DrawLine acts differently on platforms

Monkey Forums/Monkey Bug Reports/DrawLine acts differently on platforms

Goodlookinguy

(Posted 2014) [#1]

I've run into this problem and I've known about it for ages but noticed that for some reason it has never been posted, but DrawLine acts different on different platforms. This is definitely something that should be fixed so that I don't have to write these ridiculous workarounds. Like for instance with HTML5 and GLFW, I have to add 0.5 to the x and y. For HTML5 alone, I have to do a separate calculation from the one below because otherwise it doesn't come out correctly on all platforms.

Try compiling this to different platforms and notice how it has different results on many of them. Flash renders what I expect. GLFW, HTML5, and XNA all give off different results from one another.

Import mojo

#MOJO_IMAGE_FILTERING_ENABLED=False

Function Main:Int()
	New BrokenExample()
End

Class BrokenExample Extends App
	Method OnCreate()
		SetUpdateRate(15)
	End
	
	Method OnRender()
		Cls()
		SetColor(255,255,255)
		Local x, y, width, height
		
		x = 16
		y = 16
		width = 32
		height = 32
		
		DrawLine(x, y, x + width - 1, y) ' top
		DrawLine(x + width - 1, y, x + width - 1, y + height) ' right
		DrawLine(x, y + height - 1, x + width, y + height - 1) ' bottom
		DrawLine(x, y, x, y + height - 1) ' left
		DrawRect(49, 16, 3, 32)
		DrawRect(16, 12, 32, 3)
	End
End

Update
Okay, so DrawPoint also acts differently on GLFW at least.

Import mojo

#MOJO_IMAGE_FILTERING_ENABLED=False

Function Main:Int()
	New BrokenExample()
End

Class BrokenExample Extends App
	Method OnCreate()
		SetUpdateRate(15)
	End
	
	Method OnRender()
		Cls()
		SetColor(255,255,255)
		Local x, y, width, height
		
		x = 16
		y = 16
		width = 32
		height = 32
		
		'SetColor(255,0,0)
		DrawIntLine(x, y, x + width - 1, y) ' top
		'SetColor(0,255,0)
		DrawIntLine(x + width - 1, y, x + width - 1, y + height - 1) ' right
		'SetColor(0,0,255)
		DrawIntLine(x, y + height - 1, x + width - 1, y + height - 1) ' bottom
		'SetColor(255,255,255)
		DrawIntLine(x, y, x, y + height - 1) ' left
		DrawRect(49, 16, 3, 32)
		DrawRect(16, 12, 32, 3)
	End
End

' using Bresenham's line algorithm
Function DrawIntLine:Void( x1:Int, y1:Int, x2:Int, y2:Int )
	Local dx, dy, sx, sy, err, e2
	
	dx = Abs(x2 - x1)
	dy = Abs(y2 - y1)
	If x1 < x2 Then sx = 1 Else sx = -1
	If y1 < y2 Then sy = 1 Else sy = -1
	err = dx - dy
	
	While True
		DrawPoint(x1, y1)
		
		If x1 = x2 And y1 = y2 Then Exit
		
		e2 = 2 * err
		
		If e2 > -dy
			err -= dy
			x1 += sx
		End
		
		If x1 = x2 And y1 = y2
			DrawPoint(x1, y1)
			Exit
		End
		
		If e2 < dx
			err += dx
			y1 += sy
		End
	End
End

dawlane

(Posted 2014) [#2]

Not at a computer at the moment, so can't have a dig around in mojo. But maybe it's a int/float cast issue. Was testing a maze drawing routine that correctly worked as expected on GLFW, but screwed up when run on HTML and flash. Possibly a related issue or my math/logic is suspect.