Gravitational Force

 

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Gravitational Forces Behavior

property x,y,vx,vy,ax,ay,mx,my,bx,by,dt,mass,time,coef_rest,bounding_box,bounding_Rect on getPropertyDescriptionList me   set description = [:]   addProp description, #x, [#default:0.0,#format:#float,#comment:"Initial X position:"]   addProp description, #y, [#default:0.0,#format:#float,#comment:"Initial y position:"]   addProp description, #vx, [#default:50.0,#format:#float,#comment:"Initial X vel:"]   addProp description, #vy, [#default:50.0,#format:#float,#comment:"Initial y vel:"]   addProp description, #ax, [#default:0.0,#format:#float,#comment:"Initial X acc:"]   addProp description, #ay, [#default:-9.8,#format:#float,#comment:"Initial y acc:"]   addProp description, #mx, [#default:1.0,#format:#float,#comment:"Initial X slope:"]   addProp description, #my, [#default:1.0,#format:#float,#comment:"Initial y slope:"]   addProp description, #bx, [#default:0.0,#format:#float,#comment:"Initial X int:"]   addProp description, #by, [#default:0.0,#format:#float,#comment:"Initial y int:"]   addProp description, #dt, [#default:0.2,#format:#float,#comment:"Initial delta T:"]   addProp description, #bounding_Rect, [#default:1,#format:#integer,#comment:"Bounding Rect Sprite:"]   addProp description, #coef_rest, [#default:1.0,#format:#float,#comment:"Coef Restitution (0-1):"]   return description end getPropertyDescriptionList on getBehaviorDescription   -- this script doesn't bother to check for errors of any sort when   -- colliding with a "wall." Also doesn't take into account the size of the   -- bitmap so it will bounce from it's registration point.   -- The formula's use a "small delta T" approximation, and y points upward  (not down!)   return "This enables object to feel a force. Default setting are for basic gravity. Smaller dt's are more accurate, but larger ones increase rate of motion. To get started just put a bitmap ball (sprite 2) with this behavior, and have a rect as sprite 1. Be sure the ball is inside the rect at the start. Loop in the frame script and watch the ball bounce."&RETURN&RETURN&"You can see lots of examples which use variations of this behavior at http://ExploreScience.com/"&RETURN&RETURN&"Raman (pfaff@ExploreScience.com)" end getBehaviorDescription on beginSprite me   -- can set lots of initial stuff here (user adjustable fields)   set bounding_box = the rect of sprite bounding_Rect   set time = 0.0     set x = the locH of sprite the spriteNum of me   set y = (the bottom of bounding_box - the top of bounding_box) -the locV of sprite the spriteNum of me end on exitframe me   findPos   findVel   findAcc   moveObject me   -- sometimes useful to keep track of time   set time = time + dt end on findPos me   set x to x+vx*dt+ax*dt*dt   set y to y+vy*dt+ay*dt*dt end on findVel me   set vx to vx+ax*dt   set vy to vy+ay*dt end on findAcc me   --  this is where you can put the controlled force formula, where you may need to use masses.   -- can have velocity dependant forces, etc.   -- could just call a more complex movie script   set ax = ax   set ay = ay      --  an mediocre example of air drag would be   --  set ax = -.05*vx   --  set ay = min(ay - .05*vy,0.0) end on moveObject me   -- has a slope and an intercept to have things scaled when necessary   set xs to integer(mx*x+bx)   set ys to 300-integer(my*y+bx)   set ys to (the bottom of bounding_box - the top of bounding_box) -integer(my*y+by)   if xs >= the right of bounding_box or xs <= the left of bounding_box then     set vx to -vx*coef_rest   else if ys >= the bottom of bounding_box or ys <= the top of bounding_box then     set vy to -vy*coef_rest   end if   set the loc of sprite the spriteNum of me to point(xs,ys) end -- can put various handlers here to tell the sprite to change itself on setVx me, value   set vx = value end on setVy me, value   set vy = value end on tellVs me   set temp = []   set temp = [vx,vy]   return temp end