Add Rust API to grab the contents of a slint::Window into a slint::SharedImageBuffer

internal/backends/linuxkms/fullscreenwindowadapter.rs

@@ -8,6 +8,7 @@ use std::pin::Pin;
 use std::rc::Rc;
 
 use i_slint_core::api::{LogicalPosition, PhysicalSize as PhysicalWindowSize};
+use i_slint_core::graphics::SharedImageBuffer;
 use i_slint_core::graphics::{euclid, Image};
 use i_slint_core::item_rendering::ItemRenderer;
 use i_slint_core::lengths::LogicalRect;
@@ -32,6 +33,7 @@ pub trait FullscreenRenderer {
         &self,
         event_loop_handle: crate::calloop_backend::EventLoopHandle,
     ) -> Result<(), PlatformError>;
+    fn grab_window(&self) -> Result<SharedImageBuffer, PlatformError>;
 }
 
 pub struct FullscreenWindowAdapter {
@@ -69,6 +71,10 @@ impl WindowAdapter for FullscreenWindowAdapter {
         }
         Ok(())
     }
+
+    fn grab_window(&self) -> Result<SharedImageBuffer, PlatformError> {
+        self.renderer.grab_window()
+    }
 }
 
 impl FullscreenWindowAdapter {

internal/backends/linuxkms/renderer/femtovg.rs

@@ -3,6 +3,7 @@
 
 use std::{num::NonZeroU32, rc::Rc};
 
+use i_slint_core::graphics::SharedImageBuffer;
 use i_slint_core::item_rendering::ItemRenderer;
 use i_slint_core::platform::PlatformError;
 use i_slint_renderer_femtovg::FemtoVGRendererExt;
@@ -201,4 +202,8 @@ impl crate::fullscreenwindowadapter::FullscreenRenderer for FemtoVGRendererAdapt
     ) -> Result<(), PlatformError> {
         self.gbm_display.clone().register_page_flip_handler(event_loop_handle)
     }
+
+    fn grab_window(&self) -> Result<SharedImageBuffer, PlatformError> {
+        self.renderer.screenshot()
+    }
 }

internal/backends/linuxkms/renderer/skia.rs

@@ -6,6 +6,7 @@ use std::rc::Rc;
 use crate::display::RenderingRotation;
 use crate::drmoutput::DrmOutput;
 use i_slint_core::api::PhysicalSize as PhysicalWindowSize;
+use i_slint_core::graphics::SharedImageBuffer;
 use i_slint_core::item_rendering::ItemRenderer;
 use i_slint_core::platform::PlatformError;
 use i_slint_renderer_skia::skia_safe;
@@ -162,6 +163,10 @@ impl crate::fullscreenwindowadapter::FullscreenRenderer for SkiaRendererAdapter
     ) -> Result<(), PlatformError> {
         self.presenter.clone().register_page_flip_handler(event_loop_handle)
     }
+
+    fn grab_window(&self) -> Result<SharedImageBuffer, PlatformError> {
+        self.renderer.screenshot()
+    }
 }
 struct DrmDumbBufferAccess {
     display: Rc<crate::display::swdisplay::SoftwareBufferDisplay>,

internal/backends/linuxkms/renderer/sw.rs

@@ -4,9 +4,11 @@
 //! Delegate the rendering to the [`i_slint_core::software_renderer::SoftwareRenderer`]
 
 use i_slint_core::api::PhysicalSize as PhysicalWindowSize;
+use i_slint_core::graphics::{SharedImageBuffer, SharedPixelBuffer};
 use i_slint_core::platform::PlatformError;
 pub use i_slint_core::software_renderer::SoftwareRenderer;
 use i_slint_core::software_renderer::{PremultipliedRgbaColor, RepaintBufferType, TargetPixel};
+use std::cell::Cell;
 use std::rc::Rc;
 
 use crate::display::{Presenter, RenderingRotation};
@@ -16,6 +18,7 @@ pub struct SoftwareRendererAdapter {
     renderer: SoftwareRenderer,
     display: Rc<crate::display::swdisplay::SoftwareBufferDisplay>,
     size: PhysicalWindowSize,
+    force_next_frame_new_buffer: Cell<bool>,
 }
 
 #[repr(transparent)]
@@ -73,7 +76,12 @@ impl SoftwareRendererAdapter {
         let (width, height) = display.drm_output.size();
         let size = i_slint_core::api::PhysicalSize::new(width, height);
 
-        let renderer = Box::new(Self { renderer: SoftwareRenderer::new(), display, size });
+        let renderer = Box::new(Self {
+            renderer: SoftwareRenderer::new(),
+            display,
+            size,
+            force_next_frame_new_buffer: Default::default(),
+        });
 
         eprintln!("Using Software renderer");
 
@@ -97,10 +105,14 @@ impl crate::fullscreenwindowadapter::FullscreenRenderer for SoftwareRendererAdap
         ready_for_next_animation_frame: Box<dyn FnOnce()>,
     ) -> Result<(), PlatformError> {
         self.display.map_back_buffer(&mut |mut pixels, age| {
-            self.renderer.set_repaint_buffer_type(match age {
-                1 => RepaintBufferType::ReusedBuffer,
-                2 => RepaintBufferType::SwappedBuffers,
-                _ => RepaintBufferType::NewBuffer,
+            self.renderer.set_repaint_buffer_type(if self.force_next_frame_new_buffer.take() {
+                RepaintBufferType::NewBuffer
+            } else {
+                match age {
+                    1 => RepaintBufferType::ReusedBuffer,
+                    2 => RepaintBufferType::SwappedBuffers,
+                    _ => RepaintBufferType::NewBuffer,
+                }
             });
 
             self.renderer.set_rendering_rotation(match rotation {
@@ -137,4 +149,19 @@ impl crate::fullscreenwindowadapter::FullscreenRenderer for SoftwareRendererAdap
     ) -> Result<(), PlatformError> {
         self.display.drm_output.register_page_flip_handler(event_loop_handle)
     }
+
+    fn grab_window(&self) -> Result<SharedImageBuffer, PlatformError> {
+        let width = self.size.width;
+        let height = self.size.height;
+
+        let mut target_buffer =
+            SharedPixelBuffer::<i_slint_core::graphics::Rgb8Pixel>::new(width, height);
+
+        self.force_next_frame_new_buffer.set(true);
+        self.renderer.set_repaint_buffer_type(RepaintBufferType::NewBuffer);
+
+        let _ = self.renderer.render(target_buffer.make_mut_slice(), width as usize);
+
+        Ok(SharedImageBuffer::RGB8(target_buffer))
+    }
 }

internal/backends/qt/qt_window.rs

@@ -1979,6 +1979,28 @@ impl WindowAdapter for QtWindow {
     fn internal(&self, _: i_slint_core::InternalToken) -> Option<&dyn WindowAdapterInternal> {
         Some(self)
     }
+
+    fn grab_window(&self) -> Result<SharedImageBuffer, PlatformError> {
+        let widget_ptr = self.widget_ptr();
+
+        let size = cpp! {unsafe [widget_ptr as "QWidget*"] -> qttypes::QSize as "QSize" {
+            return widget_ptr->size();
+        }};
+
+        let rgb8_data = cpp! {unsafe [widget_ptr as "QWidget*"] -> qttypes::QByteArray as "QByteArray" {
+            QPixmap pixmap = widget_ptr->grab();
+            QImage image = pixmap.toImage();
+            image.convertTo(QImage::Format_RGB888);
+            return QByteArray(reinterpret_cast<const char *>(image.constBits()), image.sizeInBytes());
+        }};
+
+        let buffer = i_slint_core::graphics::SharedPixelBuffer::<i_slint_core::graphics::Rgb8Pixel>::clone_from_slice(
+            rgb8_data.to_slice(),
+            size.width,
+            size.height,
+        );
+        Ok(i_slint_core::graphics::SharedImageBuffer::RGB8(buffer))
+    }
 }
 
 fn into_qsize(logical_size: i_slint_core::api::LogicalSize) -> qttypes::QSize {

internal/backends/winit/lib.rs

@@ -32,7 +32,7 @@ pub struct SlintUserEvent(CustomEvent);
 mod renderer {
     use std::rc::Rc;
 
-    use i_slint_core::platform::PlatformError;
+    use i_slint_core::{graphics::SharedImageBuffer, platform::PlatformError};
 
     pub trait WinitCompatibleRenderer {
         fn render(&self, window: &i_slint_core::api::Window) -> Result<(), PlatformError>;
@@ -46,6 +46,11 @@ mod renderer {
         fn resumed(&self, _winit_window: Rc<winit::window::Window>) -> Result<(), PlatformError> {
             Ok(())
         }
+
+        fn grab_window(
+            &self,
+            window: &i_slint_core::api::Window,
+        ) -> Result<SharedImageBuffer, PlatformError>;
     }
 
     #[cfg(feature = "renderer-femtovg")]

internal/backends/winit/renderer/femtovg.rs

@@ -60,4 +60,11 @@ impl super::WinitCompatibleRenderer for GlutinFemtoVGRenderer {
     fn as_core_renderer(&self) -> &dyn Renderer {
         &self.renderer
     }
+
+    fn grab_window(
+        &self,
+        _window: &i_slint_core::api::Window,
+    ) -> Result<i_slint_core::graphics::SharedImageBuffer, PlatformError> {
+        self.renderer.screenshot()
+    }
 }

internal/backends/winit/renderer/skia.rs

@@ -101,4 +101,11 @@ impl super::WinitCompatibleRenderer for WinitSkiaRenderer {
             winit_window.scale_factor() as f32,
         )
     }
+
+    fn grab_window(
+        &self,
+        _window: &i_slint_core::api::Window,
+    ) -> Result<i_slint_core::graphics::SharedImageBuffer, PlatformError> {
+        self.renderer.screenshot()
+    }
 }

internal/backends/winit/renderer/sw.rs

@@ -5,11 +5,13 @@
 
 use core::num::NonZeroU32;
 use core::ops::DerefMut;
-use i_slint_core::graphics::Rgb8Pixel;
+use i_slint_core::graphics::{Rgb8Pixel, SharedImageBuffer, SharedPixelBuffer};
 use i_slint_core::platform::PlatformError;
 pub use i_slint_core::software_renderer::SoftwareRenderer;
 use i_slint_core::software_renderer::{PremultipliedRgbaColor, RepaintBufferType, TargetPixel};
-use std::{cell::RefCell, rc::Rc};
+use std::cell::Cell;
+use std::cell::RefCell;
+use std::rc::Rc;
 
 use super::WinitCompatibleRenderer;
 
@@ -18,6 +20,7 @@ pub struct WinitSoftwareRenderer {
     _context: softbuffer::Context<Rc<winit::window::Window>>,
     surface: RefCell<softbuffer::Surface<Rc<winit::window::Window>, Rc<winit::window::Window>>>,
     winit_window: Rc<winit::window::Window>,
+    force_next_frame_new_buffer: Cell<bool>,
 }
 
 #[repr(transparent)]
@@ -90,6 +93,7 @@ impl WinitSoftwareRenderer {
                 _context: context,
                 surface: RefCell::new(surface),
                 winit_window: winit_window.clone(),
+                force_next_frame_new_buffer: Default::default(),
             }),
             winit_window,
         ))
@@ -116,11 +120,14 @@ impl super::WinitCompatibleRenderer for WinitSoftwareRenderer {
             .buffer_mut()
             .map_err(|e| format!("Error retrieving softbuffer rendering buffer: {e}"))?;
 
-        let age = target_buffer.age();
-        self.renderer.set_repaint_buffer_type(match age {
-            1 => RepaintBufferType::ReusedBuffer,
-            2 => RepaintBufferType::SwappedBuffers,
-            _ => RepaintBufferType::NewBuffer,
+        self.renderer.set_repaint_buffer_type(if self.force_next_frame_new_buffer.take() {
+            RepaintBufferType::NewBuffer
+        } else {
+            match target_buffer.age() {
+                1 => RepaintBufferType::ReusedBuffer,
+                2 => RepaintBufferType::SwappedBuffers,
+                _ => RepaintBufferType::NewBuffer,
+            }
         });
 
         let region = if std::env::var_os("SLINT_LINE_BY_LINE").is_none() {
@@ -172,6 +179,7 @@ impl super::WinitCompatibleRenderer for WinitSoftwareRenderer {
                 }])
                 .map_err(|e| format!("Error presenting softbuffer buffer: {e}"))?;
         }
+
         Ok(())
     }
 
@@ -184,4 +192,29 @@ impl super::WinitCompatibleRenderer for WinitSoftwareRenderer {
         // and the buffer age doesn't respect that, so clean the partial rendering cache
         self.renderer.set_repaint_buffer_type(RepaintBufferType::NewBuffer);
     }
+
+    fn grab_window(
+        &self,
+        window: &i_slint_core::api::Window,
+    ) -> Result<SharedImageBuffer, PlatformError> {
+        let size = window.size();
+
+        let Some((width, height)) = size.width.try_into().ok().zip(size.height.try_into().ok())
+        else {
+            // Nothing to render
+            return Err("grab_window() called on window with invalid size".into());
+        };
+
+        // We could use Surface::fetch() here, but it's only implemented on X11 and Web.
+
+        let mut target_buffer =
+            SharedPixelBuffer::<i_slint_core::graphics::Rgb8Pixel>::new(width, height);
+
+        self.force_next_frame_new_buffer.set(true);
+        self.renderer.set_repaint_buffer_type(RepaintBufferType::NewBuffer);
+
+        let _ = self.renderer.render(target_buffer.make_mut_slice(), width as usize);
+
+        Ok(SharedImageBuffer::RGB8(target_buffer))
+    }
 }

internal/backends/winit/winitwindowadapter.rs

@@ -643,6 +643,10 @@ impl WindowAdapter for WinitWindowAdapter {
     ) -> Result<raw_window_handle::DisplayHandle<'_>, raw_window_handle::HandleError> {
         raw_window_handle::HasDisplayHandle::display_handle(&self.winit_window)
     }
+
+    fn grab_window(&self) -> Result<SharedImageBuffer, PlatformError> {
+        self.renderer().grab_window(self.window())
+    }
 }
 
 impl WindowAdapterInternal for WinitWindowAdapter {

internal/core/api.rs

@@ -9,6 +9,7 @@ This module contains types that are public and re-exported in the slint-rs as we
 
 #[cfg(target_has_atomic = "ptr")]
 pub use crate::future::*;
+use crate::graphics::SharedImageBuffer;
 use crate::input::{KeyEventType, MouseEvent};
 use crate::item_tree::ItemTreeVTable;
 use crate::window::{WindowAdapter, WindowInner};
@@ -622,6 +623,14 @@ impl Window {
     pub fn window_handle(&self) -> WindowHandle {
         WindowHandle { adapter: self.0.window_adapter() }
     }
+
+    /// Returns an image buffer with the rendered contents.
+    ///
+    /// Note that this function may be slow to call. Reading from the framebuffer previously
+    /// rendered, too, may take a long time.
+    pub fn grab_window(&self) -> Result<SharedImageBuffer, PlatformError> {
+        self.0.window_adapter().grab_window()
+    }
 }
 
 pub use crate::SharedString;

internal/core/window.rs

@@ -10,7 +10,7 @@ use crate::api::{
     CloseRequestResponse, LogicalPosition, PhysicalPosition, PhysicalSize, PlatformError, Window,
     WindowPosition, WindowSize,
 };
-use crate::graphics::Point;
+use crate::graphics::{Point, SharedImageBuffer};
 use crate::input::{
     key_codes, ClickState, InternalKeyboardModifierState, KeyEvent, KeyEventType, MouseEvent,
     MouseInputState, TextCursorBlinker,
@@ -153,6 +153,12 @@ pub trait WindowAdapter {
     ) -> Result<raw_window_handle_06::DisplayHandle<'_>, raw_window_handle_06::HandleError> {
         Err(raw_window_handle_06::HandleError::NotSupported)
     }
+
+    /// Re-implement this function to support [`Window::grab_window()`], i.e. return
+    /// the contents of the window in an image buffer.
+    fn grab_window(&self) -> Result<SharedImageBuffer, PlatformError> {
+        Err("WindowAdapter::grab_window is not implemented by the platform".into())
+    }
 }
 
 /// Implementation details behind [`WindowAdapter`], but since this

internal/renderers/femtovg/lib.rs

@@ -11,9 +11,9 @@ use std::rc::{Rc, Weak};
 
 use i_slint_common::sharedfontdb;
 use i_slint_core::api::{RenderingNotifier, RenderingState, SetRenderingNotifierError};
-use i_slint_core::graphics::BorderRadius;
-use i_slint_core::graphics::FontRequest;
 use i_slint_core::graphics::{euclid, rendering_metrics_collector::RenderingMetricsCollector};
+use i_slint_core::graphics::{BorderRadius, SharedImageBuffer};
+use i_slint_core::graphics::{FontRequest, SharedPixelBuffer};
 use i_slint_core::item_rendering::ItemRenderer;
 use i_slint_core::items::TextWrap;
 use i_slint_core::lengths::{
@@ -172,6 +172,23 @@ impl FemtoVGRenderer {
         })
     }
 
+    /// Returns an image buffer of what was rendered last by reading the previous front buffer (using glReadPixels).
+    pub fn screenshot(&self) -> Result<SharedImageBuffer, PlatformError> {
+        self.opengl_context.ensure_current()?;
+        let screenshot = self
+            .canvas
+            .borrow_mut()
+            .screenshot()
+            .map_err(|e| format!("FemtoVG error reading current back buffer: {e}"))?;
+
+        use rgb::ComponentBytes;
+        Ok(SharedImageBuffer::RGBA8(SharedPixelBuffer::clone_from_slice(
+            screenshot.buf().as_bytes(),
+            screenshot.width() as u32,
+            screenshot.height() as u32,
+        )))
+    }
+
     /// Render the scene using OpenGL.
     pub fn render(&self) -> Result<(), i_slint_core::platform::PlatformError> {
         self.internal_render_with_post_callback(