Open the Scene Demo Window

Oct 13, 2025 by talynt.org 88 views

Introduction

In this article, we will discuss a bug that affects the text selection functionality in TextEdit when it is placed inside a Scene. This issue can be reproduced in the web demo provided by eGUI. We will go through the steps to reproduce the bug, the expected behavior, and the additional context that highlights a broader issue with input and painters using different coordinate spaces.

Describe the Bug

Text selection in a TextEdit is broken if the TextEdit is placed inside a Scene. This can directly be reproduced in the web demo provided by eGUI.

To Reproduce

To reproduce this bug, follow these steps:

Visit the Web Demo: Go to https://www.egui.rs/#demo.
Open the Scene Demo Window: Open the Scene demo window.
Type Something in the TextEdit Widget: Type something in the TextEdit widget.
Try to Select the Typed Text: Try to select the typed text by dragging.
Observe the Behavior: It likely won't work (unless the scene is panned exactly in the right place).
Pan Around in the Scene: If you're lucky and it works, pan around in the scene and try again.

Expected Behavior

The expected behavior is that selecting text works.

Desktop

The bug is observed on the following desktop configurations:

OS: OSX
Native App & Arc Browser

Additional Context

I have a potential fix for this bug, which is specific to TextEdit. However, I'm worried that this highlights a broader issue with (cursor) input and painters using different coordinate spaces as soon as a "Scene" component is involved. This is further problematic as developers of widgets are likely to assume these use the same space, and hence create widgets that subtly (or not so subtly) break once used within a Scene.

Understanding the Issue

The issue arises from the fact that the Scene component uses a different coordinate space than the TextEdit widget. This difference in coordinate spaces causes the text selection functionality to break. The Scene component is designed to provide a 3D view of the scene, while the TextEdit widget is designed to provide a 2D view of the text. When the TextEdit widget is placed inside the Scene component, the two different coordinate spaces cause the text selection functionality to fail.

Potential Fix

I have a potential fix for this bug, which is specific to TextEdit. The fix involves modifying the TextEdit widget to use the same coordinate space as the Scene component. This can be achieved by using a transformation matrix to convert the coordinates of the TextEdit widget to the coordinate space of the Scene component.

Broader Issue

The issue with the TextEdit widget is not an isolated problem. It highlights a broader issue with (cursor) input and painters using different coordinate spaces as soon as a "Scene" component is involved. This is a common problem in 3D graphics, where different components may use different coordinate spaces. To resolve this issue, developers need to ensure that all components use the same coordinate space.

Conclusion

Introduction

In our previous article, we discussed a bug that affects the text selection functionality in TextEdit when it is placed inside a Scene. This issue can be reproduced in the web demo provided by eGUI. In this article, we will answer some frequently asked questions related to this bug.

Q: What is the cause of the text selection bug in TextEdit?

A: The cause of the text selection bug in TextEdit is the difference in coordinate spaces between the Scene component and the TextEdit widget. The Scene component uses a 3D coordinate space, while the TextEdit widget uses a 2D coordinate space. This difference in coordinate spaces causes the text selection functionality to fail.

Q: How can I reproduce the bug?

A: To reproduce the bug, follow these steps:

Visit the web demo provided by eGUI at https://www.egui.rs/#demo.
Open the Scene demo window.
Type something in the TextEdit widget.
Try to select the typed text by dragging.
Observe the behavior. It likely won't work (unless the scene is panned exactly in the right place).

Q: What is the expected behavior?

A: The expected behavior is that selecting text works.

Q: Is this bug specific to TextEdit?

A: No, this bug is not specific to TextEdit. It highlights a broader issue with (cursor) input and painters using different coordinate spaces as soon as a "Scene" component is involved.

Q: How can I fix the bug?

A: A potential fix involves modifying the TextEdit widget to use the same coordinate space as the Scene component. This can be achieved by using a transformation matrix to convert the coordinates of the TextEdit widget to the coordinate space of the Scene component.

Q: What are the implications of this bug?

A: The implications of this bug are that developers of widgets may assume that these use the same space, and hence create widgets that subtly (or not so subtly) break once used within a Scene. This highlights a broader issue with (cursor) input and painters using different coordinate spaces as soon as a "Scene" component is involved.

Q: Can this bug be fixed in the Scene component?

A: Yes, this bug can be fixed in the Scene component by modifying it to use the same coordinate space as the TextEdit widget. However, this would require significant changes to the Scene component and may have unintended consequences.

Q: What is the status of the bug?

A: The status of the bug is that it is currently being investigated and a potential fix is being developed.

Conclusion

In conclusion, the text selection functionality in TextEdit is broken when placed inside a Scene. This issue can be reproduced in the web demo provided by eGUI. The bug is caused by the difference in coordinate spaces between the Scene component and the TextEdit widget. A potential fix involves modifying the TextEdit widget to use the same coordinate space as the Scene component. However, this highlights a broader issue with (cursor) input and painters using different coordinate spaces as soon as a "Scene" component is involved.