Images display briefly before disappearing - Upgrading 0.16 to 0.17

[JosephCatrambone]

Hi, all! I'm upgrading a project from an old version of egui to 0.17.

My application (an image search engine) did a lot of work with tracking texture_ids to try and keep memory usage down. With retained image, I swapped out a lot of the references and my results page now has an issue where the results appear for a split second before disappearing. Here's a video of the issue:

pixelbox_2022-03-25_23-02-21.mp4

I have diffs of the branch (JosephCatrambone/pixelbox#5) and I think it's something to do with this:

let tex_id = fetch_or_generate_thumbnail(res, thumbnail_cache, ctx);
ui.image(tex_id, [res.thumbnail_resolution.0 as f32, res.thumbnail_resolution.1 as f32]) ...

Note that I'm keeping the texture ids in the hashmap and NOT retained image.

/// Given the thumbnail cache and an image ID, will attempt to load the TextureID from the cache.
/// On a cache hit, will return the TextureID.
/// On a cache miss, will take the RGB enumeration and generate a new thumbnail, then return the ID.
pub fn fetch_or_generate_thumbnail(res: &IndexedImage, thumbnail_cache: &mut HashMap::<i64, egui::TextureId>, ctx: &egui::Context) -> egui::TextureId {
	match thumbnail_cache.get(&res.id) {
		Some(tid) => tid.clone(),
		None => {
			//let tid = thumbnail_to_egui_element(res, frame);
			let tid = RetainedImage::from_color_image(
				&res.path,
				egui::ColorImage::from_rgba_unmultiplied(
					[res.thumbnail_resolution.0 as usize, res.thumbnail_resolution.1 as usize],
					&img_to_rgba(res, 255u8)
				)
			);
			let tex_id = tid.texture_id(ctx);
			thumbnail_cache.insert(res.id, tex_id.clone());
			tex_id
		}
	}
}

I have some borrowing and ownership issues if I use RetainedImage, but ultimately if that's the right way to do it I can make the shift to keeping references to them. I'm not 100% sure how I'd do that, but I can figure it out.

Is cloning the texture_id the source of this flashing, or is it another matter entirely that I'm missing?

[emilk]

You create a RetainedImage, and then it directly goes out of scope, and Drops, killing the image it is containing. So the texture id is dangling. You should store the whole RetainedImage in the thumbnail_cache (i.e. retain it).

[JosephCatrambone]

Thank you! Much obliged.

I ended up fighting with ownership of the RetainedImage for a while and accidentally discovering that ctx.load_texture(...); was a drop-in replacement for the earlier approach in app. Since it unblocks other changes I'm doing that for now, but I'll open a ticket in my project to swap for RetainedImage because that sounds like the right thing to do -- just have to spend more time to figure it out.

This was the hack: JosephCatrambone/pixelbox@eb798d3

This is the ticket to use RetainedImage: JosephCatrambone/pixelbox#6

Thanks again for making egui. It's a brilliant library.