bouncing_lines
Line segments bouncing off the window edges. A compute pass integrates the simple physics;
a LINE_LIST pipeline draws the result.
cargo run --features examples --example bouncing_lines
What it demonstrates
LINE_LISTtopology- Compute dispatch feeding a raster pass in one retained scheme
Source
examples/bouncing_lines.rs:
//! Bouncing lines example - animated lines bouncing off walls.
//!
//! Demonstrates retained scheme with compute dispatch → offscreen render → copy-to-present.
//!
//! Run with: cargo run --example bouncing_lines
use anyhow::Result;
use goldy::{
Buffer, BufferKind, Color, ComputePipeline, 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_LINES: u32 = 20;
#[goldy::gpu]
struct Line {
p1: [f32; 2],
v1: [f32; 2],
p2: [f32; 2],
v2: [f32; 2],
color_index: u32,
}
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 Bouncing Lines Example");
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,
line_buffer: Buffer,
render_shader: ShaderModule,
render_pipeline: RenderPipeline,
frame_count: u32,
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::LineList,
..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,
line_buffer: &Buffer,
scene_rt: &Lease<LeaseRenderTarget>,
) {
scheme
.node("update_lines", compute_pipeline)
.with_parcel(line_buffer, NodeAccess::ReadWrite)
.dispatch(NUM_LINES.div_ceil(64).max(1), 1, 1);
let bg_color = Color {
r: 0.05,
g: 0.05,
b: 0.1,
a: 1.0,
};
let mut pass = scheme.render_pass("bouncing_lines", scene_rt, TargetLoad::Clear(bg_color));
pass.with_parcel(line_buffer, NodeAccess::Read);
pass.set_pipeline(render_pipeline);
pass.draw(0..2, 0..NUM_LINES);
pass.finish();
}
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.line_buffer,
&self.scene_rt,
);
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/bouncing_lines_update.slang"),
&[Line::GPU_TYPE],
)?;
let render_shader = ShaderModule::from_slang_with_gpu_types(
&device,
include_str!("../shaders/bouncing_lines_render.slang"),
&[Line::GPU_TYPE],
)?;
let mut lines = Vec::with_capacity(NUM_LINES as usize);
for idx in 0..NUM_LINES {
let angle = (idx as f32 / NUM_LINES as f32) * std::f32::consts::PI * 2.0;
lines.push(Line {
p1: [angle.cos() * 0.3, angle.sin() * 0.3],
v1: [0.01 * (idx as f32 * 0.7).cos(), 0.012 * (idx as f32 * 0.9).sin()],
p2: [-angle.cos() * 0.3, -angle.sin() * 0.3],
v2: [-0.011 * (idx as f32 * 1.1).cos(), 0.009 * (idx as f32 * 1.3).sin()],
color_index: idx,
});
}
let line_buffer = device.acquire_buffer_with_data(&lines, BufferKind::Scattered)?;
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,
&line_buffer,
&scene_rt,
);
let present = Self::bind_frame(&mut scheme, &scene_rt, surface.as_ref(), readback.as_ref())?;
println!("Created bouncing lines with {} lines", NUM_LINES);
Ok(Self {
window,
device,
ctx,
surface,
capture,
readback,
present,
scheme,
scene_rt,
compute_pipeline,
line_buffer,
render_shader,
render_pipeline,
frame_count: 0,
start_time: std::time::Instant::now(),
})
}
fn render(&mut self) -> Result<()> {
self.frame_count += 1;
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
);
}
}
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 - Bouncing Lines", 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 matches!(event.logical_key, Key::Named(NamedKey::Escape)) {
event_loop.exit();
}
}
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/bouncing_lines_update.slang:
// Bouncing lines compute shader
// Updates line endpoint positions with wall bouncing physics
import goldy_exp;
static const uint NUM_LINES = 20;
[goldy_compute]
[numthreads(64, 1, 1)]
void cs_main(Scattered<Line> LINES, ThreadId id) {
uint idx = id.x;
if (idx >= NUM_LINES) return;
Line line = LINES[idx];
// Update positions
line.p1 += line.v1;
line.p2 += line.v2;
// Bounce endpoint 1 off walls
if (line.p1.x < -1.0 || line.p1.x > 1.0) {
line.v1.x = -line.v1.x;
line.p1.x = clamp(line.p1.x, -1.0, 1.0);
}
if (line.p1.y < -1.0 || line.p1.y > 1.0) {
line.v1.y = -line.v1.y;
line.p1.y = clamp(line.p1.y, -1.0, 1.0);
}
// Bounce endpoint 2 off walls
if (line.p2.x < -1.0 || line.p2.x > 1.0) {
line.v2.x = -line.v2.x;
line.p2.x = clamp(line.p2.x, -1.0, 1.0);
}
if (line.p2.y < -1.0 || line.p2.y > 1.0) {
line.v2.y = -line.v2.y;
line.p2.y = clamp(line.p2.y, -1.0, 1.0);
}
LINES[idx] = line;
}
shaders/bouncing_lines_render.slang:
// Bouncing lines rendering shader
// Visualizes lines using instancing with LineList topology
import goldy_exp;
struct VSOutput {
float4 position : SV_Position;
float4 color : COLOR;
};
static const float4 colors[6] = {
float4(1.0, 0.0, 0.0, 1.0), // Red
float4(0.0, 1.0, 0.0, 1.0), // Green
float4(0.0, 0.0, 1.0, 1.0), // Blue
float4(1.0, 1.0, 0.0, 1.0), // Yellow
float4(1.0, 0.0, 1.0, 1.0), // Magenta
float4(0.0, 1.0, 1.0, 1.0), // Cyan
};
[goldy_vertex]
VSOutput vs_main(Scattered<Line> LINES, VertexId vertexID, InstanceId instanceID) {
VSOutput output;
Line line = LINES[instanceID.value];
float2 pos = (vertexID.value == 0) ? line.p1 : line.p2;
output.position = float4(pos, 0.0, 1.0);
output.color = colors[line.color_index % 6];
return output;
}
[goldy_fragment]
float4 fs_main(VSOutput input) : SV_Target {
return input.color;
}