feat(ffvk): bindgen shim for FFmpeg's Vulkan hwcontext (pf-ffvk)

ffmpeg-sys-next binds a curated header list that omits every hwcontext_*.h, so AVVulkanDeviceContext/AVVulkanFramesContext/AVVkFrame — the surface that lets FFmpeg's Vulkan Video decoder run on the presenter's own VkDevice and hand the decoded VkImages back — had no Rust bindings at all. pf-ffvk generates them at build time from the SYSTEM headers, which is the only ABI-safe option: the struct layout depends on FF_API_* deprecation gates resolved in libavutil/version.h (confirmed: FFmpeg 8.1 still carries the FIXED_QUEUES fields). Ships ash<->vulkan.h handle conversions; opaque AVHW*/AVFrame types keep ffmpeg-sys-next the owner of the core surface (pointer casts across). Needs vulkan-headers (Arch) / libvulkan-dev (CI, added); PF_FFVK_VULKAN_INCLUDE overrides for cross builds. Verified: bindgen layout tests pass, av_vk_frame_alloc links and zero-initializes. Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
2026-07-07 21:21:37 +02:00
parent 6dd2213a20
commit 58ccd530fc
7 changed files with 203 additions and 0 deletions
@@ -0,0 +1,75 @@
+//! Generate bindings for `libavutil/hwcontext_vulkan.h` against the SYSTEM headers.
+//!
+//! ffmpeg-sys-next binds a curated header list that omits every hwcontext_*.h; the
+//! Vulkan hwcontext structs (`AVVulkanDeviceContext`, `AVVkFrame`) are what let us run
+//! FFmpeg's Vulkan Video decoder on the presenter's own VkDevice and read the decoded
+//! VkImages back. Their layout depends on compile-time FF_API_* deprecation gates in
+//! libavutil/version.h, so bindgen over the installed header is the only ABI-safe
+//! source of truth — hand transcription would silently skew on the next FFmpeg bump.
+//!
+//! Non-Linux targets get an empty file: the workspace builds on macOS (clients/apple is
+//! the client there), and this shim is Linux-client plumbing only.
+
+use std::env;
+use std::path::PathBuf;
+
+fn main() {
+    println!("cargo:rerun-if-changed=wrapper.h");
+    let out = PathBuf::from(env::var("OUT_DIR").unwrap()).join("bindings.rs");
+
+    if env::var("CARGO_CFG_TARGET_OS").as_deref() != Ok("linux") {
+        std::fs::write(&out, "// pf-ffvk: Linux-only, empty on this target\n").unwrap();
+        return;
+    }
+
+    // Include paths from pkg-config (libavutil for the hwcontext header; the Vulkan
+    // headers usually live in /usr/include, but honor a registered vulkan.pc too).
+    // PF_FFVK_VULKAN_INCLUDE prepends an explicit Vulkan-Headers include dir — for
+    // cross builds and boxes without the system package.
+    println!("cargo:rerun-if-env-changed=PF_FFVK_VULKAN_INCLUDE");
+    let mut includes: Vec<PathBuf> = Vec::new();
+    if let Ok(dir) = env::var("PF_FFVK_VULKAN_INCLUDE") {
+        includes.push(PathBuf::from(dir));
+    }
+    let avutil = pkg_config::Config::new()
+        .cargo_metadata(false)
+        .probe("libavutil")
+        .expect("pkg-config: libavutil not found — install the FFmpeg dev package");
+    includes.extend(avutil.include_paths);
+    if let Ok(vk) = pkg_config::Config::new()
+        .cargo_metadata(false)
+        .probe("vulkan")
+    {
+        includes.extend(vk.include_paths);
+    }
+
+    let mut builder = bindgen::Builder::default()
+        .header("wrapper.h")
+        // The whole point of this crate: the Vulkan hwcontext surface…
+        .allowlist_type("AVVulkan.*")
+        .allowlist_type("AVVkFrame.*")
+        .allowlist_function("av_vk_frame_alloc")
+        .allowlist_function("av_vkfmt_from_pixfmt")
+        // …plus nothing else of FFmpeg: the core types these structs reference only
+        // ever appear behind pointers here, so keep them opaque instead of duplicating
+        // ffmpeg-sys-next's definitions (callers cast pointers between the crates).
+        .opaque_type("AVHWDeviceContext")
+        .opaque_type("AVHWFramesContext")
+        .opaque_type("AVBufferRef")
+        .opaque_type("AVFrame")
+        .derive_debug(false)
+        .layout_tests(true);
+    for dir in &includes {
+        builder = builder.clang_arg(format!("-I{}", dir.display()));
+    }
+    let bindings = builder.generate().expect(
+        "bindgen over libavutil/hwcontext_vulkan.h failed — is `vulkan-headers` installed? \
+         (the header includes <vulkan/vulkan.h>)",
+    );
+    bindings.write_to_file(&out).unwrap();
+
+    // The av_vk_* symbols live in libavutil, which ffmpeg-sys-next already links into
+    // every consumer of this crate; no extra link flags needed. Emitting the lib anyway
+    // keeps `cargo test -p pf-ffvk` linking standalone.
+    println!("cargo:rustc-link-lib=avutil");
+}