App is flickering when svg is being redrawn

[danielrh]

Description

When I try to render an SVG, the whole window flickers occasionally

Often the first frame would not render, so to workaround that I added a timer to keep rendering, but then I noticed, when I launched 16 of the apps using
`for i in {0..15}; do ./target/release/svg-arch &done
many of them would flicker

Version / OS

Ubuntu 18.04

• azul version:

• Operating system:

• Windowing system (X11 or Wayland, Linux only):

Steps to Reproduce

build
https://github.com/danielrh/azul_gui_test

run 16 at a time
using
for i in {1..16}; do ./target/release/svg-arch &done

I suspect it happens for fewer but that the framerate is too high to pick up on it.
Some of the windows stay black at the end of this, especially for higher numbers of apps

This is the code:

extern crate azul;
use std::time::Duration;
use azul::{
    prelude::*,
    widgets::{button::Button, svg::*},
};


const SVG: &str = include_str!("../../img/tiger.svg");

#[derive(Debug)]
struct MyAppData {
    cache: SvgCache,
    layers: Vec<(SvgLayerId, SvgStyle)>,
    frame_count: u64,
}

type CbInfo<'a, 'b> = CallbackInfo<'a, 'b, MyAppData>;

impl Layout for MyAppData {
    fn layout(&self, _info: LayoutInfo<Self>) -> Dom<MyAppData> {
        let ptr = StackCheckedPointer::new(self, self).unwrap();
      Dom::div().with_child(
        Dom::gl_texture(draw_svg, ptr).with_id("svg-container"),
      )
    }
}

fn timer_callback(state: TimerCallbackInfo<MyAppData>) -> (UpdateScreen, TerminateTimer) {
  eprintln!("cb {}", state.state.frame_count);
  (Redraw, if state.state.frame_count >= 256 {
    TerminateTimer::Terminate
  }else {
    TerminateTimer::Continue
  })
}
fn draw_svg(info: GlCallbackInfoUnchecked<MyAppData>) -> GlCallbackReturn {
  let cb = |info: GlCallbackInfo<MyAppData, MyAppData>| {
            use azul::widgets::svg::SvgLayerResource::*;

    info.state.frame_count += 1;
    let map = info.state;
    let logical_size = info.bounds.get_logical_size();
    Some(Svg::with_layers(map.layers.iter().map(|e| Reference(*e)).collect())
         .render_svg(&map.cache, &info.layout_info.window, logical_size))
  };
    unsafe {
        info.invoke_callback(cb)
    }
}


fn main() {

    let mut svg_cache = SvgCache::empty();
    let mut svg_layers = svg_cache.add_svg(&SVG).unwrap();
    let app_data = MyAppData {
        cache: svg_cache,
        layers: svg_layers,
        frame_count: 0,
    };

  let mut app = App::new(app_data, AppConfig::default()).unwrap();
    let window = app.create_window(WindowCreateOptions::default(), css::native()).unwrap();
  let timer = Timer::new(timer_callback).with_interval(Duration::from_millis(5));
  app.app_state.add_timer(TimerId::new(), timer);
    app.run(window).unwrap();
}

Additional Information

The screenshot is a moment in time...but most windows have their black frame...the sixteen windows flicker back and forth until the timer stops

[danielrh]

This is on 46e5f18 (latest master)
if you want it to flicker forever back and forth you can get rid of the >= 256 or make it larger like >= 256256256
I've had cases where the last frame has one of the windows permanently black until I mouse over it or otherwise force a redraw on it

[fschutt]

well tbh I'm amazed it worked at all ;)

The flickering-and-redrawing bugs should all be fixed by the upgrade to glutin >= 0.22, since glutin / winit now have a new event-loop model. The reason that it flickers is because on Windows, winit ignores the first redrawing command when resizing, so I added a "force redraw" cache, so that basically the window isn't redrawn once, but twice (since the first redraw is always ignored). On other platforms however, this leads to flickering.

I've upgraded glutin on the /unvendor_dependencies branch, but I haven't yet ported the code for actually drawing something, right now it just compiles and shows a blank window. I'm currently rather busy, it will take a few months for me to fix all the redrawing bugs, so don't hold your breath.

[danielrh]

Could you conditionally compile the windows-specific fix to only activate on windows? Would that fix this issue until the glutin upgrade?

[fschutt]

The windowing system was now completely rewritten, so it's likely that this bug doesn't appear anymore (dependency on glutin / winit was removed because I couldn't debug these "integration" issues).