add initial scanline visualization for the billboards task

scanline/billboards_of_ny.py

@@ -0,0 +1,51 @@
+from manim import *
+
+field = Rectangle(width=10.0, height=5.0)
+
+class Billboard(Rectangle):
+    
+    def __init__(self, x, y, w, h):
+        Rectangle.__init__(self, width=w, height=h)
+        self.x = x
+        self.y = y
+        self.w = w
+        self.h = h
+        self.align_to(field, UL)
+        self.shift(x*RIGHT + y*DOWN)
+
+class Scanline(VGroup):
+
+    def __init__(self):
+        self.line = Line(field.get_top(), field.get_bottom(), color=RED).align_to(field, LEFT)
+        self.tops = dict()
+        VGroup.__init__(self)
+        self.add(self.line)
+
+    def insert(self, y):
+        self.tops[y] = Dot().move_to(self.line.get_top()).shift(y*DOWN)
+        self.add(self.tops[y])
+
+    def delete(self, y):
+        self.remove(self.tops[y])
+        del self.tops[y]
+
+
+class Main(Scene):
+    def construct(self):
+
+        boards = [Billboard(x, y, w, h) for x, y, w, h in [(1, 0, 3, 3), (2, 2, 5, 2)]]
+        self.add(*boards)
+
+        poi = sorted([(b.x, 1, i) for i, b in enumerate(boards)] + [(b.x + b.w, -1, i) for i, b in enumerate(boards)])
+        
+        scan = Scanline()
+
+        for x, left, i in poi:
+            self.play(scan.animate.move_to(field.get_left() + x*RIGHT))
+            if left == 1:
+                scan.insert(boards[i].y)
+            else:
+                scan.delete(boards[i].y)
+
+
+        self.wait(2)