/*
* Copyright (c) 2023.
*
* This software is free software;
*
* You can redistribute it or modify it under terms of the MIT, Apache License or Zlib license
*/
//! Up-sampling routines
//!
//! The main upsampling method is a bi-linear interpolation or a "triangle
//! filter " or libjpeg turbo `fancy_upsampling` which is a good compromise
//! between speed and visual quality
//!
//! # The filter
//! Each output pixel is made from `(3*A+B)/4` where A is the original
//! pixel closer to the output and B is the one further.
//!
//! ```text
//!+---+---+
//! | A | B |
//! +---+---+
//! +-+-+-+-+
//! | |P| | |
//! +-+-+-+-+
//! ```
//!
//! # Horizontal Bi-linear filter
//! ```text
//! |---+-----------+---+
//! | | | |
//! | A | |p1 | p2| | B |
//! | | | |
//! |---+-----------+---+
//!
//! ```
//! For a horizontal bi-linear it's trivial to implement,
//!
//! `A` becomes the input closest to the output.
//!
//! `B` varies depending on output.
//! - For odd positions, input is the `next` pixel after A
//! - For even positions, input is the `previous` value before A.
//!
//! We iterate in a classic 1-D sliding window with a window of 3.
//! For our sliding window approach, `A` is the 1st and `B` is either the 0th term or 2nd term
//! depending on position we are writing.(see scalar code).
//!
//! For vector code see module sse for explanation.
//!
//! # Vertical bi-linear.
//! Vertical up-sampling is a bit trickier.
//!
//! ```text
//! +----+----+
//! | A1 | A2 |
//! +----+----+
//! +----+----+
//! | p1 | p2 |
//! +----+-+--+
//! +----+-+--+
//! | p3 | p4 |
//! +----+-+--+
//! +----+----+
//! | B1 | B2 |
//! +----+----+
//! ```
//!
//! For `p1`
//! - `A1` is given a weight of `3` and `B1` is given a weight of 1.
//!
//! For `p3`
//! - `B1` is given a weight of `3` and `A1` is given a weight of 1
//!
//! # Horizontal vertical downsampling/chroma quartering.
//!
//! Carry out a vertical filter in the first pass, then a horizontal filter in the second pass.
use crate::components::UpSampler;
mod scalar;
// choose best possible implementation for this platform
pub fn choose_horizontal_samp_function(_use_unsafe: bool) -> UpSampler {
return scalar::upsample_horizontal;
}
pub fn choose_hv_samp_function(_use_unsafe: bool) -> UpSampler {
return scalar::upsample_hv;
}
pub fn choose_v_samp_function(_use_unsafe: bool) -> UpSampler {
return scalar::upsample_vertical;
}
/// Upsample nothing
pub fn upsample_no_op(
_input: &[i16], _in_ref: &[i16], _in_near: &[i16], _scratch_space: &mut [i16],
_output: &mut [i16]
) {
}