manipulatine "output" picture..

sure. After calling renderworld, modify the pixels of the backbuffer. However, this strategy is way to slow. simply writepixelfast and readpixelfast would take a while, much less additional calculation.

here are some better methods that do it differently:

http://www.blitzbasic.com/codearcs/codearcs.php?code=814 - HAven't used myself, but looks good

There's one by Arkon that is probably in the code arcs, but I couldn't find it, so here:

Global ark_blur_image, ark_blur_texture, ark_sw, ark_sh

Function CreateBlurImage()
	ark_sw = GraphicsWidth()
	ark_sh = GraphicsHeight()	
	;Create sprite
	Local spr = CreateMesh(camera)
	Local sf = CreateSurface(spr)
	AddVertex sf, -1, 1, 0, 0, 0
	AddVertex sf, 1, 1, 0, 1, 0
	AddVertex sf, -1, -1, 0, 0, 1
	AddVertex sf, 1, -1, 0, 1, 1
	AddTriangle sf, 0, 1, 2
	AddTriangle sf, 3, 2, 1
	EntityFX spr, 17
	ScaleEntity spr, 1024.0 / Float(ark_sw), 1024.0 / Float(ark_sw), 1
	PositionEntity spr, 0, 0, 1.0001
	EntityOrder spr, -100000
	EntityBlend spr, 1
	ark_blur_image = spr
	;Create blur texture
	ark_blur_texture = CreateTexture(1024, 1024, 256)
	EntityTexture spr, ark_blur_texture
End Function

Function UpdateBlur(power#)
	EntityAlpha ark_blur_image, power#
	CopyRect  ark_sw / 2 - 512, ark_sh / 2 - 512, 1024, 1024, 0, 0, BackBuffer(), TextureBuffer(ark_blur_texture)	
End Function