Raycasting

Intermediate Programmer

Raycasting traces an invisible line through the scene to find intersecting colliders. This is useful, for example, to check which objects are in a gun's line of fire, or are under the mouse cursor when the user clicks.

Note

Raycasting uses colliders to calculate intersections. It ignores entities that have no collider component. For more information, see Colliders.

To use a raycast, in the current Simulation, use [Simulation.Raycast](xref:Stride.Physics.Simulation.Raycast(Vector3, Vector3, CollisionFilterGroups, CollisionFilterGroupFlags, bool)).

For an example of raycasting, see the Physics Sample project included with Stride.

Example code

This code sends a raycast from the mouse's screen position:

public static bool ScreenPositionToWorldPositionRaycast(Vector2 screenPos, CameraComponent camera, Simulation simulation)
{
    Matrix invViewProj = Matrix.Invert(camera.ViewProjectionMatrix);

    // Reconstruct the projection-space position in the (-1, +1) range.
    //    Don't forget that Y is down in screen coordinates, but up in projection space
    Vector3 sPos;
    sPos.X = screenPos.X * 2f - 1f;
    sPos.Y = 1f - screenPos.Y * 2f;

    // Compute the near (start) point for the raycast
    // It's assumed to have the same projection space (x,y) coordinates and z = 0 (lying on the near plane)
    // We need to unproject it to world space
    sPos.Z = 0f;
    var vectorNear = Vector3.Transform(sPos, invViewProj);
    vectorNear /= vectorNear.W;

    // Compute the far (end) point for the raycast
    // It's assumed to have the same projection space (x,y) coordinates and z = 1 (lying on the far plane)
    // We need to unproject it to world space
    sPos.Z = 1f;
    var vectorFar = Vector3.Transform(sPos, invViewProj);
    vectorFar /= vectorFar.W;

    // Raycast from the point on the near plane to the point on the far plane and get the collision result
    var result = simulation.Raycast(vectorNear.XYZ(), vectorFar.XYZ());
    return result.Succeeded;
}

Note

There are multiple ways to retrieve a reference to this Simulation from inside one of your ScriptComponent:

• The recommended way is through a reference to a physics component, something like myRigidBody.Simulation or myCollision.Simulation as it is the fastest.
• Then through SceneSystem by calling SceneSystem.SceneInstance.GetProcessor<PhysicsProcessor>()?.Simulation.
• Or through this.GetSimulation(), note that the this is required as it is an extension method.

See also

• Colliders