How to zoom in image window

Question

This is my code.
I can enlarge the image, but not at some point. How to zoom to the point of the mouse when I turn the mouse wheel?

Variables: -

private double m_dZoomscale = 1.0; //THIS IS THE ZOOM SCALE TO WHICH EACH OBJECT //ARE ZOOMED IN THE CANVAS public static double s_dScrollValue = .01; //scale factor value for mouse scroll zooming 

Paint Code: -

 private void m_Picturebox_Canvas_Paint(object sender, PaintEventArgs e) { Graphics g = e.Graphics; g.ScaleTransform((float)m_dZoomscale, (float)m_dZoomscale); } 

Main code: -

  protected override void OnMouseWheel(MouseEventArgs mea) { m_Picturebox_Canvas.Focus(); if (m_Picturebox_Canvas.Focused == true) { if (mea.Delta > 0) { ZoomInScroll(); } else if (mea.Delta < 0) { ZoomOutScroll(); } } } 

Subfunctions are as follows: -

  //FUNCTION FOR MOUSE SCROL ZOOM-IN private void ZoomInScroll() { m_dZoomscale = m_dZoomscale + s_dScrollValue; m_Picturebox_Canvas.Invalidate(); } //FUNCTION FOR MOUSE SCROL ZOOM-IN private void ZoomOutScroll() { m_dZoomscale = m_dZoomscale - s_dScrollValue; m_Picturebox_Canvas.Invalidate(); } 

Answer 1

Here's how you achieve it (description below):

Variables

 // this tracks the transformation applied to the PictureBox Graphics private Matrix transform = new Matrix(); public static double s_dScrollValue = 1.01; // zoom factor 

Paint code

 private void m_Picturebox_Canvas_Paint(object sender, PaintEventArgs e) { Graphics g = e.Graphics; g.Transform = transform; } 

Scroll code

 protected override void OnMouseWheel(MouseEventArgs mea) { m_Picturebox_Canvas.Focus(); if (m_Picturebox_Canvas.Focused == true && mea.Delta != 0) { ZoomScroll(mea.Location, mea.Delta > 0); } } 

Zoom function

 //FUNCTION FOR MOUSE SCROL ZOOM-IN private void ZoomScroll(Point location, bool zoomIn) { // make zoom-point (cursor location) our origin transform.Translate(-location.X, -location.Y); // perform zoom (at origin) if(zoomIn) transform.Scale(s_dScrollValue, s_dScrollValue); else transform.Scale(1 / s_dScrollValue, 1 / s_dScrollValue); // translate origin back to cursor transform.Translate(location.X, location.Y); m_Picturebox_Canvas.Invalidate(); } 

Description

First of all, as you can see, I combined the two scaling methods with one method: ZoomScroll Otherwise, we will duplicate a lot of logic ...

So what is being done here? I think it’s clear that we also need to apply the translation to the Graphics object. We "accumulate" all the transformations applied to the PictureBox in the Matrix field.

You have successfully scaled your image, but always with the beginning (upper left corner of the PictureBox ) as the local center of your zoom operation - this is how Scale / ScaleTransform ! Therefore, to scale to another, you must perform the following steps:

• translate the world, so the point you want to scale is a new origin (for example, your cursor is at 12|34 , so we translate to -12|-34 )
• now that the desired spot is our new origin, scale
• move the world back, so the starting point will again be under your cursor.