crabshell-render 0.3.0

//! Images: PNG, JPEG, GIF, WebP and SVG files, decoded under size caps and
//! scaled to the size they are drawn at. Image files come from other
//! programs and the network, so every decoder is told the caps before it
//! allocates.

use std::io::Cursor;
use std::num::NonZeroU64;
use std::path::Path;

use crabshell_ui::Fit;
use resvg::usvg;
use tiny_skia::{FilterQuality, Pixmap, PixmapPaint, PixmapRef, Transform};
use zune_jpeg::JpegDecoder;
use zune_jpeg::zune_core::bytestream::ZCursor;
use zune_jpeg::zune_core::colorspace::ColorSpace;
use zune_jpeg::zune_core::options::DecoderOptions;

use crate::icons::{decode_png, halve, premultiplied, read_capped, svg_tree};

/// The largest image file read, in bytes.
const MAX_BYTES: u64 = 32 * 1024 * 1024;

/// The largest SVG image read, in bytes.
const MAX_SVG_BYTES: u64 = 4 * 1024 * 1024;

/// The widest and tallest image decoded, in pixels.
const MAX_SIDE: u32 = 8192;

/// The most pixels an image may have: a 6K picture, 96 MiB decoded.
const MAX_PIXELS: u64 = 24_000_000;

/// The file at `path` as a `width` by `height` pixmap, scaled as `fit`
/// says.
pub(crate) fn rasterize(path: &Path, width: u32, height: u32, fit: Fit) -> Result<Pixmap, String> {
  if width == 0 || height == 0 {
    return Err(String::from("an image with no pixels"));
  }
  match decode(path)? {
    Picture::Svg(tree) => svg(&tree, width, height, fit),
    Picture::Pixels(image) => scale(image.as_ref(), width, height, fit),
  }
}

/// A decoded image file: pixels, or an SVG to draw at any size.
pub(crate) enum Picture {
  Pixels(Pixmap),
  Svg(Box<usvg::Tree>),
}

/// Reads and decodes the file at `path` under the caps. The format comes
/// from the extension.
pub(crate) fn decode(path: &Path) -> Result<Picture, String> {
  let extension = path
    .extension()
    .and_then(|extension| extension.to_str())
    .map(str::to_ascii_lowercase);
  let image = match extension.as_deref() {
    Some("svg") => {
      let tree = svg_tree(&read_capped(path, MAX_SVG_BYTES)?)?;
      return Ok(Picture::Svg(Box::new(tree)));
    }
    Some("png") => decode_png(&read_capped(path, MAX_BYTES)?, MAX_SIDE, MAX_PIXELS)?,
    Some("jpg" | "jpeg") => jpeg(&read_capped(path, MAX_BYTES)?)?,
    Some("gif") => gif(&read_capped(path, MAX_BYTES)?)?,
    Some("webp") => webp(&read_capped(path, MAX_BYTES)?)?,
    _ => {
      return Err(String::from(
        "images must be .png, .jpg, .gif, .webp or .svg files",
      ));
    }
  };
  Ok(Picture::Pixels(image))
}

/// Refuses a `width` by `height` image past the caps.
pub(crate) fn check(width: u32, height: u32) -> Result<(), String> {
  if width == 0 || height == 0 {
    return Err(String::from("an image with no pixels"));
  }
  if width > MAX_SIDE || height > MAX_SIDE || u64::from(width) * u64::from(height) > MAX_PIXELS {
    return Err(format!(
      "a {width}x{height} image is larger than {MAX_SIDE} pixels a side or {MAX_PIXELS} pixels"
    ));
  }
  Ok(())
}

fn jpeg(data: &[u8]) -> Result<Pixmap, String> {
  let options = DecoderOptions::default()
    .set_max_width(MAX_SIDE as usize)
    .set_max_height(MAX_SIDE as usize)
    .jpeg_set_out_colorspace(ColorSpace::RGBA);
  let mut decoder = JpegDecoder::new_with_options(ZCursor::new(data), options);
  decoder
    .decode_headers()
    .map_err(|error| error.to_string())?;
  let info = decoder.info().ok_or("a JPEG without a size")?;
  let (width, height) = (u32::from(info.width), u32::from(info.height));
  check(width, height)?;
  let rgba = decoder.decode().map_err(|error| error.to_string())?;
  premultiplied(rgba, width, height)
}

/// The first frame of a GIF, on its whole canvas.
pub(crate) fn gif(data: &[u8]) -> Result<Pixmap, String> {
  let mut options = gif::DecodeOptions::new();
  options.set_color_output(gif::ColorOutput::RGBA);
  if let Some(limit) = NonZeroU64::new(MAX_PIXELS * 4) {
    options.set_memory_limit(gif::MemoryLimit::Bytes(limit));
  }
  let mut decoder = options
    .read_info(Cursor::new(data))
    .map_err(|error| error.to_string())?;
  let (width, height) = (u32::from(decoder.width()), u32::from(decoder.height()));
  check(width, height)?;
  let frame = decoder
    .read_next_frame()
    .map_err(|error| error.to_string())?
    .ok_or("a GIF with no frames")?;
  if frame.width == 0 || frame.height == 0 {
    return Err(String::from("a GIF frame with no pixels"));
  }
  let mut rgba = vec![0; width as usize * height as usize * 4];
  // A frame may cover only part of the canvas; the rest stays clear.
  let (left, top) = (u32::from(frame.left), u32::from(frame.top));
  let frame_width = usize::from(frame.width);
  for (row, line) in frame.buffer.chunks_exact(frame_width * 4).enumerate() {
    let y = top + row as u32;
    if y >= height || left >= width {
      continue;
    }
    let columns = frame_width.min((width - left) as usize);
    let start = (y as usize * width as usize + left as usize) * 4;
    rgba[start..start + columns * 4].copy_from_slice(&line[..columns * 4]);
  }
  premultiplied(rgba, width, height)
}

/// A WebP, or the first frame of an animated one.
// shortcut: image-webp sizes a lossy frame from its own header, up to
// 16383 a side, before checking it against the canvas size checked here;
// cap it in image-webp or parse the VP8 header if that matters.
fn webp(data: &[u8]) -> Result<Pixmap, String> {
  let mut decoder =
    image_webp::WebPDecoder::new(Cursor::new(data)).map_err(|error| error.to_string())?;
  let (width, height) = decoder.dimensions();
  check(width, height)?;
  decoder.set_memory_limit((MAX_PIXELS * 4) as usize);
  let size = decoder
    .output_buffer_size()
    .ok_or("the WebP is too large to decode")?;
  let mut buffer = vec![0; size];
  decoder
    .read_image(&mut buffer)
    .map_err(|error| error.to_string())?;
  let rgba = if decoder.has_alpha() {
    buffer
  } else {
    buffer
      .as_chunks::<3>()
      .0
      .iter()
      .flat_map(|&[r, g, b]| [r, g, b, 255])
      .collect()
  };
  premultiplied(rgba, width, height)
}

pub(crate) fn svg(tree: &usvg::Tree, width: u32, height: u32, fit: Fit) -> Result<Pixmap, String> {
  let size = tree.size();
  let mut pixmap = Pixmap::new(width, height).ok_or("an image with no pixels")?;
  let transform = placement((size.width(), size.height()), (width, height), fit);
  resvg::render(tree, transform, &mut pixmap.as_mut());
  Ok(pixmap)
}

/// `image` scaled into a `width` by `height` pixmap as `fit` says. An
/// image more than twice the size is first halved, averaging each 2 by 2
/// block, so detail shrinks smoothly instead of flickering.
pub(crate) fn scale(
  image: PixmapRef<'_>,
  width: u32,
  height: u32,
  fit: Fit,
) -> Result<Pixmap, String> {
  let mut halved;
  let mut image = image;
  loop {
    let (x, y) = factors(
      (image.width() as f32, image.height() as f32),
      (width, height),
      fit,
    );
    // shortcut: halves only while both axes shrink past half, so a Fill
    // squashing one axis alone can alias; halve per axis if that shows.
    if x >= 0.5 || y >= 0.5 {
      break;
    }
    halved = halve(image)?;
    image = halved.as_ref();
  }
  let mut pixmap = Pixmap::new(width, height).ok_or("an image with no pixels")?;
  let transform = placement(
    (image.width() as f32, image.height() as f32),
    (width, height),
    fit,
  );
  let paint = PixmapPaint {
    quality: FilterQuality::Bicubic,
    ..PixmapPaint::default()
  };
  pixmap.draw_pixmap(0, 0, image, &paint, transform, None);
  Ok(pixmap)
}

/// How much `fit` scales a `source` sized picture across and down to fill
/// `target`.
pub(crate) fn factors(source: (f32, f32), target: (u32, u32), fit: Fit) -> (f32, f32) {
  let across = target.0 as f32 / source.0;
  let down = target.1 as f32 / source.1;
  match fit {
    Fit::Fill => (across, down),
    Fit::Contain => (across.min(down), across.min(down)),
    Fit::Cover => (across.max(down), across.max(down)),
  }
}

/// Scales a `source` sized picture as `fit` says and centers it in
/// `target`; a cover's overflow is cut by the target's edges.
fn placement(source: (f32, f32), target: (u32, u32), fit: Fit) -> Transform {
  let (x, y) = factors(source, target, fit);
  Transform::from_scale(x, y).post_translate(
    (target.0 as f32 - source.0 * x) / 2.0,
    (target.1 as f32 - source.1 * y) / 2.0,
  )
}