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36 lines
2.3 KiB
Markdown
36 lines
2.3 KiB
Markdown
# Responsive Charts
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When it comes to change the chart size based on the window size, a major limitation is that the canvas *render* size (`canvas.width` and `.height`) can **not** be expressed with relative values, contrary to the *display* size (`canvas.style.width` and `.height`). Furthermore, these sizes are independent from each other and thus the canvas *render* size does not adjust automatically based on the *display* size, making the rendering inaccurate.
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The following examples **do not work**:
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- `<canvas height="40vh" width="80vw">`: **invalid** values, the canvas doesn't resize ([example](https://codepen.io/chartjs/pen/oWLZaR))
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- `<canvas style="height:40vh; width:80vw">`: **invalid** behavior, the canvas is resized but becomes blurry ([example](https://codepen.io/chartjs/pen/WjxpmO))
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Chart.js provides a [few options](#configuration-options) to enable responsiveness and control the resize behavior of charts by detecting when the canvas *display* size changes and update the *render* size accordingly.
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## Configuration Options
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| Name | Type | Default | Description
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| ---- | ---- | ------- | -----------
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| `responsive` | `Boolean` | `true` | Resizes the chart canvas when its container does ([important note...](#important-note)).
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| `responsiveAnimationDuration` | `Number` | `0` | Duration in milliseconds it takes to animate to new size after a resize event.
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| `maintainAspectRatio` | `Boolean` | `true` | Maintain the original canvas aspect ratio `(width / height)` when resizing.
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| `onResize` | `Function` | `null` | Called when a resize occurs. Gets passed two arguments: the chart instance and the new size.
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## Important Note
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Detecting when the canvas size changes can not be done directly from the `CANVAS` element. Chart.js uses its parent container to update the canvas *render* and *display* sizes. However, this method requires the container to be **relatively positioned** and **dedicated to the chart canvas only**. Responsiveness can then be achieved by setting relative values for the container size ([example](https://codepen.io/chartjs/pen/YVWZbz)):
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```html
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<div class="chart-container" style="position: relative; height:40vh; width:80vw">
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<canvas id="chart"></canvas>
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</div>
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```
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The chart can also be programmatically resized by modifying the container size:
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```javascript
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chart.canvas.parentNode.style.height = '128px';
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```
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