feat: window screenshot (PrintWindow), name-based window resolution

crates/client/src/screenshot.rs

@@ -117,6 +117,76 @@ pub fn take_screenshot() -> Result<(String, u32, u32), String> {
     }
 }
 
+/// Capture a specific window using PrintWindow (works even if occluded).
+#[cfg(windows)]
+pub fn take_window_screenshot(window_id: u64) -> Result<(String, u32, u32), String> {
+    use windows::Win32::Foundation::{HWND, RECT};
+    use windows::Win32::Graphics::Gdi::{
+        CreateCompatibleBitmap, CreateCompatibleDC, DeleteDC, DeleteObject,
+        GetDIBits, SelectObject, BITMAPINFO, BITMAPINFOHEADER, DIB_RGB_COLORS,
+    };
+    use windows::Win32::UI::WindowsAndMessaging::{GetWindowRect, PrintWindow, PW_RENDERFULLCONTENT};
+    use windows::Win32::Graphics::Gdi::GetDC;
+    use windows::Win32::Graphics::Gdi::ReleaseDC;
+
+    let hwnd = HWND(window_id as isize);
+
+    unsafe {
+        let mut rect = RECT::default();
+        GetWindowRect(hwnd, &mut rect).map_err(|e| format!("GetWindowRect failed: {e}"))?;
+        let width = (rect.right - rect.left) as u32;
+        let height = (rect.bottom - rect.top) as u32;
+        if width == 0 || height == 0 {
+            return Err(format!("Window has zero size: {width}x{height}"));
+        }
+
+        let hdc_screen = GetDC(None);
+        let hdc_mem = CreateCompatibleDC(hdc_screen);
+        let hbm = CreateCompatibleBitmap(hdc_screen, width as i32, height as i32);
+        let old_obj = SelectObject(hdc_mem, hbm);
+
+        // PrintWindow captures the window even if it's behind others
+        PrintWindow(hwnd, hdc_mem, PW_RENDERFULLCONTENT);
+
+        let mut bmi = BITMAPINFO {
+            bmiHeader: BITMAPINFOHEADER {
+                biSize: std::mem::size_of::<BITMAPINFOHEADER>() as u32,
+                biWidth: width as i32,
+                biHeight: -(height as i32),
+                biPlanes: 1,
+                biBitCount: 32,
+                biCompression: 0,
+                biSizeImage: 0,
+                biXPelsPerMeter: 0,
+                biYPelsPerMeter: 0,
+                biClrUsed: 0,
+                biClrImportant: 0,
+            },
+            bmiColors: [Default::default()],
+        };
+
+        let mut pixel_buf: Vec<u8> = vec![0u8; (width * height * 4) as usize];
+        GetDIBits(hdc_mem, hbm, 0, height, Some(pixel_buf.as_mut_ptr() as *mut _), &mut bmi, DIB_RGB_COLORS);
+
+        SelectObject(hdc_mem, old_obj);
+        DeleteObject(hbm);
+        DeleteDC(hdc_mem);
+        ReleaseDC(None, hdc_screen);
+
+        // BGRA → RGBA
+        for chunk in pixel_buf.chunks_exact_mut(4) { chunk.swap(0, 2); }
+
+        let png_bytes = encode_png(&pixel_buf, width, height)?;
+        let b64 = base64::engine::general_purpose::STANDARD.encode(&png_bytes);
+        Ok((b64, width, height))
+    }
+}
+
+#[cfg(not(windows))]
+pub fn take_window_screenshot(_window_id: u64) -> Result<(String, u32, u32), String> {
+    Err("Window screenshot only supported on Windows".to_string())
+}
+
 #[cfg(not(windows))]
 pub fn take_screenshot() -> Result<(String, u32, u32), String> {
     // Stub for non-Windows builds