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//! A module for different pixel layouts.
//!
//! The `*Layout` traits define generic standard layouts with a normal form. Other traits provide
//! operations to convert between layouts, operations on the underlying image bytes, etc.
use crate::texel::MaxAligned;
use crate::{AsTexel, Texel};
use ::alloc::boxed::Box;
use core::{alloc, cmp};
mod matrix;
use crate::image::{Coord, ImageMut, ImageRef};
pub use crate::stride::{BadStrideError, StrideSpec, StridedBytes, StridedLayout, Strides};
/// A byte layout that only describes the user bytes.
///
/// This is a minimal implementation of the basic `Layout` trait. It does not provide any
/// additional semantics for the buffer bytes described by it. All other layouts may be converted
/// into this layout.
pub struct Bytes(pub usize);
/// Describes the byte layout of an texture element, untyped.
///
/// This is not so different from `Texel` and `Layout` but is a combination of both. It has the
/// same invariants on alignment as the former which being untyped like the latter. The alignment
/// of an element must be at most that of [`MaxAligned`] and the size must be a multiple of its
/// alignment.
///
/// This type is a lower semi lattice. That is, given two elements the type formed by taking the
/// minimum of size and alignment individually will always form another valid element. This
/// operation is implemented in the [`Self::infimum`] method.
#[derive(Clone, Copy, Debug, PartialEq, Eq, Ord, Hash)]
pub struct TexelLayout {
size: usize,
align: usize,
}
/// A descriptor of the layout of image bytes.
///
/// There is no color space and no strict type interpretation here, just some mapping to required
/// bytes for such a fixed buffer and a width and height of the described image. This means that
/// the byte usage for a particular buffer needs to be independent of the content, in particular
/// can not be based on compressibility.
///
/// There is one more thing that differentiates an image from an encoded format. It is expected
/// that the image can be unfolded into some matrix of independent pixels (with potentially
/// multiple channels) without any arithmetic or conversion function. Independent here means that,
/// when supplied with the missing color space and type information, there should exist an
/// `Fn(U) -> T` that can map these pixels independently into some linear color space.
///
/// This property holds for any packed, strided or planar RGB/YCbCr/HSV format as well as chroma
/// subsampled YUV images and even raw Bayer filtered images.
pub trait Layout {
fn byte_len(&self) -> usize;
}
/// Convert one layout to a less strict one.
///
/// In contrast to `From`/`Into` which is mostly assumed to model a lossless conversion the
/// conversion here may generalize but need not be lossless. For example, the `Bytes` layout is the
/// least descriptive layout that exists and any layout can decay into it. However, it should be
/// clear that this conversion is never lossless.
///
/// In general, a layout `L` should implement `Decay<T>` if any image with layouts of type `T` is
/// also valid for some layout of type `L`. A common example would be if a crate strictly adds more
/// information to a predefined layout, then it should also decay to that layout.
///
/// Also note that this trait is not reflexive, in contrast to `From` and `Into` which are. This
/// avoids collisions in impls. In particular, it allows adding blanket impls of the form
///
/// ```ignore
/// struct Local;
///
/// impl Trait for Local { /* … */ }
///
/// impl<T: Trait> Decay<T> for Local { /* … */ }
/// ```
///
/// Otherwise, the instantiation `T = U` would collide with the reflexive impl.
///
/// ## Design
///
/// We consider re-rebalanced coherence rules ([RFC2451]) in this design especially to define the
/// receiver type and the type parameter. Note that adding a blanket impl is a breaking change
/// except under a special rule allowed in that RFC. To quote it here:
///
/// > RFC #1023 is amended to state that adding a new impl to an existing trait is considered a
/// > breaking change unless, given impl<P1..=Pn> Trait<T1..=Tn> for T0:
/// > * At least one of the types T0..=Tn must be a local type, added in this revision. Let Ti be
/// > the first such type.
/// > * No uncovered type parameters P1..=Pn appear in T0..Ti (excluding Ti)
/// >
/// > [...]
/// >
/// > However, the following impls would not be considered a breaking change: [...]
/// > * `impl<T> OldTrait<T> for NewType`
///
/// Let's say we want to introduce a new desciptor trait for matrix-like layouts. Then we can ship
/// a new type representing the canonical form of this matrix trait and in the same revision define
/// a blanket impl that allows other layouts to decay to it. This wouldn't be possible if the
/// parameters were swapped. We can then let this specific type (it may contain covered type
/// parameters) decay to any other previously defined layout to provide interoperability with older
/// code.
///
/// [RFC2451]: https://rust-lang.github.io/rfcs/2451-re-rebalancing-coherence.html
///
pub trait Decay<T>: Layout {
fn decay(from: T) -> Self;
}
impl<T: Layout> Decay<T> for Bytes {
fn decay(from: T) -> Bytes {
Bytes(from.byte_len())
}
}
/// Convert a layout to a stricter one.
///
/// ## Design
///
/// A comment on the design space available for this trait.
///
/// (TODO: wrong) We require that the trait is
/// implemented for the type that is _returned_. If we required that the trait be implemented for
/// the receiver then this would restrict third-parties from using it to its full potential. In
/// particular, since `Mend` is a foreign trait the coherence rules make it impossible to specify:
///
/// TODO Terminology: https://rust-lang.github.io/rfcs/2451-re-rebalancing-coherence.html
///
/// ```ignore
/// impl<T> Mend<LocalType> for T {}
/// ```
///
/// TODO: rewrite this...
///
/// ```ignore
/// impl<T> Mend<T> for LocalType {}
/// ```
///
/// The forms of evolution that we want to keep open:
/// * Introduce a new form of mending between existing layouts. For example, a new color space
/// transformation should be able to translate between existing types. Note that we will assume
/// that in such a case the type parameters do not appear uncovered in the target or the source
/// so that having either as the trait receiver (T0) allows this.
/// * An *upgrader* type should be able to mend a <T: LocalOrForeignTrait> into a chosen layout.
/// * TODO: When add a new layout type which mender types and targets do we want?
///
/// The exact form thus simply depends on expected use and the allow evolution for this crate.
/// Consider in particular this coherence/SemVer rule:
///
/// > Adding any impl with an uncovered type parameter is considered a major breaking change.
///
/// TODO
///
/// TODO: comment and consider `&self`.
///
pub trait Mend<From> {
type Into: Layout;
fn mend(self, from: &From) -> Self::Into;
}
/// Try to convert a layout to a stricter one.
pub trait TryMend<From> {
type Into: Layout;
type Err;
fn try_mend(self, from: &From) -> Result<Self::Into, Self::Err>;
}
/// A layout that can be emptied.
///
/// This trait contains all layout types from which we can steal their memory buffer. This is
/// incredibly useful for fallible operations that change the _type_ of a buffers layout. Instead
/// of being required to take the buffer by value and return the original in case of an error they
/// can use the much natural signature:
///
/// * `fn mutate(&mut self) -> Result<Converted, Err>`
///
/// where semantics are that the buffer is unchanged in case of error but has been moved to the
/// type `Converted` in case of success. This is very similar to the method `Vec::take` and others.
///
/// It is expected that the `byte_len` is `0` after the operation.
///
/// This trait is _not_ simply a clone of `Default`. While we expect that the described image
/// contains no bytes after the operation other data such as channel count, color space
/// information, image plane order, alpha interpretation should be retained.
pub trait Take: Layout {
fn take(&mut self) -> Self;
}
/// A layout that is a slice of samples.
///
/// These layouts are represented with a slice of a _single_ type of samples. In particular these
/// can be addressed and mutated independently.
pub trait SliceLayout: Layout {
/// The sample type itself.
type Sample;
/// Get the sample description.
fn sample(&self) -> Texel<Self::Sample>;
/// The number of samples.
///
/// A slice with the returned length should have the byte length returned in `byte_len`.
fn len(&self) -> usize {
self.byte_len() / self.sample().size()
}
}
/// A layout of individually addressable raster elements.
///
/// Often referred to as 'pixels', this is a special form of texels that represent a single group
/// of color channels that form one color impression.
///
/// Note that it does not prescribe any particular order of arrangement of these channels. Indeed,
/// they could be in column major format, in row major format, ordered according to some space
/// filling curve, etc. Also, multiple pixels may form one group of subsampled channels.
pub trait Raster<Pixel>: Layout + Sized {
fn dimensions(&self) -> Coord;
fn get(from: ImageRef<&Self>, at: Coord) -> Option<Pixel>;
}
/// A raster layout where one can change pixel values independently.
///
/// In other words, requires that texels are actually one-by-one blocks of pixels.
///
/// Note that it does not prescribe any particular order of arrangement of these texels. Indeed,
/// they could be in column major format, in row major format, ordered according to some space
/// filling curve, etc. but subsampled images are not easily possible as pixels can not be written
/// to independently.
pub trait RasterMut<Pixel>: Raster<Pixel> {
fn put(into: ImageMut<&mut Self>, at: Coord, val: Pixel);
/// Evaluate a function on each texel of the raster image.
fn shade(mut image: ImageMut<&mut Self>, mut f: impl FnMut(u32, u32, &mut Pixel)) {
let Coord(bx, by) = image.layout().dimensions();
for y in 0..by {
for x in 0..bx {
let mut pixel = Self::get(image.as_ref().as_deref(), Coord(x, y)).unwrap();
f(x, y, &mut pixel);
Self::put(image.as_mut().as_deref_mut(), Coord(x, y), pixel);
}
}
}
}
/// A dynamic descriptor of an image's layout.
///
/// FIXME: figure out if this is 'right' to expose in this crate.
#[derive(Clone, Debug, PartialEq, Eq, Hash)]
pub(crate) struct DynLayout {
pub(crate) repr: LayoutRepr,
}
#[derive(Clone, Copy, Debug, PartialEq, Eq, Hash)]
pub(crate) enum LayoutRepr {
Matrix(MatrixBytes),
Yuv420p(Yuv420p),
}
/// A matrix of packed texels (channel groups).
///
/// This is a simple layout of exactly width·height homogeneous pixels.
#[derive(Clone, Copy, Debug, PartialEq, Eq, Hash)]
pub struct MatrixBytes {
pub(crate) element: TexelLayout,
pub(crate) first_dim: usize,
pub(crate) second_dim: usize,
}
/// A matrix of packed texels (channel groups).
///
/// The underlying buffer may have more data allocated than this region and cause the overhead to
/// be reused when resizing the image. All ways to construct this already check that all pixels
/// within the resulting image can be addressed via an index.
pub struct Matrix<P> {
pub(crate) width: usize,
pub(crate) height: usize,
pub(crate) pixel: Texel<P>,
}
/// A layout that's a matrix of elements.
pub trait MatrixLayout: Layout {
/// The valid matrix specification of this layout.
///
/// This call should not fail, or panic. Otherwise, prefer an optional getter for the
/// [`StridedBytes`] and have the caller decay their own buffer.
fn matrix(&self) -> MatrixBytes;
}
/// Planar chroma 2×2 block-wise sub-sampled image.
///
/// FIXME: figure out if this is 'right' to expose in this crate.
#[derive(Clone, Copy, Debug, PartialEq, Eq, Hash)]
pub(crate) struct Yuv420p {
channel: TexelLayout,
width: u32,
height: u32,
}
/// An error indicating that mending failed due to mismatching pixel attributes.
///
/// This struct is used when a layout with dynamic pixel information should be mended into another
/// layout with static information or a more restrictive combination of layouts. One example is the
/// conversion of a dynamic matrix into a statically typed layout.
#[derive(Debug, Default, PartialEq, Eq, Hash)]
pub struct MismatchedPixelError {
_private: (),
}
impl Bytes {
/// Forget all layout semantics except the number of bytes used.
pub fn from_layout(layout: impl Layout) -> Self {
Bytes(layout.byte_len())
}
}
impl TexelLayout {
/// Construct an element from a self-evident pixel.
pub fn from_pixel<P: AsTexel>() -> Self {
let pix = P::texel();
TexelLayout {
size: pix.size(),
align: pix.align(),
}
}
/// An element with maximum size and no alignment requirements.
///
/// This constructor is mainly useful for the purpose of using it as a modifier. When used with
/// [`Self::infimum`] it will only shrink the alignment and keep the size unchanged.
pub const MAX_SIZE: Self = {
TexelLayout {
size: isize::MAX as usize,
align: 1,
}
};
/// Create an element for a fictional type with specific layout.
///
/// It's up to the caller to define or use an actual type with that same layout later. This
/// skips the check that such a type must not contain any padding and only performs the layout
/// related checks.
pub fn with_layout(layout: alloc::Layout) -> Option<Self> {
if layout.align() > MaxAligned::texel().align() {
return None;
}
if layout.size() % layout.align() != 0 {
return None;
}
Some(TexelLayout {
size: layout.size(),
align: layout.align(),
})
}
/// Convert this into a type layout.
///
/// This can never fail as `TexelLayout` refines the standard library layout type.
pub fn layout(self) -> alloc::Layout {
alloc::Layout::from_size_align(self.size, self.align).expect("Valid layout")
}
/// Reduce the alignment of the element.
///
/// This will perform the same modification as `repr(packed)` on the element's type.
///
/// # Panics
///
/// This method panics if `align` is not a valid alignment.
#[must_use = "This does not modify `self`."]
pub fn packed(self, align: usize) -> TexelLayout {
assert!(align.is_power_of_two());
let align = self.align.min(align);
TexelLayout { align, ..self }
}
/// Create an element having the smaller of both sizes and alignments.
#[must_use = "This does not modify `self`."]
pub fn infimum(self, other: Self) -> TexelLayout {
// We still have size divisible by align. Whatever the smaller of both, it's divisible by
// its align and thus also by the min of both alignments.
TexelLayout {
size: self.size.min(other.size),
align: self.align.min(other.align),
}
}
/// Get the size of the element.
pub const fn size(self) -> usize {
self.size
}
/// Get the minimum required alignment of the element.
pub const fn align(self) -> usize {
self.size
}
pub const fn superset_of(&self, other: TexelLayout) -> bool {
self.size >= other.size && self.align >= other.align
}
}
impl DynLayout {
pub fn byte_len(&self) -> usize {
match self.repr {
LayoutRepr::Matrix(matrix) => matrix.byte_len(),
LayoutRepr::Yuv420p(matrix) => matrix.byte_len(),
}
}
}
impl MatrixBytes {
pub fn empty(element: TexelLayout) -> Self {
MatrixBytes {
element,
first_dim: 0,
second_dim: 0,
}
}
pub fn from_width_height(
element: TexelLayout,
first_dim: usize,
second_dim: usize,
) -> Option<Self> {
let max_index = first_dim.checked_mul(second_dim)?;
let _ = max_index.checked_mul(element.size)?;
Some(MatrixBytes {
element,
first_dim,
second_dim,
})
}
/// Get the element type of this matrix.
pub const fn element(&self) -> TexelLayout {
self.element
}
/// Get the width of this matrix.
pub const fn width(&self) -> usize {
self.first_dim
}
/// Get the height of this matrix.
pub const fn height(&self) -> usize {
self.second_dim
}
/// Get the required bytes for this layout.
pub const fn byte_len(self) -> usize {
// Exactly this does not overflow due to construction.
self.element.size * self.len()
}
/// The number of pixels in this layout
pub const fn len(self) -> usize {
self.first_dim * self.second_dim
}
}
impl Yuv420p {
pub fn from_width_height(channel: TexelLayout, width: u32, height: u32) -> Option<Self> {
use core::convert::TryFrom;
if width % 2 != 0 || height % 2 != 0 {
return None;
}
let mwidth = usize::try_from(width).ok()?;
let mheight = usize::try_from(height).ok()?;
let y_count = mwidth.checked_mul(mheight)?;
let uv_count = y_count / 2;
let count = y_count.checked_add(uv_count)?;
let _ = count.checked_mul(channel.size)?;
Some(Yuv420p {
channel,
width,
height,
})
}
pub const fn byte_len(self) -> usize {
let ylen = (self.width as usize) * (self.height as usize) * self.channel.size;
ylen + ylen / 2
}
}
impl Layout for Bytes {
fn byte_len(&self) -> usize {
self.0
}
}
impl<'lt, T: Layout + ?Sized> Layout for &'lt T {
fn byte_len(&self) -> usize {
(**self).byte_len()
}
}
impl<'lt, T: Layout + ?Sized> Layout for &'lt mut T {
fn byte_len(&self) -> usize {
(**self).byte_len()
}
}
impl Take for Bytes {
fn take(&mut self) -> Self {
Bytes(core::mem::take(&mut self.0))
}
}
impl Layout for DynLayout {
fn byte_len(&self) -> usize {
DynLayout::byte_len(self)
}
}
impl Layout for MatrixBytes {
fn byte_len(&self) -> usize {
MatrixBytes::byte_len(*self)
}
}
impl Take for MatrixBytes {
fn take(&mut self) -> Self {
core::mem::replace(self, MatrixBytes::empty(self.element))
}
}
impl<P> MatrixLayout for Matrix<P> {
fn matrix(&self) -> MatrixBytes {
self.into_matrix_bytes()
}
}
/// Remove the strong typing for dynamic channel type information.
impl<L: MatrixLayout> Decay<L> for MatrixBytes {
fn decay(from: L) -> MatrixBytes {
from.matrix()
}
}
/// Try to use the matrix with a specific pixel type.
impl<P> TryMend<MatrixBytes> for Texel<P> {
type Into = Matrix<P>;
type Err = MismatchedPixelError;
fn try_mend(self, matrix: &MatrixBytes) -> Result<Matrix<P>, Self::Err> {
Matrix::with_matrix(self, *matrix).ok_or_else(MismatchedPixelError::default)
}
}
impl<T> SliceLayout for &'_ T
where
T: SliceLayout,
{
type Sample = T::Sample;
fn sample(&self) -> Texel<Self::Sample> {
(**self).sample()
}
}
impl<T> SliceLayout for &'_ mut T
where
T: SliceLayout,
{
type Sample = T::Sample;
fn sample(&self) -> Texel<Self::Sample> {
(**self).sample()
}
}
/// Convert a pixel to an element, discarding the exact type information.
impl<P> From<Texel<P>> for TexelLayout {
fn from(pix: Texel<P>) -> Self {
TexelLayout {
size: pix.size(),
align: pix.align(),
}
}
}
impl<L: Layout + ?Sized> Layout for Box<L> {
fn byte_len(&self) -> usize {
(**self).byte_len()
}
}
impl<L: Layout> Decay<L> for Box<L> {
fn decay(from: L) -> Box<L> {
Box::new(from)
}
}
/// The partial order of elements is defined by comparing size and alignment.
///
/// This turns it into a semi-lattice structure, with infimum implementing the meet operation. For
/// example, the following comparison all hold:
///
/// ```
/// # use image_texel::texels::{U8, U16};
/// # use image_texel::layout::TexelLayout;
/// let u8 = TexelLayout::from(U8);
/// let u8x2 = TexelLayout::from(U8.array::<2>());
/// let u8x3 = TexelLayout::from(U8.array::<3>());
/// let u16 = TexelLayout::from(U16);
///
/// assert!(u8 < u16, "due to size and alignment");
/// assert!(u8x2 < u16, "due to its alignment");
/// assert!(!(u8x3 < u16) && !(u16 < u8x3), "not comparable");
///
/// let meet = u8x3.infimum(u16);
/// assert!(meet <= u8x3);
/// assert!(meet <= u16);
/// assert!(meet == u16.packed(1), "We know it precisely here {:?}", meet);
/// ```
impl cmp::PartialOrd for TexelLayout {
fn partial_cmp(&self, other: &Self) -> Option<cmp::Ordering> {
if self.size == other.size && self.align == other.align {
Some(cmp::Ordering::Equal)
} else if self.size <= other.size && self.align <= other.align {
Some(cmp::Ordering::Less)
} else if self.size >= other.size && self.align >= other.align {
Some(cmp::Ordering::Greater)
} else {
None
}
}
}
macro_rules! bytes_from_layout {
($layout:path) => {
impl From<$layout> for Bytes {
fn from(layout: $layout) -> Self {
Bytes::from_layout(layout)
}
}
};
(<$($bound:ident),*> $layout:ident) => {
impl<$($bound),*> From<$layout <$($bound),*>> for Bytes {
fn from(layout: $layout <$($bound),*>) -> Self {
Bytes::from_layout(layout)
}
}
};
}
bytes_from_layout!(DynLayout);
bytes_from_layout!(MatrixBytes);
bytes_from_layout!(<P> Matrix);
impl From<MatrixBytes> for DynLayout {
fn from(matrix: MatrixBytes) -> Self {
DynLayout {
repr: LayoutRepr::Matrix(matrix),
}
}
}
impl From<Yuv420p> for DynLayout {
fn from(matrix: Yuv420p) -> Self {
DynLayout {
repr: LayoutRepr::Yuv420p(matrix),
}
}
}
impl<P> From<Matrix<P>> for MatrixBytes {
fn from(mat: Matrix<P>) -> Self {
MatrixBytes {
element: mat.pixel().into(),
first_dim: mat.width(),
second_dim: mat.height(),
}
}
}
/// Note: on 64-bit targets only the first `u32::MAX` dimensions appear accessible.
impl<P> Raster<P> for Matrix<P> {
fn dimensions(&self) -> Coord {
use core::convert::TryFrom;
let width = u32::try_from(self.width()).unwrap_or(u32::MAX);
let height = u32::try_from(self.height()).unwrap_or(u32::MAX);
Coord(width, height)
}
fn get(from: ImageRef<&Self>, Coord(x, y): Coord) -> Option<P> {
if from.layout().in_bounds(x as usize, y as usize) {
let index = from.layout().index_of(x as usize, y as usize);
let texel = from.layout().sample();
from.as_slice().get(index).map(|v| texel.copy_val(v))
} else {
None
}
}
}
impl<P> RasterMut<P> for Matrix<P> {
fn put(into: ImageMut<&mut Self>, Coord(x, y): Coord, val: P) {
if into.layout().in_bounds(x as usize, y as usize) {
let index = into.layout().index_of(x as usize, y as usize);
if let Some(dst) = into.into_mut_slice().get_mut(index) {
*dst = val;
}
}
}
}