The function is specified using normal coordinates. The function draw_it translates to pixel coordinates and does clippling if required.Clipping may be set on or off. Move the box with the left upper pixel coordinates: all content will move with it.
The x-y origin is set using relative position within the box (i.e. values between 0 and 1).
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graphics ! graphics clear .8,.8,.8 ' test program
fill color .8,.8,.8 ! draw color 0,0,0
box(10,40,300,300,.5,.5,30) ' define the graphics box
draw color 0,0,0 ! draw size 1
for a=0 to 51 step .1 ' draw a spiral
r=a/10 ! xn=r*cos(a) ! yn=r*sin(a)
draw_it(xo,yo,xn,yn,0) ! xo=xn ! yo=yn
next a
draw_it(-4,6,4,-7,0) ' draw an un-clipped line
draw_it(3,6,-2,-10,1) ' draw a clipped line
refresh
end
def box(xlu,ylu,width,height,xm,ym,scale)
' xlu and ylu = left upper corner in pixel coordinates
' width and height = size of graphics box in pixels
' xm and ym = relative position of graph origin
' scale = number of pixels per graph unit
'
org_x=xlu+xm*width ! org_y=ylu+(1-ym)*height
xrl=xlu+width ! yrl=ylu+height
refresh off
draw size 4
draw rect xlu-4,ylu-4 to xrl+4,yrl+4
draw size 1 ! draw alpha .2
for x=org_x to xrl step scale ! draw line x,ylu to x,yrl ! next x
for x=org_x to xlu step -scale ! draw line x,ylu to x,yrl ! next x
for y=org_y to yrl step scale ! draw line xlu,y to xrl,y ! next y
for y=org_y to ylu step -scale ! draw line xlu,y to xrl,y ! next y
draw color 0,0,1 ! draw size 2 ! draw alpha 1
draw line xlu,org_y to xrl,org_y
draw line org_x,ylu to org_x,yrl
refresh
end def
def draw_it(xs,ys,xe,ye,clip)
' all 4 coordinates in graph units
'
x1=box.org_x+box.scale*xs ! y1=box.org_y-box.scale*ys
x2=box.org_x+box.scale*xe ! y2=box.org_y-box.scale*ye
if not clip then draw
dx=x2-x1 ! dy=y2-y1
if dx<>0 then p=dy/dx else p=sign(dy)*1000
q=y1-x1*p
if x1<box.xlu then ' clip left side of the box
if x2<box.xlu then return
x1=box.xlu ! y1=p*x1+q
end if
if x2>box.xrl then ' clip right side
if x1>box.xrl then return
x2=box.xrl ! y2=p*x2+q
end if
if y1<box.ylu then ' clip upper side
if y2<box.ylu then return
y1=box.ylu ! x1=(y1-q)/p
end if
if y2>box.yrl then ' clip lower side
if y1>box.yrl then return
y2=box.yrl ! x2=(y2-q)/p
end if
draw:
draw line x1,y1 to x2,y2
end def
