Coliding or subtracting graphic objets

[ioptic]

Hi all,

I have another intereting programming problem.

I am trying to do a subractive graphic.
Here it goes.

1 draw the first sphere with a small radius
2 draw a second sphere with a much larger radius ( is can also be an egg shaped object)
3 I make them collide.
4 I asume that the area of the colision becomes invisible by taking on the colour of the background.
5 The remaining area (pls see attachment) then becomes a section of a sphere or which can be rotated, zoomed, shaded etc...
(http://www.i-optic.com/3dshape.jpg) in case the attachment can't be seen.

What are the chances of doing this with thinbasic ?
Do I first calculate the geometric area of the remaining sphere section and then render it ?
where to start ?

Best regards
Rob
-o-o-

[Michael Hartlef]

Sorry, my english isn't my native language so somtimes I have to ask again before I can try to help.

So before I go searching a formular on the net, do you want the colliding area to become a 3D modell that can be transformed or do you want the rest of the first sphere and the rest of the 2nd sphere to become a 3D model?

[ErosOlmi]

Mike,

just in case you didn't noticed it, Rob is from Australia so his reply can arrive a some hours time

Ciao
Eros

[Michael Hartlef]

No problem. I have patience. I'm already googling up the term Constructive solid geometry.

http://en.wikipedia.org/wiki/Constru...solid_geometry

I'm sure once I understand exactly what he wants to make, we can come up with a solution for it. I find the stuff he does very interesing. A project like this can help pushing TBGL and other modules a little again.

[Michael Hartlef]

Also it could probably help Francko with his 3D modeller project. No good 3D modelling software without boolean operations, or

[ErosOlmi]

Yes, it seems to me to recall very closely your 3D/2D example:
http://community.thinbasic.com/index.php?topic=1292.0

[ioptic]

Hi,
am awake again

I am trying to keep the black -remaining section of the black sphere, and then zoom, rotate it etc...
A kind of subtractive collision of geometric objects.

best regards
Rob
-o-o-

[Petr Schreiber]

Hi Rob,

CSG is not implemented yet, but here is code you can just copy and paste and you will see one of the ways to create and manipulate 2 spheres.
So "geometry subtracting" is not here yet, but you can get basic idea how 3D works in ThinBasic.
[code=thinbasic]
Uses "TBGL"

BEGIN CONST
' -- Scene IDs
%sScene = 1

' -- Entity IDs
%eCamera = 1
%eLight

%eSpherePivot

%eSphereA
%eSphereB
END CONST

FUNCTION TBMAIN()
LOCAL hWnd As DWORD
LOCAL FrameRate AS DOUBLE

' -- Create and show window
hWnd = TBGL_CreateWindowEx("Two spheres - press ESC to quit", 640, 480, 32, %TBGL_WS_WINDOWED or %TBGL_WS_CLOSEBOX)
TBGL_ShowWindow

' -- Create scene
TBGL_SceneCreate(%sScene)

' -- Higher number, higher quality
TBGL_SetPrimitiveQuality 50

' -- Create basic entities
' -- Create camera to look from 15, 15, 15 to 0, 0, 0
TBGL_EntityCreateCamera(%sScene, %eCamera)
TBGL_EntitySetPos(%sScene, %eCamera, 0, 0, 7)
TBGL_EntitySetTargetPos(%sScene, %eCamera, 0, 0, 0)

' -- Create point light
TBGL_EntityCreateLight(%sScene, %eLight)
TBGL_EntitySetPos(%sScene, %eLight, 0, 10, 10)

' -- Create something to look at
TBGL_EntityCreatePivot(%sScene, %eSpherePivot)

TBGL_EntityCreateSphere(%sScene, %eSphereA, %eSpherePivot, 1)
TBGL_EntitySetColor(%sScene, %eSphereA, 255, 128, 0)
TBGL_EntitySetPos(%sScene, %eSphereA, -0.5, 0, 0)

TBGL_EntityCreateSphere(%sScene, %eSphereB, %eSpherePivot, 1.5)
TBGL_EntitySetColor(%sScene, %eSphereB, 0, 128, 255)
TBGL_EntitySetPos(%sScene, %eSphereB, 1, 0, 0)

' -- Resets status of all keys
TBGL_ResetKeyState()

' -- Main loop
While TBGL_IsWindow(hWnd)
FrameRate = TBGL_GetFrameRate

TBGL_ClearFrame

TBGL_SceneRender(%sScene)

TBGL_DrawFrame

' -- ESCAPE key to exit application
If TBGL_GetWindowKeyState(hWnd, %VK_ESCAPE) Then Exit While

' -- Spheres are attached to pivot point, when we turn or move pivot, spheres will go with it
IF TBGL_GetWindowKeyState(hWnd, %VK_LEFT) Then
TBGL_EntityTurn(%sScene, %eSpherePivot, 0,-90/FrameRate, 0)
ELSEIF TBGL_GetWindowKeyState(hWnd, %VK_RIGHT) Then
TBGL_EntityTurn(%sScene, %eSpherePivot, 0, 90/FrameRate, 0)
END IF

IF TBGL_GetWindowKeyState(hWnd, %VK_PGUP) Then
TBGL_EntityMove(%sScene, %eSpherePivot, 0, 0,-1/FrameRate)
ELSEIF TBGL_GetWindowKeyState(hWnd, %VK_PGDN) Then
TBGL_EntityMove(%sScene, %eSpherePivot, 0, 0, 1/FrameRate)
END IF

Wend

TBGL_DestroyWindow
END FUNCTION
[/code]

[ErosOlmi]

Just for the "ignorant" (meaning in Latin: ignore) like me: [wiki=Constructive_solid_geometry]CSG[/wiki]

[Michael Clease]

Look at rendering to a texture would be my suggestion.