geom-demo/geom/demos/vec_proj.py

from .. import HEIGHT, WIDTH, get_cursor_pos
from ..colors import *
from ..math import *
from ..draw import *

class VecProj:

    title = "Vector Projection"

    def handle_key_down(self, key):
        pass

    def render(self, surface):
        x1 = -(WIDTH / 4)
        y1 = 100
        x2 = WIDTH / 4
        y2 = 0

        cx, cy = get_cursor_pos()

        lx, ly = x2 - x1, y2 - y1           # line vector
        llen = length(lx, ly)
        lnx, lny = lx / llen, ly / llen     # line normal
        lcx, lcy = cx - x1, cy - y1         # line start - cursor vector

        proj = dot(lcx, lcy, lx, ly) / llen
        nearest_point = add(x1, y1, *scale(lnx, lny, proj))

        line(surface, GREEN, (cx, cy), nearest_point, 2)
        line(surface, WHITE, (cx, cy), (x1, y1), 2)
        line(surface, YELLOW, (x1, y1), (x2, y2), 2)
        line(surface, RED, (x1, y1), nearest_point, 4)