Fluid/Path-building thingy-jig

I love the bottom texture, looks like some kind of wood grain or rope.

I've done a little altering of the code. Nothing major, just something so you can turn the grid on/off and fiddled with the particle color code.

SeedRnd MilliSecs()
Graphics 800, 600, 0, 1

Const TRAILS=0

If Not trails Then SetBuffer BackBuffer()




Global MAXX	= GraphicsWidth()
Global MAXY	= GraphicsHeight()

Const GRIDX			= 40
Const GRIDY			= 30
Const CELL			= 20
Const MIDCELL		= 10

Const NUM_PARTICLES = 5000
Const PARTICLE_TURN = 15
Const PARTICLE_SPEED= 2
Const GRID_TURN 	= 1

Const RECT_SIZE     = 50
Const RECT_SPEED    = 2


Dim grid(GRIDX, GRIDY)

For y = 0 To GRIDY - 1: For x = 0 To GRIDX - 1
	grid(x, y) = Rand(360)
Next: Next


Type p_dat
	Field x#, y#
	Field ang
	Field r, g, b, dec_col
End Type

Global p.p_dat

For n=0 To NUM_PARTICLES - 1
	p.p_dat = New p_dat
		p\x = Rnd(0,MAXX-1)
		p\y = Rnd(0,MAXY-1)
		p\ang = Rnd(360)
		p\r = 64
		p\g = 64
		p\b = Rnd(64) + 192
		p\dec_col = (p\r * $FF00) + (p\g * $FF) + p\b
Next

Repeat
	If Not trails Then Flip:Cls


	; Move particles
	For p.p_dat = Each p_dat
		gx = Int(p\x / CELL)
		gy = Int(p\y / CELL)
		
		g=grid(gx, gy)
		p\ang=anglemoveto(p\ang,g,PARTICLE_TURN)
		
		;only change the grid angle if it is at least 30 degrees different from the particle's angle
		If Abs(angledif(g,p\ang))>30 Then
			grid(gx, gy)=anglemoveto(g,p\ang,GRID_TURN)
		EndIf

		
		h# = Sin(p\ang) * PARTICLE_SPEED
		v# = Cos(p\ang) * PARTICLE_SPEED
		
		p\x = p\x + h#
		p\y = p\y + v#
		
		If p\x < 0 Then
			p\x = p\x + MAXX
		ElseIf p\x >= MAXX Then
			p\x = p\x - MAXX
		EndIf
		If p\y < 0 Then
			p\y = p\y + MAXY
		ElseIf p\y >= MAXY Then
			p\y = p\y - MAXY
		EndIf
	Next



	If trails Then
		LockBuffer BackBuffer()
		For p = Each p_dat
			WritePixel p\x, p\y, p\dec_col
		Next
		UnlockBuffer BackBuffer()

		For p = Each p_dat
			movex=Sin(p\ang)*Rnd(1,RECT_SPEED)
			movey=Cos(p\ang)*Rnd(1,RECT_SPEED)
			size=Rand(2,rect_size)
			x=p\x-size/2
			y=p\y-size/2
			CopyRect x,y,size,size,x+movex,y+movey
		Next
		
	Else
		count = MilliSecs()
		
		LockBuffer BackBuffer()

		; Draw particles
		For p = Each p_dat
			WritePixel p\x, p\y, p\dec_col
		Next
		
		; Draw grid
		If grid_switch Then
			Color 44, 44, 44
			For y = 0 To GRIDY - 1: For x = 0 To GRIDX - 1
				x1 = x * CELL + MIDCELL
				y1 = y * CELL + MIDCELL
				
				x2 = x1 + Sin(grid(x, y)) * MIDCELL
				y2 = y1 + Cos(grid(x, y)) * MIDCELL
			
				Line x1, y1, x2, y2
			
			Next: Next
		End If
		
		UnlockBuffer BackBuffer()

		count = MilliSecs() - count




		
		Color 255, 255, 255

		If KeyHit(34) Then grid_switch = Not grid_switch

		If KeyHit(59) Then showhelp = Not showhelp

		If showhelp Then
			Text 10, 10, "Render time: " + count + " m/sec"
			Text 10, 30, "G   - Show/Hide Grid"
			Text 10, 46, "R   - Randomise all squares"
			Text 10, 62, "F   - Flip direction of grid"
			Text 10, 78, "Esc - quit"
		Else
			Text 10, 10, "F1 - help"
		End If
	
		If KeyHit(33) Then
			Cls
			For y = 0 To GRIDY - 1: For x=0 To GRIDX - 1
				grid(x, y) = turn * 90
			Next: Next
			turn = turn + 1
			If turn>3 Then turn=0
		End If

		If KeyHit(19) Then
			Cls
			For y = 0 To GRIDY - 1: For x=0 To GRIDX - 1
				grid(x, y) = Rnd(360)
			Next: Next
		End If	
	
	EndIf
	
Until KeyHit(1)
End




;makes the angle a little closer to the target angle and returns it
Function AngleMoveTo#(anglenow#,angletar#,amount#)

	amount=amount*Sgn(angletar-anglenow)

	If Abs(angletar-anglenow)>180 Then
		anglenow=anglenow-amount
	Else
		anglenow=anglenow+amount
	EndIf
	
	If anglenow<0 Then
		anglenow=anglenow+360
	ElseIf anglenow>360 Then
		anglenow=anglenow-360
	EndIf

	Return anglenow
End Function



;how far away two angles are, assuming they can skip over the end of anglemax to get to 0
;gives positive and negative return values
Function AngleDif#(anglenow#,angletar#,anglemax=360)
	Local temp#

	temp#=angletar-anglenow
	If temp>+anglemax/2 Then Return temp-anglemax
	If temp<-anglemax/2 Then Return temp+anglemax
	Return temp
End Function