Simple shadows

What I've found works well is storing the pixels for your lightmap in an array. You then "draw" your shadows to the lightmap array, blur the pixels as many times as you need, then WPF the pixels to your texture. Here is the piece of code that I use to do this:

 
For n=0 To LMBlur	;number of blur operations to apply
	For y=1 To LMscrH-2		;height of lightmap array
		For x=1 To LMscrW-2		;width of lightmap array
			c=LMbuffer(x,y)
			If (c And $FFFFFF) > 0
				c1=LMbuffer(x-1,y)	
				c2=LMbuffer(x+1,y)
				c3=LMbuffer(x,y+1)
				c4=LMbuffer(x,y-1)
				r=c Shr 16 And $FF : g=c Shr 8 And $FF : b=c And $FF
				rl=c1 Shr 16 And $FF : gl=c1 Shr 8 And $FF : bl=c1 And $FF
				rr=c2 Shr 16 And $FF : gr=c2 Shr 8 And $FF : br=c2 And $FF
				rd=c3 Shr 16 And $FF : gd=c3 Shr 8 And $FF : bd=c3 And $FF
				ru=c4 Shr 16 And $FF : gu=c4 Shr 8 And $FF : bu=c4 And $FF
				rd=((r Shl 1)+(rl+rr+rd+ru) Shr 1)Shr 2
				gr=((g Shl 1)+(gl+gr+gd+gu) Shr 1)Shr 2
				bl=((b Shl 1)+(bl+br+bd+bu) Shr 1)Shr 2
				LMbuffer(x,y)=(((rd Shl 8)+gr) Shl 8)+bl
			EndIf
		Next
	Next
Next

buf=TextureBuffer(LMtex)
LockBuffer buf
For y=0 To LMscrH-1
	For x=0 To LMscrW-1
		xx=lmbox+x : yy=lmboy+y
		If xx<LMtexW And YY<LMtexH
			WritePixelFast lmbox+x,lmboy+y,LMbuffer(x,y),buf
		EndIf
	Next
Next
UnlockBuffer buf

I'm not sure that this is the best way but if I only update my lightmap every 2-3 frames and the texture isn't too big it's pretty fast even with a lot of blurring passes. Plus, it looks really nice!