Make vertical lines drawing possible.

Make plot method detecting out of bounds case.

Create a file with points separated with lines (4 digits per line). Read it and display on screen. Detect buffer size you need to display everything.

Extend engine to draw line with multiple colors (one line - one color). Depending of your platform, solution could be different.

Make method rect(int x, int y, int width, int height, chat c, int color) to draw a rectangle.

Create conway's game of life.