111 lines
3.4 KiB
Python
111 lines
3.4 KiB
Python
import pyqtgraph as pg
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import numpy as np
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import time
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from relax import relax
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class ChainSim(pg.QtCore.QObject):
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stepped = pg.QtCore.Signal()
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relaxed = pg.QtCore.Signal()
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def __init__(self):
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pg.QtCore.QObject.__init__(self)
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self.damping = 0.1 # 0=full damping, 1=no damping
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self.relaxPerStep = 10
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self.maxTimeStep = 0.01
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self.pos = None # (Npts, 2) float
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self.mass = None # (Npts) float
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self.fixed = None # (Npts) bool
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self.links = None # (Nlinks, 2), uint
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self.lengths = None # (Nlinks), float
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self.push = None # (Nlinks), bool
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self.pull = None # (Nlinks), bool
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self.initialized = False
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self.lasttime = None
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self.lastpos = None
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def init(self):
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if self.initialized:
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return
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assert None not in [self.pos, self.mass, self.links, self.lengths]
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if self.fixed is None:
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self.fixed = np.zeros(self.pos.shape[0], dtype=bool)
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if self.push is None:
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self.push = np.ones(self.links.shape[0], dtype=bool)
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if self.pull is None:
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self.pull = np.ones(self.links.shape[0], dtype=bool)
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# precompute relative masses across links
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l1 = self.links[:,0]
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l2 = self.links[:,1]
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m1 = self.mass[l1]
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m2 = self.mass[l2]
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self.mrel1 = (m1 / (m1+m2))[:,np.newaxis]
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self.mrel1[self.fixed[l1]] = 1 # fixed point constraint
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self.mrel1[self.fixed[l2]] = 0
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self.mrel2 = 1.0 - self.mrel1
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for i in range(100):
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self.relax(n=10)
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self.initialized = True
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def makeGraph(self):
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#g1 = pg.GraphItem(pos=self.pos, adj=self.links[self.rope], pen=0.2, symbol=None)
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brushes = np.where(self.fixed, pg.mkBrush(0,0,0,255), pg.mkBrush(50,50,200,255))
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g2 = pg.GraphItem(pos=self.pos, adj=self.links[self.push & self.pull], pen=0.5, brush=brushes, symbol='o', size=(self.mass**0.33), pxMode=False)
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p = pg.ItemGroup()
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#p.addItem(g1)
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p.addItem(g2)
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return p
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def update(self):
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# approximate physics with verlet integration
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now = pg.ptime.time()
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if self.lasttime is None:
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dt = 0
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else:
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dt = now - self.lasttime
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self.lasttime = now
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if self.lastpos is None:
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self.lastpos = self.pos
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# remember fixed positions
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fixedpos = self.pos[self.fixed]
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while dt > 0:
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dt1 = min(self.maxTimeStep, dt)
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dt -= dt1
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# compute motion since last timestep
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dx = self.pos - self.lastpos
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self.lastpos = self.pos
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# update positions for gravity and inertia
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acc = np.array([[0, -5]]) * dt1
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inertia = dx * (self.damping**(dt1/self.mass))[:,np.newaxis] # with mass-dependent damping
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self.pos = self.pos + inertia + acc
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self.pos[self.fixed] = fixedpos # fixed point constraint
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# correct for link constraints
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self.relax(self.relaxPerStep)
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self.stepped.emit()
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def relax(self, n=50):
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# speed up with C magic
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relax(self.pos, self.links, self.mrel1, self.mrel2, self.lengths, self.push, self.pull, n)
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self.relaxed.emit()
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