Midpoint Scrolling

How do you you use the midpoint formula to scroll in between (>amount here<) objects? I know that you use the midpoint formula to set the position of a "scroller" that scrolls the screen. What I don't know is how to loop through the actives (more than one type) and get the midpoint.

To get an average you get the sum of the X's and Y's and divide them by the amount of objects.

That's a straight average, though, and would pull the screen further over in one direction if more objects were on one side. To get the midpoint, you'd need to find the minimum X/Y out of the group, the maximum X/Y, and set the position to halfway between them. That's just a general outline, because I don't really know the best way to actually do that...

What I don't know is how to get the individual X's and Y's of each object.

To get the midpoint
1. Give all the objects you want to test the same qualifier (Group.Neutral)
2. Create several counters: MinX, MinY, MaxX, MaxY, MidX, MidY
3. Do the following code:
[events]
*Start of Frame
-(Group.Neutral) : Spread value 0 in Alterable Value A
*Always
-(Counter MinX) : Set Counter to X( "(Group.Neutral)" )
-(Counter MaxX) : Set Counter to X( "(Group.Neutral)" )
-(Counter MinY) : Set Counter to Y( "(Group.Neutral)" )
-(Counter MaxY) : Set Counter to Y( "(Group.Neutral)" )
-Start loop "midpoint" NObjects( "(Group.Neutral)" ) times
-(Counter MidX) : Set Counter to(value( "(Counter MinX)" )+value( "(Counter MaxX)" ))/2
-(Counter MidY) : Set Counter to(value( "(Counter MinY)" )+value( "(Counter MaxY)" ))/2
*On loop "midpoint"
+Alterable Value A of(Group.Neutral) = LoopIndex("midpoint")
+X position of(Group.Neutral) < value( "(Counter MinX)" )
-(Counter MinX) : Set Counter to X( "(Group.Neutral)" )
*On loop "midpoint"
+Alterable Value A of(Group.Neutral) = LoopIndex("midpoint")
+X position of(Group.Neutral) > value( "(Counter MaxX)" )
-(Counter MaxX) : Set Counter to X( "(Group.Neutral)" )
*On loop "midpoint"
+Alterable Value A of(Group.Neutral) = LoopIndex("midpoint")
+Y position of(Group.Neutral) > value( "(Counter MaxY)" )
-(Counter MaxY) : Set Counter to Y( "(Group.Neutral)" )
*On loop "midpoint"
+Alterable Value A of(Group.Neutral) = LoopIndex("midpoint")
+Y position of(Group.Neutral) < value( "(Counter MinY)" )
-(Counter MinY) : Set Counter to Y( "(Group.Neutral)" )
[/events]

I'm not quite sure what you mean. If you mean an object (or vertex) that hangs between two objects then this example might help:

http://raytrace.sitesled.com/Examples/example15.mfa

The formula is just a simple one dimentional Ecludeien distance formula with an addition to find the percentage that the marker should be along the line of interpolation.

For your question:

ScrollX = X("1")+(X("1")-X("2"))/2
ScrollY = Y("1")+(Y("1")-Y("2"))/2

If you drop me an email at pkb@iol.ie I'll send you a copy of my Camera Control tutorial which shows how to create mid point scrolling with up to four objects on screen. It is 480Kb in size.