Polys from a bitmap

Blitz3D Forums/Blitz3D Programming/Polys from a bitmap

MadJack

(Posted 2009) [#1]

I want to set up a map that displays a series of coloured areas overlaying a landscape. Ideally the coloured areas would be polys rather than an overlying bitmap so that everything's sharp and I can manipulate individual areas without too much trouble.

I could create the polys in a modelling package but I'm fairly sure I'm going to be doing a lot of tweaking before the map's in a final form and a quicker way might be to have a bitmap containing the coloured areas and then the game code generates polys from the (unique) areas of colour.

Thing is, has anyone come across code to identify areas of colour within a bitmap and generate polys for them?

RifRaf

(Posted 2009) [#2]

I didnt test this, but it *should work, the getcolor can be changed to readpixelfast after you lock the buffer

This is an adaptation of a floor/terrain loader, so the resulting mesh is parellell to the ground. easily remedied if you need it facing cam just tilt the pitch 90 degrees.

basically you toss an image , color and color tolerance, and it makes quads for you only on the pixels that have the proper color, and spits out a flat mesh.

This will create pretty high polycount meshes on large images though. You would then need to modify the routine to find rectangles of similar color and make larger scaled quads to cover the region. as it is its one quad per pixel, similar to many heightmap loaders only it can weed out unwanted regions based on colors.

;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
;;;;         F U N C T I O N          ;;;
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Function CreateLayer(image,r=255,g=255,b=255,tol=1,scale#=2.0)
SetBuffer ImageBuffer(image)
Local x#
Local y#
Local z#
segsx=ImageWidth(image)
segsy=ImageHeight(image)

mesh=CreateMesh()
surf=CreateSurface(mesh)


For I=1 To segsx
     For II=1 To segsy
          GetColor(i,ii)

          If ColorRed() < r + tol And ColorRed() >r - tol Then
          	If ColorGreen() < g + tol And ColorGreen() >g - tol Then
          		If ColorBlue() < b + tol And ColorBlue() >b - tol Then
		          addquad(mesh,surf,i,ii,1)
				EndIf
			EndIf
		 EndIf	
	Next
Next
UpdateNormals mesh
ScaleMesh mesh,scale*2,scale*2,scale*2
UpdateNormals mesh
PositionEntity mesh,0,.25,0
setbuffer backbuffer()
Return mesh
End Function

;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
;;;;         F U N C T I O N          ;;;
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
Function addquad(mesh,surf,qx,qy,segs=1)
Local ccc=0
Local a=AddVertex(surf,qx     ,0,qy     ,1 ,0) ; swap these for a different start orientation
Local b=AddVertex(surf,qx+segs,0,qy     ,1 ,1) ; swap these for a different start orientation
Local c=AddVertex(surf,qx+segs,0,qy+segs,0 ,1) ; swap these for a different start orientation
Local d=AddVertex(surf,qx     ,0,qy+segs,0 ,0) ; swap these for a different start orientation
AddTriangle( surf,c,b,a)
AddTriangle( surf,d,c,a)
End Function

MadJack

(Posted 2009) [#3]

RR

Thanks for that idea - leads me onto another idea.

1, Make a list of edge pixels.
2, test each pixel as a start pixel and each pixel as an end pixel.
3, test each pixel to see if it would be on the line between start/end pixels. If so, remove from the list.
4, Rinse/repeat until all pixels have been tested.
5, sort remaining pixels by y and then x
6, create polys

Warner

(Posted 2009) [#4]

Is that called 'vectorizing'? It could be complex.
http://www.google.com/search?q=vectorization+algorithms&rls=p,com.microsoft:en-gb
Or search for "bitmap to polygon".
Actually, in the searches, I found this article:
http://cardhouse.com/computer/vector.htm
Maybe it helps, it contains source code.

Guy Fawkes

(Posted 2009) [#5]

warner, i take it ur home from vacation?

Warner

(Posted 2009) [#6]

Sure, back again. It was dreadfull living in a tent without a computer. Allthough .. does a PDA count as a computer? :)

MadJack

(Posted 2009) [#7]

Is that called 'vectorizing'? It could be complex.

Yeah - I've got it working roughly but it falls over when a corner angle is obtuse. I could spend too much time on this - probably better just to allow for area drawing/defining in the game editor.

Guy Fawkes

(Posted 2009) [#8]

warner, check ur mail

MadJack

(Posted 2009) [#9]

Actually, cause I know people will be desperately interested in this, I've created a strategic map mesh in a modeling package and given each area one of twenty different surfaces. The blitz code loads this mesh and checks the vertices for each surface. If the vertex being checked is distant from the previous, then it must be a new area (can't have two areas adjacent using the same surface). The corners for this area are then stored under a new index number.

A final check finds areas that are adjacent to the current area are stored as well. Means I can adjust vertex positions in my modelling package and have the data reprocess in blitz.