src/dawn/samples/ComputeBoids.cpp - dawn - Git at Google

 // Copyright 2017 The Dawn & Tint Authors
 //
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are met:
 //
 // 1. Redistributions of source code must retain the above copyright notice, this
 //    list of conditions and the following disclaimer.
 //
 // 2. Redistributions in binary form must reproduce the above copyright notice,
 //    this list of conditions and the following disclaimer in the documentation
 //    and/or other materials provided with the distribution.
 //
 // 3. Neither the name of the copyright holder nor the names of its
 //    contributors may be used to endorse or promote products derived from
 //    this software without specific prior written permission.
 //
 // THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
 // AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 // IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
 // DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
 // FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 // DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
 // SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
 // CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
 // OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
 // OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.

 #include <array>
 #include <cstring>
 #include <random>
 #include <vector>

 #include "dawn/samples/SampleUtils.h"

 #include "dawn/utils/ComboRenderPipelineDescriptor.h"
 #include "dawn/utils/SystemUtils.h"
 #include "dawn/utils/WGPUHelpers.h"

 wgpu::Device device;
 wgpu::Queue queue;
 wgpu::SwapChain swapchain;
 wgpu::TextureView depthStencilView;

 wgpu::Buffer modelBuffer;
 std::array<wgpu::Buffer, 2> particleBuffers;

 wgpu::RenderPipeline renderPipeline;

 wgpu::Buffer updateParams;
 wgpu::ComputePipeline updatePipeline;
 std::array<wgpu::BindGroup, 2> updateBGs;

 size_t pingpong = 0;

 static const uint32_t kNumParticles = 1024;

 struct Particle {
     std::array<float, 2> pos;
     std::array<float, 2> vel;
 };

 struct SimParams {
     float deltaT;
     float rule1Distance;
     float rule2Distance;
     float rule3Distance;
     float rule1Scale;
     float rule2Scale;
     float rule3Scale;
     int particleCount;
 };

 void initBuffers() {
     std::array<std::array<float, 2>, 3> model = {{
         {-0.01, -0.02},
         {0.01, -0.02},
         {0.00, 0.02},
     }};
     modelBuffer =
         dawn::utils::CreateBufferFromData(device, &model, sizeof(model), wgpu::BufferUsage::Vertex);

     SimParams params = {0.04f, 0.1f, 0.025f, 0.025f, 0.02f, 0.05f, 0.005f, kNumParticles};
     updateParams = dawn::utils::CreateBufferFromData(device, &params, sizeof(params),
                                                      wgpu::BufferUsage::Uniform);

     std::vector<Particle> initialParticles(kNumParticles);
     {
         std::mt19937 generator;
         std::uniform_real_distribution<float> dist(-1.0f, 1.0f);
         for (auto& p : initialParticles) {
             p.pos = {dist(generator), dist(generator)};
             p.vel = {dist(generator) * 0.1f, dist(generator) * 0.1f};
         }
     }

     for (size_t i = 0; i < 2; i++) {
         wgpu::BufferDescriptor descriptor;
         descriptor.size = sizeof(Particle) * kNumParticles;
         descriptor.usage =
             wgpu::BufferUsage::CopyDst | wgpu::BufferUsage::Vertex | wgpu::BufferUsage::Storage;
         particleBuffers[i] = device.CreateBuffer(&descriptor);

         queue.WriteBuffer(particleBuffers[i], 0,
                           reinterpret_cast<uint8_t*>(initialParticles.data()),
                           sizeof(Particle) * kNumParticles);
     }
 }

 void initRender() {
     wgpu::ShaderModule vsModule = dawn::utils::CreateShaderModule(device, R"(
         struct VertexIn {
             @location(0) a_particlePos : vec2f,
             @location(1) a_particleVel : vec2f,
             @location(2) a_pos : vec2f,
         };

         @vertex
         fn main(input : VertexIn) -> @builtin(position) vec4f {
             var angle : f32 = -atan2(input.a_particleVel.x, input.a_particleVel.y);
             var pos : vec2f = vec2f(
                 (input.a_pos.x * cos(angle)) - (input.a_pos.y * sin(angle)),
                 (input.a_pos.x * sin(angle)) + (input.a_pos.y * cos(angle)));
             return vec4f(pos + input.a_particlePos, 0.0, 1.0);
         }
     )");

     wgpu::ShaderModule fsModule = dawn::utils::CreateShaderModule(device, R"(
         @fragment
         fn main() -> @location(0) vec4f {
             return vec4f(1.0, 1.0, 1.0, 1.0);
         }
     )");

     depthStencilView = CreateDefaultDepthStencilView(device);

     dawn::utils::ComboRenderPipelineDescriptor descriptor;

     descriptor.vertex.module = vsModule;
     descriptor.vertex.bufferCount = 2;
     descriptor.cBuffers[0].arrayStride = sizeof(Particle);
     descriptor.cBuffers[0].stepMode = wgpu::VertexStepMode::Instance;
     descriptor.cBuffers[0].attributeCount = 2;
     descriptor.cAttributes[0].offset = offsetof(Particle, pos);
     descriptor.cAttributes[0].format = wgpu::VertexFormat::Float32x2;
     descriptor.cAttributes[1].shaderLocation = 1;
     descriptor.cAttributes[1].offset = offsetof(Particle, vel);
     descriptor.cAttributes[1].format = wgpu::VertexFormat::Float32x2;
     descriptor.cBuffers[1].arrayStride = 2 * sizeof(float);
     descriptor.cBuffers[1].attributeCount = 1;
     descriptor.cBuffers[1].attributes = &descriptor.cAttributes[2];
     descriptor.cAttributes[2].shaderLocation = 2;
     descriptor.cAttributes[2].format = wgpu::VertexFormat::Float32x2;

     descriptor.cFragment.module = fsModule;
     descriptor.EnableDepthStencil(wgpu::TextureFormat::Depth24PlusStencil8);
     descriptor.cTargets[0].format = GetPreferredSwapChainTextureFormat();

     renderPipeline = device.CreateRenderPipeline(&descriptor);
 }

 void initSim() {
     wgpu::ShaderModule module = dawn::utils::CreateShaderModule(device, R"(
         struct Particle {
             pos : vec2f,
             vel : vec2f,
         };
         struct SimParams {
             deltaT : f32,
             rule1Distance : f32,
             rule2Distance : f32,
             rule3Distance : f32,
             rule1Scale : f32,
             rule2Scale : f32,
             rule3Scale : f32,
             particleCount : u32,
         };
         struct Particles {
             particles : array<Particle>,
         };
         @binding(0) @group(0) var<uniform> params : SimParams;
         @binding(1) @group(0) var<storage, read_write> particlesA : Particles;
         @binding(2) @group(0) var<storage, read_write> particlesB : Particles;

         // https://github.com/austinEng/Project6-Vulkan-Flocking/blob/master/data/shaders/computeparticles/particle.comp
         @compute @workgroup_size(64)
         fn main(@builtin(global_invocation_id) GlobalInvocationID : vec3u) {
             var index : u32 = GlobalInvocationID.x;
             if (index >= params.particleCount) {
                 return;
             }
             var vPos : vec2f = particlesA.particles[index].pos;
             var vVel : vec2f = particlesA.particles[index].vel;
             var cMass : vec2f = vec2f(0.0, 0.0);
             var cVel : vec2f = vec2f(0.0, 0.0);
             var colVel : vec2f = vec2f(0.0, 0.0);
             var cMassCount : u32 = 0u;
             var cVelCount : u32 = 0u;
             var pos : vec2f;
             var vel : vec2f;

             for (var i : u32 = 0u; i < params.particleCount; i = i + 1u) {
                 if (i == index) {
                     continue;
                 }

                 pos = particlesA.particles[i].pos.xy;
                 vel = particlesA.particles[i].vel.xy;
                 if (distance(pos, vPos) < params.rule1Distance) {
                     cMass = cMass + pos;
                     cMassCount = cMassCount + 1u;
                 }
                 if (distance(pos, vPos) < params.rule2Distance) {
                     colVel = colVel - (pos - vPos);
                 }
                 if (distance(pos, vPos) < params.rule3Distance) {
                     cVel = cVel + vel;
                     cVelCount = cVelCount + 1u;
                 }
             }

             if (cMassCount > 0u) {
                 cMass = (cMass / vec2f(f32(cMassCount), f32(cMassCount))) - vPos;
             }

             if (cVelCount > 0u) {
                 cVel = cVel / vec2f(f32(cVelCount), f32(cVelCount));
             }
             vVel = vVel + (cMass * params.rule1Scale) + (colVel * params.rule2Scale) +
                 (cVel * params.rule3Scale);

             // clamp velocity for a more pleasing simulation
             vVel = normalize(vVel) * clamp(length(vVel), 0.0, 0.1);
             // kinematic update
             vPos = vPos + (vVel * params.deltaT);

             // Wrap around boundary
             if (vPos.x < -1.0) {
                 vPos.x = 1.0;
             }
             if (vPos.x > 1.0) {
                 vPos.x = -1.0;
             }
             if (vPos.y < -1.0) {
                 vPos.y = 1.0;
             }
             if (vPos.y > 1.0) {
                 vPos.y = -1.0;
             }

             // Write back
             particlesB.particles[index].pos = vPos;
             particlesB.particles[index].vel = vVel;
             return;
         }
     )");

     auto bgl = dawn::utils::MakeBindGroupLayout(
         device, {
                     {0, wgpu::ShaderStage::Compute, wgpu::BufferBindingType::Uniform},
                     {1, wgpu::ShaderStage::Compute, wgpu::BufferBindingType::Storage},
                     {2, wgpu::ShaderStage::Compute, wgpu::BufferBindingType::Storage},
                 });

     wgpu::PipelineLayout pl = dawn::utils::MakeBasicPipelineLayout(device, &bgl);

     wgpu::ComputePipelineDescriptor csDesc;
     csDesc.layout = pl;
     csDesc.compute.module = module;
     csDesc.compute.entryPoint = "main";
     updatePipeline = device.CreateComputePipeline(&csDesc);

     for (uint32_t i = 0; i < 2; ++i) {
         updateBGs[i] = dawn::utils::MakeBindGroup(
             device, bgl,
             {
                 {0, updateParams, 0, sizeof(SimParams)},
                 {1, particleBuffers[i], 0, kNumParticles * sizeof(Particle)},
                 {2, particleBuffers[(i + 1) % 2], 0, kNumParticles * sizeof(Particle)},
             });
     }
 }

 wgpu::CommandBuffer createCommandBuffer(const wgpu::TextureView backbufferView, size_t i) {
     auto& bufferDst = particleBuffers[(i + 1) % 2];
     wgpu::CommandEncoder encoder = device.CreateCommandEncoder();

     {
         wgpu::ComputePassEncoder pass = encoder.BeginComputePass();
         pass.SetPipeline(updatePipeline);
         pass.SetBindGroup(0, updateBGs[i]);
         pass.DispatchWorkgroups(kNumParticles / 64);
         pass.End();
     }

     {
         dawn::utils::ComboRenderPassDescriptor renderPass({backbufferView}, depthStencilView);
         wgpu::RenderPassEncoder pass = encoder.BeginRenderPass(&renderPass);
         pass.SetPipeline(renderPipeline);
         pass.SetVertexBuffer(0, bufferDst);
         pass.SetVertexBuffer(1, modelBuffer);
         pass.Draw(3, kNumParticles);
         pass.End();
     }

     return encoder.Finish();
 }

 void init() {
     device = CreateCppDawnDevice();

     queue = device.GetQueue();
     swapchain = GetSwapChain();

     initBuffers();
     initRender();
     initSim();
 }

 void frame() {
     wgpu::TextureView backbufferView = swapchain.GetCurrentTextureView();

     wgpu::CommandBuffer commandBuffer = createCommandBuffer(backbufferView, pingpong);
     queue.Submit(1, &commandBuffer);
     swapchain.Present();
     DoFlush();

     pingpong = (pingpong + 1) % 2;
 }

 int main(int argc, const char* argv[]) {
     if (!InitSample(argc, argv)) {
         return 1;
     }
     init();

     while (!ShouldQuit()) {
         ProcessEvents();
         frame();
         dawn::utils::USleep(16000);
     }
 }
	// Copyright 2017 The Dawn & Tint Authors
	//
	// Redistribution and use in source and binary forms, with or without
	// modification, are permitted provided that the following conditions are met:
	//
	// 1. Redistributions of source code must retain the above copyright notice, this
	// list of conditions and the following disclaimer.
	//
	// 2. Redistributions in binary form must reproduce the above copyright notice,
	// this list of conditions and the following disclaimer in the documentation
	// and/or other materials provided with the distribution.
	//
	// 3. Neither the name of the copyright holder nor the names of its
	// contributors may be used to endorse or promote products derived from
	// this software without specific prior written permission.
	//
	// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
	// AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
	// IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
	// DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
	// FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
	// DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
	// SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
	// CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
	// OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
	// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.

	#include <array>
	#include <cstring>
	#include <random>
	#include <vector>

	#include "dawn/samples/SampleUtils.h"

	#include "dawn/utils/ComboRenderPipelineDescriptor.h"
	#include "dawn/utils/SystemUtils.h"
	#include "dawn/utils/WGPUHelpers.h"

	wgpu::Device device;
	wgpu::Queue queue;
	wgpu::SwapChain swapchain;
	wgpu::TextureView depthStencilView;

	wgpu::Buffer modelBuffer;
	std::array<wgpu::Buffer, 2> particleBuffers;

	wgpu::RenderPipeline renderPipeline;

	wgpu::Buffer updateParams;
	wgpu::ComputePipeline updatePipeline;
	std::array<wgpu::BindGroup, 2> updateBGs;

	size_t pingpong = 0;

	static const uint32_t kNumParticles = 1024;

	struct Particle {
	std::array<float, 2> pos;
	std::array<float, 2> vel;
	};

	struct SimParams {
	float deltaT;
	float rule1Distance;
	float rule2Distance;
	float rule3Distance;
	float rule1Scale;
	float rule2Scale;
	float rule3Scale;
	int particleCount;
	};

	void initBuffers() {
	std::array<std::array<float, 2>, 3> model = {{
	{-0.01, -0.02},
	{0.01, -0.02},
	{0.00, 0.02},
	}};
	modelBuffer =
	dawn::utils::CreateBufferFromData(device, &model, sizeof(model), wgpu::BufferUsage::Vertex);

	SimParams params = {0.04f, 0.1f, 0.025f, 0.025f, 0.02f, 0.05f, 0.005f, kNumParticles};
	updateParams = dawn::utils::CreateBufferFromData(device, &params, sizeof(params),
	wgpu::BufferUsage::Uniform);

	std::vector<Particle> initialParticles(kNumParticles);
	{
	std::mt19937 generator;
	std::uniform_real_distribution<float> dist(-1.0f, 1.0f);
	for (auto& p : initialParticles) {
	p.pos = {dist(generator), dist(generator)};
	p.vel = {dist(generator) * 0.1f, dist(generator) * 0.1f};
	}
	}

	for (size_t i = 0; i < 2; i++) {
	wgpu::BufferDescriptor descriptor;
	descriptor.size = sizeof(Particle) * kNumParticles;
	descriptor.usage =
	wgpu::BufferUsage::CopyDst \| wgpu::BufferUsage::Vertex \| wgpu::BufferUsage::Storage;
	particleBuffers[i] = device.CreateBuffer(&descriptor);

	queue.WriteBuffer(particleBuffers[i], 0,
	reinterpret_cast<uint8_t*>(initialParticles.data()),
	sizeof(Particle) * kNumParticles);
	}
	}

	void initRender() {
	wgpu::ShaderModule vsModule = dawn::utils::CreateShaderModule(device, R"(
	struct VertexIn {
	@location(0) a_particlePos : vec2f,
	@location(1) a_particleVel : vec2f,
	@location(2) a_pos : vec2f,
	};

	@vertex
	fn main(input : VertexIn) -> @builtin(position) vec4f {
	var angle : f32 = -atan2(input.a_particleVel.x, input.a_particleVel.y);
	var pos : vec2f = vec2f(
	(input.a_pos.x * cos(angle)) - (input.a_pos.y * sin(angle)),
	(input.a_pos.x * sin(angle)) + (input.a_pos.y * cos(angle)));
	return vec4f(pos + input.a_particlePos, 0.0, 1.0);
	}
	)");

	wgpu::ShaderModule fsModule = dawn::utils::CreateShaderModule(device, R"(
	@fragment
	fn main() -> @location(0) vec4f {
	return vec4f(1.0, 1.0, 1.0, 1.0);
	}
	)");

	depthStencilView = CreateDefaultDepthStencilView(device);

	dawn::utils::ComboRenderPipelineDescriptor descriptor;

	descriptor.vertex.module = vsModule;
	descriptor.vertex.bufferCount = 2;
	descriptor.cBuffers[0].arrayStride = sizeof(Particle);
	descriptor.cBuffers[0].stepMode = wgpu::VertexStepMode::Instance;
	descriptor.cBuffers[0].attributeCount = 2;
	descriptor.cAttributes[0].offset = offsetof(Particle, pos);
	descriptor.cAttributes[0].format = wgpu::VertexFormat::Float32x2;
	descriptor.cAttributes[1].shaderLocation = 1;
	descriptor.cAttributes[1].offset = offsetof(Particle, vel);
	descriptor.cAttributes[1].format = wgpu::VertexFormat::Float32x2;
	descriptor.cBuffers[1].arrayStride = 2 * sizeof(float);
	descriptor.cBuffers[1].attributeCount = 1;
	descriptor.cBuffers[1].attributes = &descriptor.cAttributes[2];
	descriptor.cAttributes[2].shaderLocation = 2;
	descriptor.cAttributes[2].format = wgpu::VertexFormat::Float32x2;

	descriptor.cFragment.module = fsModule;
	descriptor.EnableDepthStencil(wgpu::TextureFormat::Depth24PlusStencil8);
	descriptor.cTargets[0].format = GetPreferredSwapChainTextureFormat();

	renderPipeline = device.CreateRenderPipeline(&descriptor);
	}

	void initSim() {
	wgpu::ShaderModule module = dawn::utils::CreateShaderModule(device, R"(
	struct Particle {
	pos : vec2f,
	vel : vec2f,
	};
	struct SimParams {
	deltaT : f32,
	rule1Distance : f32,
	rule2Distance : f32,
	rule3Distance : f32,
	rule1Scale : f32,
	rule2Scale : f32,
	rule3Scale : f32,
	particleCount : u32,
	};
	struct Particles {
	particles : array<Particle>,
	};
	@binding(0) @group(0) var<uniform> params : SimParams;
	@binding(1) @group(0) var<storage, read_write> particlesA : Particles;
	@binding(2) @group(0) var<storage, read_write> particlesB : Particles;

	// https://github.com/austinEng/Project6-Vulkan-Flocking/blob/master/data/shaders/computeparticles/particle.comp
	@compute @workgroup_size(64)
	fn main(@builtin(global_invocation_id) GlobalInvocationID : vec3u) {
	var index : u32 = GlobalInvocationID.x;
	if (index >= params.particleCount) {
	return;
	}
	var vPos : vec2f = particlesA.particles[index].pos;
	var vVel : vec2f = particlesA.particles[index].vel;
	var cMass : vec2f = vec2f(0.0, 0.0);
	var cVel : vec2f = vec2f(0.0, 0.0);
	var colVel : vec2f = vec2f(0.0, 0.0);
	var cMassCount : u32 = 0u;
	var cVelCount : u32 = 0u;
	var pos : vec2f;
	var vel : vec2f;

	for (var i : u32 = 0u; i < params.particleCount; i = i + 1u) {
	if (i == index) {
	continue;
	}

	pos = particlesA.particles[i].pos.xy;
	vel = particlesA.particles[i].vel.xy;
	if (distance(pos, vPos) < params.rule1Distance) {
	cMass = cMass + pos;
	cMassCount = cMassCount + 1u;
	}
	if (distance(pos, vPos) < params.rule2Distance) {
	colVel = colVel - (pos - vPos);
	}
	if (distance(pos, vPos) < params.rule3Distance) {
	cVel = cVel + vel;
	cVelCount = cVelCount + 1u;
	}
	}

	if (cMassCount > 0u) {
	cMass = (cMass / vec2f(f32(cMassCount), f32(cMassCount))) - vPos;
	}

	if (cVelCount > 0u) {
	cVel = cVel / vec2f(f32(cVelCount), f32(cVelCount));
	}
	vVel = vVel + (cMass * params.rule1Scale) + (colVel * params.rule2Scale) +
	(cVel * params.rule3Scale);

	// clamp velocity for a more pleasing simulation
	vVel = normalize(vVel) * clamp(length(vVel), 0.0, 0.1);
	// kinematic update
	vPos = vPos + (vVel * params.deltaT);

	// Wrap around boundary
	if (vPos.x < -1.0) {
	vPos.x = 1.0;
	}
	if (vPos.x > 1.0) {
	vPos.x = -1.0;
	}
	if (vPos.y < -1.0) {
	vPos.y = 1.0;
	}
	if (vPos.y > 1.0) {
	vPos.y = -1.0;
	}

	// Write back
	particlesB.particles[index].pos = vPos;
	particlesB.particles[index].vel = vVel;
	return;
	}
	)");

	auto bgl = dawn::utils::MakeBindGroupLayout(
	device, {
	{0, wgpu::ShaderStage::Compute, wgpu::BufferBindingType::Uniform},
	{1, wgpu::ShaderStage::Compute, wgpu::BufferBindingType::Storage},
	{2, wgpu::ShaderStage::Compute, wgpu::BufferBindingType::Storage},
	});

	wgpu::PipelineLayout pl = dawn::utils::MakeBasicPipelineLayout(device, &bgl);

	wgpu::ComputePipelineDescriptor csDesc;
	csDesc.layout = pl;
	csDesc.compute.module = module;
	csDesc.compute.entryPoint = "main";
	updatePipeline = device.CreateComputePipeline(&csDesc);

	for (uint32_t i = 0; i < 2; ++i) {
	updateBGs[i] = dawn::utils::MakeBindGroup(
	device, bgl,
	{
	{0, updateParams, 0, sizeof(SimParams)},
	{1, particleBuffers[i], 0, kNumParticles * sizeof(Particle)},
	{2, particleBuffers[(i + 1) % 2], 0, kNumParticles * sizeof(Particle)},
	});
	}
	}

	wgpu::CommandBuffer createCommandBuffer(const wgpu::TextureView backbufferView, size_t i) {
	auto& bufferDst = particleBuffers[(i + 1) % 2];
	wgpu::CommandEncoder encoder = device.CreateCommandEncoder();

	{
	wgpu::ComputePassEncoder pass = encoder.BeginComputePass();
	pass.SetPipeline(updatePipeline);
	pass.SetBindGroup(0, updateBGs[i]);
	pass.DispatchWorkgroups(kNumParticles / 64);
	pass.End();
	}

	{
	dawn::utils::ComboRenderPassDescriptor renderPass({backbufferView}, depthStencilView);
	wgpu::RenderPassEncoder pass = encoder.BeginRenderPass(&renderPass);
	pass.SetPipeline(renderPipeline);
	pass.SetVertexBuffer(0, bufferDst);
	pass.SetVertexBuffer(1, modelBuffer);
	pass.Draw(3, kNumParticles);
	pass.End();
	}

	return encoder.Finish();
	}

	void init() {
	device = CreateCppDawnDevice();

	queue = device.GetQueue();
	swapchain = GetSwapChain();

	initBuffers();
	initRender();
	initSim();
	}

	void frame() {
	wgpu::TextureView backbufferView = swapchain.GetCurrentTextureView();

	wgpu::CommandBuffer commandBuffer = createCommandBuffer(backbufferView, pingpong);
	queue.Submit(1, &commandBuffer);
	swapchain.Present();
	DoFlush();

	pingpong = (pingpong + 1) % 2;
	}

	int main(int argc, const char* argv[]) {
	if (!InitSample(argc, argv)) {
	return 1;
	}
	init();

	while (!ShouldQuit()) {
	ProcessEvents();
	frame();
	dawn::utils::USleep(16000);
	}
	}