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

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This commit is contained in:
Sebastian Dröge 2022-01-14 21:47:08 +02:00
parent 2bb500db0b
commit ce1a25a128
2 changed files with 74 additions and 98 deletions
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171
examples/src/bin/overlay-composition.rs
View file

@ -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::*;
@ -150,106 +146,87 @@ 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 */
let frame_width = info.width() as usize;
let frame_height = info.height() as usize;
let stride = 4 * frame_width;
let frame_size = stride * frame_height;
/* Create a Cairo image surface to draw into and the context around it. */
let surface = cairo::ImageSurface::create(
cairo::Format::ARgb32,
info.width() as i32,
info.height() as i32,
)
.unwrap();
let cr = cairo::Context::new(&surface).expect("Failed to create cairo context");
cr.save().expect("Failed to save state");
cr.set_operator(cairo::Operator::Clear);
cr.paint().expect("Failed to clear background");
cr.restore().expect("Failed to restore state");
// The image we draw (the text) will be static, but we will change the
// transformation on the drawing context, which rotates and shifts everything
// that we draw afterwards. Like this, we have no complicated calulations
// in the actual drawing below.
// Calling multiple transformation methods after each other will apply the
// new transformation on top. If you repeat the cr.rotate(angle) line below
// this a second time, everything in the canvas will rotate twice as fast.
cr.translate(
f64::from(info.width()) / 2.0,
f64::from(info.height()) / 2.0,
);
cr.rotate(angle);
// This loop will render 10 times the string "GStreamer" in a circle
for i in 0..10 {
// Cairo, like most rendering frameworks, is using a stack for transformations
// with this, we push our current transformation onto this stack - allowing us
// to make temporary changes / render something / and then returning to the
// previous transformations.
cr.save().expect("Failed to save state");
let angle = (360. * f64::from(i)) / 10.0;
let red = (1.0 + f64::cos((angle - 60.0) * PI / 180.0)) / 2.0;
cr.set_source_rgb(red, 0.0, 1.0 - red);
cr.rotate(angle * PI / 180.0);
// Update the text layout. This function is only updating pango's internal state.
// So e.g. that after a 90 degree rotation it knows that what was previously going
// to end up as a 200x100 rectangle would now be 100x200.
pangocairo::functions::update_layout(&cr, &**layout);
let (width, _height) = layout.size();
// Using width and height of the text, we can properly possition it within
// our canvas.
cr.move_to(
-(f64::from(width) / f64::from(pango::SCALE)) / 2.0,
-(f64::from(info.height())) / 2.0,
);
// After telling the layout object where to draw itself, we actually tell
// it to draw itself into our cairo context.
pangocairo::functions::show_layout(&cr, &**layout);
// Here we go one step up in our stack of transformations, removing any
// changes we did to them since the last call to cr.save();
cr.restore().expect("Failed to restore state");
}
/* Drop the Cairo context to release the additional reference to the data and
* then take ownership of the data. This only works if we have the one and only
* reference to the image surface */
drop(cr);
let stride = surface.stride();
let data = surface.take_data().unwrap();
/* Create an RGBA buffer, and add a video meta that the videooverlaycomposition expects */
let mut buffer = gst::Buffer::with_size(frame_size).unwrap();
let mut buffer = gst::Buffer::from_mut_slice(data);
gst_video::VideoMeta::add(
gst_video::VideoMeta::add_full(
buffer.get_mut().unwrap(),
gst_video::VideoFrameFlags::empty(),
gst_video::VideoFormat::Bgra,
frame_width as u32,
frame_height as u32,
info.width(),
info.height(),
&[0],
&[stride],
)
.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,
frame_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");
cr.set_operator(cairo::Operator::Clear);
cr.paint().expect("Failed to clear background");
cr.restore().expect("Failed to restore state");
// The image we draw (the text) will be static, but we will change the
// transformation on the drawing context, which rotates and shifts everything
// that we draw afterwards. Like this, we have no complicated calulations
// in the actual drawing below.
// Calling multiple transformation methods after each other will apply the
// new transformation on top. If you repeat the cr.rotate(angle) line below
// this a second time, everything in the canvas will rotate twice as fast.
cr.translate(
f64::from(info.width()) / 2.0,
f64::from(info.height()) / 2.0,
);
cr.rotate(angle);
// This loop will render 10 times the string "GStreamer" in a circle
for i in 0..10 {
// Cairo, like most rendering frameworks, is using a stack for transformations
// with this, we push our current transformation onto this stack - allowing us
// to make temporary changes / render something / and then returning to the
// previous transformations.
cr.save().expect("Failed to save state");
let angle = (360. * f64::from(i)) / 10.0;
let red = (1.0 + f64::cos((angle - 60.0) * PI / 180.0)) / 2.0;
cr.set_source_rgb(red, 0.0, 1.0 - red);
cr.rotate(angle * PI / 180.0);
// Update the text layout. This function is only updating pango's internal state.
// So e.g. that after a 90 degree rotation it knows that what was previously going
// to end up as a 200x100 rectangle would now be 100x200.
pangocairo::functions::update_layout(&cr, &**layout);
let (width, _height) = layout.size();
// Using width and height of the text, we can properly possition it within
// our canvas.
cr.move_to(
-(f64::from(width) / f64::from(pango::SCALE)) / 2.0,
-(f64::from(info.height())) / 2.0,
);
// After telling the layout object where to draw itself, we actually tell
// it to draw itself into our cairo context.
pangocairo::functions::show_layout(&cr, &**layout);
// Here we go one step up in our stack of transformations, removing any
// changes we did to them since the last call to cr.save();
cr.restore().expect("Failed to restore state");
}
// Safety: The surface still owns a mutable reference to the buffer but our reference
// to the surface here is the last one. After dropping the surface the buffer would be
// freed, so we keep an additional strong reference here before dropping the surface,
// which is then returned. As such it's guaranteed that nothing is using the buffer
// anymore mutably.
drop(cr);
unsafe {
assert_eq!(
cairo::ffi::cairo_surface_get_reference_count(surface.to_raw_none()),
1
);
let buffer = glib::translate::from_glib_none(buffer_ptr);
drop(surface);
buffer
}
};
/* 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,
frame_height as u32,
info.width(),
info.height(),
gst_video::VideoOverlayFormatFlags::PREMULTIPLIED_ALPHA,
);

1
examples/src/bin/pango-cairo.rs
View file

@ -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::*;