Midpoint Scrolling

[Mr_Monkey]

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.

[Joshtek]

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

[DavidN]

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...

[Mr_Monkey]

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

[Joshtek]

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 Min : Set Counter to X( "(Group.Neutral)" )
-(Counter Max : 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 Mid : Set Counter to(value( "(Counter Min" )+value( "(Counter Max" ))/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 Min" )
-(Counter Min : Set Counter to X( "(Group.Neutral)" )
*On loop "midpoint"
+Alterable Value A of(Group.Neutral) = LoopIndex("midpoint")
+X position of(Group.Neutral) > value( "(Counter Max" )
-(Counter Max : 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]

[raytrace]

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

[Paul_Boland]

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.