stet_render/
png_sink.rs

1// stet - A PostScript Interpreter
2// Copyright (c) 2026 Scott Bowman
3// SPDX-License-Identifier: Apache-2.0 OR MIT
4
5//! PNG output sink — streams rendered RGBA rows to a PNG file.
6
7use std::io::Write;
8
9use stet_graphics::device::{PageSink, PageSinkFactory};
10
11/// Factory that creates `PngSink` instances for each page.
12pub struct PngSinkFactory;
13
14impl PageSinkFactory for PngSinkFactory {
15    fn create_sink(&self, output_path: &str) -> Result<Box<dyn PageSink>, String> {
16        Ok(Box::new(PngSink {
17            output_path: output_path.to_string(),
18            writer: None,
19        }))
20    }
21}
22
23/// Streams RGBA rows to a PNG file.
24struct PngSink {
25    output_path: String,
26    writer: Option<PngStreamWriter>,
27}
28
29/// Wraps the png crate's streaming writer.
30struct PngStreamWriter {
31    stream: png::StreamWriter<'static, std::io::BufWriter<std::fs::File>>,
32    // Keep the Writer alive — StreamWriter borrows from it.
33    // We use `Box::leak` to give the Writer a 'static lifetime,
34    // then reclaim it in `finish()`.
35    _writer_box: *mut png::Writer<std::io::BufWriter<std::fs::File>>,
36}
37
38// Safety: PngStreamWriter is only used from a single thread at a time.
39unsafe impl Send for PngStreamWriter {}
40
41impl PngStreamWriter {
42    fn new(output_path: &str, width: u32, height: u32, band_h: u32) -> Result<Self, String> {
43        let file = std::fs::File::create(output_path)
44            .map_err(|e| format!("Failed to create PNG '{}': {}", output_path, e))?;
45        let buf_writer = std::io::BufWriter::with_capacity(256 * 1024, file);
46
47        let mut encoder = png::Encoder::new(buf_writer, width, height);
48        encoder.set_color(png::ColorType::Rgba);
49        encoder.set_depth(png::BitDepth::Eight);
50        encoder.set_compression(png::Compression::Default);
51        encoder.set_adaptive_filter(png::AdaptiveFilterType::Adaptive);
52
53        let writer = encoder
54            .write_header()
55            .map_err(|e| format!("Failed to write PNG header '{}': {}", output_path, e))?;
56
57        // Leak the Writer to get a 'static reference for StreamWriter.
58        let writer_box = Box::into_raw(Box::new(writer));
59        let stream = unsafe { &mut *writer_box }
60            .stream_writer_with_size(band_h as usize * width as usize * 4)
61            .map_err(|e| format!("Failed to create PNG stream '{}': {}", output_path, e))?;
62
63        Ok(Self {
64            stream,
65            _writer_box: writer_box,
66        })
67    }
68
69    fn write_all(&mut self, data: &[u8]) -> Result<(), String> {
70        self.stream
71            .write_all(data)
72            .map_err(|e| format!("Failed to write PNG data: {}", e))
73    }
74
75    fn finish(self) -> Result<(), String> {
76        self.stream
77            .finish()
78            .map_err(|e| format!("Failed to finish PNG: {}", e))?;
79        // Reclaim the leaked Writer box.
80        unsafe {
81            let _ = Box::from_raw(self._writer_box);
82        }
83        Ok(())
84    }
85}
86
87impl PageSink for PngSink {
88    fn begin_page(&mut self, width: u32, height: u32) -> Result<(), String> {
89        let writer = PngStreamWriter::new(&self.output_path, width, height, height)?;
90        self.writer = Some(writer);
91        Ok(())
92    }
93
94    fn write_rows(&mut self, rgba_rows: &[u8], _num_rows: u32) -> Result<(), String> {
95        let writer = self
96            .writer
97            .as_mut()
98            .ok_or("PngSink: begin_page not called")?;
99        writer.write_all(rgba_rows)
100    }
101
102    fn end_page(&mut self) -> Result<(), String> {
103        let writer = self.writer.take().ok_or("PngSink: begin_page not called")?;
104        writer.finish()
105    }
106}
stet_render/png_sink.rs

stet_render/
png_sink.rs
