precomputed shade algo, viewport basic render

engine/types/rect.go

@@ -56,6 +56,6 @@ func (self *Rect) Intersects(other *Rect) bool {
 	return false
 }
 
-func (r *Rect) InBounds (x,y int) bool {
-	return x >= r.X && x <= (r.X + r.W) && y >= r.Y && y <= (r.Y + r.H)
+func (r *Rect) InBounds (c Coords) bool {
+	return c.X >= r.X && c.X <= (r.X + r.W -1) && c.Y >= r.Y && c.Y <= (r.Y + r.H -1)
 }