Box2D UDF - Physics and Game Engine for AutoIT

[seangriffin]

This is my first release of Box2D for AutoIT.  A very fun and exciting UDF to be bringing to you all.  For those who don't know, Box2D is a physics engine (see http://box2d.org/).  It simulates physical systems using rigid bodies and collision detection.  It is arguably the most prevalent physics engine in existence, within popular physics-based games like Angry Birds using it, and is also at the core of other advanced physics engines such as Unity.

For a quick demonstration of this UDF in action see the following YouTube video ->  https://youtu.be/h5QH1O63Wik

Or play "Angry Nerds", the demo game, for yourself.  Visit the EXAMPLES section below.

Box2D is purely a mathematical engine.  It can model physics numerically.  This in itself is quite interesting, however it really shines when applied to a good graphics engine.  Recently I posted my SFML UDF over here ...

After benchmarking several popular graphics engines (i.e. GDI+, Direct2D, Irrlicht and SFML) with this Box2D UDF I've selected SFML as my favourite, and the engine that I believe performs the best (fastest) with a rich set of functions appropriate for any physics engine.  With Box2D married with SFML, and running on AutoIT, the results are stunning.

A HUGE THANK-YOU to jRowe and linus (for the Irrlicht UDF) and UEZ for his post on GDI+ loading screens and trancexx and Eukalyptus for their work on Direct2D.  Without their talents I would not have been able to reach this point on my own.

The Box2D library is available for C++.  Way back in 2010 it was ported to Pure C by "Paril" and made available on Google Code and known as "Box2C".  Google Code has since been shut down but the but the archive of Box2C still exists to this day here -> https://code.google.com/archive/p/box2c.  This is the library which I have ported to AutoIT in this UDF.

SFML I am also porting to AutoIT under a separate UDF, as linked above.

Building this UDF has been a dream come true.  I've been fascinated by physics-based games as far back as the golden age of gaming in the 80's, with thrust style games like Asteroids and platformers like Donkey Kong.  I admired game developers like Jeremy Smith who created what may have been the first true game physics engines for the home computers.  I was astonished by their talents in games like Thrust and Exile for the C64.  Over the years I've attempted to mimic at least some of their success in my own games but alas I can not match their skills.  Now much older automation tools have become my game.  I use them almost every day, AutoIT included.  I've dabbled in other languages for physics game development, like Scratch and Unity, but sadly I had wondered why AutoIT, with all it's glorious capabilities and rapid scripting features, didn't have such a feature.  Hence this UDF.

This UDF demands a big time investment, and I am time poor, but I have a keen interest in the topic and will do my best to continue it's development.  I am only a hobbyist game developer and welcome comments and suggestions from those far smarter than I on this topic.

REQUIREMENTS:

• AutoIt3 3.2 or higher

LIST OF FUNCTIONS (in progress):

I've split this UDF into two halves.  "Box2C.au3" is a UDF specifically for Box2C, the C API for Box2D.  It provides the mathematics behind the engine.  Additionally I'm providing "Box2CEx.au3" as an Extension that provides the graphics and gaming functions for Box2D.

Within the core "Box2C.au3" UDF:

• _Box2C_Startup
• _Box2C_Shutdown
• _Box2C_b2Vec2_Constructor
• _Box2C_b2Vec2_Length
• _Box2C_b2Vec2_Distance
• _Box2C_b2World_Constructor
• _Box2C_b2World_CreateBody
• _Box2C_b2World_DestroyBody
• _Box2C_b2World_CreateFixture
• _Box2C_b2World_CreateFixtureFromShape
• _Box2C_b2World_Step
• _Box2C_b2BoxShape_Constructor
• _Box2C_b2CircleShape_Constructor
• _Box2C_b2PolygonShape_Constructor
• _Box2C_b2PolygonShape_Set
• _Box2C_b2PolygonShape_CrossProductVectorScalar
• _Box2C_b2PolygonShape_CrossProductVectorVector
• _Box2C_b2PolygonShape_Normalize
• _Box2C_b2PolygonShape_ComputeCentroid
• _Box2C_b2BodyDef_Constructor
• _Box2C_b2Body_DestroyFixture
• _Box2C_b2Body_GetPosition
• _Box2C_b2Body_SetPosition
• _Box2C_b2Body_GetAngle
• _Box2C_b2Body_SetAngle
• _Box2C_b2Body_SetAwake
• _Box2C_b2Body_SetTransform
• _Box2C_b2Body_GetLinearVelocity
• _Box2C_b2Body_SetLinearVelocity
• _Box2C_b2Body_GetAngularVelocity
• _Box2C_b2Body_SetAngularVelocity
• _Box2C_b2Body_ApplyForce
• _Box2C_b2Body_ApplyForceAtBody
• _Box2C_b2Body_ApplyDirectionalForceAtBody
• _Box2C_b2Body_ApplyTorque
• _Box2C_b2Fixture_GetShape
• _Box2C_b2Fixture_GetDensity
• _Box2C_b2Fixture_SetDensity
• _Box2C_b2Fixture_GetRestitution
• _Box2C_b2Fixture_SetRestitution
• _Box2C_b2Fixture_GetFriction
• _Box2C_b2Fixture_SetFriction
• _Box2C_b2Fixture_SetSensor

Within y "Box2CEx.au3" extension:

• x_metres_to_gui_x
• y_metres_to_gui_y
• metres_to_pixels
• atan2
• radians_to_degrees
• degrees_to_radians
• _Box2C_Setup_SFML
• _Box2C_b2Vec2_GetGUIPosition
• _Box2C_b2World_Setup
• _Box2C_b2World_GDIPlusSetup
• _Box2C_b2World_SetPixelsPerMetre
• _Box2C_b2World_SetGUIArea
• _Box2C_b2World_GetGUIArea
• _Box2C_b2World_GetGUIAreaCenter
• _Box2C_b2World_Create
• _Box2C_b2World_Step_Ex
• _Box2C_b2World_StartAnimation
• _Box2C_b2World_Animate_SFML
• _Box2C_b2World_Animate_GDIPlus
• _Box2C_b2World_WaitForAnimateEnd
• _Box2C_b2ShapeArray_AddItem_SFML
• _Box2C_b2ShapeArray_SetItem_SFML
• _Box2C_b2ShapeArray_GetItemImagePath_SFML
• _Box2C_b2PolygonShape_ArrayAdd_Irrlicht
• _Box2C_b2PolygonShape_ArrayAdd_GDIPlus
• _Box2C_b2BodyDefArray_AddItem
• _Box2C_b2FixtureArray_SetItemSensor
• _Box2C_b2FixtureArray_GetItemDensity
• _Box2C_b2FixtureArray_SetItemDensity
• _Box2C_b2FixtureArray_GetItemRestitution
• _Box2C_b2FixtureArray_SetItemRestitution
• _Box2C_b2FixtureArray_GetItemFriction
• _Box2C_b2FixtureArray_SetItemFriction
• _Box2C_b2BodyArray_AddItem_SFML
• _Box2C_b2Body_ArrayAdd_Irrlicht
• _Box2C_b2Body_ArrayAdd_GDIPlus
• _Box2C_b2BodyArray_GetItemCount
• _Box2C_b2BodyArray_GetItemPosition
• _Box2C_b2BodyArray_SetItemPosition
• _Box2C_b2BodyArray_GetItemAngle
• _Box2C_b2BodyArray_SetItemAngle
• _Box2C_b2BodyArray_GetItemLinearVelocity
• _Box2C_b2BodyArray_SetItemActive
• _Box2C_b2BodyArray_SetItemAwake
• _Box2C_b2BodyArray_SetItemImage_SFML
• _Box2C_b2BodyArray_SetItemDraw
• _Box2C_b2BodyArray_ApplyItemForceAtBody
• _Box2C_b2BodyArray_ApplyItemDirectionalForceAtBody
• _Box2C_b2BodyArray_Transform_SFML
• _Box2C_b2Body_Transform_GDIPlus
• _Box2C_b2BodyArray_Draw_SFML
• _Box2C_b2Body_ArrayDrawDisplay_SFML
• _Box2C_b2Body_Destroy
• _Box2C_b2Body_Destroy_SFML
• _Box2C_b2Body_Rotate_GDIPlus

The SFML functions used in the tests and demos will be available in the SFML UDF post (see reference above).

EXAMPLES:

For such a powerful physics engine coupled to such a powerful graphics engine (SFML) it's sad that I've only had time to build one functional game, thus far.  But it's a start.

My self-titled "Angry Nerds" is merely a demo of the same game concept as the ever-so-popular Angry Birds game.  Angry Birds itself is built on top of Box2D.  Likewise Angry Nerds.  AutoIT + Box2D + SFML to be exact.  I've compiled Angry Nerds and provided an installer also, so you can quickly run the demo for yourself.  From the Github site below (in the DOWNLOAD section) run "Box2C_Angry_Nerds_Game_SFML_installer.exe" to install the demo to a location on your computer (desktop by default).  Go into this folder and run "Box2C_Angry_Nerds_Game_SFML.exe".  All instructions are displayed in-game.  Should be quite easy to work out.

Aside from Angry Nerds there are also two test scripts:

• Box2C_linear_forces_test_SFML.au3
• Box2C_angular_forces_test_SFML.au3

Feel free to run these for a basic demonstration of rigid bodies, forces and collisions.  The heart of Box2D and any physics engine.

Lastly I also have four speed tests as follows:

• Box2C_speed_test_SFML.au3
• Box2C_speed_test_Irrlicht.au3
• Box2C_speed_test_D2D.au3
• Box2C_speed_test_GDIPlus.au3

These were my initial evaluations into a suitable graphics engine for Box2D.  I've since settled on SFML, but feel free to execute these.  Note they may become quick defective over time as the SFML functions slowly take over.

DOWNLOADS:

You can download this UDF, including the examples above and associated files, from the following GitHub page:

https://github.com/seanhaydongriffin/Box2C-UDF

Hope you all enjoy!  I certainly am :-)

Cheers,

Sean.

 

Edited May 26, 2017 by seangriffin

[UEZ]

Very impressive work! 

The physic engine is really nice implemented! 

 

Just for my curiosity - how did "GDI+ loading screens" help you?

[seangriffin]

Thanks UEZ. I had never developed graphics in Windows as low level as GDI before. Always preferring to use something simpler and higher level such as what Unity provides. I needed a graphics engine for Box2D and I knew that GDI might be my answer but I'd absolutely no clue where to start. Because of the popularity of your GDI loading screens topic I was immediately drawn to your work. Having fully functional GDI animation examples was the perfect way to explain to me, a novice, how GDI works. I've also admired your scripting skill for some time and knew it was going to be impressive, and it was. Your optimisation of the GDI calls is precisely whats required for a physics engine. also you introduced me to the low level and efficient timers in the Windows API that i didn't know existed. they help me run non time critical  script away from the time critical physics animation loop in my script. If it weren't for your demos I would not be this far advanced with Box2D.  A very big thanks to you UEZ you are brilliant! I really love the AutoIT community. 

Edited May 26, 2017 by seangriffin

[UEZ]

Thanks for your feedback. ^^

Well, GDI is much faster than GDI+ but I like the functions of GDI+ more to create better looking graphical stuff. But GDI+ is mostly too slow for really cool stuff.

Probably much better is DirectX / OpenGL / OpenCL / ... Your solution looks also very good. 

 

Nice to read that my GDI+ examples were useful.

Edited May 26, 2017 by UEZ

[seangriffin]

Really useful UEZ. I'm sure you are helping many people in need such as myself. 

[seangriffin]

To give everyone an update on this UDF.  I came to the realization that this was a little ambitious for a scripting language like AutoIT.  I still love the performance of AutoIT for most endevours, but in this case (for realtime graphics) I needed something closer to the speed of a compiled language like C.  Partly due to some posts by UEZ I was drawn towards several basic style languages, which seemed to offer the speed I was after with the simplicity of a basic language that is similar to that of AutoIT.  These included FreeBasic, BlitzBasic and PureBasic.  My attempts to get Box2D working in FreeBasic failed at the DLL level.  I'm still not sure why to this day.  I then moved to PureBasic and had immediate success there.  PureBasic also has native OpenGL support.  I initially tried the SFML library there.  It was too slow.  But after moving to direct OpenGL calls I got the great preformance I was looking for.  I then attempted to integrate LiquidFun (http://google.github.io/liquidfun) into PureBasic and to my excitment that was successful also.

So for now I'm continuing my developments of LiquidFun / Box2D physics within PureBasic.  If anyone is interested in this then check out my recent post in the PureBasic forums here -> http://www.purebasic.fr/english/viewtopic.php?f=27&t=68874

The Github repository is also here -> https://github.com/seanhaydongriffin/PB-LiquidFun-C

I'm really happy with where this is going, and perhaps I could later back-port my work and lessons learned from PureBasic to AutoIT.

Edited August 4, 2017 by seangriffin

[UEZ]

Unfortunately free version of PureBasic is limited and cannot execute larger code via the editor but it look really awesome.  

I cannot tell you why FreeBasic didn't work for you but also FB has OpenGL native support.

There is also a FreeBasic version of Particle Fluid Simulation:

expandcollapse popup

''   rough smoothed particle hydrodynamics (SPH) draft
''   Michael "h4tt3n" Nissen, july 5th 2010
''   
''   todo:
''   predefined cell neighbors
''   better kernel (less bouncy liquid)
''   better broad phase collision detection
''   better mouse interaction
''   better code structure

''   includes
#Include Once "GL/gl.bi"

''   constants
Const as single      dt                  = 0.01                                 ''   timestep
Const as single      half_dt            = 0.5*dt                              ''   half timestep
const as single      r                   = 10                                    ''   interaction radius
const as single      r_2                = 2*r                                    ''   two radius (for grid)
const as single      r_sqrd             = r*r                                    ''   radius squared
Const as single      k                      = 400                                    ''   global "spring stiffnes"
Const as single      k_near             = 3000                                 ''   local "spring stiffnes"
Const as single      viscosity         = 2                                       ''   viscosity
Const as single      rest_dens       = 6                                       ''   rest density
const as single      grav_acc         = 400                                    ''   gravity
Const as single      pi                  = 4*atn(1)                           ''   pi
Const as single      radius            = 2                                       ''   particle distance on startup
const as integer  block_width      = 60                                    ''   <--- change to reduce / increase num masses
const as integer  block_height   = 100                                    ''   
Const as integer  num_masses      = block_width*block_height   ''   total number of masses
const as integer  neighbors         = 48                                    ''   max number of neighbors
Const as integer    screen_wid       = 800                                    ''   screen width
Const as integer    screen_hgt       = 400                                    ''   screen height
Const As Single    wall_friction   = 1                                       ''   wall friction (1 = full, 0 = off)
Const As Single    interaction_Radius   = 8                              ''   mouse interaction radius

Const As Integer cell_dia                  = r
Const As Integer cell_max_masses      = 24
const as integer num_cells_row         = screen_wid/cell_dia
const As integer num_cells_col         = screen_hgt/cell_dia

Const As Integer num_cells               = num_cells_row*num_cells_col

Const As Single cell_wid                  = screen_wid/num_Cells_row
Const As single cell_hgt                  = screen_hgt/num_Cells_Col
const As single half_cell_wid            = cell_wid/2

''   types
Type CellType
   As Integer Num_Masses, Mass(1 To cell_max_masses)
End Type

type vectortype
   as single x, y
end Type

Type NeighborType
   As Integer a
   As Single Dist
   As vectortype norm_dist
End Type

type masstype
   As Integer num_neighbors
   As NeighborType Neighbor(1 To neighbors)
   as vectortype frc, vel, psn
   as Single density, angvel, torque
end Type

''   dim variables
Dim as integer    center_x    = screen_wid\2
Dim as integer    center_y   = screen_hgt\2

dim as integer mouse_x, mouse_y, mouse_x_old, mouse_y_old, mouse_vel_x, mouse_vel_y

dim Shared As masstype mass(1 to num_masses)
dim Shared As celltype cell(1 to num_cells_row, 1 To num_cells_col)

''   narrow phase collision detection. Make particles neighbors if distance < r
Sub CheckIfNeighbor(ByVal a_ As Integer, ByVal b_ As Integer)
   
   If mass(a_).num_neighbors = neighbors Then Exit sub
   If mass(b_).num_neighbors = neighbors Then Exit Sub
   
   Dim As vectortype dist
   
   dist.x = mass(b_).psn.x-mass(a_).psn.x: If Abs(dist.x) > r Then Exit Sub
   dist.y = mass(b_).psn.y-mass(a_).psn.y: If Abs(dist.y) > r Then Exit Sub
   
   Dim As Single dist_sqrd = dist.x*dist.x+dist.y*dist.y
   
   If dist_sqrd > r_sqrd Or dist_sqrd = 0 Then Exit Sub
   
   Dim As Single distance = Sqr(dist_sqrd)
   
   Dim As vectortype norm_dist = (dist.x/distance, dist.y/distance)
   
   Dim As Single density = 1 - distance / r
   
   '' create neighbors and save data
   With mass(a_)
      .num_neighbors += 1
      .Neighbor(.num_neighbors).a = b_
      .Neighbor(.num_neighbors).dist = distance
      .Neighbor(.num_neighbors).norm_dist.x = norm_dist.x
      .Neighbor(.num_neighbors).norm_dist.y = norm_dist.y
      .Density += density
   End With
   
   With mass(b_)
      .num_neighbors += 1
      .Neighbor(.num_neighbors).a = a_
      .Neighbor(.num_neighbors).dist = distance
      .Neighbor(.num_neighbors).norm_dist.x = -norm_dist.x
      .Neighbor(.num_neighbors).norm_dist.y = -norm_dist.y
      .Density += density
   End With
   
End Sub

Randomize Timer

Dim As Integer n = 1

''   place particles
For i As Integer = 1 To block_width
   For j As Integer = 1 To block_height
      With mass(n)
         .psn.x = i * radius * 2
         .psn.y = screen_hgt - j * radius * 2
         
         .psn.x += (Rnd-Rnd)
         .psn.y += (Rnd-Rnd)
         
         .vel.x += (Rnd-Rnd)
         .vel.y += (Rnd-Rnd)

      End With
      n += 1
   Next
Next

''   create opengl screen
ScreenRes screen_wid, screen_hgt, 32,, 2
glMatrixMode(GL_PROJECTION)  
glLoadIdentity()
glViewport(0, 0, screen_wid, screen_hgt)
glOrtho(0, screen_wid, screen_hgt, 0, 0, 32)
glMatrixMode(GL_MODELVIEW)
glLoadIdentity()
glClearColor (0.6, 0.7, 1.0, 0.0)
'glenable(GL_ALPHA)
glEnable(GL_BLEND)
glblendfunc(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA)
'glblendfunc(GL_DST_COLOR , GL_SRC_COLOR)

getmouse(mouse_x, mouse_y)

''   main loop
Do
   
   '' save old mouse state
   mouse_x_old = mouse_x
   mouse_y_old = mouse_y
   
   ''   get new mouse state
   getmouse(mouse_x, mouse_y)
   
   '' calc mouse velocity
   mouse_vel_x = (mouse_x-mouse_x_old)/dt
   mouse_vel_y = (mouse_y-mouse_y_old)/dt
   
   ''   mouse interaction
   for i as integer = 1 to num_masses
      with mass(i)   
         
         Dim As vectortype dst
         
         dst.x = .psn.x - mouse_x:   if dst.x > interaction_radius then continue for
         dst.y = .psn.y - mouse_y:   if dst.y > interaction_radius then continue for
         
         if dst.x*dst.x+dst.y*dst.y > interaction_Radius*interaction_Radius then continue for
         
         if mouse_vel_x then .vel.x += (mouse_vel_x-.vel.x) * 0.16
         if mouse_vel_y then .vel.y += (mouse_vel_y-.vel.y) * 0.16
         
      end with   
   Next   
   
   ''   reset particles
   for i as integer = 1 to num_masses
      With mass(i)
         .density = 0
         .num_neighbors = 0
      End With
   Next
   
   ''   reset cells
   For i As Integer = 1 To num_cells_row
      For j As Integer = 1 To num_cells_col
         cell(i, j).Num_Masses = 0
      Next
   Next
   
   ''   update grid (broad phase collision detection)
   For i as integer = 1 to num_masses
      Dim As Integer cell_row = (mass(i).Psn.y\cell_hgt)+1
      Dim as integer cell_col = (mass(i).Psn.x\cell_wid)+1
      With cell(cell_col, cell_row)
         If .num_masses = cell_max_masses Then Continue For
         .num_masses += 1
         .Mass(.num_masses) = i
      End With
   Next
   
   ''   narrow phase collision detection
   For i As Integer = 1 To num_cells_row
      For j As Integer = 1 To num_cells_col
         If cell(i, j).num_masses = 0 Then Continue For
         For k_ As Integer = 1 To cell(i, j).num_masses
            Dim As Integer a_ = cell(i, j).mass(k_)
            
            If mass(a_).num_neighbors = neighbors Then Continue For
            
            ''   cell(x, y) - self 
            For l_ As Integer = k_+1 To cell(i, j).num_masses
               CheckIfNeighbor(a_, cell(i, j).mass(l_))
            Next
            
            ''   cell(x, y) - cell(x+1, y)
            If i < num_cells_row Then
               For l_ As Integer = 1 To cell(i+1, j).num_masses
                  CheckIfNeighbor(a_, cell(i+1, j).mass(l_))
               Next
            End If
            
            If j = num_cells_col Then Continue For
            
            ''   cell(x, y) - cell(x, y+1)
            For l_ As Integer = 1 To cell(i, j+1).num_masses
               CheckIfNeighbor(a_, cell(i, j+1).mass(l_))
            Next
            
            ''   cell(x, y) - cell(x+1, y+1)
            If i < num_cells_row Then
               For l_ As Integer = 1 To cell(i+1, j+1).num_masses
                  CheckIfNeighbor(a_, cell(i+1, j+1).mass(l_))
               Next
            End If
            
            ''   cell(x, y) - cell(x-1, y+1)
            If i > 1 Then
               For l_ As Integer = 1 To cell(i-1, j+1).num_masses
                  CheckIfNeighbor(a_, cell(i-1, j+1).mass(l_))
               Next
            End If
            
         Next
      Next
   Next
      
   ''   set pressure
   For i as integer = 1 to num_masses
      
      If mass(i).num_neighbors = 0 Then Continue For

      ''   mass i global pressure
      Dim As Single pressure = -k * (mass(i).density - rest_dens)
      
      For j as integer = 1 to mass(i).num_neighbors
         
         Dim As Single gradient = 1 - mass(i).neighbor(j).dist / r
            
         Dim As Integer l = mass(i).neighbor(j).a
         
         ''   mass i + l global pressure
         Dim As Single press = (pressure - k * (mass(l).density - rest_dens) )
         
         ''   mass i + l local pressure
         press -= k_near * gradient
         
         ''   viscosity
         Dim As vectortype vel = (mass(i).vel.x-mass(l).vel.x, mass(i).vel.y-mass(l).vel.y)
            
         Dim As Single proj_vel = vel.x*mass(i).neighbor(j).norm_dist.x+vel.y*mass(i).neighbor(j).norm_dist.y
         
         press -=  viscosity * proj_vel * gradient
         
         press *= gradient
            
         mass(i).frc.x += press * mass(i).neighbor(j).norm_dist.x
         mass(i).frc.y += press * mass(i).neighbor(j).norm_dist.y
         
         mass(l).frc.x -= press * mass(i).neighbor(j).norm_dist.x
         mass(l).frc.y -= press * mass(i).neighbor(j).norm_dist.y
         
      Next
      
   Next
   
   ''   integrate (since particle mass = 1, force and acceleration are identical)
   for i as integer = 1 to num_masses
      with mass(i)
         
         .frc.y += grav_acc
         
         .vel.x += .frc.x * half_dt
         .vel.y += .frc.y * half_dt
         
         .angvel += .torque * half_dt
         
         .psn.x += .vel.x * dt + .frc.x * dt * half_dt
         .psn.y += .vel.y * dt + .frc.y * dt * half_dt
         
         .vel.x += .frc.x * half_dt
         .vel.y += .frc.y * half_dt
         
         .angvel += .torque * half_dt
         
         .frc.x = 0
         .frc.y = 0
         
         .torque = 0
         
      end with
   Next
   
   ''   keep particles inside screen
   For i as integer = 1 to num_masses
      with mass(i)
         
         if .psn.x < radius then .psn.x = radius: .vel.x = -.vel.x*wall_friction: .vel.y *= wall_friction
         if .psn.x > screen_wid - radius then .psn.x = screen_wid -radius: .vel.x = -.vel.x*wall_friction: .vel.y *= wall_friction
         
         If .psn.y < radius then .psn.y = radius: .vel.y = -.vel.y*wall_friction: .vel.x *= wall_friction
         If .psn.y > screen_hgt - radius Then .psn.y = screen_hgt -radius: .vel.y = -.vel.y*wall_friction: .vel.x *= wall_friction
         
      end with
   Next
   
   ''   draw to screen
   glClear(GL_DEPTH_BUFFER_BIT Or GL_COLOR_BUFFER_BIT)
   
   glLoadIdentity()
   
   glenable(GL_POINT_SMOOTH)
   glpointsize(r)
   glcolor4f(0.0f, 0.0f, 0.0f, 0.25f)
   
   GLbegin(GL_POINTS)
      for i as integer = 1 to num_masses
         glvertex2f(mass(i).psn.x, mass(i).psn.y)
      Next
   GLend()
   
   gldisable(GL_POINT_SMOOTH)
   glpointsize(1)
   glcolor4f(1.0f, 1.0f, 0.0f, 0.75f)
   
   glbegin(GL_POINTS)
      for i as integer = 1 to num_masses
         glvertex2f(mass(i).psn.x, mass(i).psn.y)
      Next
   GLend()
   
   GLflush()
   
   Flip()
   
   sleep 1, 1
   
Loop Until MultiKey(1)

End

 

[tarretarretarre]

I have wanted to do something like this but never found the time, thank you for sharing this!