Скачать или смотреть How to Get the Correct Position of a Tkinter Canvas After Scrolling with a Scrollbar

Learn how to ensure that your drawing on a Tkinter canvas reflects the correct position after scrolling down with a scrollbar by using canvas methods.
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Solving the Scroll Issue in Tkinter Canvases

When creating graphical applications in Python, particularly those involving drawing on a canvas with scrolling capabilities, you may encounter a frustrating issue: your drawing does not align with your cursor when you scroll down. This problem often arises in applications using the Tkinter library when implementing a custom drawing tool. If you've experienced this, don't worry! We'll walk through how to obtain the correct position of your canvas after scrolling down.

The Problem Explained

In the scenario presented, the user is building a painting application using the customtkinter module. The application includes:

A scrollable canvas.

A function to draw ovals based on the cursor's position.

However, when the user scrolls down and attempts to draw, the drawn shapes appear in the wrong location. This results from the cursor's position being relative to the window, rather than the actual canvas coordinates after scrolling.

Why This Happens

When you scroll, the visible area of the canvas changes, but the drawing function still uses the original window coordinates.

The canvas needs to convert these window coordinates to its internal coordinate system to ensure that the shapes are correctly aligned with the cursor's actual position.

The Solution: Using Canvas Methods

To remedy this issue, Tkinter provides helpful methods to convert window coordinates to canvas coordinates: canvasx() and canvasy(). Utilizing these methods will enable you to determine the proper drawing position on the canvas.

Updating the Drawing Function

Instead of using the raw event coordinates, you can leverage the canvas methods as follows:

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

Breakdown of the Code:

Extracting the Position:

event.widget.canvasx(event.x) - Converts the x-coordinate from window to canvas coordinates.

event.widget.canvasy(event.y) - Converts the y-coordinate similarly.

Calculating the Oval Bounds:

fx and fy are calculated to set the top-left corner of the oval, and lx and ly define the bottom-right corner.

Drawing the Oval:

Using create_oval() to draw the oval in the calculated position, ensuring proper alignment on the canvas.

Conclusion

With these adjustments, your drawing method will reflect the correct positions on the canvas after scrolling. Utilizing the canvasx() and canvasy() methods effectively bridges the gap between window coordinates and canvas coordinates, solving the misalignment issue.

Now you can create applications that feel intuitive and responsive, enhancing the user experience in your painting or drawing applications. Happy coding!