exr 1.74.2

Read and write OpenEXR files without any unsafe code
Documentation 
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#[macro_use]
extern crate smallvec;
extern crate half;
extern crate rand;

use std::{convert::TryInto, fs::File, io::BufWriter};

use exr::block::{writer::ChunksWriter, UncompressedBlock};

// exr imports
extern crate exr;

/// Generate a striped image on the fly and directly write that to a file
/// without allocating the whole image at once. On my machine, this program
/// produces a 3GB file while only ever allocating 4MB memory (takes a while
/// though).
fn main() {
    use attribute::*;
    use exr::{math::*, prelude::*};

    // pre-compute a list of random values
    let random_values: Vec<f32> = (0..64).map(|_| rand::random::<f32>()).collect();

    // resulting resolution (268 megapixels for 3GB files)
    let size = (2048 * 8, 2048 * 8);

    // define meta data header that will be written
    let header = exr::meta::header::Header::new(
        "test-image".try_into().unwrap(),
        size,
        smallvec![
            attribute::ChannelDescription::new("B", SampleType::F32, true),
            attribute::ChannelDescription::new("G", SampleType::F32, true),
            attribute::ChannelDescription::new("R", SampleType::F32, true),
            attribute::ChannelDescription::new("Z", SampleType::F32, true),
        ],
    );

    // define encoding that will be written
    let mut header = header.with_encoding(
        Compression::Uncompressed,
        exr::meta::BlockDescription::Tiles(TileDescription {
            tile_size: Vec2(64, 64),
            level_mode: LevelMode::Singular,
            rounding_mode: RoundingMode::Down,
        }),
        LineOrder::Increasing,
    );

    // add some random meta data
    header.own_attributes.exposure = Some(1.0);

    let headers = smallvec![header];

    // specify output path, and buffer it for better performance
    let file = BufWriter::new(File::create("3GB.exr").unwrap());

    let start_time = ::std::time::Instant::now();

    // finally write the image
    exr::block::write(file, headers, true, |meta_data, chunk_writer| {
        let blocks = meta_data.collect_ordered_blocks(|block_index| {
            let channel_description = &meta_data.headers[block_index.layer].channels;

            // fill the image file contents with one of the precomputed random values,
            // picking a different one per channel
            UncompressedBlock::from_lines(channel_description, block_index, |line_mut| {
                // TODO iterate mut instead??

                let chan = line_mut.location.channel;

                if chan == 3 {
                    // write time as depth (could also check for _meta.channels[chan].name == "Z")
                    line_mut
                        .write_samples(|_| start_time.elapsed().as_secs_f32())
                        .expect("write to line bug");
                } else {
                    // write rgba color
                    line_mut
                        .write_samples(|sample_index| {
                            random_values[(sample_index + chan) % random_values.len()]
                        })
                        .expect("write to line bug");
                }
            })
        });

        // print progress only if it advances more than 1%
        let mut current_progress_percentage = 0;

        chunk_writer
            .on_progress(|progress| {
                let new_progress = (progress * 100.0) as usize;
                if new_progress != current_progress_percentage {
                    current_progress_percentage = new_progress;
                    println!("progress: {}%", current_progress_percentage)
                }
            })
            .compress_all_blocks_parallel(&meta_data, blocks)?;

        Ok(())
    })
    .unwrap();

    // warning: highly unscientific benchmarks ahead!
    println!("\ncreated file 3GB.exr in {:?}s", start_time.elapsed().as_secs_f32());
}