# Optimizing overlapping units vision calculations in RTS using PyGame

Currently I'm developing a RTS game using Python/PyGame and I got some problems with fps drops when there are many units on the screen.

Using Snakeviz profiling I found out that the function update_vision() takes up a big majority of the processing.

This is because the function is checking every tile inside a radius of each unit (depending on the units defined vision range). When there are many units there are a lot of calculations that need to happen.

I'd like to optimize this somehow. Currently it's checking the same tiles over and over if the units vision ranges are overlapping. However I'm not sure how to go about this and would appreciate any help!


#-----Update vision & explored matrixes-----
def update_vision(self):

for i, group in enumerate(all_p_unit_sprite_list):
if i+1 != self.player:
continue

for unit in group:
rel_x, rel_y = unit.get_coord()

for row in range(-unit.vision_range, unit.vision_range + 1):
for col in range(-unit.vision_range, unit.vision_range + 1):
loc_x = rel_x + row
loc_y = rel_y + col
if 0 <= loc_x < matrix_width and 0 <= loc_y < matrix_height:
if abs(row) + abs(col) <= unit.vision_range:
map_vision_matrix[loc_y][loc_x] = 1
map_explored_matrix[loc_y][loc_x] = 1


#-----Get grid coordinates-----
def get_coord(self):
col = self.rect.centerx  // tile_size
row = self.rect.centery // tile_size
return (col, row)


Here is a suggestion:

Manage a unit number matrix like map_unit_num_matrix, The number of units on each tile is recorded. And manage a dirty mark list recording the tiles that change the number of units each frame.

Fake code for example:

#--- unit.py
class Unit:
def __init__(self) -> None:
self.tilePos = [0,0]

def move(self):
pass  // your unit moving logic
self.onMoving()

def onMoving():
newTilePos = self.get_coord()
if newTilePos == self.tilePos and newTilePos == self.tilePos:
return
GameMapManager.instance.unit_move(self.tilePos,newTilePos) //name is just for example
self.tilePos = newTilePos

#--- map.py
class GameMapManager: //it may not exist
def __init__(self) -> None:
self.map_vision_matrix = []
self.map_explored_matrix = []
self.map_unit_num_matrix = []
self.map_dirty_mark_list = []

def unit_move(self,tileFrom,tileTo):
self.map_unit_num_matrix[tileFrom][tileFrom] -= 1
self.map_unit_num_matrix[tileTo][tileTo] += 1
self.map_dirty_mark_list.append(tileFrom)
self.map_dirty_mark_list.append(tileTo)

def update_vision(self):
if not self.map_dirty_mark_list:
return
for tilePos in self.map_dirty_mark_list:
hasUnit = self.map_unit_num_matrix[tilePos][tilePos] > 0
pass // your vision/fog of war logic
self.map_dirty_mark_list = []


If the units have different field of view, you can record a field of view list or a unit list rather than unit number in the matrix.

• Thanks a lot for the suggestion! Do you mean that I should use this list to record if there are a unit on this tile and if so make vision for that tile? Rather than checking for each unit? Apr 12, 2022 at 16:03
• Basicly, yes. but the key is this dirty-mark array. You only need to focus on the modified tiles. it would be much less. The unit on each tile is recorded to achieve it : ) Sorry to reply so late. Apr 16, 2022 at 16:14