Drawing a dashed line on graphics screen from x1 y1 to x2 y2

[regoroxford]

   I have met with limited success. Ideally there is a .DLL to do the job. I have tried to use the slope to calculate radians and degrees and then
#handle, "turn degees" and #1,"go ";distance with pen "up" and "down"..... With LB 4.5.1 I am experiencing a difference between LB instructions and 
reality. For example #1, "line x1 y1 x2 y2" needs to be #1,  "Line ";x1;" ";y1;" ";x2;" ";y2
I have a large LB program for drawing line figures with colors and exact placement of new figure and lines by finding the closest corner or line end or figure center to reference.
Drawing a dashed line from x1 y1 x2 y2 at any slope has stumped me.
My current effort is not presentable at the moment.

[tsh73]

Have a look
nomainwin
global markDashStart
markDashStart = 1

open "test" for graphics_nsb_nf as #gr
#gr "trapclose [quit]"
#gr "down"

#gr "home"
#gr "posxy cx cy"
'#gr "circle 20"
'#gr "go 10"

x1=30
y1=30

x2=270
y2=140

sz=10   'dash size

#gr "color red"
#gr "place ";x1;" ";y1
#gr "circle 10"
#gr "place ";x2;" ";y2
#gr "circle 10"


#gr "color black"
'#gr "line ";x1;" ";y1;" ";x2;" ";y2
call dashLine x1,y1,x2,y2, sz

pi = acs(-1)
'print pi
r=120
markDashStart = 0
for i = 0 to 11
   a=i/12*2*pi
   x=cx+r*cos(a)
   y=cy+r*sin(a)
   'print i, a, y, r, r*sin(a)
   #gr "color black"
   call dashLine cx,cy,x,y, 3

   #gr "color red"
   #gr "place ";x;" ";y
   #gr "circle 5"

next
#gr "flush"

wait

sub dashLine x1,y1,x2,y2, sz
   d=sqr((x2-x1)^2+(y2-y1)^2)
   n=int(d/(2*sz))
   for i = 0 to n-1
       t=i/n: t2=(i+.5)/n
       xx1=int(x1+(x2-x1)*t)
       yy1=int(y1+(y2-y1)*t)
       xx2=int(x1+(x2-x1)*t2)
       yy2=int(y1+(y2-y1)*t2)
       if markDashStart then
           #gr "place ";xx1;" ";yy1
           #gr "circle 8"
       end if
       #gr "line ";xx1;" ";yy1;" ";xx2;" ";yy2
   next
   #gr "set ";x2;" ";y2    'last point?
end sub
[quit]
   close #gr
end


[tenochtitlanuk]

You might like to look at my page on drawing lines at www.diga.me.uk/bresenham.html

I've used the Bresenham method ( see Rosetta Code) to draw dashed lines, dotted lines, and lines whose colour or width changes along their length or as a function of distance from start point.

[regoroxford]

    That should be more than adequate to help me draw dashed lines today.
The reverse engineering necessary will be key to understanding.
Thanks

[Walt Decker]

Polar degrees can be found HERE

DRAW DASHED LINE FROM X1, Y1 TO X2, Y2

'
PS.SOLID      = 0
PS.DASH       = 1 'SEE .[GRAFIX_1O1.RTF,"CreatePen"].
HS.DIAGCROSS  = 5 'SEE .[GRAFIX_1O1.RTF,"CreateHatchBrush"].

FIREBRICK  = HEXDEC("&H2222B2")

PenHndl = 0
OldPen = 0
DrawDc = 0

GfxHndl = HWND(#DMO.GFX) '<--- handle to gfx box

CALLDLL #user32, "GetDC", GfxHndl AS ULONG, DrawDc AS ULONG '<--- handle to device

CALLDLL #gdi32, "CreatePen", PS.DASH AS LONG, 2 AS LONG, FIREBRICK AS ULONG, _
                PenHndl AS ULONG '<--- create the pen
'<===== ATTACH THE PEN FOR DRAWING ==========================>
CALLDLL #gdi32, "SelectObject", DrawDc AS ULONG, PenHndl AS ULONG, OldPen AS ULONG

CALLDLL #gdi32, "MoveToEx", DrawDc AS ULONG, X1 AS LONG, Y1 AS LONG, 0 AS LONG, _
                RetVal AS VOID '<--- move to line start

'<================= DRAW TO LINE END ==================>
CALLDLL #gdi32, "LineTo", DrawDc AS ULONG, X2 AS LONG, Y2 AS LONG, RetVal AS VOID

'<================= DETACH PEN ======================>
CALLDLL #gdi32, "SelectObject, DrawDc AS ULONG, OldPen AS ULONG, RetVal AS VOID

'<================ RELEASE DEVICE ===================>
CALLDLL #user32, "ReleaseDC", GfxHndl AS ULONG, DrawDc AS ULONG, RetVal AS VOID

'<=============== THIS MUST BE DONE TO MAKE IMAGE STICK ==============>
'<======= "BMPTAG" CAN BE ANY NAME YOU WANT, E.G. LINEFROM ===========>

PRINT #DMO.GFX, "GETBMP BMPTAG 0 0 ";GfxWide;" ";GfxHigh '<--- get image
PRINT #DMO.GFX, "DRAWBMP BMPTAG 0 0" '<--- redraw image
PRINT #DMO.GFX, "FLUSH" '<--- make it stick
PRINT #DMO.GFX, "DISCARD" '<--- remove meta-file
'

More info concerning API can be found in the General Discussion thread topic "Things you don't want to know about the win API"

[regoroxford]

nomainwin
open "test" for graphics_FS as #1
#1, "trapclose [quit]"
#1, "down"

x1=130
y1=130
x2=870
y2=940

sz=40  'dash size
#1, "color red" : #1,"size 6"
#1,"set ";x1;" "; y1  'setup red targets
#1,"set ";x2;" "; y2
#1, "size 1"
#1, "color black"

open "c:\lbdrawings\dashedlinedata" for output as #3 'record x & y & T & T2 data
call dashLine x1,y1,x2,y2, sz
wait

sub dashLine x1,y1,x2,y2, sz
   d=sqr((x2-x1)^2+(y2-y1)^2) 'pixels between pt1 & pt2

   n=int(d/(2*sz))  'length in pixels of (dash + no dash) (wave length)

   for i = 0 to n-1  'step thru number of wavelengths

       t=i/n         't starts small and reaches almost 1

       t2=(i+.5)/n   '

       xx1=int(x1+(x2-x1)*t)  'xx1: x1 is increased by quantity of (x2-x1) * t

       yy1=int(y1+(y2-y1)*t)  'yy1: y1 is increased proportionally * t

       xx2=int(x1+(x2-x1)*t2) 'xx2: x1 is increased an EVEN larger amt *t2

       yy2=int(y1+(y2-y1)*t2) 'yy2: y1 ...

       print #3,xx1;" ";yy1;" ";xx2;" ";yy2;" ";t;" ";t2 'recording x & y  data



       #1, "line ";xx1;" ";yy1;" ";xx2;" ";yy2 'draw one line segment


   next i
   #1, "line ";xx2;" ";yy2;" ";x2;" ";y2 'draw one line segment
end sub
[quit]
   close #1
   close #3

end



Your code was easy to modify to get dashed line I needed for my program. I'm still working to think about inching along the hypotenuse the way you did. I conceived of the idea but did not get there.