From 2eccb4023f1fe4fd0525b2e7d53356b2a9dc1f47 Mon Sep 17 00:00:00 2001
From: Orange <orange-cpp@yandex.ru>
Date: Thu, 23 Apr 2026 18:33:00 +0300
Subject: [PATCH] fix

---
 source/engines/unreal_engine/formulas.cpp | 31 ++++++++++++++++++-----
 1 file changed, 25 insertions(+), 6 deletions(-)

diff --git a/source/engines/unreal_engine/formulas.cpp b/source/engines/unreal_engine/formulas.cpp
index 1890a13..7e0b24c 100644
--- a/source/engines/unreal_engine/formulas.cpp
+++ b/source/engines/unreal_engine/formulas.cpp
@@ -2,7 +2,6 @@
 // Created by Vlad on 3/22/2025.
 //
 #include "omath/engines/unreal_engine/formulas.hpp"
-
 namespace omath::unreal_engine
 {
     Vector3<float> forward_vector(const ViewAngles& angles) noexcept
@@ -25,7 +24,7 @@ namespace omath::unreal_engine
     }
     Mat4X4 calc_view_matrix(const ViewAngles& angles, const Vector3<float>& cam_origin) noexcept
     {
-        return mat_camera_view<float, MatStoreType::ROW_MAJOR>(forward_vector(angles), -right_vector(angles),
+        return mat_camera_view<float, MatStoreType::ROW_MAJOR>(forward_vector(angles), right_vector(angles),
                                                                up_vector(angles), cam_origin);
     }
     Mat4X4 rotation_matrix(const ViewAngles& angles) noexcept
@@ -34,13 +33,33 @@ namespace omath::unreal_engine
                * mat_rotation_axis_z<float, MatStoreType::ROW_MAJOR>(angles.yaw)
                * mat_rotation_axis_y<float, MatStoreType::ROW_MAJOR>(-angles.pitch);
     }
+
+
     Mat4X4 calc_perspective_projection_matrix(const float field_of_view, const float aspect_ratio, const float near,
                                               const float far, const NDCDepthRange ndc_depth_range) noexcept
     {
-        if (ndc_depth_range == NDCDepthRange::ZERO_TO_ONE)
-            return mat_perspective_left_handed<float, MatStoreType::ROW_MAJOR, NDCDepthRange::ZERO_TO_ONE>(
-                    field_of_view, aspect_ratio, near, far);
+        // UE stores horizontal FOV in FMinimalViewInfo — mirror engine's
+        // FMinimalViewInfo::CalculateProjectionMatrixGivenViewRectangle:
+        //   XAxisMultiplier = 1 / tan(hfov/2)
+        //   YAxisMultiplier = aspect / tan(hfov/2)
+        const float inv_tan_half_hfov = 1.f / std::tan(angles::degrees_to_radians(field_of_view) / 2.f);
+        const float x_axis = inv_tan_half_hfov;
+        const float y_axis = inv_tan_half_hfov * aspect_ratio;
 
-        return mat_perspective_left_handed(field_of_view, aspect_ratio, near, far);
+        if (ndc_depth_range == NDCDepthRange::ZERO_TO_ONE)
+            return {
+                        {x_axis, 0,      0,                     0},
+                        {0,      y_axis, 0,                     0},
+                        {0,      0,      far / (far - near),   -(near * far) / (far - near)},
+                        {0,      0,      1,                     0},
+                };
+        if (ndc_depth_range == NDCDepthRange::NEGATIVE_ONE_TO_ONE)
+            return {
+                        {x_axis, 0,      0,                             0},
+                        {0,      y_axis, 0,                             0},
+                        {0,      0,      (far + near) / (far - near),  -(2.f * far * near) / (far - near)},
+                        {0,      0,      1,                             0},
+                };
+        std::unreachable();
     }
 } // namespace omath::unreal_engine