启用Display 2时Hit Camera无法识别鼠标位置的问题排查

Alright, let's break down why your Cam 1 isn't picking up mouse input when you're on Display 2, and walk through how to fix it.

Root Causes #

Your issue stems from two key problems with how Unity handles multi-display setups and camera input:

1. Unreliable Camera.main reference: Camera.main pulls the first enabled camera with the MainCamera tag. When you switch to Display 2, even if Cam 1 is still running, Unity might prioritize Cam 2 (if it's enabled) or the lookup might behave unexpectedly—breaking your raycast source.
2. Mismatched mouse coordinates across displays: Input.mousePosition uses the main display (Display 1) as its origin. When your mouse is on Display 2, its coordinates will be outside Cam 1's screen bounds (e.g., if Display 1 is 1920px wide, Display 2 mouse X will be 1920+). Using these coordinates with Cam 1's ScreenPointToRay shoots a ray outside Cam 1's view, so it never hits your ground layer.

Fix Steps #

Let's address both issues with concrete changes to your code and setup:

1. Replace Camera.main with a direct reference

Ditch the fragile tag-based lookup and reference Cam 1 directly. This eliminates any ambiguity about which camera is handling the raycast:

public class HitCameraController : MonoBehaviour { 
    // Assign Cam 1 directly in the Inspector
    public Camera hitCamera; 
    public static Vector3 mousePos; 
    public static bool gotMouse; 
    public static bool mouseMoved; 
    private Vector3 lastMouseMovement; 

    void Start () { 
        gotMouse = false; 
        mouseMoved = false; 
        lastMouseMovement = Vector3.zero;
        
        // Fallback to Camera.main if you forget to assign in Inspector
        if (hitCamera == null) {
            hitCamera = Camera.main;
        }
    } 

    void Update () { 
        // Use our direct camera reference + corrected mouse position
        Ray ray = hitCamera.ScreenPointToRay(GetMousePositionForCamera(hitCamera)); 
        RaycastHit hit; 
        LayerMask ground = LayerMask.GetMask("GroundLayer"); 

        if(Physics.Raycast(ray, out hit, 300, ground)) { 
            mousePos = new Vector3(hit.point.x, 0f, hit.point.z); 
            mouseMoved = !mousePos.Equals(lastMouseMovement); 
            lastMouseMovement = mousePos; 
            gotMouse = true; 
        } else { 
            gotMouse = false; 
        } 
    } 

    // Helper to get mouse coordinates relative to the target camera's display
    private Vector3 GetMousePositionForCamera(Camera targetCamera) {
        // Get mouse position relative to the specific display the camera is targeting
        Vector3 relativeMouse = Display.RelativeMouseAt(Input.mousePosition);
        
        // Only process input if the mouse is on the camera's display
        if (relativeMouse.z == targetCamera.targetDisplay) {
            return new Vector3(relativeMouse.x, relativeMouse.y, 0f);
        }
        // Return an off-screen position if mouse is elsewhere (prevents false raycasts)
        return new Vector3(-1f, -1f, 0f);
    }
}

2. Verify Camera Display Settings

Double-check your camera configuration in the Inspector:

• For Cam 1: Set Target Display to 1
• For Cam 2: Set Target Display to 2
  This ensures Unity routes each camera's output to the correct monitor, and our RelativeMouseAt check works as intended.

3. Optional: Cross-Display Input (If Needed)

If you want Cam 1 to handle mouse input even when the cursor is on Display 2 (e.g., cross-monitor ground selection), modify the helper method to skip the display check and convert coordinates properly:

private Vector3 GetMousePositionForCamera(Camera targetCamera) {
    // Convert global mouse position to the camera's viewport space, then back to screen space
    Vector3 viewportPos = targetCamera.ScreenToViewportPoint(Input.mousePosition);
    return targetCamera.ViewportToScreenPoint(viewportPos);
}

Note: This might feel unintuitive for users, so only use it if cross-display interaction is a requirement.

Quick Sanity Checks #

• Make sure only Cam 1 has the MainCamera tag—remove it from Cam 2 to avoid any Camera.main confusion.
• If you don't need Cam 1 active when on Display 2, you could toggle its enabled state when switching displays, but that would disable ground selection on Display 2 entirely.

内容的提问来源于stack exchange，提问作者Bradley William Elko