astcenc_compute_variance.cpp | Explore in Territory

// SPDX-License-Identifier: Apache-2.0
// ----------------------------------------------------------------------------
// Copyright 2011-2022 Arm Limited
//
// Licensed under the Apache License, Version 2.0 (the "License"); you may not
// use this file except in compliance with the License. You may obtain a copy
// of the License at:
//
//     http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
// WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
// License for the specific language governing permissions and limitations
// under the License.
// ----------------------------------------------------------------------------

#if !defined(ASTCENC_DECOMPRESS_ONLY)

/**
 * @brief Functions to calculate variance per component in a NxN footprint.
 *
 * We need N to be parametric, so the routine below uses summed area tables in order to execute in
 * O(1) time independent of how big N is.
 *
 * The addition uses a Brent-Kung-based parallel prefix adder. This uses the prefix tree to first
 * perform a binary reduction, and then distributes the results. This method means that there is no
 * serial dependency between a given element and the next one, and also significantly improves
 * numerical stability allowing us to use floats rather than doubles.
 */

#include "astcenc_internal.h"

#include <cassert>

/**
 * @brief Generate a prefix-sum array using the Brent-Kung algorithm.
 *
 * This will take an input array of the form:
 *     v0, v1, v2, ...
 * ... and modify in-place to turn it into a prefix-sum array of the form:
 *     v0, v0+v1, v0+v1+v2, ...
 *
 * @param d      The array to prefix-sum.
 * @param items  The number of items in the array.
 * @param stride The item spacing in the array; i.e. dense arrays should use 1.
 */
static void brent_kung_prefix_sum(
	vfloat4* d,
	size_t items,
	int stride
) { … }

/* See header for documentation. */
void compute_pixel_region_variance(
	astcenc_contexti& ctx,
	const pixel_region_args& arg
) { … }

/* See header for documentation. */
unsigned int init_compute_averages(
	const astcenc_image& img,
	unsigned int alpha_kernel_radius,
	const astcenc_swizzle& swz,
	avg_args& ag
) { … }

#endif
godot/thirdparty/astcenc/astcenc_compute_variance.cpp
