Fixes NDC calculation and updates formulas

include/omath/projection/camera.hpp

@@ -54,6 +54,12 @@ namespace omath::projection
         friend UnitTestProjection_Projection_Test;
 #endif
     public:
+        enum class ScreenStart
+        {
+            TOP_LEFT_CORNER,
+            BOTTOM_LEFT_CORNER,
+        };
+
         ~Camera() = default;
         Camera(const Vector3<float>& position, const ViewAnglesType& view_angles, const ViewPort& view_port,
                const FieldOfView& fov, const float near, const float far) noexcept
@@ -146,15 +152,22 @@ namespace omath::projection
             return m_origin;
         }
 
+
+        template<ScreenStart screen_start = ScreenStart::TOP_LEFT_CORNER>
         [[nodiscard]] std::expected<Vector3<float>, Error>
         world_to_screen(const Vector3<float>& world_position) const noexcept
         {
-            auto normalized_cords = world_to_view_port(world_position);
+            const auto normalized_cords = world_to_view_port(world_position);
 
             if (!normalized_cords.has_value())
                 return std::unexpected{normalized_cords.error()};
 
-            return ndc_to_screen_position(*normalized_cords);
+            if constexpr (screen_start == ScreenStart::TOP_LEFT_CORNER)
+                return ndc_to_screen_position_from_top_left_corner(*normalized_cords);
+            else if constexpr (screen_start == ScreenStart::BOTTOM_LEFT_CORNER)
+                return ndc_to_screen_position_from_bottom_left_corner(*normalized_cords);
+            else
+                std::unreachable();
         }
 
         [[nodiscard]] std::expected<Vector3<float>, Error>
@@ -225,7 +238,27 @@ namespace omath::projection
             return std::ranges::any_of(ndc.raw_array(), [](const auto& val) { return val < -1 || val > 1; });
         }
 
-        [[nodiscard]] Vector3<float> ndc_to_screen_position(const Vector3<float>& ndc) const noexcept
+        [[nodiscard]] Vector3<float>
+        ndc_to_screen_position_from_top_left_corner(const Vector3<float>& ndc) const noexcept
+        {
+            /*
+                                ^
+                                |        y
+                            1   |
+                                |
+                                |
+                    -1 ---------0--------- 1  --> x
+                                |
+                                |
+                           -1   |
+                                v
+            */
+
+            return {(ndc.x + 1.f) / 2.f * m_view_port.m_width, (ndc.y / -2.f + 0.5f) * m_view_port.m_height, ndc.z};
+        }
+
+        [[nodiscard]] Vector3<float>
+        ndc_to_screen_position_from_bottom_left_corner(const Vector3<float>& ndc) const noexcept
         {
             /*
                                 ^
@@ -239,7 +272,8 @@ 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};
+
+            return {(ndc.x + 1.f) / 2.f * m_view_port.m_width, (ndc.y / 2.f + 0.5f) * m_view_port.m_height, ndc.z};
         }
 
         [[nodiscard]] Vector3<float> screen_to_ndc(const Vector3<float>& screen_pos) const noexcept

source/engines/unity_engine/formulas.cpp

@@ -25,7 +25,7 @@ namespace omath::unity_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
@@ -37,13 +37,6 @@ namespace omath::unity_engine
     Mat4X4 calc_perspective_projection_matrix(const float field_of_view, const float aspect_ratio, const float near,
                                               const float far) noexcept
     {
-        const float fov_half_tan = std::tan(angles::degrees_to_radians(field_of_view) / 2.f);
-
-        return {
-                {1.f / (aspect_ratio * fov_half_tan), 0, 0, 0},
-                {0, 1.f / (fov_half_tan), 0, 0},
-                {0, 0, (far + near) / (far - near), -(2.f * far * near) / (far - near)},
-                {0, 0, -1.f, 0},
-        };
+        return omath::mat_perspective_right_handed(field_of_view, aspect_ratio, near, far);
     }
 } // namespace omath::unity_engine

tests/engines/unit_test_unity_engine.cpp

@@ -87,9 +87,9 @@ TEST(unit_test_unity_engine, Project)
     constexpr auto fov = omath::projection::FieldOfView::from_degrees(60.f);
 
     const auto cam = omath::unity_engine::Camera({0, 0, 0}, {}, {1280.f, 720.f}, fov, 0.03f, 1000.f);
-    const auto proj = cam.world_to_screen({5.f, 3, 10.f});
+    const auto proj = cam.world_to_screen<omath::unity_engine::Camera::ScreenStart::BOTTOM_LEFT_CORNER>({10.f, 3, 10.f});
 
-    EXPECT_NEAR(proj->x, 951.769f, 0.001f);
+    EXPECT_NEAR(proj->x, 1263.538, 0.001f);
     EXPECT_NEAR(proj->y, 547.061f, 0.001f);
 }
 

tests/general/unit_test_mat.cpp

@@ -214,3 +214,20 @@ TEST(UnitTestMatStandalone, Enverse)
 
     EXPECT_EQ(mv, m.inverted());
 }
+
+TEST(UnitTestMatStandalone, Equanity)
+{
+    constexpr omath::Vector3<float> left_handed = {0, 2, 10};
+    constexpr omath::Vector3<float> right_handed = {0, 2, -10};
+
+    auto proj_left_handed = omath::mat_perspective_left_handed(90.f, 16.f / 9.f, 0.1, 1000);
+    auto proj_right_handed = omath::mat_perspective_right_handed(90.f, 16.f / 9.f, 0.1, 1000);
+
+    auto ndc_left_handed = proj_left_handed * omath::mat_column_from_vector(left_handed);
+    auto ndc_right_handed = proj_right_handed * omath::mat_column_from_vector(right_handed);
+
+    ndc_left_handed /= ndc_left_handed.at(3, 0);
+    ndc_right_handed /= ndc_right_handed.at(3, 0);
+
+    EXPECT_EQ(ndc_left_handed, ndc_right_handed);
+}