How to get points X, Y coordinates from line angle?

So I have a 8x8 square. There is a line in it.

Line size == 8 angle == 0. 

One of line points is always on one of the top corners.

What would be a formula to retrieve points coordinates where line crosses borders of square? (positive angle m开发者_运维知识库eans one of line points is 0, 0. negative 0, 8 )

What would be math formula for each of coordinates points? (in pseudo code if possible)

line_end_x = line_start_x + cos(angle)*line_length

line_end_y = line_start_y + sin(angle)*line_length

if your line crosses a vertical edge:

intersection_x = edge_x
intersection_y = line_start_y + (intersection_x - line_start_x) * tan(angle)

if your line crosses a horizontal edge:

intersection_y = edge_y
intersection_x = line_start_x + (intersection_y - line_start_y) * tan(angle-pi/4)

EDIT: corrected