I'm trying to detect collision between planes (particles) and boxes (building bounding box) so I can prevent rain/snow particles from entering buildings.

Here is what I'm doing (not working though):

// q1, q2, q3, q4 = Particle plane verticesAABB aabb = GetBuildingBoundaryBox(); // *** The bounding box is calculated using D3DXComputeBoundingBox() ***
D3DXVECTOR3 boxPosition = GetBuildingPosition();
D3DXMATRIX matBox;
D3DXMatrixTranslation(&matBox, boxPosition.x, boxPosition.y, boxPosition.z);

D3DXVec3TransformCoord(&aabb.Min, &aabb.Min, &matBox);
D3DXVec3TransformCoord(&aabb.Max, &aabb.Max, &matBox);

Plane plane;
plane.normal = GetTriangleNormal(q1, q2, q3);
plane.offset = D3DXVec3Dot(&plane.normal, &q1);

if (TestBoxToPlaneCollision(plane, aabb))
{
    // Collision detected
} else {
    // Collision NOT detected
}

Is the above code valid? It's not working with me (It's detecting collision when there is no collision)

Collision is not the way to prevent snowflakes to enter the building! The reason is that the intersection detection will be extreamly slow!

The right way to do it is by using the Z-Depth test for the particles.

That topic is really advanced.

There are some cool workarounds:

1) Display the particles in only predefined shapes(like boxes). with that method you can control the particles. Pseudo code

CParticeEmiter snowEmiter(PARTICLE_SNOW, boundingBoxMin, boundingBoxMax); //boundingBoxMin & boundingBoxMax will defined there area where snowing is allowed

and later in your spawn method ....

void snowEmiter::spwanNewPartice()

{

const float newParticleXPox = lerp(boundingBoxMin.x, boundingBoxMax,y rndFloat(0.f, 1.f));//that line is a crap you've got the idea

.......
}

2) The second method is to move snowEmiter with the player. if the player enters a building then you will deatach the particle emitter and leave it in front of the building entrance.

There are a lot of different solutions but you've got the idea.

3) I need to make a picture for you

http://postimg.org/image/x4807pz0j/

Collision is not the way to prevent snowflakes to enter the building! The reason is that the intersection detection will be extreamly slow!

Doubt it, I have many snow rains per particle (not only one rain drop per particle)

The right way to do it is by using the Z-Depth test for the particles.

Z-Depth test? I don't know what the depth has to do with preventing particles from entering buildings

2) That's a good idea, but what if the player entered from the door and then went to look from a window upstairs? The rain/snow particles would be still infront of the door and he can't see it infront of the window.

Another problem is that the player could look at the building entrance from outside and see rain inside the building!

@nonoptimalrobot: I have the plane vertices v1, v2, v3, v4

How do I calculate the plane radius so I can do AABB to sphere collision test?

if the player is inside then:

Draw things that are outside (trees, birds stuff...)

turn off z-writing and change depth test to always succeed

draw the particles

turn z-depth buffer things back to normal

draw the building

and that is.

(in our game we have cars in tunnels ect);

@imoogiBG: I'm using soft particles, so I have to render the scene first and then the particles.

So how do I do that in soft particles? (Notice that I must render the particles AFTER the scene in soft particles)

@nonoptimalrobot: I'm already storing the particle size in the memory and then calculating the vertices prior rendering, but the size is not actually the radius.

Can someone point me to sphere/box collision detection sample? I have only implemented box/box collision detection.

Can someone point me to sphere/box collision detection sample?

http://www.wildbunny.co.uk/blog/2011/04/20/collision-detection-for-dummies/