particles
A rain and snow particle system. The compute pass integrates positions and wraps particles
at the window edges; pressing Space swaps the simulation mode at runtime.
cargo run --features examples --example particles
What it demonstrates
- Runtime switching between simulation modes
- Compute dispatch feeding an instanced raster pass
Controls
| Key | Action |
|---|---|
Space | Toggle between rain and snow |
Escape | Exit |
Source
examples/particles.rs:
//! Particles example - rain/snow particle system.
//!
//! Demonstrates retained scheme with compute dispatch → offscreen render → copy-to-present.
//!
//! Run with: `cargo run --example particles`
use anyhow::Result;
use goldy::{
Buffer, BufferFlags, BufferKind, Color, ComputePipeline, DepositTarget, DepositTransaction, Instance, Lease,
LeaseRenderTarget, MemoryExchange, NodeAccess, PrimitiveTopology, RenderPipeline, RenderPipelineDesc,
RequestAdapterOptions, RuntimeDescriptor, Scheme, ShaderModule, SurfaceConfig, SurfaceExchange, TargetLoad,
Texture, TextureFormat, Transaction, VertexBufferLayout,
};
use std::ops::Shr;
use std::sync::Arc;
use winit::{
application::ApplicationHandler,
event::WindowEvent,
event_loop::{ActiveEventLoop, ControlFlow, EventLoop},
keyboard::{Key, NamedKey},
window::{Window, WindowId},
};
mod common;
use common::CaptureDump;
const NUM_PARTICLES: u32 = 1000;
#[goldy::gpu]
struct Particle {
position: [f32; 2],
velocity: [f32; 2],
size: f32,
}
#[goldy::gpu]
struct ParticleParams {
is_snow: f32,
frame: f32,
}
static mut SEED: u32 = 42;
fn random() -> f32 {
unsafe {
SEED = SEED.wrapping_mul(1103515245).wrapping_add(12345);
SEED as f32 / u32::MAX as f32
}
}
fn main() -> Result<()> {
tracing_subscriber::fmt()
.with_env_filter(
tracing_subscriber::EnvFilter::try_from_default_env()
.unwrap_or_else(|_| tracing_subscriber::EnvFilter::new("warn")),
)
.init();
if common::capture_requested() {
let mut state = RenderState::new(None)?;
while !state.capture_done() {
state.render()?;
}
return Ok(());
}
println!("Goldy Particles Example");
println!(" Space - Toggle rain/snow");
println!(" Escape - Exit");
let event_loop = EventLoop::new()?;
event_loop.set_control_flow(ControlFlow::Poll);
let mut app = App::default();
event_loop.run_app(&mut app)?;
Ok(())
}
#[derive(Default)]
struct App {
state: Option<RenderState>,
}
struct RenderState {
window: Option<Arc<Window>>,
device: Arc<goldy::Runtime>,
ctx: goldy::Context,
surface: Option<SurfaceExchange>,
capture: Option<CaptureDump>,
readback: Option<Texture>,
present: Option<Transaction>,
scheme: Scheme,
scene_rt: Lease<LeaseRenderTarget>,
compute_pipeline: ComputePipeline,
render_shader: ShaderModule,
render_pipeline: RenderPipeline,
particle_buffer: Buffer,
params_buffer: Buffer,
upload_scheme: Scheme,
params_deposit: DepositTransaction,
is_snow: bool,
frame_count: f32,
start_time: std::time::Instant,
}
impl RenderState {
fn create_render_pipeline(
device: &goldy::Runtime,
render_shader: &ShaderModule,
format: TextureFormat,
) -> Result<RenderPipeline> {
common::render_pipeline(
device,
render_shader,
format,
RenderPipelineDesc {
vertex_layout: VertexBufferLayout::empty(),
topology: PrimitiveTopology::TriangleList,
..Default::default()
},
)
}
fn bind_frame(
scheme: &mut Scheme,
scene_rt: &Lease<LeaseRenderTarget>,
surface: Option<&SurfaceExchange>,
readback: Option<&Texture>,
) -> anyhow::Result<Option<Transaction>> {
if let Some(surface) = surface {
let present = surface.bind_render_target(scheme, scene_rt)?;
Ok(Some(present))
} else {
let readback = readback.expect("capture readback");
scheme.copy_to_texture(scene_rt, readback)?;
Ok(None)
}
}
fn record_scheme(
scheme: &mut Scheme,
compute_pipeline: &ComputePipeline,
render_pipeline: &RenderPipeline,
particle_buffer: &Buffer,
params_buffer: &Buffer,
scene_rt: &Lease<LeaseRenderTarget>,
bg_color: Color,
) {
scheme
.node("update_particles", compute_pipeline)
.with_parcel(particle_buffer, NodeAccess::ReadWrite)
.with_parcel(params_buffer, NodeAccess::Read)
.dispatch(NUM_PARTICLES.div_ceil(64), 1, 1);
let mut pass = scheme.render_pass("particles", scene_rt, TargetLoad::Clear(bg_color));
pass.with_parcel(particle_buffer, NodeAccess::Read);
pass.with_parcel(params_buffer, NodeAccess::Read);
pass.set_pipeline(render_pipeline);
pass.draw(0..6, 0..NUM_PARTICLES);
pass.finish();
}
fn background_color(is_snow: bool) -> Color {
if is_snow {
Color {
r: 0.05,
g: 0.05,
b: 0.15,
a: 1.0,
}
} else {
Color {
r: 0.02,
g: 0.02,
b: 0.05,
a: 1.0,
}
}
}
fn target(&self) -> (TextureFormat, u32, u32) {
if let Some(surface) = &self.surface {
let (width, height) = surface.size();
(surface.format(), width, height)
} else {
let capture = self.capture.as_ref().expect("capture dump");
let (width, height) = capture.size();
(CaptureDump::format(), width, height)
}
}
fn capture_done(&self) -> bool {
self.capture.as_ref().is_none_or(CaptureDump::finished)
}
fn rerecord_scheme(&mut self) {
let mut scheme = Scheme::new(&self.ctx);
let (format, width, height) = self.target();
if let Ok(rt) = self.ctx.lease_render_target(width.max(1), height.max(1), format, None) {
self.scene_rt = rt;
Self::record_scheme(
&mut scheme,
&self.compute_pipeline,
&self.render_pipeline,
&self.particle_buffer,
&self.params_buffer,
&self.scene_rt,
Self::background_color(self.is_snow),
);
if let Ok(present) = Self::bind_frame(
&mut scheme,
&self.scene_rt,
self.surface.as_ref(),
self.readback.as_ref(),
) {
self.present = present;
self.scheme = scheme;
}
}
}
fn new(window: Option<Arc<Window>>) -> Result<Self> {
let instance = Instance::new()?;
let device = Arc::new(
instance
.request_adapter(&RequestAdapterOptions::default())?
.request_runtime(&RuntimeDescriptor::default())?,
);
let ctx = device.create_context()?;
let (surface, capture, readback, format, width, height) = if let Some(window) = window.as_deref() {
let surface = SurfaceExchange::new(&ctx, window, SurfaceConfig::default())?;
let format = surface.format();
let (width, height) = surface.size();
(Some(surface), None, None, format, width, height)
} else {
let capture = CaptureDump::from_env()?;
let (width, height) = capture.size();
let readback = common::capture_readback(&device, width, height)?;
(
None,
Some(capture),
Some(readback),
CaptureDump::format(),
width,
height,
)
};
let compute_shader = ShaderModule::from_slang_with_gpu_types(
&device,
include_str!("../shaders/rain_snow_update.slang"),
&[Particle::GPU_TYPE, ParticleParams::GPU_TYPE],
)?;
let render_shader = ShaderModule::from_slang_with_gpu_types(
&device,
include_str!("../shaders/rain_snow_render.slang"),
&[Particle::GPU_TYPE, ParticleParams::GPU_TYPE],
)?;
let particles = Self::create_particles(false);
let particle_buffer = device.acquire_buffer_with_data(&particles, BufferKind::Scattered)?;
let params_buffer =
device.acquire_buffer_sized::<ParticleParams>(1, BufferKind::Broadcast, BufferFlags::empty())?;
let compute_pipeline = ComputePipeline::new(&device, &compute_shader)?;
let render_pipeline = Self::create_render_pipeline(&device, &render_shader, format)?;
let mut scheme = Scheme::new(&ctx);
let scene_rt = ctx.lease_render_target(width.max(1), height.max(1), format, None)?;
Self::record_scheme(
&mut scheme,
&compute_pipeline,
&render_pipeline,
&particle_buffer,
¶ms_buffer,
&scene_rt,
Self::background_color(false),
);
let present = Self::bind_frame(&mut scheme, &scene_rt, surface.as_ref(), readback.as_ref())?;
let mut upload_scheme = Scheme::new(&ctx);
let params_deposit = MemoryExchange::new(&ctx).bind_deposit(
&mut upload_scheme,
DepositTarget::buffer_elements::<ParticleParams>(¶ms_buffer, 1),
)?;
println!("Created rain/snow simulation with {NUM_PARTICLES} particles (Scheme + Present)");
Ok(Self {
window,
device,
ctx,
surface,
capture,
readback,
present,
scheme,
scene_rt,
compute_pipeline,
render_shader,
render_pipeline,
particle_buffer,
params_buffer,
upload_scheme,
params_deposit,
is_snow: false,
frame_count: 0.0,
start_time: std::time::Instant::now(),
})
}
fn create_particles(is_snow: bool) -> Vec<Particle> {
let mut particles = Vec::with_capacity(NUM_PARTICLES as usize);
for _ in 0..NUM_PARTICLES {
let x = random() * 2.0 - 1.0;
let y = random() * 2.2 - 1.0;
let (vx, vy, size) = if is_snow {
(
(random() - 0.5) * 0.005,
-(0.002 + random() * 0.005),
0.003 + random() * 0.008,
)
} else {
(
(random() - 0.5) * 0.002,
-(0.01 + random() * 0.02),
0.002 + random() * 0.003,
)
};
particles.push(Particle {
position: [x, y],
velocity: [vx, vy],
size,
});
}
particles
}
fn toggle_mode(&mut self) -> Result<()> {
self.is_snow = !self.is_snow;
let particles = Self::create_particles(self.is_snow);
let mut particle_upload = Scheme::new(&self.ctx);
let particle_deposit = MemoryExchange::new(&self.ctx).bind_deposit(
&mut particle_upload,
DepositTarget::buffer_elements::<Particle>(&self.particle_buffer, NUM_PARTICLES as u64),
)?;
(&particle_deposit << particles.as_slice())?;
particle_upload.submit()?;
if let Some(window) = &self.window {
window.set_title(&format!(
"Goldy - {} (Space to toggle)",
if self.is_snow { "Snow" } else { "Rain" }
));
}
self.rerecord_scheme();
Ok(())
}
fn render(&mut self) -> Result<()> {
self.frame_count += 1.0;
let params = ParticleParams {
is_snow: if self.is_snow { 1.0 } else { 0.0 },
frame: self.frame_count,
};
(&self.params_deposit << ¶ms)?;
self.upload_scheme.submit()?;
let mut submission = self.scheme.submit()?;
if let Some(present) = &self.present {
(&mut submission >> present).take()?;
} else {
let pixels = (&mut submission >> self.readback.as_ref().unwrap())
.take::<u8>()?
.to_vec();
self.capture.as_mut().unwrap().write_rgba(&pixels)?;
}
if let Some(window) = &self.window {
window.request_redraw();
}
Ok(())
}
}
impl Drop for RenderState {
fn drop(&mut self) {
let elapsed = self.start_time.elapsed().as_secs_f64();
let fps = if elapsed > 0.0 {
self.frame_count as f64 / elapsed
} else {
0.0
};
println!(
"GOLDY_PERF: frames={} elapsed={elapsed:.2}s avg_fps={fps:.1}",
self.frame_count as u64
);
}
}
impl ApplicationHandler for App {
fn resumed(&mut self, event_loop: &ActiveEventLoop) {
if self.state.is_none() {
let window = Arc::new(
event_loop
.create_window(common::hidden_window("Goldy - Rain (Space to toggle)", 800, 600))
.expect("Failed to create window"),
);
match RenderState::new(Some(window.clone())) {
Ok(mut state) => {
if let Err(e) = state.render() {
tracing::error!("First frame error: {e}");
}
common::reveal_window(&window);
self.state = Some(state);
window.request_redraw();
}
Err(e) => {
tracing::error!("Failed to create render state: {e:#}");
event_loop.exit();
}
}
}
}
fn about_to_wait(&mut self, event_loop: &ActiveEventLoop) {
if let Some(state) = &self.state {
common::exit_if_timed_out(event_loop, state.start_time);
}
}
fn window_event(&mut self, event_loop: &ActiveEventLoop, _id: WindowId, event: WindowEvent) {
match event {
WindowEvent::CloseRequested => event_loop.exit(),
WindowEvent::KeyboardInput { event, .. } if event.state.is_pressed() => {
if let Some(state) = &mut self.state {
match event.logical_key {
Key::Named(NamedKey::Escape) => event_loop.exit(),
Key::Named(NamedKey::Space) => {
if let Err(e) = state.toggle_mode() {
tracing::error!("Failed to toggle mode: {e}");
}
}
_ => {}
}
}
}
WindowEvent::Resized(size) => {
if let Some(state) = &mut self.state {
if size.width > 0 && size.height > 0 {
let Some(surface) = state.surface.as_ref() else {
return;
};
let (prev_w, prev_h) = surface.size();
if size.width == prev_w && size.height == prev_h {
return;
}
let _ = surface.resize(size.width, size.height);
let format = surface.format();
if let Ok(pipeline) =
RenderState::create_render_pipeline(&state.device, &state.render_shader, format)
{
state.render_pipeline = pipeline;
}
state.rerecord_scheme();
}
}
}
WindowEvent::RedrawRequested => {
if let Some(state) = &mut self.state {
if let Err(e) = state.render() {
tracing::error!("Render error: {e}");
}
}
}
_ => {}
}
}
}The example pulls in examples/common.rs — see Shared Helpers.
Shaders
shaders/rain_snow_update.slang:
// Rain/Snow particle compute shader
// Updates particle positions with mode-dependent physics
import goldy_exp;
static const uint NUM_PARTICLES = 1000;
float hash(float p) {
return frac(sin(p * 127.1) * 43758.5453);
}
[goldy_compute]
[numthreads(64, 1, 1)]
void cs_main(Scattered<Particle> PARTICLES, ParticleParams params, ThreadId id) {
uint idx = id.x;
if (idx >= NUM_PARTICLES) return;
Particle p = PARTICLES[idx];
bool is_snow = params.is_snow > 0.5;
p.position += p.velocity;
if (is_snow) {
float seed = float(idx) + params.frame * 0.1;
p.velocity.x += (hash(seed) - 0.5) * 0.001;
p.velocity.x = clamp(p.velocity.x, -0.01, 0.01);
}
if (p.position.y < -1.2 || p.position.x < -1.2 || p.position.x > 1.2) {
float seed = float(idx) + params.frame * 0.01;
p.position.x = hash(seed) * 2.0 - 1.0;
p.position.y = 1.0 + hash(seed + 100.0) * 0.5;
if (is_snow) {
p.velocity.x = (hash(seed + 200.0) - 0.5) * 0.005;
p.velocity.y = -(0.002 + hash(seed + 300.0) * 0.005);
p.size = 0.003 + hash(seed + 400.0) * 0.008;
} else {
p.velocity.x = (hash(seed + 200.0) - 0.5) * 0.002;
p.velocity.y = -(0.01 + hash(seed + 300.0) * 0.02);
p.size = 0.002 + hash(seed + 400.0) * 0.003;
}
}
PARTICLES[idx] = p;
}
shaders/rain_snow_render.slang:
// Rain/Snow particle rendering shader
// Visualizes particles as elongated quads using instancing
import goldy_exp;
struct VSOutput {
float4 position : SV_Position;
float4 color : COLOR;
};
static const float2 quadVerts[6] = {
float2(-1, -3), float2( 1, -3), float2( 1, 3),
float2(-1, -3), float2( 1, 3), float2(-1, 3)
};
static const float2 snowQuadVerts[6] = {
float2(-1, -1), float2( 1, -1), float2( 1, 1),
float2(-1, -1), float2( 1, 1), float2(-1, 1)
};
[goldy_vertex]
VSOutput vs_main(Scattered<Particle> PARTICLES, ParticleParams params,
VertexId vertexID, InstanceId instanceID) {
VSOutput output;
Particle p = PARTICLES[instanceID.value];
bool is_snow = params.is_snow > 0.5;
float size = p.size;
float2 localPos;
if (is_snow) {
localPos = snowQuadVerts[vertexID.value] * size;
} else {
localPos = quadVerts[vertexID.value] * size;
}
output.position = float4(p.position + localPos, 0.0, 1.0);
if (is_snow) {
float brightness = 0.7 + size * 30.0;
output.color = float4(0.95 * brightness, 0.95 * brightness, 1.0 * brightness, 0.8);
} else {
float brightness = 0.6 + size * 50.0;
output.color = float4(0.5 * brightness, 0.6 * brightness, 0.9 * brightness, 0.7);
}
return output;
}
[goldy_fragment]
float4 fs_main(VSOutput input) : SV_Target {
return input.color;
}