stride3d.stride-docs/en/manual/physics-bullet/raycasting.md

Raycasting

Intermediate Programmer

[!INCLUDE bullet-deprecation]

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.

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