Project 2D coords to 3D

This code has been declared by its author to be Public Domain code.

Project 2D coords to 3D by Rob

2002

Requires two pivots. One pivot will continually position itsself at the mouse pointer, relative to the camera. It will then fire off a ray, which, if it touches an entity, will position the second pivot at the point of 'impact'. You can then use this additional information for anything you desire.

; 2D to 3D projection by Rob Cummings
; rob@redflame.net

Global camera,cursor,ball,gw,gh

Graphics3D 640,480,16,2
camera=CreateCamera()

;orth for the sake of it
CameraProjMode camera,2
CameraZoom camera,.5

;width and height of display
gw=GraphicsWidth()
gh=GraphicsHeight()

;important. Create a 3D mouse position using a pivot.
;you need two pivots for this to work. In our case, we're
;using a ball to see where our pick took place.
cursor=CreatePivot() ; or a sprite...
MoveEntity cursor,0,0,2


; so you can see the effect. Replace with a pivot for speed.
ball=CreateSphere()
ScaleEntity ball,.2,.2,.2
EntityAlpha ball,0.5
EntityColor ball,100,100,255

;load your entity here
ent=CreateSphere(16)
EntityPickMode ent,2 ;pickable...
ScaleEntity ent,2,1,1
MoveEntity ent,0,0,1

;misc
light=CreateLight(2,camera)
LightRange light,8
MoveEntity light,10,10,-10
PositionEntity camera,0,0,-2

While Not KeyHit(1)
	TurnEntity ent,.1,.1,.1
	
	;positions	
	x#=MouseX()
	y#=MouseY()
	
	;half of screen dimensions needed
	w=GraphicsWidth()/2
	h=GraphicsHeight()/2
	
	;3D cursor positioned at 2D cursor
	PositionEntity cursor,(x-w)/w*2,-(y-h)/w*2,2

	;orient to camera
	RotateEntity cursor,EntityPitch(camera),EntityYaw(camera),0

	;pick from 3D cursor into 3D space
	cx#=EntityX(cursor)
	cy#=EntityY(cursor)
	cz#=EntityZ(cursor)
	picked=LinePick( cx,cy,cz,cx,cy,-cz*2000 ) ;2000 - distance to "cast our line"


	;show result for fun
	If picked
		ShowEntity ball
		PositionEntity ball,PickedX(),PickedY(),PickedZ()
	Else
		HideEntity ball
	EndIf	

	UpdateWorld
	RenderWorld
	Flip
Wend
End

Comments

_PJ_

2010

Any way to know the ideal size for best precision?

I assume the zbuffer would get messy if the size of the pivot's radius and the distance (I see * 2000 is used in the example) is some degree out of the scale for the camera range?

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