Support Negative `desired_width` in TextEdit

[varphone]

Support Negative desired_width in TextEdit

Summary

This PR adds support for negative values in TextEdit::desired_width(), allowing developers to specify width relative to available space by subtraction.

Changes

• Core Feature: Modified TextEdit::desired_width() to accept negative values

  • Negative values subtract from available width (e.g., -50.0 means available_width - 50.0)
  • Maintains backward compatibility with existing positive values and f32::INFINITY
  • Added documentation explaining the new behavior

• Demo: Added example showcasing the feature

  • Demonstrates a singleline TextEdit that reserves space for a Clear button
  • Made the demo window resizable to show dynamic behavior
  • Added hover tooltip for better user understanding

Use Case

This is particularly useful when you want a TextEdit to fill most of the available space while leaving room for adjacent widgets (like buttons) in the same horizontal layout:

ui.horizontal(|ui| {
    ui.add(egui::TextEdit::singleline(&mut text).desired_width(-50.0));
    if ui.button("Clear").clicked() {
        text.clear();
    }
});

Implementation Details

• Width calculation now handles three cases:
  1. f32::INFINITY: uses full available width
  2. Positive values: uses minimum of desired and available width
  3. Negative values: subtracts from available width with a minimum of 0.0

Testing

• Tested with the demo application
• Verified behavior when resizing the window
• Confirmed backward compatibility with existing code

[github-actions[bot]]

Preview available at https://egui-pr-preview.github.io/pr/7717-featuretextedit-negative-desiredwidth Note that it might take a couple seconds for the update to show up after the preview_build workflow has completed.

View snapshot changes at kitdiff

[emilk]

This feels like a unique snowflake. Why would negative values work that way for TextEdit, and nothing else?

And why can't the user just call .desired_width(ui.available_width() - 50.0) instead?