Objects behind camera?

Do a search for viewing frustrum. It has to do with collision detection etc.

better do a search on vector-dot-product.

Ehem... thanks for the ideas. But in that case I do think it''ll be easier to count the degree to the objects and decide from that.

if ( AngleToObject < PlayerAngle - 90'' && AngleToObject > PlayerAngle + 90)
{
ObjectBehindPlayer
}
else
{
OBjectInfrontOfPlayer
}

Or what!?

quote:

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Original post by MindWipe
Ehem... thanks for the ideas. But in that case I do think it''ll be easier to count the degree to the objects and decide from that.

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That''s what a dot product will get you, but without any of the trig you''d end up using to get the angles.


1) Get a normalised vector for the direction the camera is looking in. With most lookAt matrix creation functions this value is usually shoved directly into the matrix so you can extract it from there or calculate once per frame. Call this "view_direction".

2) Get the point in the world where the camera is located in world space, call this "camera_pos".

3) Get the point where the object is located in world space, call this "object_pos".



And the code:

// get vector from camera to object
vec3 u = object_pos - camera_pos;
//
// get the projection of the object onto the view direction
float t = vec3DotProduct( u, view_direction );
//
// if t>0, the object is in front of the camera
// if t<0, the object is behind the camera
 

vec3 is a simple 3d vector data type. The "operator-" for vec3 does a componentwise subtract (va.x - vb.x, va.y - vb.y, va.z - vb.z). The vec3DotProduct is res=va.x*vb.x+va.y*vb.y+va.z*vb.z.

If you need to test a sphere instead of a single point against the plane, you can do:

if ((t-radius) > 0): all sphere is in front
if ((t+radius) > 0): some or all of sphere is in front
if ((t+radius) < 0): all sphere is behind





--
Simon O''Connor
Creative Asylum Ltd
www.creative-asylum.com

Dot-product is the way to go. You don''t need to normalize the vectors if you only care about the sign of the result. (Meaning if you only care about being in front of or behind, and not how far in front of or behind.)

// Stuff you already know
vector camera_forward_dir;
vector some_obj_pos;
vector camera_pos;

// Stuff you need to calculate
vector camera_to_object_dir = some_obj_pos - camera_pos;
float dot_product = DotProduct(camera_to_object_dir, camera_forward_dir);

// > 0.0f means object in front of the camera
// < 0.0f means object behind the camera
// 0.0f means object planar with the camera

S1CA> Thanks! I''ll do that. Allways nice getting advice from an expert like you.

LordDeath> Thx to you too!

/MindWipe