Stuck with ODE physics ... No friction with spheres in IanM's update?

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Ric

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Location: object position x

Posted: 1st Feb 2006 01:39

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Using the original ode as in 5.9, a sphere moving across a surface had friction applied using 'ode set contact fdir1 object,value'. However, since updating to IanM's ODE revision (so that I could get bounce values working as well as friction), I can't get friction to apply to spheres at all, no matter how big the value. I've tried experimenting with several different contact modes but to no avail.

The relevent bit of code that's not working is:

+ Code Snippet

function setup_ball_physics()
for ball=1 to 16
  `create collision spheres
  ode create dynamic sphere ball
  ode set contact fdir1 ball,1000
  ODE SETSURFACE MODE CONTACT BOUNCE ball,1
  ode set contact bounce ball,0.4
  ode set body mass ball,1000

next ball
endfunction

and the whole test code is here .... it's a pool table, where the arrow keys are used to aim and space bar is used to shoot the cue ball.

Rem Project: ode pool
Rem Created: 29/01/2006 20:06:38

Rem ***** Main Source File *****

REM Project: Billiards Physics
if check display mode(1024,768,32)=1 then set display mode 1024,768,32
sync on
hide mouse
autocam off
position camera 0,100,-450
color backdrop 0
hide light 0
set ambient light 1
make light 1
position light 1,-500,500,-500
set light range 1,10000

ode start
ode set world gravity 0,-20,0
ode set world step 0.05
ode set world erp (0.2)*2.5
ode set world cfm (10^-5)*2.5

global dim oldballx(16) as float
global dim oldbally(16) as float
global dim oldballz(16) as float

global hit
global power#
power#=100.0

make_pool_balls()
make_pool_table()
rack_balls()
setup_ball_physics()
make_target()

starttime=timer()

do

time=timer()-starttime

if hit=0 then aim()
if spacekey()=1 and hit=0
hit=1
starttime=timer()
shoot()
endif

if hit=1
if time>5000 then hit=0
endif

ode update
update_shadows()
camera()

position object 18,object position x(16),object position y(16),object position z(16)

sync
loop

function shoot()

ODE add force 16,object position x(17)-object position x(16), object position y(16),object position z(17)-object position z(16),object position x(16),object position y(16),object position z(16)

endfunction

function make_target()
make object cube 17,1
hide object 17
make object cube 18,1
hide object 18
endfunction

function camera()
if hit=1 then smoothness=300 else smoothness=100
position camera curvevalue(object position x(18),camera position x(),50),100,curvevalue(object position z(18),camera position z(),50)
yrotate camera curveangle(object angle y(18),camera angle y(),smoothness)
move camera -5
endfunction

function aim()
yrot#=0
if leftkey()=1 then yrot#=-1
if rightkey()=1 then yrot#=1
yrotate object 18,object angle y(18)+yrot#
if upkey()=1 then inc power#,5
if power#>1 and downkey()=1 then dec power#,5
position object 17,object position x(18),object position y(18),object position z(18)
yrotate object 17,object angle y(18)
move object 17,300
line object screen x(17)-power#/10.0,object screen y(17)-power#/10.0,object screen x(17)+power#/10.0,object screen y(17)+power#/10.0
line object screen x(17)-power#/10.0,object screen y(17)+power#/10.0,object screen x(17)+power#/10.0,object screen y(17)-power#/10.0
move object 17,power#
endfunction

function setup_ball_physics()
for ball=1 to 16
  `create collision spheres
  ode create dynamic sphere ball
  ode set contact fdir1 ball,1000
  ODE SETSURFACE MODE CONTACT BOUNCE ball,1
  ode set contact bounce ball,0.4
  ode set body mass ball,1000

next ball
endfunction

function rack_balls()
fact#=sqrt(3.0)*10
position object 1,0,10,250
position object 9,10,10,250+fact#
position object 10,-10,10,250+fact#
position object 2,20,10,250+fact#*2.0
position object 8,0,10,250+fact#*2.0
position object 3,-20,10,250+fact#*2.0
position object 11,30,10,250+fact#*3.0
position object 12,10,10,250+fact#*3.0
position object 4,-10,10,250+fact#*3.0
position object 13,-30,10,250+fact#*3.0
position object 5,40,10,250+fact#*4.0
position object 14,20,10,250+fact#*4.0
position object 6,0,10,250+fact#*4.0
position object 15,-20,10,250+fact#*4.0
position object 7,-40,10,250+fact#*4.0
position object 16,0,10,-250
endfunction

function make_pool_table()
for x=0 to 10
for y=0 to 10
ink RGB(50+x*20,50+(y+x)*10,50),0
dot x,y
next y
next x
get image 20,0,0,10,10
make object plain 20,500,1000
xrotate object 20,-90
yrotate object 20,-180
texture object 20,20
set object emissive 20,rgb(50,50,10)
make object box 21,15,15,1030
texture object 21,20
position object 21,-257.5,7.5,0
make object box 22,15,15,1030
texture object 22,20
position object 22,257.5,7.5,0
make object box 23,500,15,15
texture object 23,20
position object 23,0,7.5,-507.5
make object box 24,500,15,15
texture object 24,20
position object 24,0,7.5,507.5
ink rgb(255,255,255),0

`make collision boxes
for object=20 to 24
ode create static box object
ode set contact fdir1 object, 100
next object

endfunction

function make_pool_balls()
for i=1 to 8
make object sphere i,20,20,20
select i
case 1:ink RGB(255,255,0),0:endcase
case 2:ink RGB(0,0,255),0:endcase
case 3:ink RGB(255,128,64),0:endcase
case 4:ink RGB(156,0,223),0:endcase
case 5:ink RGB(128,0,64),0:endcase
case 6:ink RGB(0,128,64),0:endcase
case 7:ink RGB(202,0,0),0:endcase
case 8:ink RGB(0,0,0),0:endcase
endselect
box 0,0,128,128:solid_circle(64,64,7,RGB(250,250,200)):ink 0,0:text 60,57,str$(i)
get image i,0,30,127,97
texture object i,i
position object i,i*20-150,10,0
next i
width1#=20
for i=9 to 15
make object sphere i,20,20,20
ink rgb(250,250,200),0
box 0,0,128,128
select i
case 9:ink RGB(255,255,0),0:endcase
case 10:ink RGB(0,0,255),0:endcase
case 11:ink RGB(255,128,64),0:endcase
case 12:ink RGB(156,0,223),0:endcase
case 13:ink RGB(128,0,64),0:endcase
case 14:ink RGB(0,128,64),0:endcase
case 15:ink RGB(202,0,0),0:endcase
endselect
for u=0 to 128
for v=0 to 128
width2#=width1#/(cos(abs(v-63)*180.0/50.0)*2.0)
if abs(u-32)<=width2# then dot u,v
if abs(u-96)<=width2# then dot u,v
box 0,0,128,40
box 0,86,128,128
next v
next u
ink 0,0
if i=9
text 60,57,str$(i)
else
text 56,57,str$(i)
endif
get image i,0,35,127,92
texture object i,i
position object i,i*20-150,10,0
next i
make object sphere 16,20,20,20
ink rgb(250,250,200),0
box 0,0,128,128
get image 16,0,35,127,92
texture object 16,16
position object 16,16*20-150,10,0

for ball=1 to 16
set object specular ball,rgb(200,200,200)
set object specular power ball,25
set object emissive ball,rgb(50,50,10)
make object sphere ball+30,20,20,20
color object ball+30,0
scale object ball+30,150,1,100
yrotate object ball+30,-45
ghost object on ball+30,4
next ball
endfunction

function solid_circle(x,y,radius,color)
lock pixels
ptr=get pixels pointer()
this=get pixels pitch()
that =bitmap depth()/8
for i=1 to radius*2
for j=1 to radius*2
pointer=ptr+((y+j-radius)*this)+(x-radius+i)*that
if (radius-i)^2+(radius-j)^2<=radius^2 then *pointer=color
next j
next i
unlock pixels
endfunction

function update_shadows()
for ball=1 to 16
position object ball+30,object position x(ball)+8,object position y(ball)-9,object position z(ball)+8
next ball
endfunction

+ Code Snippet

Rem Project: ode pool
Rem Created: 29/01/2006 20:06:38

Rem ***** Main Source File *****

REM Project: Billiards Physics
if check display mode(1024,768,32)=1 then set display mode 1024,768,32
sync on
hide mouse
autocam off
position camera 0,100,-450
color backdrop 0
hide light 0
set ambient light 1
make light 1
position light 1,-500,500,-500
set light range 1,10000

ode start
ode set world gravity 0,-20,0
ode set world step 0.05
ode set world erp (0.2)*2.5
ode set world cfm (10^-5)*2.5

global dim oldballx(16) as float
global dim oldbally(16) as float
global dim oldballz(16) as float

global hit
global power#
power#=100.0

make_pool_balls()
make_pool_table()
rack_balls()
setup_ball_physics()
make_target()

starttime=timer()

do

time=timer()-starttime

if hit=0 then aim()
if spacekey()=1 and hit=0
hit=1
starttime=timer()
shoot()
endif

if hit=1
if time>5000 then hit=0
endif

ode update
update_shadows()
camera()

position object 18,object position x(16),object position y(16),object position z(16)


sync
loop



function shoot()

ODE add force 16,object position x(17)-object position x(16), object position y(16),object position z(17)-object position z(16),object position x(16),object position y(16),object position z(16)

endfunction

function make_target()
make object cube 17,1
hide object 17
make object cube 18,1
hide object 18
endfunction

function camera()
if hit=1 then smoothness=300 else smoothness=100
position camera curvevalue(object position x(18),camera position x(),50),100,curvevalue(object position z(18),camera position z(),50)
yrotate camera curveangle(object angle y(18),camera angle y(),smoothness)
move camera -5
endfunction

function aim()
yrot#=0
if leftkey()=1 then yrot#=-1
if rightkey()=1 then yrot#=1
yrotate object 18,object angle y(18)+yrot#
if upkey()=1 then inc power#,5
if power#>1 and downkey()=1 then dec power#,5
position object 17,object position x(18),object position y(18),object position z(18)
yrotate object 17,object angle y(18)
move object 17,300
line object screen x(17)-power#/10.0,object screen y(17)-power#/10.0,object screen x(17)+power#/10.0,object screen y(17)+power#/10.0
line object screen x(17)-power#/10.0,object screen y(17)+power#/10.0,object screen x(17)+power#/10.0,object screen y(17)-power#/10.0
move object 17,power#
endfunction



function setup_ball_physics()
for ball=1 to 16
  `create collision spheres
  ode create dynamic sphere ball
  ode set contact fdir1 ball,1000
  ODE SETSURFACE MODE CONTACT BOUNCE ball,1
  ode set contact bounce ball,0.4
  ode set body mass ball,1000

next ball
endfunction

function rack_balls()
fact#=sqrt(3.0)*10
position object 1,0,10,250
position object 9,10,10,250+fact#
position object 10,-10,10,250+fact#
position object 2,20,10,250+fact#*2.0
position object 8,0,10,250+fact#*2.0
position object 3,-20,10,250+fact#*2.0
position object 11,30,10,250+fact#*3.0
position object 12,10,10,250+fact#*3.0
position object 4,-10,10,250+fact#*3.0
position object 13,-30,10,250+fact#*3.0
position object 5,40,10,250+fact#*4.0
position object 14,20,10,250+fact#*4.0
position object 6,0,10,250+fact#*4.0
position object 15,-20,10,250+fact#*4.0
position object 7,-40,10,250+fact#*4.0
position object 16,0,10,-250
endfunction

function make_pool_table()
for x=0 to 10
for y=0 to 10
ink RGB(50+x*20,50+(y+x)*10,50),0
dot x,y
next y
next x
get image 20,0,0,10,10
make object plain 20,500,1000
xrotate object 20,-90
yrotate object 20,-180
texture object 20,20
set object emissive 20,rgb(50,50,10)
make object box 21,15,15,1030
texture object 21,20
position object 21,-257.5,7.5,0
make object box 22,15,15,1030
texture object 22,20
position object 22,257.5,7.5,0
make object box 23,500,15,15
texture object 23,20
position object 23,0,7.5,-507.5
make object box 24,500,15,15
texture object 24,20
position object 24,0,7.5,507.5
ink rgb(255,255,255),0

`make collision boxes
for object=20 to 24
ode create static box object
ode set contact fdir1 object, 100
next object

endfunction

function make_pool_balls()
for i=1 to 8
make object sphere i,20,20,20
select i
case 1:ink RGB(255,255,0),0:endcase
case 2:ink RGB(0,0,255),0:endcase
case 3:ink RGB(255,128,64),0:endcase
case 4:ink RGB(156,0,223),0:endcase
case 5:ink RGB(128,0,64),0:endcase
case 6:ink RGB(0,128,64),0:endcase
case 7:ink RGB(202,0,0),0:endcase
case 8:ink RGB(0,0,0),0:endcase
endselect
box 0,0,128,128:solid_circle(64,64,7,RGB(250,250,200)):ink 0,0:text 60,57,str$(i)
get image i,0,30,127,97
texture object i,i
position object i,i*20-150,10,0
next i
width1#=20
for i=9 to 15
make object sphere i,20,20,20
ink rgb(250,250,200),0
box 0,0,128,128
select i
case 9:ink RGB(255,255,0),0:endcase
case 10:ink RGB(0,0,255),0:endcase
case 11:ink RGB(255,128,64),0:endcase
case 12:ink RGB(156,0,223),0:endcase
case 13:ink RGB(128,0,64),0:endcase
case 14:ink RGB(0,128,64),0:endcase
case 15:ink RGB(202,0,0),0:endcase
endselect
for u=0 to 128
for v=0 to 128
width2#=width1#/(cos(abs(v-63)*180.0/50.0)*2.0)
if abs(u-32)<=width2# then dot u,v
if abs(u-96)<=width2# then dot u,v
box 0,0,128,40
box 0,86,128,128
next v
next u
ink 0,0
if i=9
text 60,57,str$(i)
else
text 56,57,str$(i)
endif
get image i,0,35,127,92
texture object i,i
position object i,i*20-150,10,0
next i
make object sphere 16,20,20,20
ink rgb(250,250,200),0
box 0,0,128,128
get image 16,0,35,127,92
texture object 16,16
position object 16,16*20-150,10,0

for ball=1 to 16
set object specular ball,rgb(200,200,200)
set object specular power ball,25
set object emissive ball,rgb(50,50,10)
make object sphere ball+30,20,20,20
color object ball+30,0
scale object ball+30,150,1,100
yrotate object ball+30,-45
ghost object on ball+30,4
next ball
endfunction

function solid_circle(x,y,radius,color)
lock pixels
ptr=get pixels pointer()
this=get pixels pitch()
that =bitmap depth()/8
for i=1 to radius*2
for j=1 to radius*2
pointer=ptr+((y+j-radius)*this)+(x-radius+i)*that
if (radius-i)^2+(radius-j)^2<=radius^2 then *pointer=color
next j
next i
unlock pixels
endfunction

function update_shadows()
for ball=1 to 16
position object ball+30,object position x(ball)+8,object position y(ball)-9,object position z(ball)+8
next ball
endfunction

Any help greatly appreciated.

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Milkman

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Joined: 30th Nov 2005

Location: United States

Posted: 1st Feb 2006 01:59 Edited at: 1st Feb 2006 04:08

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Try a mass of about 10, and friction about 20 for the balls. Also, make sure the gravity is on for each ball:

+ Code Snippet

ode set gravity ball,1

One more thing: setting the friction so high for the pool table might actually cause problems; a friction of 40 should be more than enough.

hope that helps

formerly xMik

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Ric

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Location: object position x

Posted: 1st Feb 2006 02:46

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No joy unfortunately. It doesn't matter what I do to the values of mass/friction - there is still no friction whatsoever. Friction works for boxes, but not for spheres.

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Nicholas Thompson

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Posted: 1st Feb 2006 10:22

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You know what would help a GREAT deal is knowing what the hell units all this was in. I played with it last night and managed to get it working in a timer-based environment (ie not having to lock the FPS to 60), thing is, to get realistic looking gravity, I had to set gravity to -98 in the Y direction. Thats 10x more than it should be.

When you set the friction to 20, what does that mean? Friction is measure as μ (Mu) which is generally between 0.0 and 1.0 (as I recall)... Solid on Rubber is usuall between 1.0 and 4.0 - so if you had a coefficient of friction of 20 or more, you're pool ball should have more grip than Michael Schumacher!!!

The other one that confuses me is the erp and cfm values - something to do with error correction?

http://forum.antiblog.com, http://thingy-ma-jig.co.uk/new/

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Paul Johnston

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Posted: 1st Feb 2006 10:25

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Use this command on the sphere

ODE SETSURFACE MODE CONTACT APPROX1 <obj>,1

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Nicholas Thompson

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Posted: 1st Feb 2006 11:28

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what does that do?

http://forum.antiblog.com, http://thingy-ma-jig.co.uk/new/

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Ric

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Location: object position x

Posted: 1st Feb 2006 11:37

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That made it roll instead of sliding - but since installing IanM's update, balls seem to roll without needing it. And it still doesn't provide any friction for slowing down spheres - they just keep rolling forever.

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Paul Johnston

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Posted: 1st Feb 2006 11:45

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It's supposed to change the method of calculating friction, sphere's didn't use to roll without it.

Now it sounds like something else is playing up.

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BatVink

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Posted: 1st Feb 2006 14:24

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Quote: "When you set the friction to 20, what does that mean"

Friction is set as an angle

A setting of zero is no friction, the angle is parallel to a flat surface. A setting of 90 is maximum friction, being applied perpendicular to a flat surface.

I'm not entering the debate as to whether that's acceptable or not, I'm not qualified and I don't care

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Ric

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Posted: 1st Feb 2006 19:58

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Where's Ian when you need him?! I'm thinking he may be the only one who can figure this one out.

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Tachyon

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Posted: 1st Feb 2006 20:08 Edited at: 1st Feb 2006 20:09

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Quote: "Where's Ian when you need him?!"

...

Quote: "IanM Moderator
Location: In my moon base"

That was to fun to be left out...
Could it be possile to make "cheat" friction by adding linear velocity to opposite direction at increasing ammount until ode says that that sphere doesnt move?
Other way is to play with anglecular velocity, that shouldnt create any problems with direction, becouse that ball rotates to the direction where it is heading to. That command rotates the ball, right?

By the way, does this problem include in wrapper only, or in Ode c++ thingy?

(2b)||C!(2b) (It's C++) vs. TO B OR NOT 2B (It's DarkBasic!)

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IanM

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Posted: 1st Feb 2006 20:32

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It's not actually friction that is causing you a problem - it's the fact that there was a ... workaround (let's be charitable here

) in the original code that reduced the angular momentum by around 10% each call to the update command.

The workaround was there to stop a problem in ODE that sometimes causes the angular momentum of an object to increase to infinity. I replaced it with a maximum setting instead - I didn't think about how it would affect existing functionality. Anyway ...

When I changed your code to set the fdir1 of all balls to 90, everything settled down, except for the cue ball. I'll tinker a little more and see if I'm still missing something.

For free Plug-ins and source code http://www.matrix1.demon.co.uk

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Zotoaster

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Posted: 1st Feb 2006 20:34

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Do you have to use ODE just for the friction? Why don't you just multiply the speed of the ball my something less than one, viola, friction

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Ric

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Posted: 2nd Feb 2006 00:53

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Yeah - that was so obvious I didn't think of it! Works as a make-do for the time being, although if the engine took care of the physics I'd hopefully have more control over how the balls roll/slide across the surface - at the moment they do a bit of both!

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DarkBASIC Professional Discussion / Stuck with ODE physics ... No friction with spheres in IanM's update?