From eb1f5d49ff7e83f23148b35f989e23ab761181df Mon Sep 17 00:00:00 2001
From: lisyarus <lisyarus@gmail.com>
Date: Fri, 2 Oct 2020 19:18:55 +0300
Subject: [PATCH] Add a free-flying camera

---
 libs/geom/include/psemek/geom/camera.hpp | 13 +++++++++++++
 libs/geom/source/camera.cpp              | 13 +++++++++++++
 2 files changed, 26 insertions(+)

diff --git a/libs/geom/include/psemek/geom/camera.hpp b/libs/geom/include/psemek/geom/camera.hpp
index 6adf6c36..c9ca2d9c 100644
--- a/libs/geom/include/psemek/geom/camera.hpp
+++ b/libs/geom/include/psemek/geom/camera.hpp
@@ -92,4 +92,17 @@ namespace psemek::geom
 		matrix<float, 4, 4> view() const override;
 	};
 
+	struct free_camera
+		: perspective_camera
+	{
+		// assumes up is +Z
+		// azimuthal angle is in XY plane
+		// both angles zero gives X right, Y forward, and Z up
+
+		float azimuthal_angle;
+		float elevation_angle;
+		point<float, 3> pos;
+
+		matrix<float, 4, 4> view() const override;
+	};
 }
diff --git a/libs/geom/source/camera.cpp b/libs/geom/source/camera.cpp
index 2dee85a7..f3311cce 100644
--- a/libs/geom/source/camera.cpp
+++ b/libs/geom/source/camera.cpp
@@ -120,4 +120,17 @@ namespace psemek::geom
 		return tr.homogeneous_matrix();
 	}
 
+	matrix<float, 4, 4> free_camera::view() const
+	{
+		auto tr =
+			  swap<float, 3>(1, 2).transform()
+			* scale<float, 3>({1.f, -1.f, 1.f}).transform()
+			* plane_rotation<float, 3>(1, 2, elevation_angle).transform()
+			* plane_rotation<float, 3>(1, 0, azimuthal_angle).transform()
+			* translation<float, 3>({ -pos[0], -pos[1], -pos[2] }).transform()
+			;
+
+		return tr.homogeneous_matrix();
+	}
+
 }