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I know how to draw horizontal lines by doing 

LOOP1 STR R5, #0    ;starting ixel
ADD R5, R5, #1   ;increment of pixel on coordinate
ADD R7, R7 #-1  ;decrement to the desired length counter 
BRp LOOP1    ;keeps looping until register with desired length is zero

Obviously the registers will be different for whatever the user chooses for the counter and coordinate locations but these were just numbers from my previous code. What would be a way to manipulate that code to draw a vertical line? I'm not completely comfortable with the formatting of the code on this website yet either so please excuse me if I am wrong in a few areas.

michaelm1088
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1 Answers1

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The difference between horizontal line and vertical line is how we increment the pixel position.

Let's note that a two dimensional coordinate can (and must) be mapped to a one dimensional system by a formula like rowCoordinate * columSize + columnCoordinate.  (Memory is a one-dimensional system, it doesn't have two dimensions so we use this kind of mapping.)

So, as you have shown, we can draw a horizontal line by traversing each pixel from (row,0) to (row,columnSize-1).  By the mapping formula above, we go from

(row,c) to (row,c+1) by simply adding 1 to the address of the pixels.

To draw a vertical line, we want to vary the row position and keep the column position fixed as in: from (0,col) to (rowSize-1,col).

According to the mapping of 2d to 1d, that means going from

(r,col) to (r+1,col) we need to increment by columnSize instead of 1.

Erik Eidt
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    Perfect, thank you so much! I mapped out NCSU in excel so i could write the code for the design and put it into Pennsim and knew how to make all the horizontal lines for the letters but was not sure how to incorporate the vertical lines for them. Appreciate it a lot and stay safe! – michaelm1088 Apr 22 '20 at 00:44