Images are drawn with white pixel border

[ghost]

Describe the bug
In the web-version, when an image is drawn to pixel-coordinates with a decimal component (e.g. 100.6), then white pixels occur where presumably those fractional pixels would have been.

To Reproduce
Start the following code with cargo web start --release --open:

use quicksilver::{geom::*, graphics::*, lifecycle::*, Result};

fn main() {
    run(Settings::default(), app);
}

async fn app(window: Window, mut gfx: Graphics, mut events: EventStream) -> Result<()> {
    
    //render image with just a dark-grey background color
    gfx.clear(Color::from_rgba(33, 33, 33, 1.0));
    let mut surface = Surface::new(
        &gfx,
        Image::from_raw(&gfx, None, 512, 512, PixelFormat::RGBA)?,
    )?;
    gfx.fit_to_surface(&surface)?;
    gfx.flush(Some(&surface))?;
    let image = surface.detach().expect("The image failed to detach.");
    
    
    gfx.clear(Color::BLACK);
    gfx.fit_to_window(&window);
    let image_size = Vector::new(100.0, 100.0);
    
    //normal image drawn without problem
    gfx.draw_image(
        &image,
        Rectangle::new(
            Vector::new(100.0, 100.0),
            image_size,
        ),
    );
    
    //image drawn to fractional pixels (shows white line at top and left side)
    gfx.draw_image(
        &image,
        Rectangle::new(
            Vector::new(300.6, 100.6), //mind the .6 (the effect is less visible for other decimal values)
            image_size,
        ),
    );
    
    //image drawn with rotation (also shows white line at top and left side)
    gfx.set_transform(Transform::rotate(33));
    gfx.draw_image(
        &image,
        Rectangle::new(
            Vector::new(400.0, 100.0),
            image_size,
        ),
    );
    
    gfx.present(&window)?;
    loop {
        while let Some(_) = events.next_event().await {}
    }
}

Environment and versions

• Environment: openSUSE Tumbleweed 20200331, tested in Firefox and Chromium-based Falkon
• Rust compiler version: Stable 1.42

$ rustc -vV
rustc 1.42.0 (b8cedc004 2020-03-09)
binary: rustc
commit-hash: b8cedc00407a4c56a3bda1ed605c6fc166655447
commit-date: 2020-03-09
host: x86_64-unknown-linux-gnu
release: 1.42.0
LLVM version: 9.0

• Quicksilver version: 0.4.0-alpha0.2, tested only with stdweb

[ryanisaacg]

Thanks for the detailed report! When I get some time to look into this, it will definitely help with getting this fixed 👍

[ryanisaacg]

I haven't had time to test this as much as I'd like, but I've determined the following:

• The bug is present when running under WebGL and WebGL 2
• The bug does not appear to be present when running under desktop GL (at least on macOS)

This will make it a little hard to track down, but I'll keep looking.