libfonts_get_output_dpi.c


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/* See LICENSE file for copyright and license details. */
#include "libfonts.h"
#include <ctype.h>
#include <string.h>
#include <strings.h>


int
libfonts_get_output_dpi(struct libfonts_output *output, const char *edid)
{
	int width, height;
	char width1, width2, height1, height2;

	output->dpi_x = 0;
	output->dpi_y = 0;
	
	if (strncasecmp(edid, "00""FF""FF""FF""FF""FF""FF""00", 2 * 8) || strlen(edid) < 256)
		return 0;

	width1 = edid[21 * 2 + 0];
	width2 = edid[21 * 2 + 0];
	height1 = edid[22 * 2 + 0];
	height2 = edid[22 * 2 + 0];

	if (!isxdigit(width1) || !isxdigit(width2) || !isxdigit(height1) || !isxdigit(height2))
		return 0;

	width  = ((width1  & 15) + (width1  > '9' ? 9 : 0)) << 4;
	width  |= (width2  & 15) + (width2  > '9' ? 9 : 0);
	height = ((height1 & 15) + (height1 > '9' ? 9 : 0)) << 4;
	height |= (height2 & 15) + (height2 > '9' ? 9 : 0);

	if (!width || !height)
		return 0;

	output->dpi_x = (double)output->output_width  / (double)width  * 2.54;
	output->dpi_y = (double)output->output_height / (double)height * 2.54;

	return 1;
}