TCl Proc to output list or collection - arrays

Question

My Question is as follows:
Objective or problem statement : Find the dots in rectangle that are separated by a distance and store it in a list (collection) which will be my final output
Spec:
We start with an x offset and y offset to begin with and then we keep on incrementing in x and y direction till we reach upper right rectangle boundary.
Expected Output
My rect_boundary is {0 0} {112 96} as llx lry urx ury (lower left x, lower right y, upper right x .... cordinates) It can change each time based on procedural argument , rectangle box can be (00) (200 200) I have used this as an example
x offset for first red box = 5
y offset from first red box to boundary = 5
Distance between 1st and 2nd dot = 45, Distance between 2 and 3 = 45 , Distance between 4 and 5 = 45, Distance between 6 and 7 = 45 , so basically all horizontal points are separated by a distance of 45, that will always stay constant.
1 , 2 and 4 form a triangle, so "4 is located exactly in center of 1 and 2 but vertical distance of 45.
Example: 1st point = (5 5 ) , 2nd point = (50 5) so position of "4th point" will be ((5+50/2), 5+45) i.e., (27.5 50)
Position of 5th point on row 2 will be dependent on 4 as their cordinate will be (27.5+45, 50) = (72.5 50)
Now position of 6 and 7 point in rectangle will also be dependent on point 4
Center Point = Box 4 (x, y+45) = (27.5 95) and Box 6 = {(27.5 -45/2) 95) = (5, 95)
i.e Point 6 will be exactly on top of Point 1 = (5, 95)
What I have tried so far and it is giving slightly different output
set output [open "output.txt" w]
proc getPointList {rect_boundary xOffset yOffset } {
global output
set cordlist $rect_boundary
set xl [lindex $cordlist 0]
set yl [lindex $cordlist 1]
set xh [lindex $cordlist 2]
set yh [lindex $cordlist 3]
set xIncr 45
set yIncr 45
set x_margin 2
set y_margin 2
set count 0
set list ""
for {set y [expr {$yl +$yOffset}]} {$y <= $yh} {incr y $yIncr} {
for {set x [expr {$xl + $xOffset}]} {$x <= $xh } {incr x $xIncr} {
set point_lookup_window [list [list [expr {$x - $x_margin}] [expr {$y - $y_margin}]] [list [expr {$x + $x_margin}] [expr {$y + $y_margin}]]]
set point_list [index collection [(#some logic_ get_boxes -within $point_lookup_window] 0]
}
incr count
puts $point_list
}
}
set rect_boundary {0 0 111 96}
set xOffset 5
set yOffset 5
getPointList $rect_boundary $xOffset $yOffset
close $output
Note: Rectanglular boundary and offsets will change as they are procedural arguments
Above code gives me equidistant points (have shown dots) as follows, so need the calculation from 2nd row onwards working
Please help expedite and feel free to ask questions.

Answer 1

For each row, you're initializing x at the same value, $xl + $xOffset.
That's what you want for the 1st, 3rd, 5th, ... rows, but x in the even rows should be initialized by an extra half of $xIncr.
I see you're setting a count variable which will keep track of the odd/even rows. You can use this variable to make odd/even rows different.
for {set y [expr {$yl +$yOffset}]} {$y <= $yh} {incr y $yIncr} {
# Define x_start differently on odd/even rows
if {$count % 2 == 0} {
set x_start [expr {$xl + $xOffset}]
} else {
set x_start [expr {$xl + $xOffset + $xIncr/2}]
}
# Iterate x as usual.
for {set x $x_start} {$x <= $xh } {incr x $xIncr} {
...
...
}
incr count
puts $point_list
}