neatvnc/src/pixels.c

/*
 * Copyright (c) 2019 Andri Yngvason
 *
 * Permission to use, copy, modify, and/or distribute this software for any
 * purpose with or without fee is hereby granted, provided that the above
 * copyright notice and this permission notice appear in all copies.
 *
 * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES WITH
 * REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY
 * AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY SPECIAL, DIRECT,
 * INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM
 * LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE
 * OR OTHER TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR
 * PERFORMANCE OF THIS SOFTWARE.
 */

#include "rfb-proto.h"
#include <stdlib.h>
#include <assert.h>

#define POPCOUNT(x) __builtin_popcount(x)   

void pixel32_to_cpixel(uint8_t *restrict dst,
		       const struct rfb_pixel_format* dst_fmt,
		       const uint32_t *restrict src,
		       const struct rfb_pixel_format* src_fmt,
		       size_t bytes_per_cpixel, size_t len)
{
	assert(src_fmt->true_colour_flag);
	assert(src_fmt->bits_per_pixel == 32);
	assert(src_fmt->depth <= 32);
	assert(dst_fmt->true_colour_flag);
	assert(dst_fmt->bits_per_pixel <= 32);
	assert(dst_fmt->depth <= 24);
	assert(bytes_per_cpixel <= 3 && bytes_per_cpixel >= 1);

	uint32_t src_red_shift = src_fmt->red_shift;
	uint32_t src_green_shift = src_fmt->green_shift;
	uint32_t src_blue_shift = src_fmt->blue_shift;

	uint32_t dst_red_shift = dst_fmt->red_shift;
	uint32_t dst_green_shift = dst_fmt->green_shift;
	uint32_t dst_blue_shift = dst_fmt->blue_shift;

	uint32_t src_red_max = src_fmt->red_max;
	uint32_t src_green_max = src_fmt->green_max;
	uint32_t src_blue_max = src_fmt->blue_max;

	uint32_t dst_red_max = dst_fmt->red_max;
	uint32_t dst_green_max = dst_fmt->green_max;
	uint32_t dst_blue_max = dst_fmt->blue_max;

	uint32_t src_red_bits = POPCOUNT(src_fmt->red_max);
	uint32_t src_green_bits = POPCOUNT(src_fmt->green_max);
	uint32_t src_blue_bits = POPCOUNT(src_fmt->blue_max);

	uint32_t dst_red_bits = POPCOUNT(dst_fmt->red_max);
	uint32_t dst_green_bits = POPCOUNT(dst_fmt->green_max);
	uint32_t dst_blue_bits = POPCOUNT(dst_fmt->blue_max);

	uint32_t dst_endian_correction;

#define CONVERT_PIXELS(cpx, px) \
	{ \
		uint32_t r, g, b; \
		r = ((px >> src_red_shift) & src_red_max) << dst_red_bits \
			>> src_red_bits << dst_red_shift; \
		g = ((px >> src_green_shift) & src_green_max) << dst_green_bits \
			>> src_green_bits << dst_green_shift; \
		b = ((px >> src_blue_shift) & src_blue_max) << dst_blue_bits \
			>> src_blue_bits << dst_blue_shift; \
		cpx = r | g | b; \
	}

	switch (bytes_per_cpixel) {
	case 3:
		if (dst_fmt->bits_per_pixel == 32 && dst_fmt->depth <= 24) {
			uint32_t min_dst_shift = dst_red_shift;
			if (min_dst_shift > dst_green_shift)
				min_dst_shift = dst_green_shift;
			if (min_dst_shift > dst_blue_shift)
				min_dst_shift = dst_blue_shift;

			dst_red_shift -= min_dst_shift;
			dst_green_shift -= min_dst_shift;
			dst_blue_shift -= min_dst_shift;
		}

		dst_endian_correction = dst_fmt->big_endian_flag ? 16 : 0;

		while (len--) {
			uint32_t cpx, px = *src++;

			CONVERT_PIXELS(cpx, px)

			*dst++ = (cpx >> (16 ^ dst_endian_correction)) & 0xff;
			*dst++ = (cpx >> 8) & 0xff;
			*dst++ = (cpx >> (0 ^ dst_endian_correction)) & 0xff;
		}
		break;
	case 2:
		dst_endian_correction = dst_fmt->big_endian_flag ? 8 : 0;

		while (len--) {
			uint32_t cpx, px = *src++;

			CONVERT_PIXELS(cpx, px)

			*dst++ = (cpx >> (8 ^ dst_endian_correction)) & 0xff;
			*dst++ = (cpx >> (0 ^ dst_endian_correction)) & 0xff;
		}
		break;
	case 1:
		while (len--) {
			uint32_t cpx, px = *src++;

			CONVERT_PIXELS(cpx, px)

			*dst++ = cpx & 0xff;
		}
		break;
	default:
		abort();
	}

#undef CONVERT_PIXELS
}