// This file is part of the materials accompanying the book 
// "The Elements of Computing Systems" by Nisan and Schocken, 
// MIT Press. Book site: www.idc.ac.il/tecs
// File name: projects/06/rect/Rect.asm

// Draws a rectangle at the top left corner of the screen.
// The rectangle is 16 pixels wide and R0 pixels high.
   @0
   D=M                 //height is in D
   @INFINITE_LOOP      //jump if 0 or neg
   D;JLE 
   @counter            //counter begins with the value of height
   M=D
   @SCREEN
   D=A
   @address
   M=D
(LOOP)
   @address            //where to write on the screen
   A=M                 //write pixels by setting individual pixels to 1
   M=-1                //this -1 sets 16 pixels at a time
   @address
   D=M
   @32                 //32 is the number of 16 bit words in a row (512 bits per row)
   D=D+A
   @address            //where to write on the screen -the next row in this case
   M=D
   @counter            //counter (height) is decremented by 1
   MD=M-1
   @LOOP
   D;JGT
(INFINITE_LOOP)
   @INFINITE_LOOP
   0;JMP