This script, developed for RPG Maker VX Ace from pseudocode provided by FlyingJester, allows you to draw a line between two specified points on a bitmap.
To use it, simply call $game_system.draw_line(bitmap, x1, y1, x2, y2, colour) where bitmap is the bitmap object you want to draw the line on, x1 and y1 are the X and Y coordinate of the first point, x2 and y2 are the X and Y coordinate of the second point, and colour is any valid instance of the Color class.
It seems to be code for an in-game graphics editor. The code defines drawing each pixel in a line between two points. You would have to code the other stuff in, like the stuff involved in moving some kind of cursor to the two points you want.
Nice job! It looks like you tried hard too make it. I was going to make an artpad demo game and this was the best script I could find. Totall credit to you.