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Content

• Features
• Getting started
• Usage
  • Highlight a simple text
  • Highlight a text field
  • Highlight a text span
• You may like to know
  • Change the corner radius
  • Known issues with the text field,
  • Deep dive
• Contribution

Features

• ✅ Highlight Text
• ✅ Highlight Text Field
• ✅ Highlight Text Span

Getting started

Import the package:

import 'package:rounded_background_text/rounded_background_text.dart';

Usage

Highlight a simple text:

RoundedBackgroundText(
  'A cool text to be highlighted',
  style: const TextStyle(fontWeight: FontWeight.bold),
  backgroundColor: Colors.white,
),

Multiline text is also supported

RoundedBackgroundText(
  'A cool text to be highlighted\nWith two lines or more',
  style: const TextStyle(fontWeight: FontWeight.bold),
  backgroundColor: Colors.amber,
),

Highlight a text field:

You must use a TextEditingController

RoundedBackgroundTextField(
  backgroundColor: Colors.blue,
  style: const TextStyle(fontWeight: FontWeight.bold),
  textAlign: TextAlign.center,
),

The text will be highlighted as the user types

The text highlight will follow the text field scroll position.

Highlight a text span:

Highlight a small part of a text

RichText(
  text: TextSpan(
    text: 'Start your text and ',
    children: [
      RoundedBackgroundTextSpan(
        text: 'highlight something',
        backgroundColor: Colors.blue,
      ),
      const TextSpan(text: ' when necessary'),
    ],
  ),
),

Select a highlighted text:

Use RoundedBackgroundText.selectable to make the text selectable:

RoundedBackgroundText.selectable(
  'A cool highlighted text to be selected',
  style: const TextStyle(fontWeight: FontWeight.bold),
  backgroundColor: Colors.white,
),

You may like to know:

Change the corner radius

You can change the radius of the corners by setting innerRadius and outerRadius:

RoundedBackgroundText(
  'A cool text to be highlighted',
  style: const TextStyle(fontWeight: FontWeight.bold),
  backgroundColor: Colors.white,
  innerRadius: 15.0,
  outerRadius: 10.0,
),

The max allowed value is 20.0. The min is 0.0

Deep dive

This section explains, with details, how the background painting works.

RoundedBackgroundText doesn't use a Text widget under the hood. Instead, it uses a custom text painter to paint the text above the background. As soon as the RoundedBackgroundText widget is initialized, the line metrics for the text is calculated (See computeLineMetrics), and is recalculated when the text changes or when the parent width changes. This is done at built time, resulting in a smooth experience for the user.

To paint the background, the line metrics generated before is used. Each line has 4 properties:

• x - where the line starts horizontally within the size
• y - where the line starts vertically within the size
• width - the horizontal size of the line
• height - the vertical size of the line

With these values, we can generate the background for each line. The background is generated around the whole text: from top-left to bottom-left to bottom-right to top-right to top-left. This makes it easy to calculate when there is a corner, either outer or inner.

The inner and outer radius are dynamically calculated based on the line height, provided by the line metrics, and the given innerRadius and outerRadius, respectively. By default, innerRadius is 10.0 and outerRadius is 10.0. For safety, in order to keep the roundnesses correct, these values must be in the bounds of 0.0 (min) and 20.0 max, otherwise the painting would be out the line.

Contribution

Feel free to file an issue if you find a problem or make pull requests.

All contributions are welcome!