ctt 0.4.0

Compress images to GPU texture formats
Documentation 
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//! Block-compression step — runs an encoder backend across every surface in
//! an [`Image`]. Input must already be the format the encoder requires
//! (typically `R8G8B8A8_UNORM` / `R32G32B32A32_SFLOAT`).

use crate::encoders::Encoder;
#[cfg_attr(
    not(any(
        feature = "encoder-bc7enc",
        feature = "encoder-intel",
        feature = "encoder-etcpak",
        feature = "encoder-amd",
        feature = "encoder-astcenc",
    )),
    expect(unused_imports)
)]
use crate::encoders::backend::Encoder as _;
use crate::error::{Error, Result};
use crate::quality::Quality;
use crate::surface::{Image, Surface};
use crate::vk_format::FormatExt;

/// A resolved encoder step: what format to encode to, the chosen encoder
/// (and its settings), and the universal quality preset.
pub struct EncoderStep {
    pub target_format: ktx2::Format,
    pub quality: Quality,
    pub encoder: Encoder,
}

impl EncoderStep {
    /// The uncompressed format the encoder requires as input.
    pub fn required_input(&self) -> Result<ktx2::Format> {
        let raw = required_input_for(&self.encoder, self.target_format)?;
        let (required, _) = raw.normalize();
        Ok(required)
    }
}

/// Run the encoder across every surface of the image.
pub fn encode_all(image: Image, step: &EncoderStep) -> Result<Image> {
    profiling::scope!("encode_all");

    let mut new_surfaces = Vec::with_capacity(image.surfaces.len());
    for (layer_idx, layer) in image.surfaces.iter().enumerate() {
        let mut new_mips = Vec::with_capacity(layer.len());
        for (mip_idx, surface) in layer.iter().enumerate() {
            profiling::scope!("encode_mip", encoder_name(&step.encoder));
            log::debug!(
                "Compressing layer {layer_idx}, mip {mip_idx}: {}x{} to {:?} using {}",
                surface.width,
                surface.height,
                step.target_format,
                encoder_name(&step.encoder),
            );

            let output_format = step.target_format.denormalize(surface.color_space);
            let data = compress_with(&step.encoder, surface, output_format, step.quality)?;

            let bpp_block = step.target_format.bytes_per_block().unwrap_or(16) as u32;
            let (bw, _bh) = step.target_format.block_size().unwrap_or((4, 4));
            let blocks_x = surface.width.div_ceil(bw as u32);

            new_mips.push(Surface {
                data,
                width: surface.width,
                height: surface.height,
                depth: surface.depth,
                stride: blocks_x * bpp_block,
                slice_stride: surface.slice_stride,
                format: step.target_format,
                color_space: surface.color_space,
                alpha: surface.alpha,
            });
        }
        new_surfaces.push(new_mips);
    }

    Ok(Image {
        surfaces: new_surfaces,
        kind: image.kind,
    })
}

/// Auto-pick: first compiled-in backend that supports `target` wins.
fn pick_auto(target: ktx2::Format) -> Result<Encoder> {
    #[cfg(feature = "encoder-bc7enc")]
    if crate::encoders::bc7enc::Bc7encEncoder::supported_formats().contains(&target) {
        return Ok(Encoder::Bc7enc(Default::default()));
    }
    #[cfg(feature = "encoder-intel")]
    if crate::encoders::ispc::IspcEncoder::supported_formats().contains(&target) {
        return Ok(Encoder::Intel(Default::default()));
    }
    #[cfg(feature = "encoder-etcpak")]
    if crate::encoders::etcpak::EtcpakEncoder::supported_formats().contains(&target) {
        return Ok(Encoder::Etcpak(Default::default()));
    }
    #[cfg(feature = "encoder-amd")]
    if crate::encoders::compressonator::CompressonatorEncoder::supported_formats().contains(&target)
    {
        return Ok(Encoder::Amd(Default::default()));
    }
    #[cfg(feature = "encoder-astcenc")]
    if crate::encoders::astcenc::AstcencEncoder::supported_formats().contains(&target) {
        return Ok(Encoder::Astcenc(Default::default()));
    }
    let _ = target;
    Err(Error::UnsupportedFormat(format!(
        "no compiled-in encoder supports {target:?}"
    )))
}

#[cfg_attr(
    not(any(
        feature = "encoder-bc7enc",
        feature = "encoder-intel",
        feature = "encoder-etcpak",
        feature = "encoder-amd",
        feature = "encoder-astcenc",
    )),
    expect(dead_code)
)]
fn require_supports(supported: &[ktx2::Format], target: ktx2::Format, name: &str) -> Result<()> {
    if supported.contains(&target) {
        Ok(())
    } else {
        Err(Error::UnsupportedFormat(format!(
            "encoder '{name}' does not support {target:?}"
        )))
    }
}

fn required_input_for(encoder: &Encoder, target: ktx2::Format) -> Result<ktx2::Format> {
    #[cfg(feature = "encoder-astcenc")]
    use crate::encoders::astcenc::AstcencEncoder;
    #[cfg(feature = "encoder-bc7enc")]
    use crate::encoders::bc7enc::Bc7encEncoder;
    #[cfg(feature = "encoder-amd")]
    use crate::encoders::compressonator::CompressonatorEncoder;
    #[cfg(feature = "encoder-etcpak")]
    use crate::encoders::etcpak::EtcpakEncoder;
    #[cfg(feature = "encoder-intel")]
    use crate::encoders::ispc::IspcEncoder;

    match encoder {
        Encoder::Auto => {
            let resolved = pick_auto(target)?;
            required_input_for(&resolved, target)
        }
        #[cfg(feature = "encoder-bc7enc")]
        Encoder::Bc7enc(s) => {
            require_supports(Bc7encEncoder::supported_formats(), target, "bc7e")?;
            Ok(Bc7encEncoder::required_input_format(target, s))
        }
        #[cfg(feature = "encoder-intel")]
        Encoder::Intel(s) => {
            require_supports(IspcEncoder::supported_formats(), target, "intel")?;
            Ok(IspcEncoder::required_input_format(target, s))
        }
        #[cfg(feature = "encoder-etcpak")]
        Encoder::Etcpak(s) => {
            require_supports(EtcpakEncoder::supported_formats(), target, "etcpak")?;
            Ok(EtcpakEncoder::required_input_format(target, s))
        }
        #[cfg(feature = "encoder-amd")]
        Encoder::Amd(s) => {
            require_supports(CompressonatorEncoder::supported_formats(), target, "amd")?;
            Ok(CompressonatorEncoder::required_input_format(target, s))
        }
        #[cfg(feature = "encoder-astcenc")]
        Encoder::Astcenc(s) => {
            require_supports(AstcencEncoder::supported_formats(), target, "astcenc")?;
            Ok(AstcencEncoder::required_input_format(target, s))
        }
    }
}

fn compress_with(
    encoder: &Encoder,
    surface: &Surface,
    output_format: ktx2::Format,
    quality: Quality,
) -> Result<Vec<u8>> {
    let (base, _) = output_format.normalize();
    match encoder {
        Encoder::Auto => {
            let resolved = pick_auto(base)?;
            compress_with(&resolved, surface, output_format, quality)
        }
        #[cfg(feature = "encoder-bc7enc")]
        Encoder::Bc7enc(s) => {
            crate::encoders::bc7enc::Bc7encEncoder::compress(surface, output_format, quality, s)
        }
        #[cfg(feature = "encoder-intel")]
        Encoder::Intel(s) => {
            crate::encoders::ispc::IspcEncoder::compress(surface, output_format, quality, s)
        }
        #[cfg(feature = "encoder-etcpak")]
        Encoder::Etcpak(s) => {
            crate::encoders::etcpak::EtcpakEncoder::compress(surface, output_format, quality, s)
        }
        #[cfg(feature = "encoder-amd")]
        Encoder::Amd(s) => crate::encoders::compressonator::CompressonatorEncoder::compress(
            surface,
            output_format,
            quality,
            s,
        ),
        #[cfg(feature = "encoder-astcenc")]
        Encoder::Astcenc(s) => {
            crate::encoders::astcenc::AstcencEncoder::compress(surface, output_format, quality, s)
        }
    }
}

fn encoder_name(encoder: &Encoder) -> &'static str {
    match encoder {
        Encoder::Auto => "auto",
        #[cfg(feature = "encoder-bc7enc")]
        Encoder::Bc7enc(_) => crate::encoders::bc7enc::Bc7encEncoder::name(),
        #[cfg(feature = "encoder-intel")]
        Encoder::Intel(_) => crate::encoders::ispc::IspcEncoder::name(),
        #[cfg(feature = "encoder-etcpak")]
        Encoder::Etcpak(_) => crate::encoders::etcpak::EtcpakEncoder::name(),
        #[cfg(feature = "encoder-amd")]
        Encoder::Amd(_) => crate::encoders::compressonator::CompressonatorEncoder::name(),
        #[cfg(feature = "encoder-astcenc")]
        Encoder::Astcenc(_) => crate::encoders::astcenc::AstcencEncoder::name(),
    }
}