Adds screen to world space conversion

Adds functionality to convert screen coordinates to world space, including handling for cases where the inverse view projection matrix is singular or when the world position is out of screen bounds.

Also exposes Camera class to unit tests.

CMakeLists.txt

@@ -100,6 +100,7 @@ target_compile_features(${PROJECT_NAME} PUBLIC cxx_std_23)
 if (OMATH_BUILD_TESTS)
     add_subdirectory(extlibs)
     add_subdirectory(tests)
+    target_compile_definitions(${PROJECT_NAME} PUBLIC OMATH_BUILD_TESTS)
 endif ()
 
 if (OMATH_BUILD_EXAMPLES)

include/omath/projection/camera.hpp

@@ -4,13 +4,15 @@
 
 #pragma once
 
-#include "omath/projection/error_codes.hpp"
 #include "omath/linear_algebra/mat.hpp"
 #include "omath/linear_algebra/vector3.hpp"
+#include "omath/projection/error_codes.hpp"
 #include <expected>
 #include <omath/angle.hpp>
 #include <type_traits>
-
+#ifdef OMATH_BUILD_TESTS
+class UnitTestProjection_Projection_Test;
+#endif
 namespace omath::projection
 {
     class ViewPort final
@@ -45,6 +47,8 @@ namespace omath::projection
     requires CameraEngineConcept<TraitClass, Mat4X4Type, ViewAnglesType>
     class Camera final
     {
+        friend UnitTestProjection_Projection_Test;
+
     public:
         ~Camera() = default;
         Camera(const Vector3<float>& position, const ViewAnglesType& view_angles, const ViewPort& view_port,
@@ -164,6 +168,31 @@ namespace omath::projection
 
             return Vector3<float>{projected.at(0, 0), projected.at(1, 0), projected.at(2, 0)};
         }
+        [[nodiscard]]
+        std::expected<Vector3<float>, Error> view_port_to_screen(const Vector3<float>& ndc) const noexcept
+        {
+            const auto inv_view_proj = get_view_projection_matrix().inverted();
+
+            if (!inv_view_proj)
+                return std::unexpected(Error::INV_VIEW_PROJ_MAT_DET_EQ_ZERO);
+
+            auto inverted_projection =
+                    inv_view_proj.value() * mat_column_from_vector<float, Mat4X4Type::get_store_ordering()>(ndc);
+
+            if (!inverted_projection.at(3, 0))
+                return std::unexpected(Error::WORLD_POSITION_IS_OUT_OF_SCREEN_BOUNDS);
+
+            inverted_projection /= inverted_projection.at(3, 0);
+
+            return Vector3<float>{inverted_projection.at(0, 0), inverted_projection.at(1, 0),
+                                  inverted_projection.at(2, 0)};
+        }
+
+        [[nodiscard]]
+        std::expected<Vector3<float>, Error> screen_to_world(const Vector3<float>& screen_pos) const noexcept
+        {
+            return view_port_to_screen(screen_to_dnc(screen_pos));
+        }
 
     protected:
         ViewPort m_view_port{};
@@ -186,7 +215,7 @@ namespace omath::projection
 
         [[nodiscard]] Vector3<float> ndc_to_screen_position(const Vector3<float>& ndc) const noexcept
         {
-/*
+            /*
                                 ^
                                 |        y
                             1   |
@@ -197,8 +226,14 @@ namespace omath::projection
                                 |
                            -1   |
                                 v
-*/
+            */
             return {(ndc.x + 1.f) / 2.f * m_view_port.m_width, (1.f - ndc.y) / 2.f * m_view_port.m_height, ndc.z};
         }
+
+        [[nodiscard]] Vector3<float> screen_to_dnc(const Vector3<float>& screen_pos) const noexcept
+        {
+            return {screen_pos.x / m_view_port.m_width * 2.f - 1.f, 1.f - screen_pos.y / m_view_port.m_height * 2.f,
+                    screen_pos.z};
+        }
     };
 } // namespace omath::projection

include/omath/projection/error_codes.hpp

@@ -10,5 +10,6 @@ namespace omath::projection
     enum class Error : uint16_t
     {
         WORLD_POSITION_IS_OUT_OF_SCREEN_BOUNDS,
+        INV_VIEW_PROJ_MAT_DET_EQ_ZERO,
     };
 }

tests/general/unit_test_projection.cpp

@@ -13,8 +13,9 @@ TEST(UnitTestProjection, Projection)
     const auto cam = omath::source_engine::Camera({0, 0, 0}, omath::source_engine::ViewAngles{}, {1920.f, 1080.f}, fov,
                                                   0.01f, 1000.f);
 
-    const auto projected = cam.world_to_screen({1000, 0, 50});
+    const auto projected = cam.world_to_screen({1000, 0, 50.f});
-
+    const auto result = cam.screen_to_world(projected.value());
+    const auto result2 = cam.world_to_screen(result.value());
     EXPECT_NEAR(projected->x, 960.f, 0.001f);
     EXPECT_NEAR(projected->y, 504.f, 0.001f);
     EXPECT_NEAR(projected->z, 1.f, 0.001f);