Скачать или смотреть Fixing Text Position in PyQtGraph with QLabel: A Solution for Image Overlays

Discover how to maintain fixed text overlay positions using `QLabel` in PyQtGraph and PySide2, allowing for effective image display while ensuring text remains static during pan/zoom.
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This video is based on the question https://stackoverflow.com/q/66327667/ asked by the user 'Oli N' ( https://stackoverflow.com/u/13756359/ ) and on the answer https://stackoverflow.com/a/66327824/ provided by the user 'eyllanesc' ( https://stackoverflow.com/u/6622587/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

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Introduction

If you're working with PyQtGraph and PySide2 to visualize 2D images, such as CT or MRI datasets, you may have come across the challenge of overlaying text onto your images. The need to keep that text static while users pan and zoom through images is essential for providing critical information — like pixel size or viewing parameters — in a consistent and user-friendly manner. In this guide, we will address the specific issues you've encountered and present a solution to achieve fixed text positions in your image viewer.

The Problem

When overlaying text on images in PyQtGraph, you might want certain text to maintain its screen position regardless of any zoom or pan actions performed by the user. Common challenges when trying to implement this include:

Difficulty in disabling user-dragging on legend items.

Inability to control the text's position effectively using methods like .setPos().

Issues with hiding unwanted lines or styling in legend items.

Choosing between different text overlay options like LabelItem or TextItem, and understanding their behavior in relation to image positioning.

Why Choose QLabel?

While LabelItem and TextItem are commonly used in PyQtGraph, they can sometimes keep shifting with the image, making it difficult to maintain a steady textual reference. A better approach involves using a QLabel within the viewport of the QGraphicsView used by ImageView. This method allows for the creation of labels that will not be impacted by the movement of the image itself.

Solution: Implementing Fixed Text with QLabel

Here’s how you can implement a fixed text overlay using QLabel in your PyQtGraph application:

Step 1: Modify the MyImageWidget Class

Below is an example of how you can modify your existing MyImageWidget class to include a QLabel that functions as a static overlay for text.

[[See Video to Reveal this Text or Code Snippet]]

Step 2: Understand the Code

Class Initialization: Like before, you inherit from pg.ImageView and perform your standard UI management.

Image Setup: You generate a random image, allowing for a dynamic view.

Adding QLabel: By creating a QLabel and attaching it directly to the viewport, you position it using move(), which refers to its location in the viewport rather than the image itself. This is where the magic happens — the label will stay in the specified location even when the image moves or scales.

Step 3: Run the Application

Finally, make sure to run the application using the standard PyQt execution pattern:

[[See Video to Reveal this Text or Code Snippet]]

Conclusion

By using QLabel within the QGraphicsView viewport in your PyQtGraph application, you can effectively maintain static text overlays regardless of user interactions with the image. This solution not only resolves the issues with dragging and positioning that come with LabelItem or TextItem, but it allows you to create a more professional and user-friendly interface. Happy coding!