit size called cqmin which is the lowest size of the inline or block sizes. Set container wrapper as a container of type size so the content responds to both block and inline dimesions then set the width of the canvas to 100cqmin. Use aspect-ratio to maintain the, er, aspect ratio. See example below. I’ve put a codepen of it here too.

ctx = document.querySelector("canvas").getContext("2d");
ctx.fillStyle = "#FF0000"; ctx.fillRect(0, 0, 1000, 1000);
ctx.fillStyle = "#00FF00"; ctx.fillRect(1000, 1000, 1000, 1000);
ctx.fillStyle = "#0000FF"; ctx.fillRect(2000, 2000, 1000, 1000);
ctx.fillStyle = "#000000"; ctx.fillRect(3000, 0, 1000, 1000);

* {
  padding: 0;
  margin: 0;
}

.page {
  display: flex;
  flex-direction: column;
  height: 100vh;
}

.toolbar {
  background-color: yellow;
  flex: 0 0 5em;
}

.container {
  background-color: orange;
  flex: 1 0 0;
  display: flex;
}

.left {
  container-type: size;
  background-color: magenta;
  flex: 1 0 0;
  display: flex;
  align-items: center;
  justify-content: center;
}

.right {
  background-color: salmon;
  flex: 0 0 10em;
}

.canvas-wrapper {
  position: relative;
  width: 100cqmin;
}

.button {
  background-color: yellow;
  position: absolute;
  top: 0;
  right: 0;
  width: 1em;
  height: 1em;
}

canvas {
  width: 100%;
  aspect-ratio: 4/3;
  background-color: white;
}

<div class="page">
  <div class="toolbar">
    TOOLBAR OF HEIGHT 5 EM
  </div>
  <div class="container">
    <div class="left">
      <div class="canvas-wrapper">
        <canvas width="4000" height="3000"></canvas>
        <div class="button">+</div>
      </div>
    </div>
    <div class="right">
      RIGHT OF WIDTH 10 EM
    </div>
  </div>
</div>

This is based on my other answer on the related question. The idea is:

Use Flexbox to create fixed + fluid layout
Place the canvas inside the fluid section
Use relative + absolute positioning to scale and center the canvas element

ctx = document.querySelector("canvas").getContext("2d");
ctx.fillStyle = "#FF0000";
ctx.fillRect(0, 0, 1000, 1000);
ctx.fillStyle = "#00FF00";
ctx.fillRect(1000, 1000, 1000, 1000);
ctx.fillStyle = "#0000FF";
ctx.fillRect(2000, 2000, 1000, 1000);
ctx.fillStyle = "#000000";
ctx.fillRect(3000, 0, 1000, 1000);

body {
  margin: 0;
}

.page {
  height: 100vh;
  display: flex;
  flex-direction: column;
}

.toolbar {
  background-color: yellow;
  flex: 0 0 5em;
}

.container {
  background-color: orange;
  flex: 1 1 auto;
  /* make it the wrapper for two column layout */
  display: flex;
  flex-direction: row;
}

.left {
  background-color: magenta;
  flex: 1 1 auto;
  /* make it the wrapper for canvas */
  position: relative;
}

.right {
  background-color: salmon;
  flex: 0 0 10em;
  align-self: center;
}

canvas {
  background-color: gray;
  position: absolute;
  left: 0;
  right: 0;
  top: 0;
  bottom: 0;
  margin: auto;
  width: auto;
  height: auto;
  max-width: 100%;
  max-height: 100%;
}

<div class="page">
  <div class="toolbar">
    TOOLBAR OF HEIGHT 5 EM
  </div>
  <div class="container">
    <div class="left">
      <canvas width="4000" height="3000"></canvas>
    </div>
    <div class="right">
      RIGHT OF WIDTH 10 EM
    </div>
  </div>
</div>

To handle the + button, I suggest a similar solution where you wrap the canvas and the button inside a wrapper element which is forced to act like an inline-replaced element:

ctx = document.querySelector("canvas").getContext("2d");
ctx.fillStyle = "#FF0000";
ctx.fillRect(0, 0, 1000, 1000);
ctx.fillStyle = "#00FF00";
ctx.fillRect(1000, 1000, 1000, 1000);
ctx.fillStyle = "#0000FF";
ctx.fillRect(2000, 2000, 1000, 1000);
ctx.fillStyle = "#000000";
ctx.fillRect(3000, 0, 1000, 1000);

body {
  margin: 0;
}

.page {
  height: 100vh;
  display: flex;
  flex-direction: column;
}

.toolbar {
  background-color: yellow;
  flex: 0 0 5em;
}

.container {
  background-color: orange;
  flex: 1 1 auto;
  /* make it the wrapper for two column layout */
  display: flex;
  flex-direction: row;
}

.left {
  background-color: magenta;
  flex: 1 1 auto;
  /* make it the wrapper for canvas */
  position: relative;
}

.right {
  background-color: salmon;
  flex: 0 0 10em;
  align-self: center;
}

.canvas-wrapper {
  background-color: gray;
  position: absolute;
  left: 0;
  right: 0;
  top: 0;
  bottom: 0;
  margin: auto;
  max-width: 100%;
  max-height: 100%;
}

canvas {
  display: block;
  width: 100%;
  height: 100%;
}

.button {
  background-color: yellow;
  position: absolute;
  top: 0;
  right: 0;
  width: 1em;
}

<div class="page">
  <div class="toolbar">
    TOOLBAR OF HEIGHT 5 EM
  </div>
  <div class="container">
    <div class="left">
      <div class="canvas-wrapper" style="aspect-ratio: 4000 / 3000;">
        <canvas width="4000" height="3000"></canvas>
        <div class="button">+</div>
      </div>
    </div>
    <div class="right">
      RIGHT OF WIDTH 10 EM
    </div>
  </div>
</div>

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