I need to create a quick-n-dirty knob control in Visual Basic 2005 Express, the value of which is incremented/decremented by "grabbing" it with the mouse and moving the cursor up/down. Because the knob itself doesn't move, I need to keep tracking the mouse movement outside of the rectangle of the control.
I use a Label with an ImageList to implement this (I have a list of 127 bitmaps representing the knob in various positions).
Which events should I react to?
You need the control to handle three events: Mouse Down, Mouse Move and Mouse Up. On the Mouse Down event, you will need to capture the mouse. This means the mouse messages are sent to the control that has the capture. In the mouse move event, if the input is captured then update the displayed image depending on the amount the mouse moved. In the mouse up event, release the capture if the input is captured.
The boolean jjnguy suggests is unnecessary as the Capture property of a Control is readable so it's possible to determine if the capture has been set.
Skizz
Your problem will be to determine which bitmap you have to display based upon the coordinates the mouse reports in the mouse_move event. You'll need to perform some magic to transform the coordinates and come up with a value that you can use to pick the right image.
It doesn't sound too complicated, just a little bit of trial and error in the math. Skizz has already show you how to capture the events.