Filled Rotated Ellipses

This code has been declared by its author to be Public Domain code.

Filled Rotated Ellipses by JBR

2011

Calculates 90 points on the ellipse, then rotates them, then calculates the left & right x coordinate for each scanline of the ellipse. Then I use Rect to draw the line between.
I use a very fast DrawLine function - can't remember where I got it.
I get around 300ms for 1000 ellipses, but if you edit out the Rect I get around 30ms - It is the Rect that takes the time.

; SPEEDY ROTATED ELLIPSE PLOTTING

Graphics3D 800,600,32,2
SetBuffer BackBuffer()

Global G_Screen_Width = GraphicsWidth()
Global G_Screen_Hight = GraphicsHeight()

Dim a_x%(90), a_y%(90), left_side%(G_Screen_Hight-1), rite_side%(G_Screen_Hight-1)


Repeat

	Cls
	
	G_Angle# = Rnd(0,360)
		
	time = MilliSecs()

	For ellipse = 1 To 1000
		create_ellipse( 0,0, 100.0, 50.0, G_Angle#, 255,0,255 )
	Next
	
	time = MilliSecs()-time

	Flip
	
	Color 255,255,255
	Text 0,0,"Time to draw 1000 :"+time+" millisecs"
	Text 0,12,"Press Space"
	Flip
	WaitKey()
		
Until KeyDown(1)

Flip
FlushKeys()
WaitKey()
End






;-----------------------------------------------------------------------------------------
Function create_ellipse( centre_x#, centre_y#, radius_x#, radius_y#, angle#, red,gre,blu )

	Local cos_a# = Cos( angle# )
	Local sin_a# = Sin( angle# )
	
	For angle# = 0 To 90
		Local x# = radius_x# * Cos(angle#*4.0)			; simple ellipse
		Local y# = radius_y# * Sin(angle#*4.0)
		
		Local rot_x# = (x#*cos_a#) - (y#*sin_a#)		; rotated ellipse
		Local rot_y# = (x#*sin_a#) + (y#*cos_a#)
		
		a_x%( angle# ) = G_Screen_Width/2 + centre_x# + rot_x#		; adjusted for origin in middle of screen
		a_y%( angle# ) = G_Screen_Hight/2 + centre_y# + rot_y#
	Next

	For i = 0 To G_Screen_Hight-1					; init the left/rite sides to impossible values
		left_side(i) = 1000000
		rite_side(i) = -1000000
	Next
	
	For lline = 0 To 90-1							; draw the lines
		Local x0 = a_x%(lline)
		Local y0 = a_y%(lline)
		Local x1 = a_x%(lline+1)
		Local y1 = a_y%(lline+1)
		
		If x0<0 Then x0=0							; clipping left/top
		If y0<0 Then y0=0
		If x1<0 Then x1=0
		If y1<0 Then y1=0
		
		If x0>=G_Screen_Width Then x0=G_Screen_Width-1		;clipping rite/bottom
		If y0>=G_Screen_Hight Then y0=G_Screen_Hight-1
		If x1>=G_Screen_Width Then x1=G_Screen_Width-1
		If y1>=G_Screen_Hight Then y1=G_Screen_Hight-1

;		Function DrawLine(x0, y0, x1, y1)
		Local dx,dy,sx,sy,err,e2
		dx = Abs(x1-x0)
		dy = Abs(y1-y0) 
		If x0 < x1 Then sx = 1 Else sx = -1
		If y0 < y1 Then sy = 1 Else sy = -1
		err = dx-dy
 
		Repeat
			If x0 < left_side(y0) Then left_side(y0) = x0
			If x0 > rite_side(y0) Then rite_side(y0) = x0
			
			If x0 = x1 And y0 = y1 Exit
			e2 = 2*err
			If e2 > -dy Then 
				err = err - dy
				x0 = x0 + sx
			End If
			If e2 <  dx Then 
				err = err + dx
				y0 = y0 + sy 
			End If
		Forever

	Next
	
	Color red,gre,blu

	For scan_line = 0 To G_Screen_Hight-1			; now scan the lines
		Local x_left = left_side(scan_line)
		Local x_rite = rite_side(scan_line)
		Local width  = x_rite-x_left
		
		If width > 0 Then
			Rect x_left, scan_line, width, 1
		EndIf

	Next
	
End Function

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