Simulate and light the smoke on the GPU and make rain and snow of particles

2026-10-28 19:17:28 +01:00 · 2026-10-20 16:44:27 +02:00
parent 6a109e984c
commit 867497b658
22 changed files with 1637 additions and 13 deletions
--- a/rendering/opengl46/opengl46gpuparticles.cpp
+++ b/rendering/opengl46/opengl46gpuparticles.cpp
@@ -0,0 +1,472 @@
+/*
+This Source Code Form is subject to the
+terms of the Mozilla Public License, v.
+2.0. If a copy of the MPL was not
+distributed with this file, You can
+obtain one at
+http://mozilla.org/MPL/2.0/.
+*/
+
+#include "stdafx.h"
+#include "rendering/opengl46/opengl46gpuparticles.h"
+
+#include "rendering/particles.h"
+#include "simulation/simulationenvironment.h"
+#include "utilities/Globals.h"
+#include "utilities/Logs.h"
+#include "utilities/Timer.h"
+#include "utilities/utilities.h"
+#include "gl/vao.h"
+
+namespace
+{
+
+// places of the smoke at most, all sources together (48 bytes each, as many again for the draw); the sources past it get none
+std::uint32_t constexpr MAX_SMOKE_PLACES{1u << 19};
+// the origin of the smoke moves by whole steps when the camera gets this far from it
+double constexpr ORIGIN_STEP{256.0};
+double constexpr ORIGIN_REACH{1024.0};
+// how much the smoke scatters the light onwards (Henyey-Greenstein)
+float constexpr SMOKE_FORWARD{0.3f};
+
+// the boxes of the rain and snow around the camera: their sizes (metres) and the shares of the particles in each
+std::array<float, 3> constexpr BOX_SIZE{10.f, 24.f, 60.f};
+std::array<float, 3> constexpr BOX_SHARE{0.2f, 0.35f, 0.45f};
+
+// what the rain and the snow are like: the speed of the fall (m/s), how long a streak lasts (s, the eye's or the camera's
+// exposure), opacity, how much a drop or a flake scatters the light onwards and how bright it is against a white surface
+struct precipitation_kind
+{
+	float fall;
+	float exposure;
+	float opacity;
+	float forward;
+	float brightness;
+};
+precipitation_kind constexpr RAIN{7.f, 0.025f, 0.5f, 0.6f, 0.6f};
+precipitation_kind constexpr SNOW{1.1f, 0.01f, 0.85f, 0.25f, 0.9f};
+// the share of the wind of the environment the drops and flakes drift with (as the old cylinder leant with it)
+double constexpr WIND_SHARE{0.5};
+// the camera faster than this from a frame to the next was moved, not driven or flown
+double constexpr CAMERA_JUMP{120.0};
+
+std::unique_ptr<gl::program> make_program(std::vector<std::string> const &Names)
+{
+	std::vector<std::unique_ptr<gl::shader>> shaders;
+	std::vector<std::reference_wrapper<const gl::shader>> references;
+	for (auto const &name : Names)
+	{
+		shaders.emplace_back(std::make_unique<gl::shader>(name));
+		references.emplace_back(*shaders.back());
+	}
+	return std::make_unique<gl::program>(references);
+}
+
+std::uint32_t groups(std::uint32_t const Count)
+{
+	return (Count + gl::PARTICLE_GROUP_SIZE - 1) / gl::PARTICLE_GROUP_SIZE;
+}
+
+} // namespace
+
+opengl46_gpu_particles::~opengl46_gpu_particles()
+{
+	// the vertex array goes with the context; deleted here only if it's still there
+	if ((m_vao != 0) && (::glfwGetCurrentContext() != nullptr))
+		::glDeleteVertexArrays(1, &m_vao);
+}
+
+bool opengl46_gpu_particles::init()
+{
+	if (m_state != 0)
+		return m_state > 0;
+	m_state = -1;
+	try
+	{
+		m_smokesimulate = make_program({"particles_smoke_simulate.comp"});
+		m_smokeprepare = make_program({"particles_smoke_prepare.comp"});
+		m_smokedraw = make_program({"particles_smoke.vert", "particles_smoke.frag"});
+		m_precipitationprepare = make_program({"particles_precipitation.comp"});
+		m_precipitationdraw = make_program({"particles_precipitation.vert", "particles_precipitation.frag"});
+	}
+	catch (gl::shader_exception const &e)
+	{
+		ErrorLog("particles: can't use the programs of the particles of the gpu, the smoke stays on the cpu: " + std::string(e.what()));
+		return false;
+	}
+
+	// the attributes of the instances: three vec4 of gl::particle_draw
+	::glCreateVertexArrays(1, &m_vao);
+	for (GLuint attribute = 0; attribute < 3; ++attribute)
+	{
+		::glEnableVertexArrayAttrib(m_vao, attribute);
+		::glVertexArrayAttribFormat(m_vao, attribute, 4, GL_FLOAT, GL_FALSE, attribute * sizeof(glm::vec4));
+		::glVertexArrayAttribBinding(m_vao, attribute, 0);
+	}
+	::glVertexArrayBindingDivisor(m_vao, 0, 1);
+
+	m_smokecommand = std::make_unique<gl::ssbo>(4 * sizeof(GLuint), gl::PARTICLE_COMMAND_SSBO_BINDING);
+	m_precipitationcommand = std::make_unique<gl::ssbo>(4 * sizeof(GLuint), gl::PARTICLE_COMMAND_SSBO_BINDING);
+	m_smokereadback = std::make_unique<gl::readback>(4 * sizeof(GLuint));
+	m_precipitationreadback = std::make_unique<gl::readback>(4 * sizeof(GLuint));
+	m_state = 1;
+	return true;
+}
+
+bool opengl46_gpu_particles::smoke_available()
+{
+	return init();
+}
+
+bool opengl46_gpu_particles::precipitation_available()
+{
+	return init();
+}
+
+void opengl46_gpu_particles::clear()
+{
+	m_pool.clear();
+	m_requested.clear();
+	m_poolfull = false;
+	m_sourcerecords.clear();
+	m_places = 0;
+	m_particles.reset();
+	m_sources.reset();
+	m_owners.reset();
+	m_smokeoutput.reset();
+	m_precipitationoutput.reset();
+	m_precipitationcapacity = 0;
+	m_originset = false;
+	m_lastupdate = 0;
+}
+
+void opengl46_gpu_particles::layout(particle_manager &Particles)
+{
+	auto const &sources{Particles.sequence()};
+	// the sources already laid out which asked for the same places since
+	std::size_t kept{0};
+	while ((kept < m_requested.size()) && (kept < sources.size()) && (m_requested[kept] == sources[kept].max_particles()))
+		++kept;
+	if ((kept == m_requested.size()) && (kept == sources.size()) && m_particles)
+		return;
+	if (kept < m_requested.size())
+	{
+		// a source went away or changed: all anew
+		kept = 0;
+		m_pool.clear();
+		m_requested.clear();
+		m_places = 0;
+		m_poolfull = false;
+	}
+	auto const oldplaces{m_places};
+
+	auto first{m_places};
+	m_pool.resize(sources.size());
+	m_requested.resize(sources.size());
+	for (std::size_t i = kept; i < sources.size(); ++i)
+	{
+		m_requested[i] = sources[i].max_particles();
+		auto const size{static_cast<std::uint32_t>(std::min<std::size_t>(m_requested[i], MAX_SMOKE_PLACES))};
+		m_pool[i] = pool_source{};
+		if (first + size > MAX_SMOKE_PLACES)
+		{
+			if (false == m_poolfull)
+				WriteLog("particles: the smoke of some sources left out, over " + std::to_string(MAX_SMOKE_PLACES) + " places of particles");
+			m_poolfull = true;
+			continue;
+		}
+		m_pool[i].first = first;
+		m_pool[i].size = size;
+		first += size;
+	}
+	m_places = first;
+
+	std::vector<std::uint32_t> owners(std::max<std::uint32_t>(m_places, 1), 0);
+	for (std::size_t i = 0; i < m_pool.size(); ++i)
+		std::fill_n(owners.begin() + m_pool[i].first, m_pool[i].size, static_cast<std::uint32_t>(i));
+
+	auto const places{static_cast<GLsizeiptr>(std::max<std::uint32_t>(m_places, 1))};
+	// the particles of the places kept go over to the new storage, the new places are dead
+	auto particles{std::make_unique<gl::ssbo>(places * static_cast<GLsizeiptr>(sizeof(gl::particle_smoke)), gl::PARTICLE_SSBO_BINDING)};
+	::glClearNamedBufferData(*particles, GL_R32UI, GL_RED_INTEGER, GL_UNSIGNED_INT, nullptr);
+	if (m_particles && (oldplaces > 0) && (kept > 0))
+		::glCopyNamedBufferSubData(*m_particles, *particles, 0, 0, static_cast<GLsizeiptr>(oldplaces) * static_cast<GLsizeiptr>(sizeof(gl::particle_smoke)));
+	m_particles = std::move(particles);
+
+	auto const ensure = [](std::unique_ptr<gl::ssbo> &Buffer, GLsizeiptr const Size, GLuint const Binding) {
+		if (!Buffer)
+			Buffer = std::make_unique<gl::ssbo>(Size, Binding);
+		else
+			Buffer->resize(Size);
+	};
+	ensure(m_owners, places * static_cast<GLsizeiptr>(sizeof(std::uint32_t)), gl::PARTICLE_OWNER_SSBO_BINDING);
+	ensure(m_smokeoutput, places * static_cast<GLsizeiptr>(sizeof(gl::particle_draw)), gl::PARTICLE_OUTPUT_SSBO_BINDING);
+	ensure(m_sources, static_cast<GLsizeiptr>(std::max<std::size_t>(sources.size(), 1) * sizeof(gl::particle_smoke_source)), gl::PARTICLE_SOURCE_SSBO_BINDING);
+	m_owners->update(owners.data(), 0, static_cast<GLsizeiptr>(owners.size() * sizeof(std::uint32_t)));
+	m_sourcerecords.resize(sources.size(), gl::particle_smoke_source{});
+}
+
+void opengl46_gpu_particles::simulate_smoke(particle_manager &Particles, glm::dvec3 const &Camera)
+{
+	if (false == init())
+		return;
+	layout(Particles);
+	if (Particles.updates() == m_lastupdate)
+		return;
+	m_lastupdate = Particles.updates();
+	if (m_places == 0)
+		return;
+
+	// the origin of the positions near the camera; when it moves, the particles move by as much the other way
+	glm::vec3 shift{0.f};
+	auto const snapped{glm::floor(Camera / ORIGIN_STEP) * ORIGIN_STEP};
+	if (false == m_originset)
+	{
+		m_origin = snapped;
+		m_originset = true;
+	}
+	else if (glm::length(Camera - m_origin) > ORIGIN_REACH)
+	{
+		shift = glm::vec3{m_origin - snapped};
+		m_origin = snapped;
+	}
+
+	// the light of the smoke as the cpu works it out, for gfx.smoke.lighting off
+	auto const oldlight{(glm::vec3{Global.DayLight.ambient} + 0.35f * glm::vec3{Global.DayLight.diffuse}) * simulation::Environment.light_intensity()};
+	auto const &sources{Particles.sequence()};
+	m_smokealive = 0;
+	for (std::size_t i = 0; i < sources.size(); ++i)
+	{
+		auto const &state{sources[i].gpu()};
+		auto &pool{m_pool[i]};
+		auto &record{m_sourcerecords[i]};
+		auto const spawns{(pool.size > 0) ? std::min(state.spawns, pool.size) : 0u};
+		record.pool = glm::uvec4{pool.first, pool.size, pool.head, spawns};
+		record.location = glm::vec4{glm::vec3{state.location - m_origin}, 0.f};
+		record.previous = glm::vec4{glm::vec3{state.previous - m_origin}, 0.f};
+		record.launch = glm::vec4{state.inclination[0], state.inclination[1], state.velocity[0], state.velocity[1]};
+		record.initial = glm::vec4{state.size[0], state.size[1], state.opacity[0], state.opacity[1]};
+		record.sizechange = glm::vec4{state.sizechange[0], state.sizechange[1], state.sizechange[2], 0.f};
+		record.opacitychange = glm::vec4{state.opacitychange[0], state.opacitychange[1], state.opacitychange[2], 0.f};
+		record.motion = glm::vec4{state.rise, state.damping, state.risemin, 0.f};
+		record.color = glm::vec4{glm::clamp(state.color, glm::vec3{0.f}, glm::vec3{1.f}), 0.f};
+		record.oldcolor = glm::vec4{glm::clamp(state.color * oldlight, glm::vec3{0.f}, glm::vec3{1.f}), 0.f};
+		if (pool.size > 0)
+		{
+			pool.head = (pool.head + spawns) % pool.size;
+			if (spawns > 0)
+				m_smokealive += pool.size;
+		}
+	}
+	if (false == m_sourcerecords.empty())
+		m_sources->update(m_sourcerecords.data(), 0, static_cast<GLsizeiptr>(m_sourcerecords.size() * sizeof(gl::particle_smoke_source)));
+
+	m_simulatetimer.begin();
+	m_particles->bind_base();
+	m_sources->bind_base();
+	m_owners->bind_base();
+	auto const wind{glm::vec3{simulation::Environment.wind()}};
+	auto &program{*m_smokesimulate};
+	::glProgramUniform1ui(program, 0, m_places);
+	::glProgramUniform4f(program, 1, static_cast<float>(Particles.timedelta()), shift.x, shift.y, shift.z);
+	::glProgramUniform4f(program, 2, wind.x, wind.y, wind.z, 0.f);
+	::glProgramUniform1ui(program, 3, static_cast<GLuint>(m_lastupdate));
+	program.dispatch(groups(m_places));
+	::glMemoryBarrier(GL_SHADER_STORAGE_BARRIER_BIT);
+	m_simulatetimer.end();
+}
+
+std::array<glm::vec4, 5> opengl46_gpu_particles::planes(view const &View)
+{
+	// the sides and the near side of the clip space, w >= 0 (the far plane is at infinity)
+	auto const matrix{glm::transpose(View.projection * View.modelview)};
+	std::array<glm::vec4, 5> result{matrix[3] + matrix[0], matrix[3] - matrix[0], matrix[3] + matrix[1], matrix[3] - matrix[1], matrix[3]};
+	for (auto &plane : result)
+	{
+		auto const length{glm::length(glm::vec3{plane})};
+		if (length > 0.f)
+			plane /= length;
+	}
+	return result;
+}
+
+void opengl46_gpu_particles::collect(gl::readback &Readback, std::size_t &Drawn)
+{
+	GLuint command[4];
+	if (Readback.pop(command))
+		Drawn = command[1];
+}
+
+void opengl46_gpu_particles::draw(GLuint const Output, GLuint const Command, gl::program &Program)
+{
+	auto const culling{::glIsEnabled(GL_CULL_FACE) == GL_TRUE};
+	if (culling)
+		::glDisable(GL_CULL_FACE);
+	Program.bind();
+	// the vertex array is bound behind the back of gl::vao, which is told nothing is bound afterwards
+	gl::vao::unbind();
+	::glVertexArrayVertexBuffer(m_vao, 0, Output, 0, sizeof(gl::particle_draw));
+	::glBindVertexArray(m_vao);
+	::glBindBuffer(GL_DRAW_INDIRECT_BUFFER, Command);
+	::glDrawArraysIndirect(GL_TRIANGLE_STRIP, nullptr);
+	::glBindBuffer(GL_DRAW_INDIRECT_BUFFER, 0);
+	gl::vao::unbind();
+	gl::program::unbind();
+	if (culling)
+		::glEnable(GL_CULL_FACE);
+}
+
+std::size_t opengl46_gpu_particles::render_smoke(view const &View)
+{
+	if ((false == init()) || (m_places == 0))
+		return 0;
+	collect(*m_smokereadback, m_smokedrawn);
+
+	m_smoketimer.begin();
+	GLuint const command[4]{4, 0, 0, 0};
+	m_smokecommand->update(command, 0, sizeof(command));
+	m_particles->bind_base();
+	m_sources->bind_base();
+	m_owners->bind_base();
+	m_smokeoutput->bind_base();
+	m_smokecommand->bind_base();
+	auto &program{*m_smokeprepare};
+	auto const origin{glm::vec3{m_origin - View.camera}};
+	auto const viewplanes{planes(View)};
+	::glProgramUniform1ui(program, 0, m_places);
+	::glProgramUniform3f(program, 1, origin.x, origin.y, origin.z);
+	::glProgramUniformMatrix4fv(program, 2, 1, GL_FALSE, glm::value_ptr(View.modelview));
+	::glProgramUniform4f(program, 3, Global.gfx_smoke_lighting ? 1.f : 0.f, SMOKE_FORWARD, static_cast<float>(m_places), 0.f);
+	::glProgramUniform4fv(program, 4, 5, glm::value_ptr(viewplanes[0]));
+	program.dispatch(groups(m_places));
+	::glMemoryBarrier(GL_COMMAND_BARRIER_BIT | GL_VERTEX_ATTRIB_ARRAY_BARRIER_BIT | GL_BUFFER_UPDATE_BARRIER_BIT);
+
+	::glProgramUniform4f(*m_smokedraw, 0, View.soft ? Global.gfx_particles_soft : 0.f, 0.f, 0.f, 0.f);
+	draw(*m_smokeoutput, *m_smokecommand, *m_smokedraw);
+	m_smoketimer.end();
+
+	m_smokereadback->push(*m_smokecommand);
+	return m_smokedrawn;
+}
+
+std::size_t opengl46_gpu_particles::render_precipitation(view const &View, bool const Snow, float const Intensity, unsigned int const Frame)
+{
+	if (false == init())
+		return 0;
+	collect(*m_precipitationreadback, m_precipitationdrawn);
+
+	auto const &kind{Snow ? SNOW : RAIN};
+	// once per frame: the time moves on, the particles drift with the wind and fall, the camera has its velocity
+	if ((false == m_framestarted) || (Frame != m_frame))
+	{
+		m_framestarted = true;
+		m_frame = Frame;
+		auto const seconds{Timer::GetDeltaTime()};
+		if (seconds > 0.0)
+		{
+			auto const wind{glm::dvec3{simulation::Environment.wind()} * WIND_SHARE};
+			for (std::size_t box = 0; box < BOX_SIZE.size(); ++box)
+			{
+				auto const size{static_cast<double>(BOX_SIZE[box])};
+				m_drift[box] = glm::mod(m_drift[box] + wind * seconds, size);
+				m_fall[box] = std::fmod(m_fall[box] + kind.fall * seconds, 16.0 * size);
+			}
+			m_time = std::fmod(m_time + seconds, 3600.0);
+			if (m_camerastarted)
+			{
+				auto const velocity{(View.camera - m_lastcamera) / seconds};
+				if (glm::length(velocity) < CAMERA_JUMP)
+					m_cameravelocity = glm::mix(m_cameravelocity, velocity, 1.0 - std::exp(-10.0 * seconds));
+			}
+		}
+		m_lastcamera = View.camera;
+		m_camerastarted = true;
+	}
+
+	// the particles, more of them in heavier rain or snow
+	auto const most{static_cast<std::uint32_t>(std::max(Global.gfx_precipitation_particles, 0))};
+	auto const count{static_cast<std::uint32_t>(most * std::clamp(0.15f + 0.85f * Intensity, 0.f, 1.f))};
+	m_precipitationcount = count;
+	m_precipitationsnow = Snow;
+	if (count == 0)
+		return 0;
+	if (m_precipitationcapacity < count)
+	{
+		m_precipitationcapacity = std::max(count, most);
+		auto const size{static_cast<GLsizeiptr>(m_precipitationcapacity) * static_cast<GLsizeiptr>(sizeof(gl::particle_draw))};
+		if (!m_precipitationoutput)
+			m_precipitationoutput = std::make_unique<gl::ssbo>(size, gl::PARTICLE_OUTPUT_SSBO_BINDING);
+		else
+			m_precipitationoutput->resize(size);
+	}
+
+	m_precipitationtimer.begin();
+	GLuint const command[4]{4, 0, 0, 0};
+	m_precipitationcommand->update(command, 0, sizeof(command));
+	m_precipitationoutput->bind_base();
+	m_precipitationcommand->bind_base();
+	auto &program{*m_precipitationprepare};
+	auto const second{static_cast<std::uint32_t>(count * BOX_SHARE[0])};
+	auto const third{static_cast<std::uint32_t>(count * (BOX_SHARE[0] + BOX_SHARE[1]))};
+	::glProgramUniform4ui(program, 0, second, third, count, Snow ? 1u : 0u);
+	std::array<glm::vec4, 3> offsets;
+	for (std::size_t box = 0; box < BOX_SIZE.size(); ++box)
+	{
+		auto const size{static_cast<double>(BOX_SIZE[box])};
+		offsets[box] = glm::vec4{glm::vec3{glm::mod(m_drift[box] - glm::mod(View.camera, size), size)}, static_cast<float>(m_fall[box])};
+	}
+	::glProgramUniform4fv(program, 1, 3, glm::value_ptr(offsets[0]));
+	::glProgramUniform4f(program, 4, BOX_SIZE[0], BOX_SIZE[1], BOX_SIZE[2], 0.f);
+	auto const velocity{glm::vec3{glm::dvec3{simulation::Environment.wind()} * WIND_SHARE - m_cameravelocity}};
+	::glProgramUniform4f(program, 5, velocity.x, velocity.y, velocity.z, kind.fall);
+	::glProgramUniform4f(program, 6, static_cast<float>(m_time), kind.exposure, kind.opacity, static_cast<float>(m_precipitationcapacity));
+	::glProgramUniformMatrix4fv(program, 7, 1, GL_FALSE, glm::value_ptr(View.modelview));
+	::glProgramUniform4f(program, 11, 1.f, kind.forward, kind.brightness, 0.f);
+	auto const viewplanes{planes(View)};
+	::glProgramUniform4fv(program, 12, 5, glm::value_ptr(viewplanes[0]));
+	program.dispatch(groups(count));
+	::glMemoryBarrier(GL_COMMAND_BARRIER_BIT | GL_VERTEX_ATTRIB_ARRAY_BARRIER_BIT | GL_BUFFER_UPDATE_BARRIER_BIT);
+
+	// the width of a pixel a metre in front of the camera, for the least width of a streak
+	auto const pixel{(View.height > 0) && (View.projection[1][1] != 0.f) ? 2.f / (std::abs(View.projection[1][1]) * static_cast<float>(View.height)) : 0.f};
+	::glProgramUniform4f(*m_precipitationdraw, 0, View.soft ? 0.25f * Global.gfx_particles_soft : 0.f, 0.f, 0.f, 0.f);
+	::glProgramUniform4f(*m_precipitationdraw, 1, pixel, 0.f, 0.f, 0.f);
+	draw(*m_precipitationoutput, *m_precipitationcommand, *m_precipitationdraw);
+	m_precipitationtimer.end();
+
+	m_precipitationreadback->push(*m_precipitationcommand);
+	return m_precipitationdrawn;
+}
+
+std::string opengl46_gpu_particles::info() const
+{
+	if (m_state <= 0)
+		return {};
+	std::string text;
+	if (m_places > 0)
+		text += " smoke of the gpu: " + std::to_string(m_smokedrawn) + " drawn, " + std::to_string(m_places) + " places of " + std::to_string(m_pool.size()) + " sources ("
+		        + std::to_string(m_smokealive) + " of the ones which bore lately)" + (m_poolfull ? ", some sources left out" : "") + "\n";
+	if (m_precipitationcount > 0)
+		text += std::string(" ") + (m_precipitationsnow ? "snow" : "rain") + " of the gpu: " + std::to_string(m_precipitationdrawn) + " of " + std::to_string(m_precipitationcount)
+		        + " drawn\n";
+	return text;
+}
+
+std::string opengl46_gpu_particles::info_times()
+{
+	std::string text;
+	auto const add = [&text](gl::gpu_timer &Timer, char const *Name) {
+		if (auto const time = Timer.result())
+			text += std::string(text.empty() ? " particles:" : ",") + " " + Name + " " + to_string(static_cast<double>(*time) / 1000000.0, 3) + " ms";
+	};
+	if (m_places > 0)
+	{
+		add(m_simulatetimer, "smoke simulation");
+		add(m_smoketimer, "smoke");
+	}
+	if (m_precipitationcount > 0)
+		add(m_precipitationtimer, m_precipitationsnow ? "snow" : "rain");
+	if (false == text.empty())
+		text += "\n";
+	return text;
+}
--- a/rendering/opengl46/opengl46gpuparticles.h
+++ b/rendering/opengl46/opengl46gpuparticles.h
@@ -0,0 +1,137 @@
+/*
+This Source Code Form is subject to the
+terms of the Mozilla Public License, v.
+2.0. If a copy of the MPL was not
+distributed with this file, You can
+obtain one at
+http://mozilla.org/MPL/2.0/.
+*/
+
+#pragma once
+
+#include <array>
+#include <memory>
+#include <string>
+#include <vector>
+#include <glm/glm.hpp>
+
+#include "gl/shader.h"
+#include "gl/ssbo.h"
+#include "gl/ubo.h"
+#include "gl/query.h"
+#include "gl/readback.h"
+
+class particle_manager;
+
+// particles of the gpu for the opengl 4.6 renderer: the smoke and the rain or snow.
+//
+// smoke: the sources (particle_manager in its gpu mode) work out on the cpu only how many particles they bear in an update of
+// the simulation and what these start from; the particles are kept in a storage buffer, a ring of places for each source, and
+// simulated by a compute pass once per update (particles_smoke_simulate.comp). in every colour pass which draws them another
+// compute pass (particles_smoke_prepare.comp) leaves out the dead ones and the ones out of the view, lights the rest with the
+// lights of the pass and adds them to an indirect draw of billboards (particles_smoke.vert/.frag).
+//
+// rain and snow: particles in three boxes around the camera, each repeated along the world axes, which keep no state: their
+// place follows from their number, how far the wind took them and how far they fell (particles_precipitation.comp), drawn as
+// streaks of their motion against the camera (particles_precipitation.vert/.frag).
+//
+// the positions of the smoke are kept from an origin near the camera, moved by whole steps as the camera goes, so they keep
+// their precision far from the centre of the scenery
+class opengl46_gpu_particles
+{
+  public:
+	opengl46_gpu_particles() = default;
+	~opengl46_gpu_particles();
+	opengl46_gpu_particles(opengl46_gpu_particles const &) = delete;
+	opengl46_gpu_particles &operator=(opengl46_gpu_particles const &) = delete;
+
+	// what a colour pass draws with
+	struct view
+	{
+		glm::mat4 modelview; // world axes around the camera to the view space of the pass
+		glm::mat4 projection;
+		glm::dvec3 camera;
+		int height{0}; // of the target, pixels
+		bool soft{false}; // the resolved depth of the scene drawn so far is bound to gl::SCENE_DEPTH_TEX
+	};
+
+	// whether the programs could be made; without them the smoke stays on the cpu and the rain is the old cylinder
+	bool smoke_available();
+	bool precipitation_available();
+	// once per update of the particle manager (in its gpu mode): the births and the change of the smoke. Camera: of the view
+	void simulate_smoke(particle_manager &Particles, glm::dvec3 const &Camera);
+	// draws the smoke the view sees, with the texture bound to unit 0. returns: particles drawn, as read back a few frames later
+	std::size_t render_smoke(view const &View);
+	// draws the rain (Snow false) or the snow of the intensity 0-1. Frame: number of the frame, the time moves on once per frame.
+	// returns: particles drawn, read back
+	std::size_t render_precipitation(view const &View, bool Snow, float Intensity, unsigned int Frame);
+	// drops what is on the gpu, e.g. when the context goes
+	void clear();
+
+	std::string info() const;
+	std::string info_times();
+
+  private:
+	struct pool_source
+	{
+		std::uint32_t first{0};
+		std::uint32_t size{0};
+		std::uint32_t head{0};
+	};
+
+	bool init();
+	// the places of the sources in the storage: sources added after the others get theirs after the places already given, and
+	// the particles stay; otherwise all is laid out anew
+	void layout(particle_manager &Particles);
+	// reads back the instances counted by a pass; Drawn is left as it was when nothing came back yet
+	static void collect(gl::readback &Readback, std::size_t &Drawn);
+	// the planes of the view of the pass, for the culling of the compute passes
+	static std::array<glm::vec4, 5> planes(view const &View);
+	void draw(GLuint Output, GLuint Command, gl::program &Program);
+
+	int m_state{0}; // 0: not set up yet, 1: ready, -1: can't be used
+	std::unique_ptr<gl::program> m_smokesimulate;
+	std::unique_ptr<gl::program> m_smokeprepare;
+	std::unique_ptr<gl::program> m_smokedraw;
+	std::unique_ptr<gl::program> m_precipitationprepare;
+	std::unique_ptr<gl::program> m_precipitationdraw;
+	GLuint m_vao{0}; // the attributes of the instances, from the buffer of the draw bound to it before the draw
+
+	// smoke
+	std::vector<pool_source> m_pool;
+	std::vector<std::size_t> m_requested; // the sizes the sources asked for
+	std::vector<gl::particle_smoke_source> m_sourcerecords;
+	std::uint32_t m_places{0};
+	bool m_poolfull{false}; // some sources got no places
+	std::unique_ptr<gl::ssbo> m_particles;
+	std::unique_ptr<gl::ssbo> m_sources;
+	std::unique_ptr<gl::ssbo> m_owners;
+	std::unique_ptr<gl::ssbo> m_smokeoutput;
+	std::unique_ptr<gl::ssbo> m_smokecommand;
+	std::unique_ptr<gl::readback> m_smokereadback;
+	std::uint64_t m_lastupdate{0};
+	glm::dvec3 m_origin{0.0};
+	bool m_originset{false};
+	std::size_t m_smokedrawn{0};
+	std::size_t m_smokealive{0}; // places of the sources which bore particles lately
+	gl::gpu_timer m_simulatetimer;
+	gl::gpu_timer m_smoketimer;
+
+	// rain and snow
+	std::unique_ptr<gl::ssbo> m_precipitationoutput;
+	std::unique_ptr<gl::ssbo> m_precipitationcommand;
+	std::unique_ptr<gl::readback> m_precipitationreadback;
+	std::uint32_t m_precipitationcapacity{0};
+	unsigned int m_frame{0};
+	bool m_framestarted{false};
+	std::array<glm::dvec3, 3> m_drift{}; // how far the wind took the particles of each box, within the box
+	std::array<double, 3> m_fall{}; // how far they fell, within 16 sizes of the box
+	double m_time{0.0}; // seconds, for the flutter of the flakes
+	glm::dvec3 m_lastcamera{0.0};
+	glm::dvec3 m_cameravelocity{0.0};
+	bool m_camerastarted{false};
+	std::size_t m_precipitationdrawn{0};
+	std::uint32_t m_precipitationcount{0};
+	bool m_precipitationsnow{false};
+	gl::gpu_timer m_precipitationtimer;
+};
--- a/rendering/opengl46/opengl46renderer.cpp
+++ b/rendering/opengl46/opengl46renderer.cpp
@@ -865,6 +865,7 @@ void opengl46_renderer::SwapBuffers()
    m_debugtimestext += m_localshadows.info_times();
    if( Global.gfx_shadow_sdsm )
        m_debugtimestext += m_shadowfit.info_times();
+    m_debugtimestext += m_gpuparticles.info_times();
    m_debugtimestext += "uilayer: " + to_string( Timer::subsystem.gfx_gui.average(), 2 ) + " ms\n";
    if( DebugModeFlag )
        m_debugtimestext += m_textures.info();
@@ -964,6 +965,7 @@ void opengl46_renderer::SwapBuffers()
        + ( Global.gfx_lights_clustered ? "clustered" : "first " + std::to_string( std::max( Global.DynamicLightCount, 0 ) ) )
        + "\n" + m_locallights.info()
        + m_localshadows.info()
+        + m_gpuparticles.info()
        + m_instancecull.info();
    if( Global.gfx_gpucull_shadows ) {
        for( std::size_t cascade = 0; cascade < m_shadowcull.size(); ++cascade ) {
@@ -1062,6 +1064,21 @@ void opengl46_renderer::draw_debug_ui()
    }
    ImGui::End();

+    if (ImGui::Begin("Particles"))
+    {
+        ImGui::Checkbox("smoke simulated and drawn on the gpu (gfx.smoke.gpu)", &Global.gfx_smoke_gpu);
+        if (Global.gfx_smoke_gpu)
+            ImGui::Checkbox("smoke lit by the sun, the sky and the lamps (gfx.smoke.lighting)", &Global.gfx_smoke_lighting);
+        ImGui::Checkbox("rain and snow as particles of the gpu (gfx.precipitation.gpu)", &Global.gfx_precipitation_gpu);
+        if (Global.gfx_precipitation_gpu)
+            ImGui::SliderInt("particles of the heaviest rain or snow (gfx.precipitation.particles)", &Global.gfx_precipitation_particles, 0, 262144);
+        ImGui::SliderFloat("soft particles, share of their size, 0: off (gfx.particles.soft)", &Global.gfx_particles_soft, 0.f, 4.f, "%.2f");
+        auto const info{m_gpuparticles.info()};
+        if (!info.empty())
+            ImGui::TextUnformatted(info.c_str() + 1);
+    }
+    ImGui::End();
+
    if (ImGui::Begin("Sky and exposure"))
    {
        m_sky.draw_debug_ui();
@@ -1464,6 +1481,12 @@ void opengl46_renderer::Render_pass(viewport_config &vp, rendermode const Mode)
 		Render_Alpha(simulation::Region);
 		Render_editor_overlay();

+		// the depth drawn so far, which the particles of the gpu fade in front of
+		m_particlesoft =
+			( Global.gfx_particles_soft > 0.f )
+			&& ( ( Global.Smoke && Global.gfx_smoke_gpu && ( false == simulation::Particles.sequence().empty() ) ) || ( Global.gfx_precipitation_gpu && ( Global.Overcast > 1.f ) ) )
+			&& Setup_Particles_Depth( vp );
+
 		// particles
 		Render_particles();

@@ -6897,10 +6920,59 @@ void opengl46_renderer::Render_particles()
 	model_ubo->update(model_ubs);

 	Bind_Texture(0, m_smoketexture);
+	// the smoke of the gpu, when its programs could be made; otherwise the particle manager simulates it on the cpu. a switch
+	// takes effect from the next update of the manager
+	auto const gpu{Global.gfx_smoke_gpu && m_gpuparticles.smoke_available()};
+	simulation::Particles.gpu(gpu);
+	if (gpu)
+	{
+		if (Global.Smoke)
+		{
+			m_gpuparticles.simulate_smoke(simulation::Particles, m_renderpass.pass_camera.position());
+			m_renderpass.draw_stats.particles = static_cast<int>(m_gpuparticles.render_smoke(Particles_View()));
+		}
+		return;
+	}
 	m_particlerenderer.update(m_renderpass.pass_camera);
    m_renderpass.draw_stats.particles = m_particlerenderer.render();
 }

+opengl46_gpu_particles::view opengl46_renderer::Particles_View() const
+{
+	GLint viewport[4];
+	::glGetIntegerv(GL_VIEWPORT, viewport);
+	opengl46_gpu_particles::view view;
+	view.modelview = OpenGLMatrices.data(GL_MODELVIEW);
+	view.projection = OpenGLMatrices.data(GL_PROJECTION);
+	view.camera = m_renderpass.pass_camera.position();
+	view.height = viewport[3];
+	view.soft = m_particlesoft;
+	return view;
+}
+
+bool opengl46_renderer::Setup_Particles_Depth(viewport_config &Viewport)
+{
+	// the fading works out the distance from the depth as the contact shadows do (Contact_Shadows_Wanted())
+	if (Global.gfx_skippipeline || Global.bWireFrame || (Viewport.msaa_fb == nullptr))
+		return false;
+	auto const &projection{scene_ubs.projection};
+	if ((projection[2][3] == 0.f) || (projection[2][2] != 0.f) || (projection[3][2] <= 0.f))
+		return false;
+	if (false == Resolved_Depth_Target(Viewport))
+		return false;
+	// making the target binds it
+	Viewport.msaa_fb->bind();
+	// the scissor test would limit the blit
+	auto const scissor{::glIsEnabled(GL_SCISSOR_TEST) == GL_TRUE};
+	if (scissor)
+		::glDisable(GL_SCISSOR_TEST);
+	::glBlitNamedFramebuffer(*Viewport.msaa_fb, *Viewport.clusters_depth_fb, 0, 0, Viewport.width, Viewport.height, 0, 0, Viewport.width, Viewport.height, GL_DEPTH_BUFFER_BIT, GL_NEAREST);
+	if (scissor)
+		::glEnable(GL_SCISSOR_TEST);
+	::glBindTextureUnit(gl::SCENE_DEPTH_TEX, Viewport.clusters_depth_tex->id);
+	return true;
+}
+
 void opengl46_renderer::Render_vr_models()
 {
    if (!vr)
@@ -6927,6 +6999,15 @@ void opengl46_renderer::Render_precipitation()
 		return;
 	}

+	if (Global.gfx_precipitation_gpu && m_gpuparticles.precipitation_available())
+	{
+		// the particles of the gpu: the overcast above 1 is how heavy the rain or snow is
+		model_ubs.set_modelview(OpenGLMatrices.data(GL_MODELVIEW));
+		model_ubo->update(model_ubs);
+		m_gpuparticles.render_precipitation(Particles_View(), Global.Weather == "snow:", std::clamp(Global.Overcast - 1.f, 0.f, 1.f), m_framestamp);
+		return;
+	}
+
 	::glPushMatrix();
 	// tilt the precipitation cone against the velocity vector for crude motion blur
 	// include current wind vector while at it
--- a/rendering/opengl46/opengl46renderer.h
+++ b/rendering/opengl46/opengl46renderer.h
@@ -13,6 +13,7 @@ http://mozilla.org/MPL/2.0/.
 #include "rendering/openglcamera.h"
 #include "rendering/opengl46/opengl46light.h"
 #include "rendering/opengl46/opengl46particles.h"
+#include "rendering/opengl46/opengl46gpuparticles.h"
 #include "rendering/opengl46/opengl46skydome.h"
 #include "rendering/opengl46/opengl46precipitation.h"
 #include "simulation/simulationenvironment.h"
@@ -447,6 +448,9 @@ class opengl46_renderer : public gfx_renderer {
 	void Setup_Contact_Shadows( viewport_config &Viewport );
 	// makes the target of the resolved depth of the viewport if it isn't there yet; false if it can't be made
 	bool Resolved_Depth_Target( viewport_config &Viewport );
+	// resolves the depth drawn so far in the colour pass of the viewport for the soft particles (gfx.particles.soft) and binds it
+	// to gl::SCENE_DEPTH_TEX; false when the viewport has no such depth
+	bool Setup_Particles_Depth( viewport_config &Viewport );
 	// the direction the sun shadows are cast in (the sun, its height capped by gfx.shadow.angle.min), and the rotation from
 	// the world to the space of the light of the cascades: x and y across the maps, z along the light
 	glm::vec3 Shadow_Light_Vector() const;
@@ -495,6 +499,8 @@ class opengl46_renderer : public gfx_renderer {
 	void Render(TMemCell *Memcell);
 	void Render_particles();
 	void Render_precipitation();
+	// the view of the colour pass being drawn, for the particles of the gpu
+	opengl46_gpu_particles::view Particles_View() const;
 	// the grass of the heightmap terrain around the camera of the main view; Future: the matrix of the motion vectors
 	void Render_grass(glm::mat4 const &Future);
  void Render_vr_models();
@@ -588,6 +594,8 @@ class opengl46_renderer : public gfx_renderer {
    opengl46_skydome m_skydomerenderer;
    opengl46_precipitation m_precipitationrenderer;
    opengl46_particles m_particlerenderer; // particle visualization subsystem
+    opengl46_gpu_particles m_gpuparticles; // the smoke, rain and snow of the gpu (gfx.smoke.gpu, gfx.precipitation.gpu)
+    bool m_particlesoft{false}; // the depth for the soft particles is bound in the colour pass being drawn

 	unsigned int m_framestamp; // id of currently rendered gfx frame
 	float m_framerate;