Texture loading in egui

[emilk]

This continues #999 by moving texture allocation from epi into egui proper.

With this PR you can convert an image into a texture using egui::Context::load_texture. This returns an egui::TextureHandle which can be used with e.g. ui.image(…). The TextureHandle uses ref-counting, and when the last TextureHandle is dropped, the texture is freed. This makes it far more ergonomic and convenient to show images in egui.

Here is an example of how to use it: https://github.com/emilk/egui/blob/master/eframe/examples/image.rs

Backend integrations need to adapt by handling the new epaint::TexturesDelta each frame, a struct that specifies what textures were loaded and freed each frame.

[yuribudilov]

Hello

I can not get eframe example (image.rs) to compile, there is no egui::ColorImage found and a few other errors.
Using latest eframe/egui/epi 0.16.0 in Cargo.toml.

Also, image:: did not compile so I included image crate (0.24.0) in my Cargo.toml, I dont know if this is correct.

Sorry, I am totally new to egui/eframe/epi and the examples in eframe are just fragments of code, not complete cargo projects.

fn load_image(image_data: &[u8]) -> Result<egui::ColorImage, image::ImageError> {
    use image::GenericImageView as _;
    let image = image::load_from_memory(image_data)?;
    let size = [image.width() as _, image.height() as _];
    let image_buffer = image.to_rgba8();
    let pixels = image_buffer.as_flat_samples();
    Ok(egui::ColorImage::from_rgba_unmultiplied(
        size,
        pixels.as_slice(),
    ))
}

thank for for any assistance

[Born2Go]

I struggled with this too, in my case I managed to make it work using eframe::epi::Image
I think this struct have been renamed/moved and the examples not updated yet

[emilk]

Soon 0.17.0 is released and this will become a lot simpler by using egui_extras::RetainedImage (#1282)