Moving a character/object in any given direction

[kevin]

 
Moving a character/object in any given direction


 This version uses TRIG

PlayBASIC Code: [Select]

; run this program really slow so we can see it
   Setfps 10  


   // how fast should it move
   Speed =5


   ; run the whole thing in a loop..
   Do

      // Pick angle to move in at random (0 to 360 degrees)
      Angle#=rnd(360)

      // Plot the distance we're moving from the origin point.  
      For Distance=0 to 200 step speed

         // clear the screen
         Cls 0   

         // calc the X/y# coordinate from the origin.
         x#=400+cos(angle#)*Distance      
         y#=300+sin(angle#)*Distance      

         // draw the origin point
         centertext 400,300-20,"Start POint"
         circlec 400,300,5,true,rgb(255,0,0)

         print "Angle:"+str$(Angle#)+" Degrees"
         
         Circle x#,y#,5,true
         centertext x#,y#-25,"Distance From Start"+Str$(Distance)

         Sync      
      next
       loop

 Here's a version using LERP (linear interpolation) function.

PlayBASIC Code: [Select]

   // Force the program to run slower so we can see what's it's doing
   Setfps 20

   // Start of the progtrams main DO/LOOP 
   Do

      // Randomly Pick our objects Starting point
      OriginX#=Rnd(GetScreenWidth())
      OriginY#=Rnd(GetScreenHeight())

      // Randomly Pick the objects destination point
      DestX#   =Rnd(GetScreenWidth())
      DestY#   =Rnd(GetScreenHeight())


      // run through and plot the objects movement along this path 
      for lp=0 to 100

         // Clear the screen to black
            cls rgb(0,0,0)


         // DRaw Starting point      
            Circlec OriginX#,OriginY#,5,true,rgb(255,255,255)
      
         // DRaw Destination point      
            Circlec DestX#,DestY#,5,true,rgb(255,255,255)

         // Draw line to represent the path the object is taking
            Linec OriginX#,OriginY#,DestX#,DestY#,rgb(0,0,200)

   
         // Calc a point along this path at a given percentage 
            x#,y#= Lerp(OriginX#,OriginY#,DestX#,DestY#, lp/100.0)
            
         // point the current posiiton
            Circlec X#,Y#,5,true,rgb(255,0,0)

         // Show the screen to the user   
            Sync      

         // Continue this FOR/NEXT loop
      next

      // Jump back to the DO startment to keep this program running
   loop

Psub Lerp(OriginX#,OriginY#,DestX#,DestY#, Scaler#)
   Scaler#=ClipRange#(Scaler#,0,1)
   x#=OriginX#+((DestX#-OriginX#)*Scaler#)
   y#=OriginY#+((DestY#-OriginY#)*Scaler#)
Endpsub x#,y#

[hartnell]

Semi related : lengthdir_x( ) and length_dir( ) are exceedingly useful functions in GM (gm sucks!) that PB doesn't have.

http://gamemaker.wikicomplete.info/gml:lengthdir_x

-- hartnell

[kevin]

 Considering , finding the length is as simple subtracting the Origin from the dest..

LengthX=DestX-OriginX
LengthY=DestY-OriginY
Length = Sqrt((LengthX*LengthX)+(LengthY*LengthY) )

[hartnell]

In these functions, you already know the length. :)

They are used to place a game object at a specific distance in a direction from a point.

It makes gyruss-like orbital movement a breeze :

Code Select Expand


if(keyboard_check(vk_left))
{
    dir -= 2;
}
if(keyboard_check(vk_right))
{
    dir += 2;
}

image_angle = point_direction(x,y,320,240);
x = lengthdir_x(220,dir) + 320
y = lengthdir_y(220,dir) + 240


It also makes any kind of positional offset natural and easy.

This is the kind of math function that gives the same kind of improvement as GetDistance2D() does.

Simple, easy to use, makes code more readable, and doesn't scare people who are scared of math.

-- hartnell

[kevin]

There's function that already do this.  But you could just wrap them.  

PlayBASIC Code: [Select]

Psub LengthDir_X(RAdius#,Angle#)
      Dist#=CosRadius(Angle#,Radius#)
EndPsub Dist#

Psub LengthDir_Y(RAdius,Angle#)
      Dist#=SinRadius(Angle#,Radius#)
EndPsub Dist#

PlayBASIC Code: [Select]

   if keyboard_check(vk_left) then   dir = dir-2
   if keyboard_check(vk_right) then   dir = dir+2

   RotateSprite ThisSprite,DIR
   PositionSprite ThisSprite, CosNewValue(320,dir,220),SinNewValue(320,dir,220)

[hartnell]

Thanks! :)

The problem is the name. It's geared towards people who already know the math. The average noob just things, "length/distance from in a direction". I'll point to these functs in my docs.

-- hartnell

[kevin]

   Regardless of what a function is named, the user still has to understand the usage, in order to use it.