XOR graphics

[your name <your.name(at)gecm.com>]

Hi all,
	I was intrigued by someone's comments about using XOR graphics mode (I
think it was DWF).

I am using XOR to plot a moving object. It works OK on a terminal using
TRUECOLOR but screws up the colours on a terminal using PSEUDOCOLOR.

I am still trying to work this out, but I thought I'd try using a PIXMAP
window followed by a copy to the viewable window. However, this
approach, although worked OK on both terminals, was 10 times slower then
using XOR.

Since my application is time critical, it looks as if I'm stuck with
XOR.

I'm using IDL 5.2 under OpenVMS using DECWindows (X windows). Below is a
copy of my test software. I's welcome any comments (it may not be the
tidiest of code but it works).
FUNCTION Plot_rotated_shape, X, Y, Shape, Clr
    Point_1 = CONVERT_COORD(X[0], Y[0], /TO_NORMAL)	; Values in norm
coords
    Point_2 = CONVERT_COORD(X[1], Y[1], /TO_NORMAL)	; Values in norm
coords
    Ang = ATAN(Point_2[1] - Point_1[1], $
	Point_2[0] - Point_1[0]) * !RADEG	; DRAWN angle of line
    T3D, /RESET, $ 				; Create transform matrix
	ROTATE = [0, 0, Ang]			; ...rotated to fit line
    T3D, TRANSLATE = Point_2		; ...and moved to end point
    POLYFILL, Shape, COLOR = Clr, /NORMAL, /T3D	; Plot shape
    RETURN, !P.T				; Return transformation
END

PRO Initialise, Obj_1, Obj_2

DEVICE, DECOMPOSED = 0, RETAIN = 2		; Screen setup
TVLCT, [255, 155], [0, 200], [0, 255], 1	; Define colours

Obj_1.X_coord = FINDGEN(200)			; Create some data
Obj_1.Y_coord = Obj_1.X_coord ^ 2
Obj_2.X_coord = FINDGEN(200)
Obj_2.Y_coord = 40000 - Obj_2.X_coord ^ 2

PLOT, Obj_1.X_coord, Obj_1.Y_coord, TICKLEN = 1, /NODATA	; Plot axes

Shape_x = [-15.0, -15.0,  15.0,  15.0, -15.0]	; Define shape
Shape_y = [ -5.0,   5.0,   5.0,  -5.0,  -5.0]

Obj_1.Shape = CONVERT_COORD(Shape_x, Shape_y, $	; ...in normalised
	/DEVICE, /TO_NORMAL)			;    coords
Obj_2.Shape = Obj_1.Shape

END

PRO Exor

; This program draws 2 moving objects along the object trajectories.

; The objects are drawn and then redrawn which effectively erases them
; (because the XOR graphics mode is selected). No underlying info is
lost.

Obj_1 = {X_coord:FLTARR(200), Y_coord:FLTARR(200), Shape:FLTARR(3, 5)}
Obj_2 = Obj_1

Initialise, Obj_1, Obj_2			; Create some data

Start = SYSTIME(1)

FOR J = 1, 199 DO BEGIN				; Work thru all data
    PLOTS, Obj_1.X_coord[J - 1:J], Obj_1.Y_coord[J - 1:J], COLOR = 1	;
Add track
    PLOTS, Obj_2.X_coord[J - 1:J], Obj_2.Y_coord[J - 1:J], COLOR = 2	;
Add track
    DEVICE, SET_GRAPHICS_FUNCTION = 6					; Set XOR
    Obj_1_T3 = Plot_rotated_shape(Obj_1.X_coord[J - 1:J], $	; Add shape	
	Obj_1.Y_coord[J - 1:J], Obj_1.Shape, 1)
    Obj_2_T3 = Plot_rotated_shape(Obj_2.X_coord[J - 1:J], $	; Add shape
	Obj_2.Y_coord[J - 1:J], Obj_2.Shape, 2)
;   WAIT, 0.05						; Uncomment to watch plot
    POLYFILL, Obj_2.Shape, COLOR = 2, /NORMAL, /T3D	; Re-plot shapes
(delete them)
    !P.T = Obj_1_T3					; Transform to other object
    POLYFILL, Obj_1.Shape, COLOR = 1, /NORMAL, /T3D
    DEVICE, SET_GRAPHICS_FUNCTION = 3			; Reset the graphics mode
ENDFOR

PRINT, SYSTIME(1) - Start

END

PRO Pix

; This program draws 2 moving objects along the object trajectories.

; Objects are PLOTted to a pixmap, which is subsequently copied to the
; current window.

Obj_1 = {X_coord:FLTARR(200), Y_coord:FLTARR(200), Shape:FLTARR(3, 5)}
Obj_2 = Obj_1

WINDOW, 1, XSIZE = 640, YSIZE = 512		; Visible window
WINDOW, 0, XSIZE = 640, YSIZE = 512, /PIXMAP	; Define pixmap window
Initialise, Obj_1, Obj_2			; Create some data

Start = SYSTIME(1)

FOR J = 1, 199 DO BEGIN				; Work thru all data
    WSET, 0					; Use pixmap
    PLOT, Obj_1.X_coord, Obj_1.Y_coord, TICKLEN = 1, /NODATA	; Add axes
(white)
    OPLOT, Obj_1.X_coord[0:J], Obj_1.Y_coord[0:J], COLOR = 1	; Add track
    OPLOT, Obj_2.X_coord[0:J], Obj_2.Y_coord[0:J], COLOR = 2	; Add track
    Obj_1_T3 = Plot_rotated_shape(Obj_1.X_coord[J - 1:J], $	; Add shape
	Obj_1.Y_coord[J - 1:J], Obj_1.Shape, 1)
    Obj_2_T3 = Plot_rotated_shape(Obj_2.X_coord[J - 1:J], $	; Add shape
	Obj_2.Y_coord[J - 1:J], Obj_2.Shape, 2)
;   WAIT, 0.05						; Uncomment to watch plot
    WSET, 1
    DEVICE, COPY = [0, 0, 640, 512, 0, 0, 0]		; Place on visible window
ENDFOR

PRINT, SYSTIME(1) - Start

END

>EXOR
   0.601
>PIX
   6.000

Ian Dean

Ian.Dean@GECM.COM