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https://github.com/storytold/craft-libs.git
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Dylan M. Taylor
f2d658d08f
The layer every EPS reader and writer in the apps had its own copy of: where the PostScript and the previews are behind the binary header (read and write), the header comments with the bounding boxes (also deferred to the trailer), the EPSI preview bitmap, ASCII85 both ways, and telling EPS, PostScript and PostScript- or PDF-based Illustrator files apart. No PostScript interpreter. From storytold/vectorcraft at 6e873b80 (crates/eps: lib.rs, import.rs, import/preview.rs, ps.rs) and storytold/designcraft at 513f77b8 (crates/images/src/eps.rs).
60 lines
2.3 KiB
Rust
60 lines
2.3 KiB
Rust
//! The device-independent preview (EPSI): a bitmap in hexadecimal comment lines between
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//! `%%BeginPreview: width height depth lines` and `%%EndPreview` (EPSF 3.0, section 6).
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/// Largest EPSI bitmap side read (pixels).
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pub const MAX_EPSI: usize = 8192;
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/// A grey bitmap, 8 bits a pixel, row by row from the top: 0 is black, 255 white.
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#[derive(Debug, Clone, PartialEq, Eq)]
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pub struct Bitmap {
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pub width: u32,
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pub height: u32,
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pub gray: Vec<u8>,
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}
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/// The EPSI preview of `ps`, if it has one of 1, 2, 4 or 8 bits a pixel and all its samples.
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/// In the file a sample of 0 is white (EPSF 3.0: "0 is white"); the bitmap is turned around.
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pub fn epsi(ps: &[u8]) -> Option<Bitmap> {
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let text = String::from_utf8_lossy(ps);
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let mut lines = text.split(['\n', '\r']).filter(|l| !l.is_empty());
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let head = lines.find_map(|l| l.strip_prefix("%%BeginPreview:"))?;
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let mut n = head.split_whitespace().map_while(|w| w.parse::<usize>().ok());
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let (w, h, depth) = (n.next()?, n.next()?, n.next()?);
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if !(1..=MAX_EPSI).contains(&w) || !(1..=MAX_EPSI).contains(&h) || ![1, 2, 4, 8].contains(&depth) {
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return None;
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}
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let row = (w * depth).div_ceil(8);
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let need = row * h;
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let mut bytes = Vec::with_capacity(need.min(ps.len() / 2));
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let mut high = None;
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'lines: for l in lines {
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if l.starts_with("%%EndPreview") {
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break;
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}
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for digit in l.strip_prefix('%')?.chars().filter_map(|c| c.to_digit(16)) {
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match high.take() {
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None => high = Some(digit),
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Some(hi) => bytes.push((hi << 4 | digit) as u8),
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}
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if bytes.len() == need {
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break 'lines;
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}
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}
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}
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// A preview with its samples missing is none, not a blank image of the size it claims.
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if bytes.len() < need {
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return None;
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}
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let max = (1u32 << depth) - 1;
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let mut gray = Vec::with_capacity(w * h);
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for y in 0..h {
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for x in 0..w {
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let bit = y * row * 8 + x * depth;
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let byte = u32::from(bytes.get(bit / 8).copied().unwrap_or(0));
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let v = (byte >> (8 - depth - bit % 8)) & max;
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gray.push((255 - v * 255 / max) as u8);
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}
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}
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Some(Bitmap { width: w as u32, height: h as u32, gray })
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}
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