Python rectangle collision handling with pygame

Question

I've been doing extensive research on this topic for the past few days and I can't seem to find an answer for my exact problem.

So, I have a simple game set up where I have the player at 0, 0 with a width of 10x10

    player= pygame.Rect(0, 0, 10, 10)

and aside from that, the player has a velocity of x: 0, y: 10, which will make him fall (y is positive because the origin of the screen is at the top left.)

and I have a tile at 0, 100, as shown:

    dirt= pygame.Rect(0, 100, 10, 10)

so, how can I handle collision, I already know I can detect it with Rect.colliderect(Rect).

I've tried a few ways, but encountered some problems:

I can't cut the player's velocity to 0 when he hits something and then move him back until he's just touching the object because that still causes the problem of walking, when he walks, I apply +10 velocity on x, but unfortunately, the game still processes that he is falling and colliding and moving sideways, so it just moves him back to where he started.

I'm a beginner, so a simple answer would be appreciated, and I would like to not have to use any third party modules other that pygame if I didn't have to.

Update:

Here is some of the rough test code I have tried:

    def sim(obj, time, world):
        time= time / 1000
        obj.physProp['vel']= (obj.physProp['vel'][0] + (accel[0] * time), obj.physProp['vel'][1] + (accel[1] * time))
        if obj.physProp['vel'][1] > terminalY:
            obj.physProp['vel']= (obj.physProp['vel'][0], terminalY)
        obj.pos= (obj.pos[0] + (obj.physProp['vel'][0] * time) + ((accel[0] / 2) * (time ** 2)), obj.pos[1] + (obj.physProp['vel'][1] * time) + ((accel[1] / 2) * (time ** 2)))

        for ID in world:
            if obj.getRect().colliderect(world[ID].getRect()) == True:
                pass

        return (obj.pos, obj.physProp['vel'])

@vdbuilder Ok, I posted it as an update, tell me if more information would be helpful, thanks — Parker Hoyes
– Parker Hoyes, Commented Oct 25, 2012 at 1:11

DanRedux · Accepted Answer · 2012-11-03 05:36:16Z

4

Split up x/y movement.

Move x, check if colliding, if so, move back and set xspeed to 0.

Move y, check if colliding, if so, move back and set yspeed to 0.

It does mean two collisions checks per step but it's super smooth. :)

answered Nov 3, 2012 at 5:36

DanRedux

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Comments

SwiftsNamesake · Accepted Answer · 2017-08-18 16:34:28Z

1

The Pygame API invites you to write all your game subjects in an Object oriented way - so that your falling character will have all the "methods" and "attributes" to properly respond to things on the scenario - like hitting something.

So, if your character is defined for something as simple as:

class Char(object):
    # these start as class attributes, 
    # but whenever they are assigned to with a "self.var = bla" in
    # a method, an instance attribute starts existing
    x, y = 0,0
    vx, vy = 0,0

    def update(self):
        self.x += self.vx
        self.y += self.vy

And your external code, upon detecting a collision, could do just this:

def mainloop():
   while True:
       ...
       obj.update()
       if obj.getRect().colliderect(world[ID].getRect()): # don't do "== True" in `if's - it is just silly
             # take character back to the precious position
             obj.x -= obj.vx
             obj.y -= obj.vy
             # zero out velocities to make it stop:
             obj.vx = obj.vy = 0

And so on - you will soon perceive thinking of your game "things" as "objects" as they are used in programing make the code flows quite naturally - as soon as you get the way this works, look at Pygame's sprite module - which allows you to automate a lot of checks, and updates without having to explicitly write for loops for each check

edited Aug 18, 2017 at 16:34

SwiftsNamesake

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answered Oct 25, 2012 at 1:15

jsbueno

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2 Comments

Parker Hoyes Over a year ago

thanks, but I don't think this will quite work in my case, because the acceleration of gravity is constantly added to the object, if there is a collision, is is set back to 0, so if that character walks, its velocity vector will be going down and left, which is still inside of the other object, and so it will be sent back, this makes it impossible to walk.

Parker Hoyes Over a year ago

Simple fix! Instead of applying velocity when the player moves I simply move forward and check for collision, not great, but it works, thanks for your help! I'll keep that information in mind.

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