changing color of pixel on image when user clicks

Question

User-881450349 posted

I have an image control with a jpg in it. When my user clicks on a particular pixel, I would like for the pixel to change color. What is the simplest way to do this. I do not mind if it means a postback.

 

Thank you,

Sam

Answer 1

User-881450349 posted

Someone must have an idea for this surely?!

Please help,

Sam

Answer 2

User-1395392389 posted

If you don't mind the postback, this can be easily done using an ImageButton and handlling its click event:
The delegate for that event is an ImageClickEventHandler, let's say:

protected void myImg_Click(object sender, ImageClickEventArgs e){
    // coordinates of the clicked point
    int x = e.X;
    int y = e.Y;
    //
    ((ImageButton)sender).ImageUrl = string.Format(
        "~/myImagingProxy.ashx?x={0}&y={1}", x, y);
}

In the myImagingProxy,ashx file you have to handle the image generation process and the single line of code that changes the aspect of the clicked pixel:

 
public class myImagingProxy: IHttpHandler {
    
    public void ProcessRequest (HttpContext context) {
        context.Response.ContentType = "image/jpeg";
        using (Bitmap img = (Bitmap)
            Bitmap.FromFile("c:\\myJpg.jpg"))
        {
            int x = int.Parse(context.Request.QueryString["x"]);
            int y = int.Parse(context.Request.QueryString["y"]);
            img.SetPixel(x, y, Color.Red);
            img.Save(context.Response.OutputStream, 
                System.Drawing.Imaging.ImageFormat.Jpeg);
        }
    }
}
 

 That should do the work, hope it helps.

PS: the same task can be accomplished via javascript in a similar manner (getting the Mouse position on a client-side click event and matching it with the position of the underying img object)