Size of Entity in View

Blitz3D Forums/Blitz3D Programming/Size of Entity in View

BLaBZ (Posted 2009) [#1]

How do I get/Whats the equation for the size of an entity as it appears on screen? I need to scale an image depending on whether an object is close or distant from the camera

Bobysait (Posted 2009) [#2]

Maybe, 2 ways ( and many else... ) for doing this first one : (pseudo-code) you can use the MeshWidth/MeshHeight/MeshDepth to get the box ( or use a function that will return the "real box" Then, transpose values in the local camera axis and finaly, use a method to compute 3D to 2D ( or just create a 3D quad parented to camera with the calculated 3D coordinates +> easier and faster [2D accelerated 3D...] ) ; transform left edge from entity axis to camera axis TFormPoint -BoxW/2,0,0,entity,cam left point of the box : TformedX(),TFormedY(), Tformedz() Then 2 methods : method 1 +>CameraProject Camera,TformedX(),TFormedY(), Tformedz() X=ProjectedX() , Y=ProjectedY() method 2 +> Use the Depth between cam and entity depth#=tformedz() ; at "1" unit from camera : realx#=tformedx()/Depth realy#=tformedy()/Depth ;compute 3D +> 2D X=(.5+realx/2)*graphicswidth() screenratio#=Float(GraphicsHeight())/(GraphicsWidth()*2) Y#=screenratio-y/2)*GraphicsWidth() Make the same for the 5 others egdes +> +BoxW/2,0,0 +> 0,-BoxH/2,0 +> 0,+BoxH/2,0 +> 0,0,-BoxD/2 +> 0,0,-BoxD/2 For Each edge, store min and max values of X and Y Then, you'll get the bouding Rect. Second one : The "easy" method (but not efficient) +> transform coordinates from world to camera TFormPoint xEntity,yEntity,zEntity,0,cam +> get the depth Depth#=TFormedZ() +> Scale = 1/Depth ScaleImage image,1/Depth,1/Depth

BLaBZ (Posted 2009) [#3]

Thanks a lot, I'll give that a try