1 files changed, 40 insertions, 0 deletions
diff --git a/libfonts_get_output_dpi.c b/libfonts_get_output_dpi.c
new file mode 100644
index 0000000..259702a
--- /dev/null
+++ b/libfonts_get_output_dpi.c
@@ -0,0 +1,40 @@
+/* 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;
+}