How to Correctly Zoom and Translate an Image from the Mouse Location in C#?

Zooming and Translating an Image from the Mouse Location

This article addresses the issue of zooming (scaling) an image from the mouse location using transforms in the Paint event. After translating the bitmap origin to the mouse location, the image is scaled and its origin translated back. However, the image "jumps" and fails to scale from the relocated origin during the mouse location translation.

Solution:

To resolve this issue, we implement the following strategies:

1. Divide and Conquer: Break down the graphics effects and transformations into specialized methods that perform specific tasks. Design these methods to work seamlessly together when required.
2. Keep it Simple: Avoid accumulating multiple graphic transformations within Matrix operations. Use Matrix.Multiply and Matrix.RotateAt for simpler calculations.
3. Use the Right Tools: Employ a PictureBox (or a non-System flat Label) as the "canvas" instead of a Panel. PictureBox provides double-buffering by default and is designed for drawing.

For visual demonstration, our sample code implements four zoom modes in a custom PictureBoxEx control:

• ImageLocation: The image scales in place, maintaining its current position on the canvas.
• CenterCanvas: The image retains its centered position on the canvas while scaling.
• CenterMouse: The image scales and translates to center itself on the mouse pointer's current location on the canvas.
• MouseOffset: The image scales and translates to preserve a relative position determined by the initial mouse pointer location on the image.

Code:

The code provided in the answer introduces the PictureBoxEx custom control that inherits from PictureBox and includes customized functionality. It also includes the canvas variable, which represents the custom control added to the form during initialization. The ZoomMode enum is used to define the different zoom modes.

The event handlers for mouse events and the track bar, as well as the core painting logic, handle the zoom and rotation operations based on the selected zoom mode.

Remember to modify the imagePath string to the actual path of your image file before running the code.

Benefits:

This approach provides a more efficient and stable method for zooming and translating images from the mouse location. It reduces the likelihood of unexpected visual artifacts or performance issues when handling complex transformations.

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