Hi Zhang!
I'm experimenting with drag based on the non-solid object instead of setting
a damper to each body or the world. I'll check bouyancy when drag is done,
it requires more calculations to compare mass and area (displacement), but
drag will be a factor here too.
I'm working on integrating this without changing the existing collision
behavior for minimum changes.
/Peter
On 2008-08-17 (Sun) 13:34, 帆 张 wrote:
> Hi,
>
> Nice idea and suggestion! Thank you.
>
> First, "3. Algorithm For particle simulation *****DONE*******" in TODOLIST
> is a step in todolist of previous coding phase. particle simulation is very
> simple and implemented at beginning(not need to consider shape and
> constraint).
>
> Second, in fact, air friction has already been added by a simple damping
> algorithm (body.linear_vel_damping and body.angle_vel_damping). I also add a
> new test case (test5.py), it's a chain simulation with damping of velocity
> enabled. you can compare it with test4.py. :-)
>
> Best wishes
> Zhang Fan
>
> Peter Gebauer <[EMAIL PROTECTED]> 写道：
> Sweet!
>
> I have a new question as well. :)
>
> From the todo: 3. Algorithm For particle simulation *****DONE*******
> What is it? Bodies with a single point shape?
>
> I've already done a dozen experiments with the latest svn updates,
> everything looks excellent so far. I'm really impressed with Zhang Fan's
> effort. Your assistance is also appreciated. Good work guys!
>
> I see in the quote the issue of falling through other bodies, it is relevant
> to the "fluid" discussion as well. It would probably prove valuable to have
> friction in "air" as well simply to get a terminal velocity.
> I'm working on a fluid solution that would intergate nicely with solids,
> this still involves changing the behavior of a collision between two bodies.
> From what I've gathered, implementing a rudementary dynamic viscosity for
> netwonian fluids based on friction (or a separate attribute for viscosity
> where 0.0 is vacuum and 1.0 is a solid) wouldn't be that hard.
>
> /Peter
>
> On 2008-08-15 (Fri) 15:33, [EMAIL PROTECTED] wrote:
> > Peter Gebauer
> :
> >
> >> Hi again!
> >>
> >> Should have waited with my previous post, but here's a few things I don't
> >> understand:
> >>
> >> 1) if the mass of a static body is under 1.0 it behaves as a semi-solid,
> >> is this intentional? (i.e other bodies fall "into" the static body and with
> >> mass reaching 0.0 they fall right through)
> >> In test3.py, set the static body mass to 0.1, as an example.
> >
> > This is due to the fact, that the current collision algorithm is not a CCD
> > method. Thus the collision detection highly depends on the step time, size
> > and speed of a body. Other systems, which do not implement a CCD, suffer
> > from
> > the same issue. Zhang Fan wrote a lot about that in pgShapeObject.c.
> >
> > In order to get rid of that, you have to choose matching step times, sizes
> > and the speed for bodies according to your simulation needs - at least as
> > long as there is no CCD algorithm implemented :-).
> >
> >> 2) is there a way to get simulated bouncing? If there was a way to describe
> >> how much energy the object retains (in new direction) after collision, a
> >> float between 0.0 and 1.0 (0-100% energy retained, 0.01 would be a rock and
> >> 0.5 would be more of a tennis ball)?
> >
> > Simulated bouncing is implemented already. The collision energy, and how it
> > is applied on the colliding bodies, depends on the restitution set for them.
> > So, whether you will receive an elastic or inelastic collision, depends on
> > that factor. A quick search for "Coefficient of restitution" and
> > "elastic collisions" will provide you tons of explanations and even some
> > values for different materials.
> > Attached you'll find a small bouncing test script.
> >
> >> 3) can we add bouyancy? :) Body 1 is called "floater" and Body 2 is called
> >> "water", if floater is inside water it should, depending on it'
> >> displacement, either pop back up or sink to the bottom. We would
> >> be able to calculate this with the already existing shape, mass and
> >> friction
> >> attributes, but it would probably require a new boolean attribute, maybe
> >> "solid"?
> >
> > Here's how I'd do it.
> >
> > * create a World with relatively high damping, the gravity vector points to
> > the top (e.g. world.gravity = 0, -3).
> > * place body into that world with a certain damping, mass, etc.
> > * have fun watching the simulation.
> >
> > Limiting the world's area would be left to the user. As you can have
> > multiple
> > worlds, which behave completely different, you could e.g. split the screen
> > into "sky" and "sea", being two different worlds. If the body reaches a
> > certain point, you could remove it from "sea" and add it to "sky"
> > (which reminds of adding remove_* methods, so wait 'til the end of the
> > weekend before doing that ;-).
> >
> > Simulating a varying density of the world would require a slightly
> > different approach for worlds. Currently the world does not know anything
> > about its size and such, that however would be necessary, I think.
> >
> > Regards
> > Marcus
> >
> >
>
> > # The python file is under test
> >
> > import pygame
> > import physics
> > from pygame.locals import *
> >
> > def render_body(body,surface,color):
> > l = body.get_points()
> > pygame.draw.polygon(surface,color,l)
> >
> > def render_world(world,surface,color):
> > for body in world.bodies:
> > render_body(body,surface,color)
> >
> >
> > def init_world():
> > w = physics.World()
> > w.gravity = 0, 2
> >
> > body1 = physics.Body()
> > body1.shape = physics.RectShape(30, 28, 0)
> > body1.position = 400, 40
> > body1.rotation = i
> > body1.restitution = 0.9
> > body1.mass = 20
> > w.add_body(body1)
> >
> > body2 = physics.Body()
> > body2.shape = physics.RectShape (760, 20, 0)
> > body2.position = 400, 600
> > body2.restitution = 1.0
> > body2.mass = 1e100
> > body2.static = True
> > w.add_body(body2)
> > return w
> >
> >
> > def main():
> > """this function is called when the program starts.
> > it initializes everything it needs, then runs in
> > a loop until the function returns."""
> > #Initialize Everything
> > pygame.init()
> > screen = pygame.display.set_mode((800, 800))
> > pygame.display.set_caption('physics test')
> >
> > #Create The Backgound
> > background = pygame.Surface(screen.get_size())
> > background = background.convert()
> > background.fill((0,0,0))
> >
> >
> > #Display The Background
> > screen.blit(background, (0, 0))
> > pygame.display.flip()
> >
> > #Prepare Game Objects
> > clock = pygame.time.Clock()
> >
> > #rect = pygame.Rect(0,0,20,20)
> > #pointlist = [(0,10),(10,0),(0,0)]
> > white = 0, 250, 250
> > theta = 0
> > world = init_world()
> >
> >
> >
> > #Main Loop
> > while 1:
> > # t = clock.tick(60)
> > # t = t/1000.0;
> > world.update(0.02)
> > #Handle Input Events
> > for event in pygame.event.get():
> > if event.type == QUIT:
> > quit()
> > elif event.type == KEYDOWN and event.key == K_ESCAPE:
> > return
> > elif event.type == MOUSEBUTTONDOWN:
> > return
> > elif event.type is MOUSEBUTTONUP:
> > return
> >
> >
> > #Draw Everything
> > background.fill((0,0,0))
> > #print world.body_list[0]
> > render_world(world,background,white)
> > screen.blit(background, (0, 0))
> > pygame.display.flip()
> >
> >
> > #Game Over
> >
> >
> > #this calls the 'main' function when this script is executed
> > if __name__ == '__main__': main()
> >
> >
>
>
>
>
> ---------------------------------
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