Schreiben Sie eine schnellere Python-Physik-simulator

Ich gespielt haben, um mit dem schreiben meiner eigenen Physik-engine in Python als eine übung in der Physik und der Programmierung. Ich habe nach dem tutorial befindet sich hier. Das ging auch, aber dann fand ich den Artikel "Advanced character physics" von thomas jakobsen, die mit Verlet-integration für Simulationen, die ich faszinierend fand.

Habe ich schon versucht zu schreiben, meine eigenen basic-Physik-simulator mit verlet-integration, aber es erweist sich als etwas schwieriger, als ich es zunächst erwartet. Ich war auf der Suche nach Beispiel-Programme zu Lesen, und stolperte über das man in Python geschrieben und ich fand auch dieses tutorial die Verarbeitung verwendet.

Was mich beeindruckt, über die Verarbeitung version ist, wie schnell es läuft. Das Tuch alleine hat 2400 verschiedene Punkte simuliert, und das ist nicht einschließlich der stellen.

Python-Beispiel verwendet nur 256 Teilchen für das Tuch, und es läuft mit etwa 30 frames pro Sekunde. Ich habe versucht, die Erhöhung der Anzahl der Partikel, die in 2401 (es muss Platz für das Programm zu arbeiten), es lief in etwa 3 fps.

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Diese beiden arbeiten durch speichern von Instanzen der Partikel-Objekt in eine Liste, und dann die Iteration durch die Liste, indem Sie jedes Teilchen "update " position" - Methode. Als ein Beispiel, dies ist der Teil des Codes von der Verarbeitung, Skizze, berechnet für jedes Partikel die neue Position:

for (int i = 0; i < pointmasses.size(); i++) {
    PointMass pointmass = (PointMass) pointmasses.get(i);
    pointmass.updateInteractions();
    pointmass.updatePhysics(fixedDeltaTimeSeconds);
}

EDIT: Hier ist der code aus dem python-version, die ich gelinkt früher:

"""
verletCloth01.py
Eric Pavey - 2010-07-03 - www.akeric.com

Riding on the shoulders of giants.
I wanted to learn now to do 'verlet cloth' in Python\Pygame.  I first ran across
this post \ source:
http://forums.overclockers.com.au/showthread.php?t=870396
http://dl.dropbox.com/u/3240460/cloth5.py

Which pointed to some good reference, that was a dead link.  After some searching,
I found it here:
http://www.gpgstudy.com/gpgiki/GDC%202001%3A%20Advanced%20Character%20Physics
Which is a 2001 SIGGRAPH paper by Thomas Jakobsen called:
"GDC 2001: Advanced Characer Physics".

This code is a Python\Pygame interpretation of that 2001 Siggraph paper.  I did
borrow some code from 'domlebo's source code, it was a great starting point.  But
I'd like to think I put my own flavor on it.
"""

#--------------
# Imports & Initis
import sys
from math import sqrt

# Vec2D comes from here: http://pygame.org/wiki/2DVectorClass
from vec2d import Vec2d
import pygame
from pygame.locals import *
pygame.init()

#--------------
# Constants
TITLE = "verletCloth01"
WIDTH = 600
HEIGHT = 600
FRAMERATE = 60
# How many iterations to run on our constraints per frame?
# This will 'tighten' the cloth, but slow the sim.
ITERATE = 2
GRAVITY = Vec2d(0.0,0.05)
TSTEP = 2.8

# How many pixels to position between each particle?
PSTEP = int(WIDTH*.03)
# Offset in pixels from the top left of screen to position grid:
OFFSET = int(.25*WIDTH)

#-------------
# Define helper functions, classes

class Particle(object):
    """
    Stores position, previous position, and where it is in the grid.
    """
    def __init__(self, screen, currentPos, gridIndex):
        # Current Position : m_x
        self.currentPos = Vec2d(currentPos)
        # Index [x][y] of Where it lives in the grid
        self.gridIndex = gridIndex
        # Previous Position : m_oldx
        self.oldPos = Vec2d(currentPos)
        # Force accumulators : m_a
        self.forces = GRAVITY
        # Should the particle be locked at its current position?
        self.locked = False
        self.followMouse = False

        self.colorUnlocked = Color('white')
        self.colorLocked = Color('green')
        self.screen = screen

    def __str__(self):
        return "Particle <%s, %s>"%(self.gridIndex[0], self.gridIndex[1])

    def draw(self):
        # Draw a circle at the given Particle.
        screenPos = (self.currentPos[0], self.currentPos[1])
        if self.locked:
            pygame.draw.circle(self.screen, self.colorLocked, (int(screenPos[0]),
                                                         int(screenPos[1])), 4, 0)
        else:
            pygame.draw.circle(self.screen, self.colorUnlocked, (int(screenPos[0]),
                                                         int(screenPos[1])), 1, 0)

class Constraint(object):
    """
    Stores 'constraint' data between two Particle objects.  Stores this data
    before the sim runs, to speed sim and draw operations.
    """
    def __init__(self, screen, particles):
        self.particles = sorted(particles)
        # Calculate restlength as the initial distance between the two particles:
        self.restLength = sqrt(abs(pow(self.particles[1].currentPos.x -
                                       self.particles[0].currentPos.x, 2) +
                                   pow(self.particles[1].currentPos.y -
                                       self.particles[0].currentPos.y, 2)))
        self.screen = screen
        self.color = Color('red')

    def __str__(self):
        return "Constraint <%s, %s>"%(self.particles[0], self.particles[1])

    def draw(self):
        # Draw line between the two particles.
        p1 = self.particles[0]
        p2 = self.particles[1]
        p1pos = (p1.currentPos[0],
                 p1.currentPos[1])
        p2pos = (p2.currentPos[0],
                 p2.currentPos[1])
        pygame.draw.aaline(self.screen, self.color,
                           (p1pos[0], p1pos[1]), (p2pos[0], p2pos[1]), 1)

class Grid(object):
    """
    Stores a grid of Particle objects.  Emulates a 2d container object.  Particle
    objects can be indexed by position:
        grid = Grid()
        particle = g[2][4]
    """
    def __init__(self, screen, rows, columns, step, offset):

        self.screen = screen
        self.rows = rows
        self.columns = columns
        self.step = step
        self.offset = offset

        # Make our internal grid:
        # _grid is a list of sublists.
        #    Each sublist is a 'column'.
        #        Each column holds a particle object per row:
        # _grid =
        # [[p00, [p10, [etc,
        #   p01,  p11,
        #   etc], etc],     ]]
        self._grid = []
        for x in range(columns):
            self._grid.append([])
            for y in range(rows):
                currentPos = (x*self.step+self.offset, y*self.step+self.offset)
                self._grid[x].append(Particle(self.screen, currentPos, (x,y)))

    def getNeighbors(self, gridIndex):
        """
        return a list of all neighbor particles to the particle at the given gridIndex:

        gridIndex = [x,x] : The particle index we're polling
        """
        possNeighbors = []
        possNeighbors.append([gridIndex[0]-1, gridIndex[1]])
        possNeighbors.append([gridIndex[0], gridIndex[1]-1])
        possNeighbors.append([gridIndex[0]+1, gridIndex[1]])
        possNeighbors.append([gridIndex[0], gridIndex[1]+1])

        neigh = []
        for coord in possNeighbors:
            if (coord[0] < 0) | (coord[0] > self.rows-1):
                pass
            elif (coord[1] < 0) | (coord[1] > self.columns-1):
                pass
            else:
                neigh.append(coord)

        finalNeighbors = []
        for point in neigh:
            finalNeighbors.append((point[0], point[1]))

        return finalNeighbors

    #--------------------------
    # Implement Container Type:

    def __len__(self):
        return len(self.rows * self.columns)

    def __getitem__(self, key):
        return self._grid[key]

    def __setitem__(self, key, value):
        self._grid[key] = value

    #def __delitem__(self, key):
        #del(self._grid[key])

    def __iter__(self):
        for x in self._grid:
            for y in x:
                yield y

    def __contains__(self, item):
        for x in self._grid:
            for y in x:
                if y is item:
                    return True
        return False


class ParticleSystem(Grid):
    """
    Implements the verlet particles physics on the encapsulated Grid object.
    """

    def __init__(self, screen, rows=49, columns=49, step=PSTEP, offset=OFFSET):
        super(ParticleSystem, self).__init__(screen, rows, columns, step, offset)

        # Generate our list of Constraint objects.  One is generated between
        # every particle connection.
        self.constraints = []
        for p in self:
            neighborIndices = self.getNeighbors(p.gridIndex)
            for ni in neighborIndices:
                # Get the neighbor Particle from the index:
                n = self[ni[0]][ni[1]]
                # Let's not add duplicate Constraints, which would be easy to do!
                new = True
                for con in self.constraints:
                    if n in con.particles and p in con.particles:
                        new = False
                if new:
                    self.constraints.append( Constraint(self.screen, (p,n)) )

        # Lock our top left and right particles by default:
        self[0][0].locked = True
        self[1][0].locked = True
        self[-2][0].locked = True
        self[-1][0].locked = True

    def verlet(self):
        # Verlet integration step:
        for p in self:
            if not p.locked:
                # make a copy of our current position
                temp = Vec2d(p.currentPos)
                p.currentPos += p.currentPos - p.oldPos + p.forces * TSTEP**2
                p.oldPos = temp
            elif p.followMouse:
                temp = Vec2d(p.currentPos)
                p.currentPos = Vec2d(pygame.mouse.get_pos())
                p.oldPos = temp

    def satisfyConstraints(self):
        # Keep particles together:
        for c in self.constraints:
            delta =  c.particles[0].currentPos - c.particles[1].currentPos
            deltaLength = sqrt(delta.dot(delta))
            try:
                # You can get a ZeroDivisionError here once, so let's catch it.
                # I think it's when particles sit on top of one another due to
                # being locked.
                diff = (deltaLength-c.restLength)/deltaLength
                if not c.particles[0].locked:
                    c.particles[0].currentPos -= delta*0.5*diff
                if not c.particles[1].locked:
                    c.particles[1].currentPos += delta*0.5*diff
            except ZeroDivisionError:
                pass

    def accumulateForces(self):
        # This doesn't do much right now, other than constantly reset the
        # particles 'forces' to be 'gravity'.  But this is where you'd implement
        # other things, like drag, wind, etc.
        for p in self:
            p.forces = GRAVITY

    def timeStep(self):
        # This executes the whole shebang:
        self.accumulateForces()
        self.verlet()
        for i in range(ITERATE):
            self.satisfyConstraints()

    def draw(self):
        """
        Draw constraint connections, and particle positions:
        """
        for c in self.constraints:
            c.draw()
        #for p in self:
        #    p.draw()

    def lockParticle(self):
        """
        If the mouse LMB is pressed for the first time on a particle, the particle
        will assume the mouse motion.  When it is pressed again, it will lock
        the particle in space.
        """
        mousePos = Vec2d(pygame.mouse.get_pos())
        for p in self:
            dist2mouse = sqrt(abs(pow(p.currentPos.x -
                                      mousePos.x, 2) +
                                  pow(p.currentPos.y -
                                      mousePos.y, 2)))
            if dist2mouse < 10:
                if not p.followMouse:
                    p.locked = True
                    p.followMouse = True
                    p.oldPos = Vec2d(p.currentPos)
                else:
                    p.followMouse = False

    def unlockParticle(self):
        """
        If the RMB is pressed on a particle, if the particle is currently
        locked or being moved by the mouse, it will be 'unlocked'/stop following
        the mouse.
        """
        mousePos = Vec2d(pygame.mouse.get_pos())
        for p in self:
            dist2mouse = sqrt(abs(pow(p.currentPos.x -
                                      mousePos.x, 2) +
                                  pow(p.currentPos.y -
                                      mousePos.y, 2)))
            if dist2mouse < 5:
                p.locked = False

#------------
# Main Program
def main():
    # Screen Setup
    screen = pygame.display.set_mode((WIDTH, HEIGHT))
    clock = pygame.time.Clock()

    # Create our grid of particles:
    particleSystem = ParticleSystem(screen)
    backgroundCol = Color('black')

    # main loop
    looping = True
    while looping:
        clock.tick(FRAMERATE)
        pygame.display.set_caption("%s -- www.AKEric.com -- LMB: move\lock - RMB: unlock - fps: %.2f"%(TITLE, clock.get_fps()) )
        screen.fill(backgroundCol)

        # Detect for events
        for event in pygame.event.get():
            if event.type == pygame.QUIT:
                looping = False
            elif event.type == MOUSEBUTTONDOWN:
                if event.button == 1:
                    # See if we can make a particle follow the mouse and lock
                    # its position when done.
                    particleSystem.lockParticle()
                if event.button == 3:
                    # Try to unlock the current particles position:
                    particleSystem.unlockParticle()

        # Do stuff!
        particleSystem.timeStep()
        particleSystem.draw()

        # update our display:
        pygame.display.update()

#------------
# Execution from shell\icon:
if __name__ == "__main__":
    print "Running Python version:", sys.version
    print "Running PyGame version:", pygame.ver
    print "Running %s.py"%TITLE
    sys.exit(main())

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Weil beide Programme arbeiten in etwa der gleichen Weise, aber die Python-version ist SO viel langsamer, es macht mich Frage mich:

• Ist dieser Leistungsunterschied Teil der Natur von Python?
• Was sollte ich anders machen, aus den oben, wenn ich will, um eine bessere Leistung aus meinem eigenen Python-Programme? E. g speichern Sie die Eigenschaften aller Teilchen im inneren ein array anstelle der Verwendung von einzelnen Objekten, etc.

EDIT: Beantwortet!!!

@Mr E verbunden ist PyCon reden in die Kommentare und @A. Rosa Antwort mit dem die verlinkten Ressourcen-all das half ENORM, in ein besseres Verständnis, wie Sie schreiben, gut, schnelle python-code. Ich bin jetzt Bookmark diese Seite für zukünftige Referenz 😀