Search code examples
javascripthtmlcssflexbox

Force a canvas to use available space in a flex column

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)

enter image description 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 -).

Solution

  • 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>