Sensible Cartesian Co-ordinate graphics pack

Modified on 2020/06/05 10:16 by CaptainBoing — Categorized as: Graphics

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)

Example

		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

Preamble

'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

The Code

'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
	Sub Native (x,y)
		Gx=x:Gy=Gym-y
	End Sub