screenshots.rs

// Copyright 2022 the Xilem Authors
// SPDX-License-Identifier: Apache-2.0

//! Helper functions for writing snapshot tests and comparing images.

use image::{GenericImageView as _, RgbImage};
use nv_flip::{FlipImageRgb8, DEFAULT_PIXELS_PER_DEGREE};

#[cfg(docsrs)]
#[doc(hidden)]
#[macro_export]
macro_rules! include_screenshot {
    ($path:literal $(, $caption:literal)? $(,)?) => {
        concat!(
            "![", $($caption,)? "]",
            "(", "https://media.githubusercontent.com/media/linebender/xilem/",
            "masonry-v", env!("CARGO_PKG_VERSION"), "/masonry/src/", $path,
            ")",
        )
    };
}

// TODO:
// - Check whether the docs.rs trick actually works.
// - Check whether this method will work with cargo rdme.
// - Make better screenshots than the ones we currently use.

#[cfg(not(docsrs))]
#[doc(hidden)]
#[macro_export]
/// Macro used to create markdown img tag, with a different URL when uploading to docs.rs.
macro_rules! include_screenshot {
    ($path:literal $(, $caption:literal)? $(,)?) => {
        concat!(
            "![", $($caption,)? "]",
            "(", env!("CARGO_MANIFEST_DIR"), "/src/", $path, ")",
        )
    };
}

pub(crate) fn get_image_diff(ref_image: &RgbImage, new_image: &RgbImage) -> Option<RgbImage> {
    assert_eq!(
        (ref_image.width(), ref_image.height()),
        (new_image.width(), new_image.height()),
        "New image (right) has different size from old image (left)."
    );

    let ref_image_flip = FlipImageRgb8::with_data(ref_image.width(), ref_image.height(), ref_image);
    let new_image_flip = FlipImageRgb8::with_data(new_image.width(), new_image.height(), new_image);
    let error_map = nv_flip::flip(ref_image_flip, new_image_flip, DEFAULT_PIXELS_PER_DEGREE);
    let pool = nv_flip::FlipPool::from_image(&error_map);
    let mean = pool.mean();

    let is_changed = mean.abs() > 0.01;

    if !is_changed {
        return None;
    }

    let width = std::cmp::max(ref_image.width(), new_image.width());
    let height = std::cmp::max(ref_image.height(), new_image.height());

    let diff_image = RgbImage::from_fn(width, height, |x, y| {
        let ref_pixel = if ref_image.in_bounds(x, y) {
            *ref_image.get_pixel(x, y)
        } else {
            [0, 0, 0].into()
        };
        let new_pixel = if new_image.in_bounds(x, y) {
            *new_image.get_pixel(x, y)
        } else {
            [255, 255, 255].into()
        };

        if new_pixel != ref_pixel {
            new_pixel
        } else {
            [0, 0, 0].into()
        }
    });

    Some(diff_image)
}