Bresenham's line algorithm

Ok, scrap the above code. Here is a simple conversion of the original program (the original one posted by Tachyon), converted to BlitzMax. It is indeed a proper Bresenham routine, using only integer math. I like they way it handles all the different drawing directions.

It's also good in that is, visually, seems to be handling also the problem of how/when/where the `steps` on the line are produced, so that the step at the beginning of the line is the same length as the step at the end. Usually you'd get one pixel plotted, then another string of pixels immediately offset.

I happened to need a linedraw routine for my own project so it was worth converting. Thanks Tachyon for sharing.

'Bresenham linedraw in BlitzMax, adapted from C code

Strict
Graphics 640,480,0
Repeat
	Cls
	Line(320,240,MouseX(),MouseY())
	Flip
Until KeyHit(KEY_ESCAPE)
End

Function Line(X1:Int,Y1:Int,X2:Int,Y2:Int)
	'Draws a line of individual pixels from X1,Y1 to X2,Y2 at any angle
 	Local Steep:Int=Abs(Y2-Y1) > Abs(X2-X1)			'Boolean
	If Steep
		Local Temp:Int=X1; X1=Y1; Y1=Temp		'Swap X1,Y1
		Temp=X2; X2=Y2; Y2=Temp		'Swap X2,Y2
	EndIf
	Local DeltaX:Int=Abs(X2-X1)		'X Difference
	Local DeltaY:Int=Abs(Y2-Y1)		'Y Difference
	Local Error:Int=0		'Overflow counter
	Local DeltaError:Int=DeltaY		'Counter adder
	Local X:Int=X1		'Start at X1,Y1
	Local Y:Int=Y1		
	Local XStep:Int
	Local YStep:Int
	If X1<X2 Then XStep=1 Else XStep=-1	'Direction
	If Y1<Y2 Then YStep=1 Else YStep=-1	'Direction
	If Steep Then Plot(Y,X) Else Plot(X,Y)		'Draw
	While X<>X2
		X:+XStep		'Move in X
		Error:+DeltaError		'Add to counter
		If (Error Shl 1)>DeltaX		'Would it overflow?
			Y:+YStep		'Move in Y
			Error=Error-DeltaX		'Overflow/wrap the counter
		EndIf
		If Steep Then Plot(Y,X) Else Plot(X,Y)		'Draw
	Wend
End Function