texconv/twiddler.cpp at master · e-c-k-e-r/texconv · GitHub

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#include "twiddler.h"

Twiddler::Twiddler(int w, int h) {
	m_width = w;
	m_height = h;
	m_index = new int[m_width * m_height];

	int index = 0;

	if (m_width < m_height)
		for (int y=0; y<m_height; y+=m_width)
			index += twiddle(m_index, m_width, 0, y, m_width, index);
	else
		for (int x=0; x<m_width; x+=m_height)
			index += twiddle(m_index, m_width, x, 0, m_height, index);
}

Twiddler::~Twiddler() {
	delete[] m_index;
}

int Twiddler::twiddle(int* output, int stride, int x, int y, int blocksize, int seq) const {
	int before = seq;

	switch (blocksize) {
	case 1:
		output[seq++] = y * stride + x;
		break;
	default:
		blocksize = blocksize >> 1;
		seq += twiddle(output, stride, x, y, blocksize, seq);
		seq += twiddle(output, stride, x, y + blocksize, blocksize, seq);
		seq += twiddle(output, stride, x + blocksize, y, blocksize, seq);
		seq += twiddle(output, stride, x + blocksize, y + blocksize, blocksize, seq);
		break;
	}

	return (seq - before);
}