From 7e3ec23dbddeeffb594f46fdefb4bdc908ad9f5b Mon Sep 17 00:00:00 2001
From: gram <git@orsinium.dev>
Date: Tue, 15 Oct 2024 17:35:40 +0200
Subject: [PATCH 1/8] move Image into graphics

---
 src/fs.rs             | 42 +-----------------------------------------
 src/graphics/funcs.rs |  2 +-
 src/graphics/image.rs | 42 ++++++++++++++++++++++++++++++++++++++++++
 src/graphics/mod.rs   |  2 ++
 4 files changed, 46 insertions(+), 42 deletions(-)
 create mode 100644 src/graphics/image.rs

diff --git a/src/fs.rs b/src/fs.rs
index f7f7350..210d463 100644
--- a/src/fs.rs
+++ b/src/fs.rs
@@ -1,6 +1,6 @@
 //! Access file system: the game ROM files and the data dir.
 
-use crate::graphics::{Point, Size};
+use crate::graphics::*;
 #[cfg(feature = "alloc")]
 use alloc::vec;
 #[cfg(feature = "alloc")]
@@ -155,46 +155,6 @@ impl<'a> From<&'a FileBuf> for Font<'a> {
     }
 }
 
-/// A loaded image file.
-///
-/// Can be loaded as [`FileBuf`] from ROM with [`rom::load_buf`]
-/// and then cast using [Into].
-pub struct Image<'a> {
-    pub(crate) raw: &'a [u8],
-}
-
-impl<'a> From<File<'a>> for Image<'a> {
-    fn from(value: File<'a>) -> Self {
-        Self { raw: value.raw }
-    }
-}
-
-#[cfg(feature = "alloc")]
-impl<'a> From<&'a FileBuf> for Image<'a> {
-    fn from(value: &'a FileBuf) -> Self {
-        Self { raw: &value.raw }
-    }
-}
-
-impl<'a> Image<'a> {
-    /// Get a rectangle subregion of the image.
-    #[must_use]
-    pub fn sub(&self, p: Point, s: Size) -> SubImage<'a> {
-        SubImage {
-            point: p,
-            size: s,
-            raw: self.raw,
-        }
-    }
-}
-
-/// A subregion of an image. Constructed using [`Image::sub`].
-pub struct SubImage<'a> {
-    pub(crate) point: Point,
-    pub(crate) size: Size,
-    pub(crate) raw: &'a [u8],
-}
-
 mod bindings {
     #[link(wasm_import_module = "fs")]
     extern {
diff --git a/src/graphics/funcs.rs b/src/graphics/funcs.rs
index 5d04c08..053bac7 100644
--- a/src/graphics/funcs.rs
+++ b/src/graphics/funcs.rs
@@ -1,5 +1,5 @@
 use super::{bindings as b, *};
-use crate::fs::{Font, Image, SubImage};
+use crate::*;
 
 /// Fill the whole frame with the given color.
 pub fn clear_screen(c: Color) {
diff --git a/src/graphics/image.rs b/src/graphics/image.rs
new file mode 100644
index 0000000..80fe312
--- /dev/null
+++ b/src/graphics/image.rs
@@ -0,0 +1,42 @@
+use crate::*;
+
+/// A loaded image file.
+///
+/// Can be loaded as [`FileBuf`] from ROM with [`load_file_buf`]
+/// and then cast using [Into].
+pub struct Image<'a> {
+    pub(crate) raw: &'a [u8],
+}
+
+impl<'a> From<File<'a>> for Image<'a> {
+    fn from(value: File<'a>) -> Self {
+        Self { raw: value.raw }
+    }
+}
+
+#[cfg(feature = "alloc")]
+impl<'a> From<&'a FileBuf> for Image<'a> {
+    fn from(value: &'a FileBuf) -> Self {
+        Self { raw: &value.raw }
+    }
+}
+
+impl<'a> Image<'a> {
+    /// Get a rectangle subregion of the image.
+    #[must_use]
+    pub fn sub(&self, p: Point, s: Size) -> SubImage<'a> {
+        SubImage {
+            point: p,
+            size: s,
+            raw: self.raw,
+        }
+    }
+}
+
+/// A subregion of an image. Constructed using [`Image::sub`].
+#[expect(clippy::module_name_repetitions)]
+pub struct SubImage<'a> {
+    pub(crate) point: Point,
+    pub(crate) size: Size,
+    pub(crate) raw: &'a [u8],
+}
diff --git a/src/graphics/mod.rs b/src/graphics/mod.rs
index ec5a970..c75fe29 100644
--- a/src/graphics/mod.rs
+++ b/src/graphics/mod.rs
@@ -3,12 +3,14 @@
 mod angle;
 mod bindings;
 mod funcs;
+mod image;
 mod point;
 mod size;
 mod types;
 
 pub use angle::*;
 pub use funcs::*;
+pub use image::*;
 pub use point::*;
 pub use size::*;
 pub use types::*;

From 70a6cea6079917b49d89eab1d8fb5cc64e4d3b36 Mon Sep 17 00:00:00 2001
From: gram <git@orsinium.dev>
Date: Tue, 15 Oct 2024 18:15:17 +0200
Subject: [PATCH 2/8] add getters for Image

---
 src/graphics/image.rs | 77 +++++++++++++++++++++++++++++++++++++++++--
 1 file changed, 75 insertions(+), 2 deletions(-)

diff --git a/src/graphics/image.rs b/src/graphics/image.rs
index 80fe312..23d5f1b 100644
--- a/src/graphics/image.rs
+++ b/src/graphics/image.rs
@@ -3,7 +3,7 @@ use crate::*;
 /// A loaded image file.
 ///
 /// Can be loaded as [`FileBuf`] from ROM with [`load_file_buf`]
-/// and then cast using [Into].
+/// and then cast using [`Into`].
 pub struct Image<'a> {
     pub(crate) raw: &'a [u8],
 }
@@ -24,13 +24,86 @@ impl<'a> From<&'a FileBuf> for Image<'a> {
 impl<'a> Image<'a> {
     /// Get a rectangle subregion of the image.
     #[must_use]
-    pub fn sub(&self, p: Point, s: Size) -> SubImage<'a> {
+    pub const fn sub(&self, p: Point, s: Size) -> SubImage<'a> {
         SubImage {
             point: p,
             size: s,
             raw: self.raw,
         }
     }
+
+    /// Bits per pixel. One of: 1, 2, or 4.
+    #[must_use]
+    pub const fn bpp(&self) -> u8 {
+        self.raw[1]
+    }
+
+    /// The color used for transparency. If no transparency, returns [`Color::None`].
+    #[must_use]
+    pub fn transparency(&self) -> Color {
+        let c = usize::from(self.raw[4]) + 1;
+        c.try_into().unwrap_or(Color::None)
+    }
+
+    // pub fn set_transparency(&mut self, c: Color) {
+    //     let c: i32 = c.into();
+    //     if c == 0 {
+    //         self.raw[4] = 16;
+    //     } else {
+    //         self.raw[4] = c as u8;
+    //     }
+    // }
+
+    /// The number of pixels the image has.
+    #[must_use]
+    pub const fn pixels(&self) -> usize {
+        self.raw.len() * 8 / self.bpp() as usize
+    }
+
+    /// The image width in pixels.
+    #[must_use]
+    pub fn width(&self) -> u16 {
+        let big = u16::from(self.raw[2]);
+        let little = u16::from(self.raw[3]);
+        big | (little << 8)
+    }
+
+    /// The image height in pixels.
+    #[must_use]
+    pub fn height(&self) -> u16 {
+        let p = self.pixels();
+        let w = self.width() as usize;
+        p.checked_div(w).unwrap_or(0) as u16
+    }
+
+    /// The image size in pixels.
+    #[must_use]
+    pub fn size(&self) -> Size {
+        Size {
+            width: i32::from(self.width()),
+            height: i32::from(self.height()),
+        }
+    }
+
+    /// Get the color used to represent the given pixel value.
+    #[must_use]
+    pub fn get_color(&self, p: u8) -> Color {
+        if p > 15 {
+            return Color::None;
+        }
+        let byte_idx = usize::from(5 + p / 2);
+        let mut byte_val = self.raw[byte_idx];
+        if p % 2 == 0 {
+            byte_val >>= 4;
+        }
+        byte_val &= 0b1111;
+        let transp = self.raw[4];
+        if byte_val == transp {
+            return Color::None;
+        }
+        let color_val = usize::from(byte_val + 1);
+        color_val.try_into().unwrap_or(Color::None)
+    }
 }
 
 /// A subregion of an image. Constructed using [`Image::sub`].

From a64ce514b1ce169b6c8197c55764da4c52f06f25 Mon Sep 17 00:00:00 2001
From: gram <git@orsinium.dev>
Date: Tue, 15 Oct 2024 18:17:50 +0200
Subject: [PATCH 3/8] make all possible methods const

---
 src/fs.rs             | 6 +++---
 src/graphics/angle.rs | 4 ++--
 src/graphics/point.rs | 2 +-
 src/graphics/size.rs  | 2 +-
 src/graphics/types.rs | 2 +-
 src/sudo.rs           | 2 +-
 6 files changed, 9 insertions(+), 9 deletions(-)

diff --git a/src/fs.rs b/src/fs.rs
index 210d463..4fa761a 100644
--- a/src/fs.rs
+++ b/src/fs.rs
@@ -49,17 +49,17 @@ pub struct File<'a> {
 
 impl<'a> File<'a> {
     #[must_use]
-    pub fn data(&self) -> &[u8] {
+    pub const fn data(&self) -> &[u8] {
         self.raw
     }
 
     #[must_use]
-    pub fn as_font(&self) -> Font {
+    pub const fn as_font(&self) -> Font {
         Font { raw: self.raw }
     }
 
     #[must_use]
-    pub fn as_image(&self) -> Image {
+    pub const fn as_image(&self) -> Image {
         Image { raw: self.raw }
     }
 }
diff --git a/src/graphics/angle.rs b/src/graphics/angle.rs
index 973fbd5..ea2e702 100644
--- a/src/graphics/angle.rs
+++ b/src/graphics/angle.rs
@@ -26,7 +26,7 @@ impl Angle {
 
     /// An angle in radians where [TAU] (doubled [PI]) is the full circle.
     #[must_use]
-    pub fn from_radians(r: f32) -> Self {
+    pub const fn from_radians(r: f32) -> Self {
         Self(r)
     }
 
@@ -50,7 +50,7 @@ impl Angle {
 
     /// Get the angle value in radians where [TAU] (doubled [PI]) is the full circle.
     #[must_use]
-    pub fn to_radians(self) -> f32 {
+    pub const fn to_radians(self) -> f32 {
         self.0
     }
 
diff --git a/src/graphics/point.rs b/src/graphics/point.rs
index 0e62e04..765516a 100644
--- a/src/graphics/point.rs
+++ b/src/graphics/point.rs
@@ -32,7 +32,7 @@ impl Point {
 
     /// Set x and y to their absolute (non-negative) value.
     #[must_use]
-    pub fn abs(self) -> Self {
+    pub const fn abs(self) -> Self {
         Self {
             x: self.x.abs(),
             y: self.y.abs(),
diff --git a/src/graphics/size.rs b/src/graphics/size.rs
index bb1a11e..dbb9a41 100644
--- a/src/graphics/size.rs
+++ b/src/graphics/size.rs
@@ -35,7 +35,7 @@ impl Size {
 
     /// Set both width and height to their absolute (non-negative) value.
     #[must_use]
-    pub fn abs(self) -> Self {
+    pub const fn abs(self) -> Self {
         Self {
             width: self.width.abs(),
             height: self.height.abs(),
diff --git a/src/graphics/types.rs b/src/graphics/types.rs
index c88f4a0..c8871b2 100644
--- a/src/graphics/types.rs
+++ b/src/graphics/types.rs
@@ -36,7 +36,7 @@ impl Style {
     ///
     /// [`LineStyle`] is the same as [Style] except it doesn't have a fill color.
     #[must_use]
-    pub fn as_line_style(&self) -> LineStyle {
+    pub const fn as_line_style(&self) -> LineStyle {
         LineStyle {
             color: self.stroke_color,
             width: self.stroke_width,
diff --git a/src/sudo.rs b/src/sudo.rs
index 30109a1..5fd5d7c 100644
--- a/src/sudo.rs
+++ b/src/sudo.rs
@@ -57,7 +57,7 @@ impl<'a> Dir<'a> {
 
     /// Iterate over all loaded entries in the directory.
     #[must_use]
-    pub fn iter(&self) -> DirIter<'a> {
+    pub const fn iter(&self) -> DirIter<'a> {
         DirIter { raw: self.raw }
     }
 }

From 0412e33170c10d5844005216fed1a1071a963d75 Mon Sep 17 00:00:00 2001
From: gram <git@orsinium.dev>
Date: Tue, 15 Oct 2024 18:30:17 +0200
Subject: [PATCH 4/8] add missing graphics docs

---
 src/graphics/mod.rs   |  2 ++
 src/graphics/point.rs |  3 +++
 src/graphics/size.rs  |  3 +++
 src/graphics/types.rs | 22 ++++++++++++++++++++++
 src/lib.rs            |  5 ++++-
 5 files changed, 34 insertions(+), 1 deletion(-)

diff --git a/src/graphics/mod.rs b/src/graphics/mod.rs
index c75fe29..4af26d0 100644
--- a/src/graphics/mod.rs
+++ b/src/graphics/mod.rs
@@ -1,5 +1,7 @@
 //! Draw shapes, images, and text on the screen.
 
+#![deny(missing_docs)]
+
 mod angle;
 mod bindings;
 mod funcs;
diff --git a/src/graphics/point.rs b/src/graphics/point.rs
index 765516a..bb8501e 100644
--- a/src/graphics/point.rs
+++ b/src/graphics/point.rs
@@ -9,7 +9,9 @@ use nalgebra::{base::Scalar, Vector2};
 /// Typically, the upper-left corner of a bounding box of a shape.
 #[derive(Copy, Clone, Eq, PartialEq, Ord, PartialOrd, Hash, Debug, Default)]
 pub struct Point {
+    /// Pixel distance from left.
     pub x: i32,
+    /// Pixel distance from the top.
     pub y: i32,
 }
 
@@ -22,6 +24,7 @@ impl Point {
     /// The coordinate of the top-left corner on the screen.
     pub const MIN: Point = Point { x: 0, y: 0 };
 
+    /// Create a new point casting the argument types.
     #[must_use]
     pub fn new<I: Into<i32>>(x: I, y: I) -> Self {
         Self {
diff --git a/src/graphics/size.rs b/src/graphics/size.rs
index dbb9a41..8c2fb9a 100644
--- a/src/graphics/size.rs
+++ b/src/graphics/size.rs
@@ -14,7 +14,9 @@ pub const HEIGHT: i32 = 160;
 /// The width and height must be positive.
 #[derive(Copy, Clone, Eq, PartialEq, Ord, PartialOrd, Hash, Debug, Default)]
 pub struct Size {
+    /// Horizontal size in pixels.
     pub width: i32,
+    /// Vertical size in pixels.
     pub height: i32,
 }
 
@@ -25,6 +27,7 @@ impl Size {
         height: HEIGHT,
     };
 
+    /// Create a new size casting the argument types.
     #[must_use]
     pub fn new<I: Into<i32>>(width: I, height: I) -> Self {
         Self {
diff --git a/src/graphics/types.rs b/src/graphics/types.rs
index c8871b2..1a9b8ce 100644
--- a/src/graphics/types.rs
+++ b/src/graphics/types.rs
@@ -1,8 +1,11 @@
 /// The RGB value of a color in the palette.
 #[derive(Copy, Clone, Eq, PartialEq, Ord, PartialOrd, Hash, Debug, Default)]
 pub struct RGB {
+    /// Red component.
     pub r: u8,
+    /// Green component.
     pub g: u8,
+    /// Blue component.
     pub b: u8,
 }
 
@@ -47,7 +50,9 @@ impl Style {
 /// The same as [Style] but without a fill color (only stroke color and width).
 #[derive(Copy, Clone, Eq, PartialEq, Ord, PartialOrd, Hash, Debug, Default)]
 pub struct LineStyle {
+    /// The line stroke color.
     pub color: Color,
+    /// The line stroke width.
     pub width: i32,
 }
 
@@ -63,22 +68,39 @@ impl From<Style> for LineStyle {
 /// A pointer to a color in the color palette.
 #[derive(Copy, Clone, Eq, PartialEq, Ord, PartialOrd, Hash, Debug)]
 pub enum Color {
+    /// No color (100% transparency).
     None,
+    /// Black color: #1A1C2C.
     Black,
+    /// Purple color: #5D275D.
     Purple,
+    /// Red color: #B13E53.
     Red,
+    /// Orange color: #EF7D57.
     Orange,
+    /// Yellow color: #FFCD75.
     Yellow,
+    /// Light green color: #A7F070.
     LightGreen,
+    /// Green color: #38B764.
     Green,
+    /// Dark green color: #257179.
     DarkGreen,
+    /// Dark blue color: #29366F.
     DarkBlue,
+    /// Blue color: #3B5DC9.
     Blue,
+    /// Light blue color: #41A6F6.
     LightBlue,
+    /// Cyan color: #73EFF7.
     Cyan,
+    /// White color: #F4F4F4.
     White,
+    /// Light gray color: #94B0C2.
     LightGray,
+    /// Gray color: #566C86.
     Gray,
+    /// Dark gray color: #333C57.
     DarkGray,
 }
 
diff --git a/src/lib.rs b/src/lib.rs
index 1b49916..0204420 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -5,7 +5,10 @@
     clippy::alloc_instead_of_core,
     clippy::allow_attributes,
     clippy::std_instead_of_alloc,
-    clippy::std_instead_of_core
+    clippy::std_instead_of_core,
+    clippy::expect_used,
+    clippy::unwrap_used,
+    // missing_docs
 )]
 #![allow(clippy::wildcard_imports)]
 #![expect(

From 5a422c426546d7bf103a7ac865ec10d18c54772f Mon Sep 17 00:00:00 2001
From: gram <git@orsinium.dev>
Date: Tue, 15 Oct 2024 19:05:49 +0200
Subject: [PATCH 5/8] add Canvas and CanvasBuf

---
 src/fs.rs              | 10 ++++---
 src/graphics/canvas.rs | 66 ++++++++++++++++++++++++++++++++++++++++++
 src/graphics/image.rs  | 13 +++++++++
 src/graphics/mod.rs    |  2 ++
 src/sudo.rs            | 16 ++++++----
 5 files changed, 97 insertions(+), 10 deletions(-)
 create mode 100644 src/graphics/canvas.rs

diff --git a/src/fs.rs b/src/fs.rs
index 4fa761a..6f6e3a8 100644
--- a/src/fs.rs
+++ b/src/fs.rs
@@ -2,9 +2,9 @@
 
 use crate::graphics::*;
 #[cfg(feature = "alloc")]
-use alloc::vec;
+use alloc::boxed::Box;
 #[cfg(feature = "alloc")]
-use alloc::vec::Vec;
+use alloc::vec;
 
 /// Like [File] but owns the buffer.
 ///
@@ -13,7 +13,7 @@ use alloc::vec::Vec;
 /// and [`data::load`] instead.
 #[cfg(feature = "alloc")]
 pub struct FileBuf {
-    pub(crate) raw: Vec<u8>,
+    pub(crate) raw: Box<[u8]>,
 }
 
 #[cfg(feature = "alloc")]
@@ -106,7 +106,9 @@ pub fn load_file_buf(name: &str) -> Option<FileBuf> {
     }
     let mut buf = vec![0; size];
     load_file(name, &mut buf);
-    Some(FileBuf { raw: buf })
+    Some(FileBuf {
+        raw: buf.into_boxed_slice(),
+    })
 }
 
 /// Write the buffer into the given file in the data dir.
diff --git a/src/graphics/canvas.rs b/src/graphics/canvas.rs
new file mode 100644
index 0000000..80f54bd
--- /dev/null
+++ b/src/graphics/canvas.rs
@@ -0,0 +1,66 @@
+use crate::*;
+#[cfg(feature = "alloc")]
+use alloc::boxed::Box;
+#[cfg(feature = "alloc")]
+use alloc::vec;
+
+/// Canvas is an [`Image`] that can be drawn upon.
+///
+/// [`CanvasBuf`] is the same as [`Canvas`] but holds the ownership of the underlying slice.
+#[cfg(feature = "alloc")]
+#[expect(clippy::module_name_repetitions)]
+pub struct CanvasBuf {
+    pub(crate) raw: Box<[u8]>,
+}
+
+#[cfg(feature = "alloc")]
+impl CanvasBuf {
+    /// Create new empty canvas.
+    #[must_use]
+    #[expect(clippy::cast_sign_loss)]
+    pub fn new(s: Size) -> Self {
+        const HEADER_SIZE: usize = 5 + 8;
+        let body_size = s.width * s.height / 2;
+        let mut raw = vec![0; HEADER_SIZE + body_size as usize];
+        raw[0] = 0x21; // magic number
+        raw[1] = 4; // BPP
+        raw[2] = (s.width) as u8; // width
+        raw[3] = (s.width >> 8) as u8; // width
+        raw[4] = 255; // transparency
+
+        // color swaps
+        for i in 0u8..8u8 {
+            raw[5 + i as usize] = ((i * 2) << 4) | (i * 2 + 1);
+        }
+
+        Self {
+            raw: raw.into_boxed_slice(),
+        }
+    }
+
+    /// Represent the canvas as an [`Image`].
+    #[must_use]
+    pub fn as_image(&self) -> Image<'_> {
+        Image { raw: &self.raw }
+    }
+}
+
+/// Canvas is an [`Image`] that can be drawn upon.
+pub struct Canvas<'a> {
+    pub(crate) raw: &'a [u8],
+}
+
+impl<'a> Canvas<'a> {
+    /// Represent the canvas as an [`Image`].
+    #[must_use]
+    pub fn as_image(&self) -> Image<'a> {
+        Image { raw: self.raw }
+    }
+}
+
+#[cfg(feature = "alloc")]
+impl<'a> From<&'a CanvasBuf> for Canvas<'a> {
+    fn from(value: &'a CanvasBuf) -> Self {
+        Self { raw: &value.raw }
+    }
+}
diff --git a/src/graphics/image.rs b/src/graphics/image.rs
index 23d5f1b..c7cc584 100644
--- a/src/graphics/image.rs
+++ b/src/graphics/image.rs
@@ -21,6 +21,19 @@ impl<'a> From<&'a FileBuf> for Image<'a> {
     }
 }
 
+impl<'a> From<Canvas<'a>> for Image<'a> {
+    fn from(value: Canvas<'a>) -> Self {
+        Self { raw: value.raw }
+    }
+}
+
+#[cfg(feature = "alloc")]
+impl<'a> From<&'a CanvasBuf> for Image<'a> {
+    fn from(value: &'a CanvasBuf) -> Self {
+        Self { raw: &value.raw }
+    }
+}
+
 impl<'a> Image<'a> {
     /// Get a rectangle subregion of the image.
     #[must_use]
diff --git a/src/graphics/mod.rs b/src/graphics/mod.rs
index 4af26d0..8934c5e 100644
--- a/src/graphics/mod.rs
+++ b/src/graphics/mod.rs
@@ -4,6 +4,7 @@
 
 mod angle;
 mod bindings;
+mod canvas;
 mod funcs;
 mod image;
 mod point;
@@ -11,6 +12,7 @@ mod size;
 mod types;
 
 pub use angle::*;
+pub use canvas::*;
 pub use funcs::*;
 pub use image::*;
 pub use point::*;
diff --git a/src/sudo.rs b/src/sudo.rs
index 5fd5d7c..a554c23 100644
--- a/src/sudo.rs
+++ b/src/sudo.rs
@@ -2,13 +2,13 @@
 
 use crate::fs::{File, FileBuf};
 #[cfg(feature = "alloc")]
-use alloc::vec;
+use alloc::boxed::Box;
 #[cfg(feature = "alloc")]
-use alloc::vec::Vec;
+use alloc::vec;
 
 #[cfg(feature = "alloc")]
 pub struct DirBuf {
-    raw: Vec<u8>,
+    raw: Box<[u8]>,
 }
 
 #[cfg(feature = "alloc")]
@@ -19,7 +19,9 @@ impl DirBuf {
         let size = Dir::list_dirs_buf_size(name);
         let mut buf = vec![0; size];
         Dir::list_dirs(name, &mut buf);
-        Self { raw: buf }
+        Self {
+            raw: buf.into_boxed_slice(),
+        }
     }
 
     /// Iterate over all loaded entries in the directory.
@@ -121,7 +123,7 @@ pub fn load_file<'a>(path: &str, buf: &'a mut [u8]) -> File<'a> {
 
 /// Like [`load_file`] but takes care of the buffer allocation and ownership.
 ///
-/// `None` is returned if the file does not exist.
+/// [`None`] is returned if the file does not exist.
 #[cfg(feature = "alloc")]
 #[must_use]
 pub fn load_file_buf(path: &str) -> Option<FileBuf> {
@@ -137,7 +139,9 @@ pub fn load_file_buf(path: &str) -> Option<FileBuf> {
     unsafe {
         b::load_file(path_ptr, path_len, buf_ptr, buf_len);
     }
-    Some(FileBuf { raw: buf })
+    Some(FileBuf {
+        raw: buf.into_boxed_slice(),
+    })
 }
 
 /// Low-level bindings for host-defined "sudo" module.

From fcd0fe5ff7fcc67cf1ccef1da517c9119b5e47db Mon Sep 17 00:00:00 2001
From: gram <git@orsinium.dev>
Date: Tue, 15 Oct 2024 19:17:10 +0200
Subject: [PATCH 6/8] Canvas::new

---
 src/graphics/canvas.rs | 45 +++++++++++++++++++++++++++++++-----------
 1 file changed, 34 insertions(+), 11 deletions(-)

diff --git a/src/graphics/canvas.rs b/src/graphics/canvas.rs
index 80f54bd..aa29745 100644
--- a/src/graphics/canvas.rs
+++ b/src/graphics/canvas.rs
@@ -22,17 +22,7 @@ impl CanvasBuf {
         const HEADER_SIZE: usize = 5 + 8;
         let body_size = s.width * s.height / 2;
         let mut raw = vec![0; HEADER_SIZE + body_size as usize];
-        raw[0] = 0x21; // magic number
-        raw[1] = 4; // BPP
-        raw[2] = (s.width) as u8; // width
-        raw[3] = (s.width >> 8) as u8; // width
-        raw[4] = 255; // transparency
-
-        // color swaps
-        for i in 0u8..8u8 {
-            raw[5 + i as usize] = ((i * 2) << 4) | (i * 2 + 1);
-        }
-
+        prepare_slice(&mut raw, s.width);
         Self {
             raw: raw.into_boxed_slice(),
         }
@@ -51,6 +41,25 @@ pub struct Canvas<'a> {
 }
 
 impl<'a> Canvas<'a> {
+    /// Create new empty canvas using the given slice.
+    ///
+    /// Returns [`None`] if the slice is too small for the given image size.
+    /// A bigger slice than needed is fine.
+    #[must_use]
+    #[expect(clippy::cast_sign_loss)]
+    pub fn new(s: Size, raw: &'a mut [u8]) -> Option<Self> {
+        const HEADER_SIZE: usize = 5 + 8;
+        let body_size = s.width * s.height / 2;
+        let exp_size = HEADER_SIZE + body_size as usize;
+        if raw.len() < exp_size {
+            return None;
+        }
+        prepare_slice(raw, s.width);
+        Some(Self {
+            raw: &raw[..exp_size],
+        })
+    }
+
     /// Represent the canvas as an [`Image`].
     #[must_use]
     pub fn as_image(&self) -> Image<'a> {
@@ -64,3 +73,17 @@ impl<'a> From<&'a CanvasBuf> for Canvas<'a> {
         Self { raw: &value.raw }
     }
 }
+
+#[expect(clippy::cast_sign_loss)]
+fn prepare_slice(raw: &mut [u8], width: i32) {
+    raw[0] = 0x21; // magic number
+    raw[1] = 4; // BPP
+    raw[2] = width as u8; // width
+    raw[3] = (width >> 8) as u8; // width
+    raw[4] = 255; // transparency
+
+    // color swaps
+    for i in 0u8..8u8 {
+        raw[5 + i as usize] = ((i * 2) << 4) | (i * 2 + 1);
+    }
+}

From d1530b680beb86b2111480435bc7824213197145 Mon Sep 17 00:00:00 2001
From: gram <git@orsinium.dev>
Date: Tue, 15 Oct 2024 19:55:56 +0200
Subject: [PATCH 7/8] add set_canvas and unset_canvas

---
 src/graphics/bindings.rs |  2 ++
 src/graphics/canvas.rs   |  8 ++++++--
 src/graphics/funcs.rs    | 16 ++++++++++++++++
 3 files changed, 24 insertions(+), 2 deletions(-)

diff --git a/src/graphics/bindings.rs b/src/graphics/bindings.rs
index d0e0523..2d2337a 100644
--- a/src/graphics/bindings.rs
+++ b/src/graphics/bindings.rs
@@ -99,4 +99,6 @@ extern {
         sub_height: i32,
     );
     pub(crate) fn draw_image(ptr: u32, len: u32, x: i32, y: i32);
+    pub(crate) fn set_canvas(ptr: u32, len: u32);
+    pub(crate) fn unset_canvas();
 }
diff --git a/src/graphics/canvas.rs b/src/graphics/canvas.rs
index aa29745..d32d08b 100644
--- a/src/graphics/canvas.rs
+++ b/src/graphics/canvas.rs
@@ -4,6 +4,10 @@ use alloc::boxed::Box;
 #[cfg(feature = "alloc")]
 use alloc::vec;
 
+// TODO: add statically-allocated version when prepare_slice can be turned into static fn.
+// It is blocked by this feature going into stable:
+// https://github.com/rust-lang/rust/issues/57349
+
 /// Canvas is an [`Image`] that can be drawn upon.
 ///
 /// [`CanvasBuf`] is the same as [`Canvas`] but holds the ownership of the underlying slice.
@@ -30,7 +34,7 @@ impl CanvasBuf {
 
     /// Represent the canvas as an [`Image`].
     #[must_use]
-    pub fn as_image(&self) -> Image<'_> {
+    pub const fn as_image(&self) -> Image<'_> {
         Image { raw: &self.raw }
     }
 }
@@ -62,7 +66,7 @@ impl<'a> Canvas<'a> {
 
     /// Represent the canvas as an [`Image`].
     #[must_use]
-    pub fn as_image(&self) -> Image<'a> {
+    pub const fn as_image(&self) -> Image<'a> {
         Image { raw: self.raw }
     }
 }
diff --git a/src/graphics/funcs.rs b/src/graphics/funcs.rs
index 053bac7..b6ce78d 100644
--- a/src/graphics/funcs.rs
+++ b/src/graphics/funcs.rs
@@ -191,3 +191,19 @@ pub fn draw_sub_image(i: &SubImage, p: Point) {
         );
     }
 }
+
+/// Set canvas to be used for all subsequent drawing operations.
+pub fn set_canvas(c: &Canvas) {
+    let ptr = c.raw.as_ptr();
+    let len = c.raw.len();
+    unsafe {
+        b::set_canvas(ptr as u32, len as u32);
+    }
+}
+
+/// Unset canvas set by [`set_canvas`]. All subsequent drawing operations will target frame buffer.
+pub fn unset_canvas() {
+    unsafe {
+        b::unset_canvas();
+    }
+}

From fbb3086c6451187bae0a21b06332b09fbf003d10 Mon Sep 17 00:00:00 2001
From: gram <git@orsinium.dev>
Date: Sat, 19 Oct 2024 17:07:25 +0200
Subject: [PATCH 8/8] add CanvasBuf.as_canvas

---
 src/graphics/canvas.rs | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/src/graphics/canvas.rs b/src/graphics/canvas.rs
index d32d08b..1ac2cd4 100644
--- a/src/graphics/canvas.rs
+++ b/src/graphics/canvas.rs
@@ -37,6 +37,12 @@ impl CanvasBuf {
     pub const fn as_image(&self) -> Image<'_> {
         Image { raw: &self.raw }
     }
+
+    /// Represent the buffered canvas as [`Canvas`].
+    #[must_use]
+    pub const fn as_canvas(&self) -> Canvas<'_> {
+        Canvas { raw: &self.raw }
+    }
 }
 
 /// Canvas is an [`Image`] that can be drawn upon.