Knotpoint distance and creating fixed

.

Thank you both, miauu and jahman. I will work on it.

Here's an example.
You'll have to find a way to compare float values because 50.001 isn't equal to 50.000 and window will not be placed as a result.

delete objects

--  --  --  --  --  --  --  --  --  --  --  --  --  --  --  --  --  --  --  --  --  --  --  --  --  --  --  --  --  --  --  --  --  --  --  --  --  --  --  --  --  --  --  --
-- Creating Windows
--  --  --  --  --  --  --  --  --  --  --  --  --  --  --  --  --  --  --  --  --  --  --  --  --  --  --  --  --  --  --  --  --  --  --  --  --  --  --  --  --  --  --  --

fn createWindow w h = (
	
	box width:w height:h length:1
	
)

w50x150  = createWindow 50 150
w100x150 = createWindow 100 150
w150x150 = createWindow 150 150

w50x150.pos  = [-350,0,0]
w100x150.pos = [-250,0,0]
w150x150.pos = [-100,0,0]

--  --  --  --  --  --  --  --  --  --  --  --  --  --  --  --  --  --  --  --  --  --  --  --  --  --  --  --  --  --  --  --  --  --  --  --  --  --  --  --  --  --  --  --
-- Creating Main Rect
--  --  --  --  --  --  --  --  --  --  --  --  --  --  --  --  --  --  --  --  --  --  --  --  --  --  --  --  --  --  --  --  --  --  --  --  --  --  --  --  --  --  --  --

fn addRectShape shp pt w h = (
	
	addnewspline shp
	splineIndex = numSplines shp
	
	addKnot shp splineIndex #corner #line pt
	addKnot shp splineIndex #corner #line (pt + [w,0,0])
	addKnot shp splineIndex #corner #line (pt + [w,0,h])
	addKnot shp splineIndex #corner #line (pt + [0,0,h])
	close shp splineIndex
	
	updateShape shp
	
)

mainSpline = splineShape wirecolor:yellow

addRectShape mainSpline [0,0,0] 500 400 -- Main rect
addRectShape mainSpline [50,0,50] 50 150 -- Window 50x150
addRectShape mainSpline [125,0,50] 100 150 -- Window 100x150
addRectShape mainSpline [250,0,50] 150 150 -- Window 150x150

--  --  --  --  --  --  --  --  --  --  --  --  --  --  --  --  --  --  --  --  --  --  --  --  --  --  --  --  --  --  --  --  --  --  --  --  --  --  --  --  --  --  --  --
-- Checking spline shape "window" sizes and place appropriate window in it
--  --  --  --  --  --  --  --  --  --  --  --  --  --  --  --  --  --  --  --  --  --  --  --  --  --  --  --  --  --  --  --  --  --  --  --  --  --  --  --  --  --  --  --
for splineIndex = 2 /* skip first rect */ to numsplines mainSpline do (
	
	_min = [ 1e6, 1e6, 1e6 ]
	_max = [-1e6,-1e6,-1e6 ]
	
	for knotIndex = 1 to numKnots mainSpline splineIndex do (
		
		knot = getKnotPoint mainSpline splineIndex knotIndex
		
		if knot.x < _min.x do _min.x = knot.x
		if knot.y < _min.y do _min.y = knot.y
		if knot.z < _min.z do _min.z = knot.z
		if knot.x > _max.x do _max.x = knot.x
		if knot.y > _max.y do _max.y = knot.y
		if knot.z > _max.z do _max.z = knot.z
		
	)
	
	center = (_min + _max) / 2.0	
	size   = _max - _min
	
	point pos:center centermarker:on cross:off wirecolor:yellow
		
	case of (
		
		(size.x == 50 and size.z == 150) : (
			
			-- create new window or copy existing one
			
			newWindow = instance w50x150
			newWindow.center = center
			
		)
		
		(size.x == 100 and size.z == 150) : (
			
			newWindow = instance w100x150
			newWindow.center = center
			
		)
		
		(size.x == 150 and size.z == 150) : (
			
			newWindow = instance w150x150
			newWindow.center = center
			
		)
		
		
		
	)
	
)

Thank you Jahman. That is better than mine. I will use it. But still my code doesnt work. And I dont kmow why.

This row is not correct:

A	=  k11 -k12

it should be:

A	=  k11 - k12

Change it and test your code again.

Are you sure that knot 1 & 2 will always be enough to know window dimensions? What if first spline knot will be upper left and the second one lower left.. etc
I'd rather collect all spline knots to know min/max knot position of particular spline.
Then just copy the corresponding window and place it in spline center

windowObject.center = (splineMinPoint3 + splineMaxPoint3)/2.0