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src/core/ViewportCamera.h

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+#pragma once
+
+#include <pxr/base/gf/camera.h>
+#include <pxr/base/gf/matrix4d.h>
+#include <pxr/base/gf/vec3d.h>
+#include <pxr/base/gf/bbox3d.h>
+#include <pxr/base/gf/range3d.h>
+#include <pxr/base/gf/ray.h>
+#include <pxr/usd/sdf/path.h>
+#include <pxr/usd/usd/stage.h>
+#include <utility>
+
+namespace UsdLayerManager {
+
+/// Free camera ported from Pixar's usdview FreeCamera (freeCamera.py).
+/// Supports Tumble/Truck/AdjustDistance with Z-up stage handling,
+/// automatic near/far clipping plane computation from scene bbox,
+/// and USD prim-camera passthrough mode.
+class ViewportCamera {
+public:
+    enum class CameraMode { Free, UsdCamera };
+
+    static constexpr double kDefaultNear        = 1.0;
+    static constexpr double kDefaultFar         = 2000000.0;
+    static constexpr double kMaxSafeZResolution = 1e6;
+    static constexpr double kMaxGoodZResolution = 5e4;
+
+    ViewportCamera();
+
+    // -----------------------------------------------------------------------
+    // Stage (sets Z-up flag and YZUp matrices)
+    // -----------------------------------------------------------------------
+    void SetStage(pxr::UsdStageRefPtr stage);
+
+    // -----------------------------------------------------------------------
+    // Free Camera Operations (mirrors FreeCamera.py)
+    // -----------------------------------------------------------------------
+
+    /// Orbit (tumble) around center by dTheta (horizontal) and dPhi (vertical) degrees.
+    void Tumble(double dTheta, double dPhi);
+
+    /// Scale distance from center by scaleFactor.  Prevents getting stuck near zero.
+    void AdjustDistance(double scaleFactor);
+
+    /// Pan (truck) in camera-local right/up directions, world-unit deltas.
+    void Truck(double deltaRight, double deltaUp);
+
+    /// Returns pixels-to-world factor for correct Truck() scaling.
+    double ComputePixelsToWorldFactor(double viewportHeight);
+
+    /// Frame a bounding box.  frameFit=1.1 gives ~10% margin (usdview default).
+    void FrameSelection(const pxr::GfBBox3d& selBBox, double frameFit = 1.1);
+
+    // -----------------------------------------------------------------------
+    // Camera Resolution: returns GfCamera with updated transform + clipping
+    // -----------------------------------------------------------------------
+
+    /// Returns the GfCamera with up-to-date transform.
+    /// If autoClip=true, near/far are computed from stageBBox for best precision.
+    pxr::GfCamera ComputeGfCamera(const pxr::GfBBox3d& stageBBox,
+                                  bool autoClip = false);
+
+    // -----------------------------------------------------------------------
+    // Convenience Matrix Accessors
+    // -----------------------------------------------------------------------
+    pxr::GfMatrix4d GetViewMatrix();
+    pxr::GfMatrix4d GetProjectionMatrix();
+
+    // -----------------------------------------------------------------------
+    // Camera Mode
+    // -----------------------------------------------------------------------
+    CameraMode          GetMode()          const { return m_mode; }
+    const pxr::SdfPath& GetUsdCameraPath() const { return m_usdCameraPath; }
+
+    /// Switch to USD prim camera mode (renderer will call SetCameraPath).
+    void SetUsdCamera(const pxr::SdfPath& cameraPath);
+
+    /// Switch back to free camera, optionally initializing state from lastGfCamera.
+    void SwitchToFreeCamera(const pxr::GfCamera* lastGfCamera = nullptr);
+
+    // -----------------------------------------------------------------------
+    // Camera Settings
+    // -----------------------------------------------------------------------
+    double GetFOV()         const;  ///< Vertical FOV in degrees
+    void   SetFOV(double fov);
+    double GetAspectRatio() const;
+    void   SetAspectRatio(double aspect);
+
+    /// Hint for autoClip: the closest visible geometry point from pick result.
+    void SetClosestVisibleDistFromPoint(const pxr::GfVec3d& point);
+
+    // -----------------------------------------------------------------------
+    // State Queries
+    // -----------------------------------------------------------------------
+    double GetDist() const { return m_dist; }
+    bool   IsZUp()   const { return m_isZUp; }
+
+    // -----------------------------------------------------------------------
+    // Compatibility accessors (for tests and legacy callers)
+    // -----------------------------------------------------------------------
+
+    /// Returns camera position in world space.
+    pxr::GfVec3d GetEye();
+
+    /// Returns the look-at focal point (center of orbit).
+    const pxr::GfVec3d& GetFocalPoint() const { return m_center; }
+
+    /// Set the look-at focal point directly.
+    /// Used by orthographic view panning to move the center in correct
+    /// view-space directions without going through the perspective Truck() path.
+    void SetFocalPoint(const pxr::GfVec3d& center) {
+        m_center = center;
+        m_cameraTransformDirty = true;
+    }
+
+    /// Returns the current near-clip distance.
+    double GetNearClip() const {
+        return static_cast<double>(m_camera.GetClippingRange().GetMin());
+    }
+
+    /// Returns the current far-clip distance.
+    double GetFarClip() const {
+        return static_cast<double>(m_camera.GetClippingRange().GetMax());
+    }
+
+    /// Legacy: frame a GfRange3d (wraps it in a unit-matrix GfBBox3d).
+    void FrameBoundingBox(const pxr::GfRange3d& range, double frameFit = 1.1) {
+        FrameSelection(pxr::GfBBox3d(range), frameFit);
+    }
+
+    /// Legacy: orbit alias (matches old Orbit(deltaYaw, deltaPitch) signature).
+    void Orbit(double deltaYaw, double deltaPitch) {
+        Tumble(deltaYaw, deltaPitch);
+    }
+
+private:
+    void PushToCameraTransform();
+    void PullFromCameraTransform();
+    void SetClippingPlanes(const pxr::GfBBox3d& stageBBox);
+    void ResetClippingPlanes();
+    std::pair<double,double> RangeOfBoxAlongRay(
+        const pxr::GfRay& camRay, const pxr::GfBBox3d& bbox) const;
+
+    // Core camera object (owns aperture/projection/clipping/transform state)
+    pxr::GfCamera m_camera;
+    bool          m_cameraTransformDirty;
+
+    // Orbital / tumble state
+    double       m_rotTheta;  // horizontal orbit (degrees, around Y)
+    double       m_rotPhi;    // vertical orbit   (degrees, around X)
+    double       m_rotPsi;    // roll              (degrees, usually 0)
+    pxr::GfVec3d m_center;    // look-at center in world space
+    double       m_dist;      // distance camera → center
+    double       m_selSize;   // extent of last framed selection
+
+    // Stage up-axis handling
+    bool            m_isZUp;
+    pxr::GfMatrix4d m_YZUpMatrix;    // Y-up → Z-up  (rotate -90° around X)
+    pxr::GfMatrix4d m_YZUpInvMatrix; // Z-up → Y-up  (inverse)
+
+    // Auto-clip state
+    bool   m_hasClosestVisibleDist;
+    double m_closestVisibleDist;
+    double m_lastFramedDist;
+    double m_lastFramedClosestDist;
+    double m_overrideNear;  // ≤0 means "no override"
+    double m_overrideFar;   // ≤0 means "no override"
+
+    // Camera mode
+    CameraMode          m_mode;
+    pxr::SdfPath        m_usdCameraPath;
+    pxr::UsdStageRefPtr m_stage;
+};
+
+} // namespace UsdLayerManager