option nolet
ask pixels z1,z2
print "----------------------------------------------------------"
print " graph pixel   : part 2b , sub                version 1.0 "
print " peter.vlasschaert@gmail.com,10/02/2019                   "
print "----------------------------------------------------------"
! filename : graphpixelpart2bfinalsub.tru    
xmin = -5
xmax = 5
ymin = -7
ymax = 7
x_pix = z1
y_pix = z2
print
print "--------------------------"
print " draw a function y = F(x) "
print "--------------------------"
print
print "--------------------------------------------"
print " How to save pixel window  => funcpict1.bmp "
print "--------------------------------------------"
print
set window 0,x_pix-1,y_pix-1,0
set color "blue"
! draw axis
call draw_xas_usertopix(x_pix,y_pix,ymin,ymax)
call draw_yas_usertopix(x_pix,y_pix,xmin,xmax)
! draw F(x) =>
print " x: ->  y = sin(x) 'red ',cos(x) 'green' "
set color "red"
val = 0.01
for  x = xmin to xmax step val
     y = sin(x) 
call convers_usertopix(x_pix,y_pix,xmin,xmax,ymin,ymax,x,y,px,py)
     plot px,py
next x
set color "green"
for  x = xmin to xmax step val
     y = cos(x) 
call convers_usertopix(x_pix,y_pix,xmin,xmax,ymin,ymax,x,y,px,py)
     plot px,py
next x
!************************************************
! How to save canvas as a picture. (funcpict.bmp)
!************************************************
call save_pixfullwin(z1,z2,keep$)
!------------------------------------------------------------------------,
!  Create a filename. Don't need an extention; the SUB will put ".bmp"
!------------------------------------------------------------------------,
ff$="C:\download\funcpict1.bmp" ! make sure this is a valid path...
CALL Write_Image("MS BMP", keep$, ff$) ! or you can use this 
print
end

sub save_pixfullwin(z11,z22,kep$)
! <help> 
! z11 : number of pixels x-direction , start :0 to z11-1,integer >0
! z22 : number of pixels y-direction , start :0 to z22-1,integer >0
! picture hold string : kep$
!************************************************
box keep 0, z11-1, z22-1, 0 in kep$ ! kep$ memory
end sub

sub save_userfullwin(x_min,x_max,y_min,y_max,kep$)
! <help>
! x-direction : x_min < =  x < = x_max , float
! y-direction : y_min < =  x < = x_max , float
! picture hold string : kep$
!***************************************************
box keep x_min, x_max, y_min, y_max in kep$ ! kep$ memory
end sub

sub convers_usertopix(z11,z22,x_min,x_max,y_min,y_max,xx,yy,pxx,pyy)
! < help >
! z11 : number of pixels x-direction , start :0 to z11-1,integer >0
! z22 : number of pixels y-direction , start :0 to z22-1,integer >0
! x-direction : x_min < =  x < = x_max , float
! y-direction : y_min < =  y < = y_max , float
! pxx,pyy : integer > 0
!********************************************************************
dx = (x_min-x_max)
dy = (y_min-y_max)
pxx=(z11*x_min)/dx-(xx*z11)/dx
pyy=(yy*z22)/dy-(z22*y_max)/dy
end sub

sub draw_xas_usertopix(z11,z22,y_min,y_max)
! < help >
! z11 : number of pixels x-direction , start :0 to z11-1,integer >0
! z22 : number of pixels y-direction , start :0 to z22-1,integer >0
! y-direction : y_min < =  y < = y_max , float
!*******************************************************************
dy = (y_min-y_max)
pxa=0
pxb=z11
pxc=-(z22*y_max)/dy
plot lines : pxa,pxc ;pxb,pxc
end sub

sub draw_yas_usertopix(z11,z22,x_min,x_max)
! < help >
! z11 : number of pixels y-direction , start :0 to z11-1,integer >0
! z22 : number of pixels y-direction , start :0 to z22-1,integer >0
! x-direction : xmin < =  x < = x_max , float
!*******************************************************************
dx = (x_min-x_max)
pxaa=z22
pxbb=0
pxcc=(z11*x_min)/dx
plot lines : pxcc,pxaa ;pxcc,pxbb
end sub