Make orthogonal line drawing operations work with signed coordinates

The vector line drawing operation of the screen device uses optimised
methods when drawing horizontal and vertical lines. The emulator now
interprets the coordinates of these lines as signed values, to allow for
the correct rendering of orthogonal lines where the coordinates of the
left or top edges are off-screen. Diagonal lines are yet to be tackled.

The bounding-box calculations shared by the rectangle and orthogonal
line drawing methods have also been split off into their own method,
significantly reducing the code duplication between all four of the
methods which require this functionality.

This commit also makes aesthetic changes to the code in the
draw_diagonal_line method to improve readability and brevity, as a part
of the changes made to the draw_line method when the points parameter
was removed from each of the three lower line-drawing methods.

0 files changed, 0 insertions, 0 deletions