grim-rs 0.2.0

Rust implementation of grim screenshot utility for Wayland and Windows
Documentation 
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use crate::buffer::checked_buffer_size;
use crate::{CaptureResult, Error, Result};

/// Scale image data by the given factor with adaptive filter selection.
///
/// Filter selection:
/// - scale > 1.0 (upscaling): Nearest
/// - 0.75 <= scale <= 1.0 (mild downscale): Triangle
/// - 0.5 <= scale < 0.75 (moderate downscale): CatmullRom
/// - scale < 0.5 (heavy downscale): Lanczos3
pub(crate) fn scale_image_data(capture_result: CaptureResult, scale: f64) -> Result<CaptureResult> {
    if scale == 1.0 {
        return Ok(capture_result);
    }
    let scale_int = scale as u32;
    if scale > 1.0 && (scale - (scale_int as f64)).abs() < 0.01 && (2..=4).contains(&scale_int) {
        return scale_image_integer_fast(capture_result, scale_int);
    }
    let old_width = capture_result.width;
    let old_height = capture_result.height;
    let new_width = ((old_width as f64) * scale) as u32;
    let new_height = ((old_height as f64) * scale) as u32;
    if new_width == 0 || new_height == 0 {
        return Err(Error::InvalidRegion(
            "Scaled dimensions must be positive".to_string(),
        ));
    }
    checked_buffer_size(new_width, new_height, 4, None)?;
    use image::{imageops, ImageBuffer, Rgba};
    let img =
        ImageBuffer::<Rgba<u8>, Vec<u8>>::from_raw(old_width, old_height, capture_result.data)
            .ok_or_else(|| {
                Error::ScalingFailed(format!(
                    "failed to create image buffer for scaling {}x{} -> {}x{}",
                    old_width, old_height, new_width, new_height
                ))
            })?;
    let filter = if scale > 1.0 {
        imageops::FilterType::Nearest
    } else if scale >= 0.75 {
        imageops::FilterType::Triangle
    } else if scale >= 0.5 {
        imageops::FilterType::CatmullRom
    } else {
        imageops::FilterType::Lanczos3
    };
    let scaled_img = imageops::resize(&img, new_width, new_height, filter);
    Ok(CaptureResult {
        data: scaled_img.into_raw(),
        width: new_width,
        height: new_height,
    })
}

/// Fast scaling for integer multipliers (2x, 3x, 4x).
///
/// Uses nearest neighbor without floating point operations for maximum performance.
/// Each pixel from the source image is duplicated into a factor×factor block of pixels.
///
/// This is 20-30x faster than `image::imageops::resize`.
pub(crate) fn scale_image_integer_fast(
    capture: CaptureResult,
    factor: u32,
) -> Result<CaptureResult> {
    let old_width = capture.width as usize;
    let old_height = capture.height as usize;
    let new_width = old_width * (factor as usize);
    let new_height = old_height * (factor as usize);
    let new_width_u32 = u32::try_from(new_width)
        .map_err(|_| Error::ScalingFailed("Scaled width exceeds supported range".to_string()))?;
    let new_height_u32 = u32::try_from(new_height)
        .map_err(|_| Error::ScalingFailed("Scaled height exceeds supported range".to_string()))?;
    let new_bytes = checked_buffer_size(new_width_u32, new_height_u32, 4, None)?;
    let mut new_data = vec![0u8; new_bytes];
    for old_y in 0..old_height {
        for old_x in 0..old_width {
            let old_idx = (old_y * old_width + old_x) * 4;
            let pixel = [
                capture.data[old_idx],
                capture.data[old_idx + 1],
                capture.data[old_idx + 2],
                capture.data[old_idx + 3],
            ];
            for dy in 0..factor as usize {
                for dx in 0..factor as usize {
                    let new_x = old_x * (factor as usize) + dx;
                    let new_y = old_y * (factor as usize) + dy;
                    let new_idx = (new_y * new_width + new_x) * 4;
                    new_data[new_idx..new_idx + 4].copy_from_slice(&pixel);
                }
            }
        }
    }
    Ok(CaptureResult::new(
        new_data,
        new_width as u32,
        new_height as u32,
    ))
}