TITLE Cartesian Coordinates                 (Pixel2.asm)

; This program switches into 800 X 600 graphics mode and
; draws the X and Y axes of a Cartesian coordinate system.
; Switch to full-screen mode before running this program.
; Color constants are defined in Irvine16.inc.
; 

INCLUDE Irvine16.inc

Mode_6A = 6Ah   ; 800 X 600, 16 colors
X_axisY = 300
X_axisX = 50
X_axisLen = 700

Y_axisX = 400
Y_axisY = 30
Y_axisLen = 540

.data
saveMode BYTE ?

.code
main PROC
  mov ax,@data
  mov ds,ax

; Save the current video mode
  mov  ah,0Fh ; get video mode
  int  10h
  mov  saveMode,al

; Switch to a graphics mode
  mov  ah,0     ; set video mode
  mov  al,Mode_6A ; 800 X 600, 16 colors
  int  10h

; Draw the X-axis
  mov  cx,X_axisX ; X-coord of start of line
  mov  dx,X_axisY ; Y-coord of start of line
  mov  ax,X_axisLen   ; length of line
  mov  bl,white ; line color (see IRVINE16.inc)
  call DrawHorizLine  ; draw the line now

; Draw the Y-axis
  mov  cx,Y_axisX ; X-coord of start of line
  mov  dx,Y_axisY ; Y-coord of start of line
  mov  ax,Y_axisLen ; length of line
  mov  bl,white ; line color
  call DrawVerticalLine ; draw the line now

; Wait for a keystroke
  mov  ah,10h ; wait for key
  int  16h

; Restore the starting video mode
  mov  ah,0     ; set video mode
  mov  al,saveMode    ; saved video mode
  int  10h

  exit
main endp

;------------------------------------------------------
DrawHorizLine PROC
;
; Draws a horizontal line starting at position X,Y with
; a given length and color.
; Receives: CX = X-coordinate, DX = Y-coordinate,
;           AX = length, and BL = color
; Returns: nothing
;------------------------------------------------------
.data
currX WORD ?

.code
  pusha
  mov  currX,cx ; save X-coordinate
  mov  cx,ax  ; loop counter

DHL1:
  push cx ; save loop counter
  mov  al,bl  ; color
  mov  ah,0Ch ; draw pixel
  mov  bh,0 ; video page
  mov  cx,currX ; retrieve X-coordinate
  int  10h
  inc  currX  ; move 1 pixel to the right
  pop  cx ; restore loop counter
  Loop DHL1

  popa
  ret
DrawHorizLine ENDP

;------------------------------------------------------
DrawVerticalLine PROC
;
; Draws a vertical line starting at position X,Y with
; a given length and color.
; Receives: CX = X-coordinate, DX = Y-coordinate,
;           AX = length, BL = color
; Returns: nothing
;------------------------------------------------------
.data
currY WORD ?

.code
  pusha
  mov  currY,dx ; save Y-coordinate
  mov  currX,cx ; save X-coordinate
  mov  cx,ax  ; loop counter

DVL1:
  push cx ; save loop counter
  mov  al,bl  ; color
  mov  ah,0Ch ; function: draw pixel
  mov  bh,0 ; set video page
  mov  cx,currX ; set X-coordinate
  mov  dx,currY ; set Y-coordinate
  int  10h  ; draw the pixel
  inc  currY  ; move down 1 pixel
  pop  cx ; restore loop counter
  Loop DVL1

  popa
  ret
DrawVerticalLine ENDP
END main