The open source OpenXR runtime
a/math: Add projection matrix making function
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src/xrt/auxiliary/math/CMakeLists.txt
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src/xrt/auxiliary/math/CMakeLists.txt
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src/xrt/auxiliary/math/m_api.h
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src/xrt/auxiliary/math/m_api.h
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const struct xrt_matrix_4x4 *projection,
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struct xrt_matrix_4x4 *result);
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/*!
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* Compute a projection matrix with settings for Vulkan, it will also have it's
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* far plane at infinite and the NDC depth will be reversed.
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*
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* @relates xrt_matrix_4x4
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* @ingroup aux_math
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*/
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void
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math_matrix_4x4_projection_vulkan_infinite_reverse(const struct xrt_fov *fov,
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float near_plane,
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struct xrt_matrix_4x4 *result);
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/*
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*
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* Pose functions.
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src/xrt/auxiliary/math/m_matrix_projection.cpp
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src/xrt/auxiliary/math/m_matrix_projection.cpp
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// Copyright 2019-2023, Collabora, Ltd.
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// SPDX-License-Identifier: BSL-1.0
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/*!
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* @file
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* @brief Matrix function for creating projection matrices.
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* @author Jakob Bornecrantz <jakob@collabora.com>
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* @ingroup aux_math
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*/
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#include "m_mathinclude.h"
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#include "xrt/xrt_defines.h"
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/*
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*
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* Helpers.
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*
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*/
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template <typename Scalar, typename ResultType>
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void
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calc_vulkan_projection_infinite_reverse(const xrt_fov &fov, Scalar near_plane, ResultType &result)
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{
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const Scalar tan_left = static_cast<Scalar>(tan(fov.angle_left));
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const Scalar tan_right = static_cast<Scalar>(tan(fov.angle_right));
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const Scalar tan_down = static_cast<Scalar>(tan(fov.angle_down));
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const Scalar tan_up = static_cast<Scalar>(tan(fov.angle_up));
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// This is here for clarity.
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const bool vulkan_projection_space_y = true;
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const Scalar tan_width = tan_right - tan_left;
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const Scalar tan_height = vulkan_projection_space_y // Projection space y direction:
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? (tan_down - tan_up) // Vulkan Y down
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: (tan_up - tan_down); // OpenGL Y up
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const Scalar a11 = 2 / tan_width;
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const Scalar a22 = 2 / tan_height;
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const Scalar a31 = (tan_right + tan_left) / tan_width;
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const Scalar a32 = (tan_up + tan_down) / tan_height;
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/*
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* Vulkan's Z clip space is [0 .. 1] (OpenGL [-1 .. 0 .. 1]).
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* We are using reverse depth for better floating value.
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* - Near is 1
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* - Far is 0 (infinite)
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*
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* https://vincent-p.github.io/posts/vulkan_perspective_matrix/
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*/
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const Scalar a33 = 0; // vulkan = 0, opengl = -1
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const Scalar a34 = -1;
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const Scalar a43 = near_plane; // Reverse depth and half vs opengl, `-2 * near_plane`.
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// clang-format off
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result = ResultType({
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a11, 0, 0, 0,
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0, a22, 0, 0,
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a31, a32, a33, a34,
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0, 0, a43, 0,
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});
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// clang-format on
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}
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/*
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*
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* 'Exported' functions.
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*
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*/
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extern "C" void
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math_matrix_4x4_projection_vulkan_infinite_reverse(const struct xrt_fov *fov,
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float near_plane,
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struct xrt_matrix_4x4 *result)
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{
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calc_vulkan_projection_infinite_reverse<float, xrt_matrix_4x4>(*fov, near_plane, *result);
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}