Build bodies on the CPU on AMD FirePro under Metal (GPU hang on Mac Pro 2013) (#1171)

The AMD FirePro D300/D500/D700 Metal driver hangs on the tessellation compute shader and macOS resets the GPU, freezing the desktop. Bodies are built on the CPU on that device, and SOLIDCRAFT_CPU_TESS=1 forces the CPU path on any GPU. The check is a tested predicate, and the troubleshooting guide documents the variable.

crates/ui-egui/src/gpu.rs

@@ -834,6 +834,10 @@ fn tessellation(adapter: &wgpu::Adapter, device: &wgpu::Device, queue: &wgpu::Qu
         return None;
     }
     let info = adapter.get_info();
+    if hangs_on_gpu_tessellation(info.backend, &info.name) || std::env::var_os("SOLIDCRAFT_CPU_TESS").is_some() {
+        log::warn!("bodies are built on the CPU on {} ({:?})", info.name, info.backend);
+        return None;
+    }
     match solidcraft_gpu::TessGpu::with_shader(info.name.clone(), device.clone(), queue.clone(), shader) {
         Ok(t) => Some(t),
         Err(e) => {
@@ -843,6 +847,13 @@ fn tessellation(adapter: &wgpu::Adapter, device: &wgpu::Device, queue: &wgpu::Qu
     }
 }
 
+/// A device whose driver hangs on the evaluation shader, so bodies are built on the CPU there:
+/// the AMD FirePro D300/D500/D700 (Mac Pro 2013, Tahiti) under Metal, where macOS resets the GPU
+/// and the whole desktop freezes. `SOLIDCRAFT_CPU_TESS=1` forces CPU evaluation on any device.
+fn hangs_on_gpu_tessellation(backend: wgpu::Backend, name: &str) -> bool {
+    backend == wgpu::Backend::Metal && name.contains("FirePro")
+}
+
 /// Create the pipelines. Call once with the app's render state and its depth/stencil/MSAA
 /// settings. Without a stencil the section cap does not hide the inside of cut bodies. Without
 /// `gpu_meshing` (safe mode) bodies are meshed on the CPU.
@@ -1182,7 +1193,18 @@ pub fn analysis_colors(c: &crate::theme::AnalysisColors) -> [f32; 36] {
 
 #[cfg(test)]
 mod tests {
-    use egui_wgpu::wgpu::naga;
+    use egui_wgpu::wgpu::{self, naga};
+
+    /// Only the FirePro under Metal skips GPU evaluation; the same card under another backend
+    /// and other Metal GPUs keep it.
+    #[test]
+    fn firepro_under_metal_builds_bodies_on_the_cpu() {
+        assert!(super::hangs_on_gpu_tessellation(wgpu::Backend::Metal, "AMD FirePro D500"));
+        assert!(super::hangs_on_gpu_tessellation(wgpu::Backend::Metal, "AMD FirePro D700"));
+        assert!(!super::hangs_on_gpu_tessellation(wgpu::Backend::Metal, "Apple M2"));
+        assert!(!super::hangs_on_gpu_tessellation(wgpu::Backend::Metal, "AMD Radeon Pro 560X"));
+        assert!(!super::hangs_on_gpu_tessellation(wgpu::Backend::Vulkan, "AMD FirePro W5100"));
+    }
 
     /// The viewport shader parses and validates (a bad shader would only fail at run time).
     #[test]