@@ -11,7 +11,13 @@
 //! Metal-compatible IOSurface-backed BGRA buffer from a fixed ring, ready for
 //! `paint_surface` with zero further CPU touches.
 //!
-//! Run: cargo run -p cap-desktop-gpui --example camera-preview-convert-benchmark --release
+//! `--bubble` instead measures the preview's conversion at full camera size
+//! (what `main` converts every frame to) against the bubble-sized cover
+//! target, for small/medium/large bubbles on a 2x display, mirrored and not:
+//! per-frame time, bytes written per frame, the ring's resident memory, and
+//! how close each looks once gpui's linear sampler draws it at bubble size.
+//!
+//! Run: cargo run -p cap-desktop-gpui --example camera-preview-convert-benchmark --release [-- --bubble]
 
 #[cfg(not(target_os = "macos"))]
 fn main() {
@@ -20,7 +26,11 @@ fn main() {
 
 #[cfg(target_os = "macos")]
 fn main() {
-    macos::run();
+    if std::env::args().any(|arg| arg == "--bubble") {
+        macos::bubble();
+    } else {
+        macos::run();
+    }
 }
 
 #[cfg(target_os = "macos")]
@@ -249,4 +259,284 @@ mod macos {
             );
         }
     }
+
+    type CreateRotationSession = unsafe extern "C-unwind" fn(
+        Option<&cf::Allocator>,
+        *mut Option<arc::R<vt::PixelRotationSession>>,
+    ) -> cidre::os::Status;
+    type RotateImage = unsafe extern "C-unwind" fn(
+        &vt::PixelRotationSession,
+        &cv::PixelBuf,
+        &mut cv::PixelBuf,
+    ) -> cidre::os::Status;
+
+    struct FlipSession {
+        session: arc::R<vt::PixelRotationSession>,
+        rotate_image: RotateImage,
+    }
+
+    impl FlipSession {
+        fn new() -> Self {
+            let create = unsafe {
+                libc::dlsym(libc::RTLD_DEFAULT, c"VTPixelRotationSessionCreate".as_ptr())
+            };
+            let rotate = unsafe {
+                libc::dlsym(
+                    libc::RTLD_DEFAULT,
+                    c"VTPixelRotationSessionRotateImage".as_ptr(),
+                )
+            };
+            let key = unsafe {
+                libc::dlsym(
+                    libc::RTLD_DEFAULT,
+                    c"kVTPixelRotationPropertyKey_FlipHorizontalOrientation".as_ptr(),
+                )
+            };
+            assert!(!create.is_null() && !rotate.is_null() && !key.is_null());
+            let create =
+                unsafe { std::mem::transmute::<*mut libc::c_void, CreateRotationSession>(create) };
+            let rotate_image =
+                unsafe { std::mem::transmute::<*mut libc::c_void, RotateImage>(rotate) };
+            let key = unsafe { key.cast::<*const cf::String>().read().as_ref() }
+                .expect("flip property key");
+            let mut session = None;
+            unsafe { create(None, &mut session).result() }.expect("rotation session");
+            let mut session = session.expect("rotation session");
+            session
+                .set_prop(key, Some(cf::Boolean::value_true().as_ref()))
+                .expect("flip property");
+            Self {
+                session,
+                rotate_image,
+            }
+        }
+
+        fn rotate(&self, source: &cv::PixelBuf, destination: &mut cv::PixelBuf) {
+            unsafe { (self.rotate_image)(&self.session, source, destination).result() }
+                .expect("flip");
+        }
+    }
+
+    const MAIN_RING: usize = 4;
+    const PREVIEW_RING: usize = 6;
+    const QUALITY_SEED: u8 = 200;
+
+    struct Case {
+        dims: (usize, usize),
+        stats: (f64, f64, f64),
+        buffer_bytes: usize,
+        output: Vec<u8>,
+    }
+
+    fn bgra_ring(count: usize, (width, height): (usize, usize)) -> Vec<arc::R<cv::PixelBuf>> {
+        let attrs = iosurface_bgra_attrs();
+        (0..count)
+            .map(|_| {
+                let buf = cv::PixelBuf::new(width, height, cv::PixelFormat::_32_BGRA, Some(&attrs))
+                    .expect("IOSurface BGRA destination");
+                assert!(buf.io_surf().is_some());
+                buf
+            })
+            .collect()
+    }
+
+    fn run_case(
+        sources: &[arc::R<cv::PixelBuf>],
+        quality_source: &cv::PixelBuf,
+        dims: (usize, usize),
+        mirrored: bool,
+    ) -> Case {
+        let mut session = vt::PixelTransferSession::new().expect("VT session");
+        session.set_realtime(true).expect("VT realtime");
+        let flip = mirrored.then(FlipSession::new);
+        let mut ring = bgra_ring(PREVIEW_RING, dims);
+        let scratch = flip.as_ref().map(|_| bgra_ring(1, dims).remove(0));
+        let mut stats = Stats::new();
+        let mut next = 0;
+        for iteration in 0..(WARMUP + ITERATIONS) {
+            let source = &sources[iteration % sources.len()];
+            let out = &mut ring[next];
+            let started = Instant::now();
+            match (&flip, &scratch) {
+                (Some(flip), Some(scratch)) => {
+                    session.transfer(source, scratch).expect("transfer");
+                    flip.rotate(scratch, out);
+                }
+                _ => session.transfer(source, out).expect("transfer"),
+            }
+            let elapsed = started.elapsed().as_secs_f64() * 1e6;
+            next = (next + 1) % PREVIEW_RING;
+            if iteration >= WARMUP {
+                stats.push(elapsed);
+            }
+        }
+        session
+            .transfer(quality_source, &ring[0])
+            .expect("quality transfer");
+        let buffer_bytes = {
+            let ptr = ring[0].as_ref() as *const cv::PixelBuf;
+            unsafe { CVPixelBufferGetBytesPerRow(ptr) * dims.1 }
+        };
+        let output = read_bgra(&mut ring[0], dims.0, dims.1);
+        Case {
+            dims,
+            stats: stats.report(),
+            buffer_bytes,
+            output,
+        }
+    }
+
+    fn make_quality_source(width: usize, height: usize) -> arc::R<cv::PixelBuf> {
+        let mut buf = make_420v_source(width, height, QUALITY_SEED);
+        unsafe {
+            buf.lock_base_addr(cv::pixel_buffer::LockFlags::DEFAULT)
+                .result()
+                .expect("lock 420v source");
+            let y_stride = buf.plane_bytes_per_row(0);
+            let y_base = buf.plane_base_address(0).cast_mut();
+            for row in 0..height {
+                for col in 0..width {
+                    let x = col as f64 / width as f64;
+                    let y = row as f64 / height as f64;
+                    let smooth = 0.5 + 0.25 * (x * 23.0).sin() * (y * 17.0).cos();
+                    let detail = 0.15 * ((x * 640.0).sin() * (y * 360.0).sin());
+                    let edge = if ((col * 8 / width) + (row * 6 / height)) % 2 == 0 {
+                        0.1
+                    } else {
+                        -0.1
+                    };
+                    let value = (smooth + detail + edge).clamp(0.0, 1.0);
+                    *y_base.add(row * y_stride + col) = (16.0 + value * 219.0) as u8;
+                }
+            }
+            buf.unlock_lock_base_addr(cv::pixel_buffer::LockFlags::DEFAULT);
+        }
+        buf
+    }
+
+    fn area_average(pixels: &[u8], src: (usize, usize), dst: (usize, usize)) -> Vec<f64> {
+        let mut out = vec![0.0; dst.0 * dst.1 * 4];
+        for y in 0..dst.1 {
+            let y0 = y * src.1 / dst.1;
+            let y1 = ((y + 1) * src.1 / dst.1).max(y0 + 1);
+            for x in 0..dst.0 {
+                let x0 = x * src.0 / dst.0;
+                let x1 = ((x + 1) * src.0 / dst.0).max(x0 + 1);
+                let mut sum = [0.0; 4];
+                for sy in y0..y1 {
+                    for sx in x0..x1 {
+                        let offset = (sy * src.0 + sx) * 4;
+                        for (channel, total) in sum.iter_mut().enumerate() {
+                            *total += pixels[offset + channel] as f64;
+                        }
+                    }
+                }
+                let count = ((y1 - y0) * (x1 - x0)) as f64;
+                for (channel, total) in sum.iter().enumerate() {
+                    out[(y * dst.0 + x) * 4 + channel] = total / count;
+                }
+            }
+        }
+        out
+    }
+
+    fn linear_sample(pixels: &[u8], src: (usize, usize), dst: (usize, usize)) -> Vec<f64> {
+        let mut out = vec![0.0; dst.0 * dst.1 * 4];
+        let texel =
+            |x: usize, y: usize, channel: usize| pixels[(y * src.0 + x) * 4 + channel] as f64;
+        for y in 0..dst.1 {
+            let v = ((y as f64 + 0.5) * src.1 as f64 / dst.1 as f64 - 0.5)
+                .clamp(0.0, (src.1 - 1) as f64);
+            let (y0, fy) = (v.floor() as usize, v.fract());
+            let y1 = (y0 + 1).min(src.1 - 1);
+            for x in 0..dst.0 {
+                let u = ((x as f64 + 0.5) * src.0 as f64 / dst.0 as f64 - 0.5)
+                    .clamp(0.0, (src.0 - 1) as f64);
+                let (x0, fx) = (u.floor() as usize, u.fract());
+                let x1 = (x0 + 1).min(src.0 - 1);
+                for channel in 0..4 {
+                    let top = texel(x0, y0, channel) * (1.0 - fx) + texel(x1, y0, channel) * fx;
+                    let bottom = texel(x0, y1, channel) * (1.0 - fx) + texel(x1, y1, channel) * fx;
+                    out[(y * dst.0 + x) * 4 + channel] = top * (1.0 - fy) + bottom * fy;
+                }
+            }
+        }
+        out
+    }
+
+    fn psnr(reference: &[f64], candidate: &[f64]) -> f64 {
+        let mut squared = 0.0;
+        let mut count = 0usize;
+        for (pixel, other) in reference.chunks_exact(4).zip(candidate.chunks_exact(4)) {
+            for (a, b) in pixel[..3].iter().zip(&other[..3]) {
+                squared += (a - b).powi(2);
+                count += 1;
+            }
+        }
+        let mse = squared / count as f64;
+        if mse == 0.0 {
+            return f64::INFINITY;
+        }
+        10.0 * (255.0f64.powi(2) / mse).log10()
+    }
+
+    fn mb(bytes: usize) -> f64 {
+        bytes as f64 / 1_048_576.0
+    }
+
+    pub fn bubble() {
+        let bubbles = [
+            ("small 230pt round", (460.0f32, 460.0f32)),
+            ("medium 400pt round", (800.0, 800.0)),
+            ("large 600pt full", (600.0 * 16.0 / 9.0 * 2.0, 1200.0)),
+        ];
+        println!(
+            "| source | bubble | mirrored | path | output | mean us | p50 us | p95 us | MB written/frame | ring MB | PSNR at bubble size dB |"
+        );
+        println!("|---|---|---|---|---|---|---|---|---|---|---|");
+        for (width, height) in [(1280usize, 720usize), (1920, 1080), (3840, 2160)] {
+            let sources: Vec<_> = (0..SOURCE_RING)
+                .map(|seed| make_420v_source(width, height, seed as u8))
+                .collect();
+            let quality_source = make_quality_source(width, height);
+            for mirrored in [false, true] {
+                let passes = if mirrored { 2 } else { 1 };
+                let scratch = usize::from(mirrored);
+                let full = run_case(&sources, &quality_source, (width, height), mirrored);
+                for (label, physical) in bubbles {
+                    let displayed = cap_gpui_kernels::camera_preview::cover_dimensions(
+                        (width, height),
+                        (physical.0.ceil() as usize, physical.1.ceil() as usize),
+                    );
+                    let target = cap_gpui_kernels::camera_preview::quantized_target(physical)
+                        .map_or((width, height), |target| {
+                            cap_gpui_kernels::camera_preview::cover_dimensions(
+                                (width, height),
+                                target,
+                            )
+                        });
+                    let bubble = run_case(&sources, &quality_source, target, mirrored);
+                    let reference = area_average(&full.output, full.dims, displayed);
+                    for (path, case, slots) in [
+                        ("main (full size)", &full, MAIN_RING),
+                        ("branch (bubble)", &bubble, PREVIEW_RING),
+                    ] {
+                        let (mean, p50, p95) = case.stats;
+                        let shown = linear_sample(&case.output, case.dims, displayed);
+                        println!(
+                            "| {width}x{height} | {label} | {mirrored} | {path} | {}x{} | {mean:.1} | {p50:.1} | {p95:.1} | {:.2} | {:.1} | {:.2} |",
+                            case.dims.0,
+                            case.dims.1,
+                            mb(case.buffer_bytes * passes),
+                            mb(case.buffer_bytes * (slots + scratch)),
+                            psnr(&reference, &shown),
+                        );
+                    }
+                }
+            }
+        }
+        println!(
+            "ring MB: main keeps {MAIN_RING} slots (#2761 and this branch {PREVIEW_RING}), plus one scratch buffer when mirrored; PSNR compares gpui's linear sampling of each output at the displayed cover size against an area average of the full-size conversion."
+        );
+    }
 }