FotS

The standard Cartesian co-ordinate system places 0,0 in the bottom left corner of the view (ignoring offsets) e.g. like a piece of graph paper.

Modern windowing and LCD panel co-ordinate systems place 0,0 in the top left position.

The following is a series of graphics primitive subroutines that make it easy to pass conventional x,y co-ordinates and plot them correctly using the native windowing co-ordinates, using old the school drawing commands PLOT, DRAW and MOVE. This makes it a cinch to produce nice looking graphs without tying your brain in a knot with windowing co-ordinates. It also introduces the concept of a graphics cursor which leaves the “pointer” at the last referenced point on the display.

I have more to add (including a scaling ORIGIN command to place the co-ordinate system anywhere you choose) but they need some honing. Note:Always uses the current graphics pen (colour)

		cls
		For n =0 To 239 Step 8'239 To 0 Step -4
			move 239-n,n
			draw n,239
		Next
		For x=0 To Gxm Step 10
			For y=0 To Gym Step 10
				Move x,y
				circle Gx,Gy,4
				DrawR rnd*20-10,rnd*20-10
		Next y,x

'screen dimensions follow LCDPANEL settings
	Const Gxm=MM.HRes-1,Gym=MM.VRes-1 ' 0 to zzz

'The global variables Gx and Gy always contain the current graphic cursor in native co-ordinates
	Dim Integer Gx, Gy  ' current native x,y (i.e. not cartesian) coord system

'plot a point
	Sub Plot(x As Integer,y As Integer)
		Gx=x:Gy=Gym-y
		Pixel Gx,Gy
	End Sub
	
'plot a point relative to the cursor e.g. PlotR -1,-1 plots a point one pixel left and down from the current graphics cursor
	Sub PlotR(x As Integer,y As Integer)
		Gx=Gx+x:Gy=Gy-y
		Pixel Gx,Gy
	End Sub

'Draw a line from the current graphics cursor to the x,y given
	Sub Draw(x As Integer,y As Integer) 'draw a line from the current graphics cursor to the specified point
		Line Gx,Gy,x,Gym-y
		Gx=x:Gy=Gym-y
	End Sub
	
'Draw a line from the current graphics cursor to the relative point x,y from the cursor
	Sub DrawR(x As Integer,y As Integer)
		Line Gx,Gy,Gx+x,Gy-y
		Gx=Gx+x:Gy=Gy-y
	End Sub

'move the graphics cursor to the given x,y but doesn't draw anything
	Sub Move(x As Integer,y As Integer)
		Gx=x:Gy=Gym-y
	End Sub
	
'move the graphics cursor to the point x,y relative to the current cursor but doesn't draw anything
	Sub MoveR(x As Integer,y As Integer)
		Gx=Gx+x:Gy=Gy-y
	End Sub

'sets the global variables Gx and Gy to native LCD panel co-ordinates from Cartesian so 
'other drawing commands e.g. Text, Circle, Box etc. can use the Cartesian system. 
'Same as Move but more intuitive in the context of your code... maybe...
	Sub Native(x,y)
		Gx=x:Gy=Gym-y
	End Sub