Struct LiveImageDiffWriter 

pub struct LiveImageDiffWriter { /* private fields */ }

A LiveImageWriter for a producer that redraws, or copies, a whole frame every time, whether or not anything in it moved: a VM’s framebuffer copied at each vsync, a remote desktop’s screen, a renderer with no damage tracking of its own.

write_frame compares the frame with the last one it wrote and commits only the rows that changed, each cut to the span of pixels that changed in it. A frame identical to the last one commits nothing: it takes no lock, wakes no window, uploads nothing and draws nothing, so a still picture fed at 60 Hz costs the window nothing.

The comparison runs on the producer’s thread, against a copy of the last frame it keeps, never under the source’s lock: a renderer is kept waiting only while the changed rows are copied in. That copy costs one frame of memory, and the comparison a read of both frames, a fraction of a millisecond for 720 × 1280.

The result is the frame handed over. When the source no longer holds the last frame this writer wrote (another writer committed, cleared or resized it, or left a transaction abandoned), the next frame is written whole. The one change it cannot see is another writer’s write through pixels_mut left unmarked in a transaction that ended without a commit or a panic: such pixels reach no window either, until something marks them.

let source = LiveImageSource::new(LivePixelFormat::Bgrx8);
let mut writer = LiveImageDiffWriter::new(source.writer());
let mut frame = vec![0u8; 64 * 48 * 4];
assert!(writer.write_frame(64, 48, &frame, 64 * 4).unwrap().is_some());
// The same frame again: nothing is committed.
assert_eq!(writer.write_frame(64, 48, &frame, 64 * 4).unwrap(), None);
frame[0] = 255;
assert!(writer.write_frame(64, 48, &frame, 64 * 4).unwrap().is_some());

Implementations

impl LiveImageDiffWriter

pub fn new(writer: LiveImageWriter) -> LiveImageDiffWriter

pub fn write_frame( &mut self, width: u32, height: u32, src: &[u8], src_stride: usize, ) -> Result<Option<u64>, LiveImageError>

Write src, a width × height frame whose rows are src_stride bytes apart, committing only what differs from the last frame written. Some(generation) when it committed, None when the frame was identical and the source still shows it.

Errors

As LiveImageWriter::write_frame. A refused frame changes nothing, here or in the source.

pub fn forget(&mut self)

Drop the copy of the last frame, so the next frame is written whole.

pub fn writer(&self) -> &LiveImageWriter

The writer, for the source’s other operations: resize, clear, is_displayed. A frame it writes makes the next one handed to this writer go out whole.

pub fn into_writer(self) -> LiveImageWriter

The writer back, and the copy freed.

Trait Implementations

impl Debug for LiveImageDiffWriter

fn fmt(&self, f: &mut Formatter<'_>) -> Result<(), Error>

Formats the value using the given formatter.