examples: overlay-composition: Use cairo's new ImageSurfaceDataOwned to get rid of unsafe code

examples/src/bin/overlay-composition.rs

@@ -7,10 +7,6 @@
 // {videotestsrc} - {overlaycomposition} - {capsfilter} - {videoconvert} - {autovideosink}
 // The capsfilter element allows us to dictate the video resolution we want for the
 // videotestsrc and the overlaycomposition element.
-//
-// There is a small amount of unsafe code that demonstrates how to work around
-// Cairo's internal refcounting of the target buffer surface
-#![allow(clippy::non_send_fields_in_send_ty)]
 
 use gst::prelude::*;
 
@@ -150,36 +146,13 @@ fn create_pipeline() -> Result<gst::Pipeline, Error> {
         let angle = 2.0 * PI * (timestamp % (10 * gst::ClockTime::SECOND)).nseconds() as f64
             / (10.0 * gst::ClockTime::SECOND.nseconds() as f64);
 
-        /* Create a gst::Buffer for Cairo to draw into */
+        /* Create a Cairo image surface to draw into and the context around it. */
-        let frame_width = info.width() as usize;
+        let surface = cairo::ImageSurface::create(
-        let frame_height = info.height() as usize;
-        let stride = 4 * frame_width;
-        let frame_size = stride * frame_height;
-
-        /* Create an RGBA buffer, and add a video meta that the videooverlaycomposition expects */
-        let mut buffer = gst::Buffer::with_size(frame_size).unwrap();
-
-        gst_video::VideoMeta::add(
-            buffer.get_mut().unwrap(),
-            gst_video::VideoFrameFlags::empty(),
-            gst_video::VideoFormat::Bgra,
-            frame_width as u32,
-            frame_height as u32,
-        )
-        .unwrap();
-
-        let buffer = buffer.into_mapped_buffer_writable().unwrap();
-        let buffer = {
-            let buffer_ptr = unsafe { buffer.buffer().as_ptr() };
-            let surface = cairo::ImageSurface::create_for_data(
-                buffer,
             cairo::Format::ARgb32,
-                frame_width as i32,
+            info.width() as i32,
-                frame_height as i32,
+            info.height() as i32,
-                stride as i32,
         )
         .unwrap();
-
         let cr = cairo::Context::new(&surface).expect("Failed to create cairo context");
 
         cr.save().expect("Failed to save state");
@@ -233,22 +206,26 @@ fn create_pipeline() -> Result<gst::Pipeline, Error> {
             cr.restore().expect("Failed to restore state");
         }
 
-            // Safety: The surface still owns a mutable reference to the buffer but our reference
+        /* Drop the Cairo context to release the additional reference to the data and
-            // to the surface here is the last one. After dropping the surface the buffer would be
+         * then take ownership of the data. This only works if we have the one and only
-            // freed, so we keep an additional strong reference here before dropping the surface,
+         * reference to the image surface */
-            // which is then returned. As such it's guaranteed that nothing is using the buffer
-            // anymore mutably.
         drop(cr);
-            unsafe {
+        let stride = surface.stride();
-                assert_eq!(
+        let data = surface.take_data().unwrap();
-                    cairo::ffi::cairo_surface_get_reference_count(surface.to_raw_none()),
+
-                    1
+        /* Create an RGBA buffer, and add a video meta that the videooverlaycomposition expects */
-                );
+        let mut buffer = gst::Buffer::from_mut_slice(data);
-                let buffer = glib::translate::from_glib_none(buffer_ptr);
+
-                drop(surface);
+        gst_video::VideoMeta::add_full(
-                buffer
+            buffer.get_mut().unwrap(),
-            }
+            gst_video::VideoFrameFlags::empty(),
-        };
+            gst_video::VideoFormat::Bgra,
+            info.width(),
+            info.height(),
+            &[0],
+            &[stride],
+        )
+        .unwrap();
 
         /* Turn the buffer into a VideoOverlayRectangle, then place
          * that into a VideoOverlayComposition and return it.
@@ -260,8 +237,8 @@ fn create_pipeline() -> Result<gst::Pipeline, Error> {
             &buffer,
             0,
             0,
-            frame_width as u32,
+            info.width(),
-            frame_height as u32,
+            info.height(),
             gst_video::VideoOverlayFormatFlags::PREMULTIPLIED_ALPHA,
         );
 

examples/src/bin/pango-cairo.rs

@@ -10,7 +10,6 @@
 // {videotestsrc} - {cairooverlay} - {capsfilter} - {videoconvert} - {autovideosink}
 // The capsfilter element allows us to dictate the video resolution we want for the
 // videotestsrc and the cairooverlay element.
-#![allow(clippy::non_send_fields_in_send_ty)]
 
 use gst::prelude::*;