From a746ce965f3099427128b9aa187dadbfb7184860 Mon Sep 17 00:00:00 2001
From: Kevin Reid <kpreid@switchb.org>
Date: Sat, 25 Jan 2025 23:00:36 -0800
Subject: [PATCH] gpu: Expose `FrameBudget` for rendering.

Also hook it up to monitor refresh rate.
---
 all-is-cubes-desktop/src/winit.rs    | 17 ++++++++++++++---
 all-is-cubes-gpu/src/common.rs       | 15 +++++++++++++++
 all-is-cubes-gpu/src/in_wgpu/mod.rs  |  9 ++++-----
 all-is-cubes-wasm/src/web_session.rs |  8 ++++++--
 4 files changed, 39 insertions(+), 10 deletions(-)

diff --git a/all-is-cubes-desktop/src/winit.rs b/all-is-cubes-desktop/src/winit.rs
index e0ce7968c..d4bfddc28 100644
--- a/all-is-cubes-desktop/src/winit.rs
+++ b/all-is-cubes-desktop/src/winit.rs
@@ -2,7 +2,7 @@
 
 use std::mem;
 use std::sync::Arc;
-use std::time::Instant;
+use std::time::{Duration, Instant};
 
 use winit::event::{DeviceEvent, ElementState, WindowEvent};
 use winit::event_loop::{ActiveEventLoop, ControlFlow};
@@ -11,6 +11,7 @@ use winit::window::{CursorGrabMode, Window};
 use all_is_cubes::euclid::{Point2D, Size2D};
 use all_is_cubes::listen;
 use all_is_cubes_gpu::in_wgpu::SurfaceRenderer;
+use all_is_cubes_gpu::FrameBudget;
 use all_is_cubes_render::camera::{self, StandardCameras, Viewport};
 
 use all_is_cubes_ui::apps::InputProcessor;
@@ -534,9 +535,19 @@ impl RendererToWinit for SurfaceRenderer<Instant> {
         self.cameras()
     }
 
-    fn redraw(&mut self, session: &Session, _window: &Window) {
+    fn redraw(&mut self, session: &Session, window: &Window) {
+        let frame_budget = FrameBudget::from_frame_period(
+            match window
+                .current_monitor()
+                .and_then(|m| m.refresh_rate_millihertz())
+            {
+                Some(mhz) => Duration::from_secs_f32(1000.0 / mhz as f32),
+                None => Duration::from_millis(16), // assume ~60 Hz
+            },
+        );
+
         let _info = self
-            .render_frame(session.cursor_result(), |render_info| {
+            .render_frame(session.cursor_result(), &frame_budget, |render_info| {
                 format!("{}", session.info_text(render_info))
             })
             .unwrap();
diff --git a/all-is-cubes-gpu/src/common.rs b/all-is-cubes-gpu/src/common.rs
index f6d901b08..d1559ffa3 100644
--- a/all-is-cubes-gpu/src/common.rs
+++ b/all-is-cubes-gpu/src/common.rs
@@ -47,6 +47,21 @@ impl FrameBudget {
             ui: VERY_LONG,
         },
     };
+
+    /// Create a [`FrameBudget`] presumed to be a good choice when the period between frames
+    /// (reciprocal of frame rate) is this long.
+    pub fn from_frame_period(frame_period: Duration) -> Self {
+        // The fraction of the frame period not accounted for here is time left for:
+        // * the simulation, and
+        // * everything in rendering that is not explicitly budgeted.
+        // TODO: In principle we should also be negotiating with the simulation.
+        Self {
+            update_meshes: Layers {
+                world: frame_period.mul_f32(0.3),
+                ui: frame_period.mul_f32(0.2),
+            },
+        }
+    }
 }
 
 /// A Duration long enough that it is not interesting in questions of rendering, but not
diff --git a/all-is-cubes-gpu/src/in_wgpu/mod.rs b/all-is-cubes-gpu/src/in_wgpu/mod.rs
index 8161a23b8..1bcc108fc 100644
--- a/all-is-cubes-gpu/src/in_wgpu/mod.rs
+++ b/all-is-cubes-gpu/src/in_wgpu/mod.rs
@@ -166,13 +166,12 @@ impl<I: time::Instant> SurfaceRenderer<I> {
     pub fn render_frame(
         &mut self,
         cursor_result: Option<&Cursor>,
+        frame_budget: &FrameBudget,
         info_text_fn: impl FnOnce(&RenderInfo) -> String,
     ) -> Result<RenderInfo, RenderError> {
-        let update_info = self.everything.update(
-            &self.queue,
-            cursor_result,
-            &FrameBudget::SIXTY_FPS, // TODO: figure out what we're vsyncing to, instead
-        )?;
+        let update_info = self
+            .everything
+            .update(&self.queue, cursor_result, frame_budget)?;
 
         if self.viewport_dirty.get_and_clear() {
             // Test because wgpu insists on nonzero values -- we'd rather be inconsistent
diff --git a/all-is-cubes-wasm/src/web_session.rs b/all-is-cubes-wasm/src/web_session.rs
index 059b51c35..01c00a4ca 100644
--- a/all-is-cubes-wasm/src/web_session.rs
+++ b/all-is-cubes-wasm/src/web_session.rs
@@ -16,7 +16,7 @@ use web_sys::{
 use all_is_cubes::euclid::{Point2D, Vector2D};
 use all_is_cubes::listen;
 use all_is_cubes::universe::{Universe, UniverseStepInfo};
-use all_is_cubes_gpu::in_wgpu;
+use all_is_cubes_gpu::{in_wgpu, FrameBudget};
 use all_is_cubes_port::file::NonDiskFile;
 use all_is_cubes_render::camera::{GraphicsOptions, StandardCameras, Viewport};
 use all_is_cubes_ui::apps::{CursorIcon, Key};
@@ -419,7 +419,11 @@ impl WebSession {
                 WebRenderer::Wgpu(renderer) => {
                     // note: info text is HTML on web, so no string passed here
                     renderer
-                        .render_frame(inner.session.cursor_result(), |_| String::new())
+                        .render_frame(
+                            inner.session.cursor_result(),
+                            &FrameBudget::SIXTY_FPS, // TODO: try to estimate real refresh rate
+                            |_| String::new(),
+                        )
                         .expect("error in render_frame")
                 }
             };