source/src/engine/scene/camera.cpp

/*
 * Copyright (C) 2023  Christopher J. Howard
 *
 * This file is part of Antkeeper source code.
 *
 * Antkeeper source code is free software: you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 *
 * Antkeeper source code is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with Antkeeper source code.  If not, see <http://www.gnu.org/licenses/>.
 */

#include <engine/scene/camera.hpp>
#include <engine/math/quaternion.hpp>
#include <engine/math/projection.hpp>

namespace scene {

geom::ray<float, 3> camera::pick(const math::fvec2& ndc) const
{
	const auto near = m_inv_view_projection * math::fvec4{ndc[0], ndc[1], 1.0f, 1.0f};
	const auto far = m_inv_view_projection * math::fvec4{ndc[0], ndc[1], 0.0f, 1.0f};
	const auto origin = math::fvec3{near[0], near[1], near[2]} / near[3];
	const auto direction = math::normalize(math::fvec3{far[0], far[1], far[2]} / far[3] - origin);
	
	return {origin, direction};
}

math::fvec3 camera::project(const math::fvec3& object, const math::fvec4& viewport) const
{
	math::fvec4 result = m_view_projection * math::fvec4{object[0], object[1], object[2], 1.0f};
	result[0] = (result[0] / result[3]) * 0.5f + 0.5f;
	result[1] = (result[1] / result[3]) * 0.5f + 0.5f;
	result[2] = (result[2] / result[3]) * 0.5f + 0.5f;
	
	result[0] = result[0] * viewport[2] + viewport[0];
	result[1] = result[1] * viewport[3] + viewport[1];
	
	return math::fvec3(result);
}

math::fvec3 camera::unproject(const math::fvec3& window, const math::fvec4& viewport) const
{
	math::fvec4 result;
	result[0] = ((window[0] - viewport[0]) / viewport[2]) * 2.0f - 1.0f;
	result[1] = ((window[1] - viewport[1]) / viewport[3]) * 2.0f - 1.0f;
	//result[2] = window[2] * 2.0f - 1.0f; z: [-1, 1]
	//result[2] = window[2]; // z: [0, 1]
	result[2] = 1.0f - window[2]; // z: [1, 0]
	result[3] = 1.0f;
	
	result = m_inv_view_projection * result;

	return math::fvec3(result) * (1.0f / result[3]);
}

void camera::set_perspective(float vertical_fov, float aspect_ratio, float clip_near, float clip_far)
{
	// Set projection mode to perspective
	m_orthographic = false;
	
	// Update perspective projection parameters
	m_vertical_fov = vertical_fov;
	m_aspect_ratio = aspect_ratio;
	m_clip_near = clip_near;
	m_clip_far = clip_far;
	
	// Recalculate projection matrix and its inverse
	std::tie(m_projection, m_inv_projection) = math::perspective_half_z_inv(m_vertical_fov, m_aspect_ratio, m_clip_far, m_clip_near);
	
	// Recalculate view-projection matrix
	m_view_projection = m_projection * m_view;
	m_inv_view_projection = m_inv_view * m_inv_projection;
	
	// Recalculate view frustum
	update_frustum();
}

void camera::set_vertical_fov(float vertical_fov)
{
	if (!m_orthographic)
	{
		set_perspective(vertical_fov, m_aspect_ratio, m_clip_near, m_clip_far);
	}
}

void camera::set_orthographic(float clip_left, float clip_right, float clip_bottom, float clip_top, float clip_near, float clip_far)
{
	// Set projection mode to orthographic
	m_orthographic = true;
	
	// Update signed distances to clipping planes
	m_clip_left = clip_left;
	m_clip_right = clip_right;
	m_clip_bottom = clip_bottom;
	m_clip_top = clip_top;
	m_clip_near = clip_near;
	m_clip_far = clip_far;
	
	// Recalculate projection matrix and its inverse
	std::tie(m_projection, m_inv_projection) = math::ortho_half_z_inv(m_clip_left, m_clip_right, m_clip_bottom, m_clip_top, m_clip_far, m_clip_near);
	
	// Update view-projection matrix and its inverse
	m_view_projection = m_projection * m_view;
	m_inv_view_projection = m_inv_view * m_inv_projection;
	
	// Update view frustum
	update_frustum();
}

void camera::set_exposure_value(float ev100)
{
	m_exposure_value = ev100;
	// m_exposure_normalization = 1.0f / (std::exp2(m_exposure_value) * 1.2f);
	m_exposure_normalization = 1.0f / (std::exp2(m_exposure_value));
}

void camera::transformed()
{
	// Update basis vectors
	m_forward = get_rotation() * math::fvec3{0.0f, 0.0f, -1.0f};
	m_up = get_rotation() * math::fvec3{0.0f, 1.0f, 0.0f};
	
	// Recalculate view matrix and its inverse
	std::tie(m_view, m_inv_view) = math::look_at_rh_inv(get_translation(), get_translation() + m_forward, m_up);
	
	// Update view-projection matrix and its inverse
	m_view_projection = m_projection * m_view;
	m_inv_view_projection = m_inv_view * m_inv_projection;
	
	// Update view frustum
	update_frustum();
}

void camera::update_frustum()
{
	// Recalculate view frustum
	m_view_frustum.extract(m_view_projection);
	
	// Reverse half z clip-space coordinates of a cube
	constexpr math::fvec4 clip_space_cube[8] =
	{
		{-1, -1, 1, 1}, // NBL
		{ 1, -1, 1, 1}, // NBR
		{-1,  1, 1, 1}, // NTL
		{ 1,  1, 1, 1}, // NTR
		{-1, -1, 0, 1}, // FBL
		{ 1, -1, 0, 1}, // FBR
		{-1,  1, 0, 1}, // FTL
		{ 1,  1, 0, 1}  // FTR
	};
	
	// Update bounds
	m_bounds = {math::fvec3::infinity(), -math::fvec3::infinity()};
	for (std::size_t i = 0; i < 8; ++i)
	{
		const math::fvec4 frustum_corner = m_inv_view_projection * clip_space_cube[i];
		m_bounds.extend(math::fvec3(frustum_corner) / frustum_corner[3]);
	}
}

} // namespace scene