refactor(render): move lib.rs items to {blobs,bounds,clock,frame,geometry,node_checks,options,paint,renderer,renderer/images,renderer/nodes,renderer/paint,renderer/text,text_geom,threads}.rs

crates/render/src/threads.rs

@@ -0,0 +1,36 @@
+use super::*;
+
+/// A render context on the calling thread. vello_cpu's `RenderContext::new` defaults to a
+/// multithreaded dispatcher, which panics on filter effects (glows, shadows, blur).
+pub(crate) fn single_threaded_context(w: u16, h: u16) -> RenderContext {
+    RenderContext::new_with(w, h, vello_cpu::RenderSettings { num_threads: 0, ..Default::default() })
+}
+
+/// Preferred rasterizer thread count set by the app (Preferences → Performance); negative = automatic.
+static THREADS_OVERRIDE: std::sync::atomic::AtomicI32 = std::sync::atomic::AtomicI32::new(-1);
+
+/// Override the worker-thread count used by renderers created from now on (`None` = automatic).
+pub fn set_default_threads(n: Option<u16>) {
+    THREADS_OVERRIDE.store(n.map_or(-1, i32::from), std::sync::atomic::Ordering::Relaxed);
+}
+
+/// Rasterizer worker threads: 0 on wasm; otherwise one per core up to 8, leaving a core free. On a
+/// 10-core machine 8 workers render a 50,000-path page 1.4× faster than 4 (9 are slower again);
+/// the pixels don't depend on the count (`pixels_do_not_depend_on_the_thread_count`).
+pub fn default_threads() -> u16 {
+    #[cfg(target_arch = "wasm32")]
+    {
+        0
+    }
+    #[cfg(not(target_arch = "wasm32"))]
+    {
+        let o = THREADS_OVERRIDE.load(std::sync::atomic::Ordering::Relaxed);
+        if o >= 0 {
+            return o.min(64) as u16;
+        }
+        if std::env::var_os("VECTORCRAFT_RENDER_THREADS").is_some() {
+            return std::env::var("VECTORCRAFT_RENDER_THREADS").ok().and_then(|v| v.parse().ok()).unwrap_or(0);
+        }
+        std::thread::available_parallelism().map(|n| (n.get().saturating_sub(1)).min(8) as u16).unwrap_or(0)
+    }
+}