feat(graphics): add helper to find diff between images

FIXME: remotefx renders some line artefacts, likely due to bad
       compression behaviour on the tile edges.

Signed-off-by: Marc-André Lureau <marcandre.lureau@redhat.com>

Author: elmarco

Cargo.lock

@@ -30,6 +30,7 @@ yuvutils-rs = { version = "0.8", features = ["rdp"] }
 
 [dev-dependencies]
 bmp = "0.5"
+bytemuck = "1.21"
 expect-test.workspace = true
 
 [lints]

crates/ironrdp-graphics/Cargo.toml

@@ -0,0 +1,326 @@
+#[derive(Debug, PartialEq, Eq)]
+pub struct Rect {
+    pub x: usize,
+    pub y: usize,
+    pub width: usize,
+    pub height: usize,
+}
+
+impl Rect {
+    pub fn new(x: usize, y: usize, width: usize, height: usize) -> Self {
+        Self { x, y, width, height }
+    }
+
+    fn intersect(&self, other: &Rect) -> Option<Rect> {
+        let x = self.x.max(other.x);
+        let y = self.y.max(other.y);
+        let width = (self.x + self.width).min(other.x + other.width);
+        if width <= x {
+            return None;
+        }
+        let width = width - x;
+        let height = (self.y + self.height).min(other.y + other.height);
+        if height <= y {
+            return None;
+        }
+        let height = height - y;
+
+        Some(Rect::new(x, y, width, height))
+    }
+}
+
+const TILE_SIZE: usize = 64;
+
+fn find_different_tiles<const BPP: usize>(
+    image1: &[u8],
+    stride1: usize,
+    image2: &[u8],
+    stride2: usize,
+    width: usize,
+    height: usize,
+) -> Vec<bool> {
+    assert!(stride1 >= width * BPP);
+    assert!(stride2 >= width * BPP);
+    assert!(image1.len() >= (height - 1) * stride1 + width * BPP);
+    assert!(image2.len() >= (height - 1) * stride2 + width * BPP);
+
+    let tiles_x = width.div_ceil(TILE_SIZE);
+    let tiles_y = height.div_ceil(TILE_SIZE);
+    let mut tile_differences = vec![false; tiles_x * tiles_y];
+
+    tile_differences.iter_mut().enumerate().for_each(|(idx, diff)| {
+        let tile_start_x = (idx % tiles_x) * TILE_SIZE;
+        let tile_end_x = (tile_start_x + TILE_SIZE).min(width);
+        let tile_start_y = (idx / tiles_x) * TILE_SIZE;
+        let tile_end_y = (tile_start_y + TILE_SIZE).min(height);
+
+        // Check for any difference in tile using slice comparisons
+        let has_diff = (tile_start_y..tile_end_y).any(|y| {
+            let row_start1 = y * stride1;
+            let row_start2 = y * stride2;
+            let tile_row_start1 = row_start1 + tile_start_x * BPP;
+            let tile_row_end1 = row_start1 + tile_end_x * BPP;
+            let tile_row_start2 = row_start2 + tile_start_x * BPP;
+            let tile_row_end2 = row_start2 + tile_end_x * BPP;
+
+            image1[tile_row_start1..tile_row_end1] != image2[tile_row_start2..tile_row_end2]
+        });
+
+        *diff = has_diff;
+    });
+
+    tile_differences
+}
+
+fn find_different_rects<const BPP: usize>(
+    image1: &[u8],
+    stride1: usize,
+    image2: &[u8],
+    stride2: usize,
+    width: usize,
+    height: usize,
+) -> Vec<Rect> {
+    let mut tile_differences = find_different_tiles::<BPP>(image1, stride1, image2, stride2, width, height);
+
+    let mod_width = width % TILE_SIZE;
+    let mod_height = height % TILE_SIZE;
+    let tiles_x = width.div_ceil(TILE_SIZE);
+    let tiles_y = height.div_ceil(TILE_SIZE);
+
+    let mut rectangles = Vec::new();
+    let mut current_idx = 0;
+    let total_tiles = tiles_x * tiles_y;
+
+    // Process tiles in linear fashion to find rectangular regions
+    while current_idx < total_tiles {
+        if !tile_differences[current_idx] {
+            current_idx += 1;
+            continue;
+        }
+
+        let start_y = current_idx / tiles_x;
+        let start_x = current_idx % tiles_x;
+
+        // Expand horizontally as much as possible
+        let mut max_width = 1;
+        while start_x + max_width < tiles_x && tile_differences[current_idx + max_width] {
+            max_width += 1;
+        }
+
+        // Expand vertically as much as possible
+        let mut max_height = 1;
+        'vertical: while start_y + max_height < tiles_y {
+            for x in 0..max_width {
+                let check_idx = (start_y + max_height) * tiles_x + start_x + x;
+                if !tile_differences[check_idx] {
+                    break 'vertical;
+                }
+            }
+            max_height += 1;
+        }
+
+        // Calculate pixel coordinates
+        let pixel_x = start_x * TILE_SIZE;
+        let pixel_y = start_y * TILE_SIZE;
+
+        let pixel_width = if start_x + max_width == tiles_x && mod_width > 0 {
+            (max_width - 1) * TILE_SIZE + mod_width
+        } else {
+            max_width * TILE_SIZE
+        };
+
+        let pixel_height = if start_y + max_height == tiles_y && mod_height > 0 {
+            (max_height - 1) * TILE_SIZE + mod_height
+        } else {
+            max_height * TILE_SIZE
+        };
+
+        rectangles.push(Rect {
+            x: pixel_x,
+            y: pixel_y,
+            width: pixel_width,
+            height: pixel_height,
+        });
+
+        // Mark tiles as processed
+        for y in 0..max_height {
+            for x in 0..max_width {
+                let idx = (start_y + y) * tiles_x + start_x + x;
+                tile_differences[idx] = false;
+            }
+        }
+
+        current_idx += max_width;
+    }
+
+    rectangles
+}
+
+/// Helper function to find different regions in two images.
+///
+/// This function takes two images as input and returns a list of rectangles
+/// representing the different regions between the two images, in image2 coordinates.
+///
+/// ```text
+///     ┌───────────────────────────────────────────┐
+///     │ image1                                    │
+///     │                                           │
+///     │                    (x,y)                  │
+///     │                     ┌───────────────┐     │
+///     │                     │ image2        │     │
+///     │                     │               │     │
+///     │                     │               │     │
+///     │                     │               │     │
+///     │                     │               │     │
+///     │                     │               │     │
+///     │                     └───────────────┘     │
+///     │                                           │
+///     └───────────────────────────────────────────┘
+/// ```
+#[allow(clippy::too_many_arguments)]
+pub fn find_different_rects_sub<const BPP: usize>(
+    image1: &[u8],
+    stride1: usize,
+    width1: usize,
+    height1: usize,
+    image2: &[u8],
+    stride2: usize,
+    width2: usize,
+    height2: usize,
+    x: usize,
+    y: usize,
+) -> Vec<Rect> {
+    let rect1 = Rect::new(0, 0, width1, height1);
+    let rect2 = Rect::new(x, y, width2, height2);
+    let Some(inter) = rect1.intersect(&rect2) else {
+        return vec![];
+    };
+
+    let image1 = &image1[y * stride1 + x * BPP..];
+    find_different_rects::<BPP>(image1, stride1, image2, stride2, inter.width, inter.height)
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use bytemuck::cast_slice;
+
+    #[test]
+    fn test_intersect() {
+        let r1 = Rect::new(0, 0, 640, 480);
+        let r2 = Rect::new(10, 10, 10, 10);
+        let r3 = Rect::new(630, 470, 20, 20);
+
+        assert_eq!(r1.intersect(&r1).as_ref(), Some(&r1));
+        assert_eq!(r1.intersect(&r2).as_ref(), Some(&r2));
+        assert_eq!(r1.intersect(&r3), Some(Rect::new(630, 470, 10, 10)));
+        assert_eq!(r2.intersect(&r3), None);
+    }
+
+    #[test]
+    fn test_single_tile() {
+        const SIZE: usize = 128;
+        let image1 = vec![0u32; SIZE * SIZE];
+        let mut image2 = vec![0u32; SIZE * SIZE];
+        image2[65 * 128 + 65] = 1;
+        let result =
+            find_different_rects::<4>(cast_slice(&image1), SIZE * 4, cast_slice(&image2), SIZE * 4, SIZE, SIZE);
+        assert_eq!(
+            result,
+            vec![Rect {
+                x: 64,
+                y: 64,
+                width: 64,
+                height: 64
+            }]
+        );
+    }
+
+    #[test]
+    fn test_adjacent_tiles() {
+        const SIZE: usize = 256;
+        let image1 = vec![0u32; SIZE * SIZE];
+        let mut image2 = vec![0u32; SIZE * SIZE];
+        // Modify two adjacent tiles
+        image2[65 * SIZE + 65] = 1;
+        image2[65 * SIZE + 129] = 1;
+        let result =
+            find_different_rects::<4>(cast_slice(&image1), SIZE * 4, cast_slice(&image2), SIZE * 4, SIZE, SIZE);
+        assert_eq!(
+            result,
+            vec![Rect {
+                x: 64,
+                y: 64,
+                width: 128,
+                height: 64
+            }]
+        );
+    }
+
+    #[test]
+    fn test_edge_tiles() {
+        const SIZE: usize = 100;
+        let image1 = vec![0u32; SIZE * SIZE];
+        let mut image2 = vec![0u32; SIZE * SIZE];
+        image2[65 * SIZE + 65] = 1;
+        let result =
+            find_different_rects::<4>(cast_slice(&image1), SIZE * 4, cast_slice(&image2), SIZE * 4, SIZE, SIZE);
+        assert_eq!(
+            result,
+            vec![Rect {
+                x: 64,
+                y: 64,
+                width: 36,
+                height: 36
+            }]
+        );
+    }
+
+    #[test]
+    fn test_large() {
+        const SIZE: usize = 4096;
+        let image1 = vec![0u32; SIZE * SIZE];
+        let mut image2 = vec![0u32; SIZE * SIZE];
+        image2[95 * 100 + 95] = 1;
+        let _result =
+            find_different_rects::<4>(cast_slice(&image1), SIZE * 4, cast_slice(&image2), SIZE * 4, SIZE, SIZE);
+    }
+
+    #[test]
+    fn test_sub_diff() {
+        let image1 = vec![0u32; 2048 * 2048];
+        let mut image2 = vec![0u32; 1024 * 1024];
+        image2[0] = 1;
+        image2[1024 * 65 + 512 - 1] = 1;
+
+        let res = find_different_rects_sub::<4>(
+            cast_slice(&image1),
+            2048 * 4,
+            2048,
+            2048,
+            cast_slice(&image2),
+            1024 * 4,
+            512,
+            512,
+            1024,
+            1024,
+        );
+        assert_eq!(
+            res,
+            vec![
+                Rect {
+                    x: 0,
+                    y: 0,
+                    width: 64,
+                    height: 64
+                },
+                Rect {
+                    x: 448,
+                    y: 64,
+                    width: 64,
+                    height: 64
+                }
+            ]
+        )
+    }
+}

crates/ironrdp-graphics/src/diff.rs

@@ -7,6 +7,7 @@
 #![allow(clippy::cast_sign_loss)] // FIXME: remove
 
 pub mod color_conversion;
+pub mod diff;
 pub mod dwt;
 pub mod image_processing;
 pub mod pointer;