You need to find the following:
- Distance to the closest corner
- Distance to the closest edge
- (optionally) distance to the center
Basically, you want the smaller of these three values. Take the min of that for two controls to determine which is closer.
Begin when you load the form by iterating all the controls on the form and creating a collection of the class below.
To find the closest control to a point, iterate the collection (see code at bottom). Keep track of the control with the minimum distance you've found so far. You can test for ContainsPoint() if you want... if you find a control where the point falls within the control bounds, you've got your control (so long as you don't have overlapping controls). Else, when you get to the end of the collection, the control you found with the shortest distance to the center/edge is your control.
public class HitControl {
public Control ThisControl;
private Rectangle ControlBounds;
private Point Center;
public HitControl (Control FormControl) {
ControlBounds = FormControl.Bounds;
Center = new Point(ControlBounds.X + (ControlBounds.Width/2), ControlBounds.Y + (ControlBounds.Height/2));
}
// Calculate the minimum distance from the left, right, and center
public double DistanceFrom(Point TestPoint) {
// Note: You don't need to consider control center points unless
// you plan to allow for controls placed over other controls...
// Then you need to test the distance to the centers, as well,
// and pick the shortest distance of to-edge, to-side, to-corner
bool withinWidth = TestPoint.X > ControlBounds.X && TestPoint.X < ControlBounds.X + ControlBounds.Width;
bool withinHeight = TestPoint.Y > ControlBounds.Y && TestPoint.Y < ControlBounds.Y + ControlBounds.Height;
int EdgeLeftXDistance = Math.Abs(ControlBounds.X - TestPoint.X);
int EdgeRightXDistance = Math.Abs(ControlBounds.X + ControlBounds.Width - TestPoint.X);
int EdgeTopYDistance = Math.Abs(ControlBounds.Y - TestPoint.Y);
int EdgeBottomYDistance = Math.Abs(ControlBounds.Y + ControlBounds.Height - TestPoint.Y);
int EdgeXDistance = Math.Min(EdgeLeftXDistance, EdgeRightXDistance);
int EdgeYDistance = Math.Min(EdgeTopYDistance, EdgeBottomYDistance);
// Some points to consider for rectangle (100, 100, 100, 100):
// - (140, 90): Distance to top edge
// - (105, 10): Distance to top edge
// - (50, 50): Distance to upper left corner
// - (250, 50): Distance to upper right corner
// - (10, 105): Distance to left edge
// - (140, 105): Distance to top edge
// - (105, 140): Distance to left edge
// - (290, 105): Distance to right edge
// - (205, 150): Distance to right edge
// ... and so forth
// You're within the control
if (withinWidth && withinHeight) {
return Math.Min(EdgeXDistance, EdgeYDistance);
}
// You're above or below the control
if (withinWidth) {
return EdgeYDistance;
}
// You're to the left or right of the control
if (withinHeight) {
return EdgeXDistance;
}
// You're in one of the four outside corners around the control.
// Find the distance to the closest corner
return Math.Sqrt(EdgeXDistance ^ 2 + EdgeYDistance ^ 2);
}
public bool ContainsPoint (Point TestPoint) {
return ControlBounds.Contains(TestPoint);
}
}
// Initialize and use this collection
List<HitControl> hitControls = (from Control control in Controls
select new HitControl(control)).ToList();
Point testPoint = new Point(175, 619);
double distance;
double shortestDistance = 0;
HitControl closestControl = null;
foreach (HitControl hitControl in hitControls) {
// Optional... works so long as you don't have overlapping controls
// If you do, comment this block out
if (hitControl.ContainsPoint(testPoint)) {
closestControl = hitControl;
break;
}
distance = hitControl.DistanceFrom(testPoint);
if (shortestDistance == 0 || distance < shortestDistance) {
shortestDistance = distance;
closestControl = hitControl;
}
}
if (closestControl != null) {
Control foundControl = closestControl.ThisControl;
}