Drawing a Zoom Rectangle... [RESOLVED]

Maybe I'm just daft, but I've been wrangling with this for a while now. The solution is probably blindingly obvious. :rolleyes:

I've got a program that draws a rather large and detailed graph on the screen. I'd like users to be able to select a zoom function, and then drag a zoom rectangle around the area they'd like to zoom into. Since the .NET architecture did away with useful things like VB's shape controls, I'm at somewhat of a loss as to how this could be accomplished.

I already have the code for capturing the start/stop points for the rectangle and for the zooming; I just need the visual cue to let the user know that their clicking-and-dragging isn't being ignored.

Any help would be appreciated. Thanks in advance.

The usual method is to draw the lines of the rectangle using XOR.

I'm not sure how to do it in .net but in VB 6 all you had to do was set some properties of the picturebox to XOR (I think it was the Drawmode property) and then draw the lines.

Drawing a line this way will show a line, drawing that same line again will revert the pixels to their original color so you get a good dragging effect without ruining the underlying image.

when the mouse moves:
(this is pseudocode, it won't run)...

DrawOldRect() 'hides last rectangle
DrawNewRect((x,y,x1,y1) 'shows new one
OldRect = NewRect 'both probably static or global

That'll work, I guess, though with that method, the resulting color will always be some kind of inverse of the underlying graph. I'd rather have control over the exact border color.

Personally, I'd rather have a program that doesn't waste CPU power with making a drag rect look nice, but if it is pivotal to the workings of your app then there are a couple of methods that spring to mind.

1. Keep an array of the pixel colours that are to be overwritten (if the rect is 10 x 10 then you'd need 36 elements). Re-insert them when the rect has moved.

2. Copy the lines to a bitmap in memory.

I'd try the first one because it uses less ram.

Finally found what I was looking for: the BackgroundImage property. Instead of drawing the graph on the PictureBox's Image, I'll draw it onto the PictureBox's BackgroundImage. The Image can then be used for a custom drawn selection rectangle. Whenever the mouse moves, the Image can be cleared with a transparent color, and the rectangle can be redrawn.

Knew it was simple...