From 745ae0c98036808d91cea740e6bd8358351bd872 Mon Sep 17 00:00:00 2001
From: Schell Carl Scivally <efsubenovex@gmail.com>
Date: Wed, 3 Jan 2024 10:33:42 +1300
Subject: [PATCH] img-diff takes into account pixel threshold and image
 threshold

---
 crates/img-diff/src/lib.rs      | 90 ++++++++++++++++++++++++++++++---
 crates/renderling/src/skybox.rs |  1 +
 2 files changed, 85 insertions(+), 6 deletions(-)

diff --git a/crates/img-diff/src/lib.rs b/crates/img-diff/src/lib.rs
index c6b93f01..98220bf1 100644
--- a/crates/img-diff/src/lib.rs
+++ b/crates/img-diff/src/lib.rs
@@ -6,6 +6,21 @@ use std::path::Path;
 
 const TEST_IMG_DIR: &str = "../../test_img";
 const TEST_OUTPUT_DIR: &str = "../../test_output";
+const PIXEL_MAGNITUDE_THRESHOLD: f32 = 0.1;
+const IMAGE_DIFF_THRESHOLD: f32 = 0.05;
+
+fn checkerboard_background_color(x: u32, y: u32) -> Vec4 {
+    let size = 16;
+    let x_square_index = x / size;
+    let x_grey = x_square_index % 2 == 0;
+    let y_square_index = y / size;
+    let y_grey = y_square_index % 2 == 0;
+    if (x_grey && y_grey) || (!x_grey && !y_grey) {
+        Vec4::from([0.5, 0.5, 0.5, 1.0])
+    } else {
+        Vec4::from([1.0, 1.0, 1.0, 1.0])
+    }
+}
 
 #[derive(Debug, Snafu)]
 enum ImgDiffError {
@@ -13,6 +28,27 @@ enum ImgDiffError {
     ImageSize,
 }
 
+pub struct DiffCfg {
+    /// The threshold for a pixel to be considered different.
+    ///
+    /// Difference is measured as the magnitude of vector subtraction
+    /// between the two pixels.
+    pub pixel_threshold: f32,
+    /// The percentage of "different" pixels (as determined using
+    /// `pixel_threshold`) to "correct" pixels that the image must contain
+    /// before it is considered an error.
+    pub image_threshold: f32,
+}
+
+impl Default for DiffCfg {
+    fn default() -> Self {
+        Self {
+            pixel_threshold: PIXEL_MAGNITUDE_THRESHOLD,
+            image_threshold: IMAGE_DIFF_THRESHOLD,
+        }
+    }
+}
+
 fn get_results(
     left_image: &Rgba32FImage,
     right_image: &Rgba32FImage,
@@ -29,11 +65,14 @@ fn get_results(
             if left_pixel == right_pixel {
                 None
             } else {
+                // pre-multiply alpha
                 let left_pixel = Vec4::from(left_pixel.0);
+                let left_pixel = (left_pixel * left_pixel.w).xyz();
                 let right_pixel = Vec4::from(right_pixel.0);
+                let right_pixel = (right_pixel * right_pixel.w).xyz();
                 let delta = (left_pixel - right_pixel).abs();
                 if delta.length() > threshold {
-                    Some((x, y, delta))
+                    Some((x, y, delta.extend(1.0)))
                 } else {
                     None
                 }
@@ -47,8 +86,22 @@ fn get_results(
     } else {
         let mut output_image =
             image::ImageBuffer::from_pixel(width, height, Rgba([0.0, 0.0, 0.0, 0.0]));
+
+        for x in 0..width {
+            for y in 0..height {
+                output_image.put_pixel(x, y, Rgba(checkerboard_background_color(x, y).into()));
+            }
+        }
+
         for (x, y, delta) in results {
-            let color = delta.xyz().extend(1.0);
+            let bg = checkerboard_background_color(x, y);
+            let a = 1.0 - delta.z;
+            let color = Vec4::new(
+                bg.x * a + delta.x,
+                bg.y * a + delta.y,
+                bg.z * a + delta.z,
+                1.0,
+            );
             output_image.put_pixel(x, y, Rgba(color.into()));
         }
         Ok(Some((diffs, output_image)))
@@ -61,11 +114,28 @@ pub fn save(filename: &str, seen: impl Into<DynamicImage>) {
     seen.into().save(path).unwrap();
 }
 
-pub fn assert_eq(filename: &str, lhs: impl Into<DynamicImage>, rhs: impl Into<DynamicImage>) {
+pub fn assert_eq_cfg(
+    filename: &str,
+    lhs: impl Into<DynamicImage>,
+    rhs: impl Into<DynamicImage>,
+    cfg: DiffCfg,
+) {
     let lhs = lhs.into();
     let lhs = lhs.into_rgba32f();
     let rhs = rhs.into().into_rgba32f();
-    if let Some((diffs, diff_image)) = get_results(&lhs, &rhs, 0.5).unwrap() {
+    let DiffCfg {
+        pixel_threshold,
+        image_threshold,
+    } = cfg;
+    if let Some((diffs, diff_image)) = get_results(&lhs, &rhs, pixel_threshold).unwrap() {
+        println!("{filename} has {diffs} pixel differences (threshold={pixel_threshold})");
+        let percent_diff = diffs as f32 / (lhs.width() * lhs.height()) as f32;
+        println!("{filename}'s image is {percent_diff} different (threshold={image_threshold})");
+        if percent_diff < image_threshold {
+            return;
+        }
+
+
         let mut dir = Path::new(TEST_OUTPUT_DIR).join(filename);
         dir.set_extension("");
         std::fs::create_dir_all(&dir).expect("cannot create test output dir");
@@ -93,7 +163,11 @@ pub fn assert_eq(filename: &str, lhs: impl Into<DynamicImage>, rhs: impl Into<Dy
     }
 }
 
-pub fn assert_img_eq(filename: &str, seen: impl Into<DynamicImage>) {
+pub fn assert_eq(filename: &str, lhs: impl Into<DynamicImage>, rhs: impl Into<DynamicImage>) {
+    assert_eq_cfg(filename, lhs, rhs, DiffCfg::default())
+}
+
+pub fn assert_img_eq_cfg(filename: &str, seen: impl Into<DynamicImage>, cfg: DiffCfg) {
     let cwd = std::env::current_dir().expect("no cwd");
     let lhs = image::open(Path::new(TEST_IMG_DIR).join(filename)).unwrap_or_else(|_| {
         panic!(
@@ -101,5 +175,9 @@ pub fn assert_img_eq(filename: &str, seen: impl Into<DynamicImage>) {
             cwd.join(filename).display()
         )
     });
-    assert_eq(filename, lhs, seen)
+    assert_eq_cfg(filename, lhs, seen, cfg)
+}
+
+pub fn assert_img_eq(filename: &str, seen: impl Into<DynamicImage>) {
+    assert_img_eq_cfg(filename, seen, DiffCfg::default())
 }
diff --git a/crates/renderling/src/skybox.rs b/crates/renderling/src/skybox.rs
index 22d5be60..99976cee 100644
--- a/crates/renderling/src/skybox.rs
+++ b/crates/renderling/src/skybox.rs
@@ -639,6 +639,7 @@ impl Skybox {
 mod test {
     use crabslab::GrowableSlab;
     use glam::Vec3;
+    use img_diff::DiffCfg;
 
     use super::*;
     use crate::Renderling;