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3rdparty/osgXR/src/projection.cpp

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+// =============================================================================
+// Derived from openxr-simple-example
+// Copyright 2019-2021, Collabora, Ltd.
+// Which was adapted from
+// https://github.com/KhronosGroup/OpenXR-SDK-Source/blob/master/src/common/xr_linear.h
+// Copyright (c) 2017 The Khronos Group Inc.
+// Copyright (c) 2016 Oculus VR, LLC.
+// SPDX-License-Identifier: Apache-2.0
+// =============================================================================
+
+#include "projection.h"
+
+void osgXR::createProjectionFov(osg::Matrix& result,
+                                const XrFovf& fov,
+                                const float nearZ,
+                                const float farZ)
+{
+    const float tanAngleLeft = tanf(fov.angleLeft);
+    const float tanAngleRight = tanf(fov.angleRight);
+
+    const float tanAngleDown = tanf(fov.angleDown);
+    const float tanAngleUp = tanf(fov.angleUp);
+
+    const float tanAngleWidth = tanAngleRight - tanAngleLeft;
+
+    // Set to tanAngleDown - tanAngleUp for a clip space with positive Y
+    // down (Vulkan). Set to tanAngleUp - tanAngleDown for a clip space with
+    // positive Y up (OpenGL / D3D / Metal).
+    const float tanAngleHeight = tanAngleUp - tanAngleDown;
+
+    // Set to nearZ for a [-1,1] Z clip space (OpenGL / OpenGL ES).
+    // Set to zero for a [0,1] Z clip space (Vulkan / D3D / Metal).
+    const float offsetZ = nearZ;
+
+    if (farZ <= nearZ)
+    {
+        // place the far plane at infinity
+        result(0, 0) = 2 / tanAngleWidth;
+        result(1, 0) = 0;
+        result(2, 0) = (tanAngleRight + tanAngleLeft) / tanAngleWidth;
+        result(3, 0) = 0;
+
+        result(0, 1) = 0;
+        result(1, 1) = 2 / tanAngleHeight;
+        result(2, 1) = (tanAngleUp + tanAngleDown) / tanAngleHeight;
+        result(3, 1) = 0;
+
+        result(0, 2) = 0;
+        result(1, 2) = 0;
+        result(2, 2) = -1;
+        result(3, 2) = -(nearZ + offsetZ);
+
+        result(0, 3) = 0;
+        result(1, 3) = 0;
+        result(2, 3) = -1;
+        result(3, 3) = 0;
+    } else {
+        // normal projection
+        result(0, 0) = 2 / tanAngleWidth;
+        result(1, 0) = 0;
+        result(2, 0) = (tanAngleRight + tanAngleLeft) / tanAngleWidth;
+        result(3, 0) = 0;
+
+        result(0, 1) = 0;
+        result(1, 1) = 2 / tanAngleHeight;
+        result(2, 1) = (tanAngleUp + tanAngleDown) / tanAngleHeight;
+        result(3, 1) = 0;
+
+        result(0, 2) = 0;
+        result(1, 2) = 0;
+        result(2, 2) = -(farZ + offsetZ) / (farZ - nearZ);
+        result(3, 2) = -(farZ * (nearZ + offsetZ)) / (farZ - nearZ);
+
+        result(0, 3) = 0;
+        result(1, 3) = 0;
+        result(2, 3) = -1;
+        result(3, 3) = 0;
+    }
+}