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POHow did older games do collision detection with walls, floors and ceilings?
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copied!<p>I have been reading about collision detection in games on stackoverflow and other sites. A lot of them talk about BSPs, bounding elipses, integration etc. However, on the NES, they managed to do floor and wall collision detection in games and I find it hard to believe that they did many calculations to detect wall collisions.</p> <p>I guess my question is, given a level made up of just tiles, how did they detect collisions with walls and floors in games like Mario and Megaman which had little processing power?</p> <ul> <li>Did they follow the path of motion and determine the closest connecting tile? (a bit of searching) (priori)</li> <li>Did they determine a collision with the floor and then figure out the best way of adjusting the character? (posteriori) This is risky with variable timesteps, you could jump through a tile if you were fast enough. Although I assume NES games timesteps were synced with the tv's refresh rate.</li> <li>Is gravity always affecting your character when you're on the ground? Or do you just 'turn it off' when you're determined to be walking on a tile? What about when you walk off an edge of the cliff? You'd need some sort of way of determining tiles underneath you otherwise.</li> <li>If you've collided with a tile, would you just find the edge of that tile and move your character to the side of it (depending on the direction of travel)?</li> <li>what about sloping tiles like in super metroid and mario?</li> <li>What about 'platforms' where you can jump through the bottom and land on top. How would you deal with collisions with these tiles if you were doing it 'posteriori'?</li> </ul> <p>I have written some collision code that is basically 'priori' as it searches for the first tile you will hit in a certain direction. I'm just wondering if there's a better way. (just using after-the-fact collision detection instead maybe)</p> <p>eg, code to check for tile collisions for moving downward (I check vert then horizontal movement):</p> <pre><code> def tile_search_down(self, char, level): y_off = char.vert_speed assert y_off > 0 # t_ are tile coordintes # must be int.. since we're adding to it. t_upper_edge_y = int( math.ceil((char.y+char.h) / self.tile_height ) ) #lowest edge while (t_upper_edge_y*self.tile_height) < (char.y+char.h+y_off): # lowest edge + offset t_upper_edge_x = int( math.floor(char.x/self.tile_width) ) while (t_upper_edge_x*self.tile_width) < (char.x+char.w): t_x = t_upper_edge_x t_y = t_upper_edge_y if self.is_tile_top_solid(t_x, t_y, plane): char.y = t_y*self.tile_height - char.h char.vert_speed = 0.0 char.on_ground = True return t_upper_edge_x += 1 t_upper_edge_y += 1 char.y += y_off </code></pre>

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