libfonts_get_output_dpi: inversion of transformation should be used

Signed-off-by: Mattias Andrée <maandree@kth.se>

1 files changed, 74 insertions, 3 deletions

diff --git a/libfonts_get_output_dpi.c b/libfonts_get_output_dpi.c
index 8e698e2..17ae837 100644
--- a/libfonts_get_output_dpi.c
+++ b/libfonts_get_output_dpi.c
@@ -2,9 +2,74 @@
 #include "common.h"
 
 
+static int
+invert(struct libfonts_transformation *out, const struct libfonts_transformation *in)
+{
+	double m[3][3], t;
+	int i, j;
+
+#define SWAP_ROWS(A, B)\
+	do {\
+		for (i = 0; i < 6; i++) {\
+			t = m[A][i];\
+			m[A][i] = m[B][i];\
+			m[B][i] = t;\
+		}\
+	} while (0)
+
+	for (i = 0; i < 3; i++) {
+		for (j = 0; j < 3; j++) {
+			m[i][j] = in->m[i][j];
+			m[i][j + 3] = 0;
+		}
+		m[i][i + 3] = 1;
+	}
+
+	if (eq(m[0][0], 0)) {
+		if (!eq(m[1][0], 0))
+			SWAP_ROWS(0, 1);
+		else if (!eq(m[2][0], 0))
+			SWAP_ROWS(0, 2);
+		else
+			return 0;
+	}
+	for (i = 0; i < 6; i++)
+		m[0][i] /= m[0][0];
+	for (i = 0; i < 6; i++)
+		m[1][i] -= m[1][0] * m[0][i];
+	for (i = 0; i < 6; i++)
+		m[2][i] -= m[2][0] * m[0][i];
+
+	if (eq(m[1][1], 0)) {
+		if (!eq(m[2][1], 0))
+			SWAP_ROWS(1, 2);
+		else
+			return 0;
+	}
+	for (i = 1; i < 6; i++)
+		m[1][i] /= m[1][1];
+	for (i = 1; i < 6; i++)
+		m[2][i] -= m[2][1] * m[1][i];
+	for (i = 1; i < 6; i++)
+		m[0][i] -= m[0][1] * m[1][i];
+
+	if (eq(m[2][2], 0))
+		return 0;
+	for (i = 2; i < 6; i++)
+		m[2][i] /= m[2][2];
+	for (i = 2; i < 6; i++)
+		m[1][i] -= m[1][1] * m[2][i];
+	for (i = 2; i < 6; i++)
+		m[0][i] -= m[0][1] * m[2][i];
+
+	return 1;
+}
+
+
 int
 libfonts_get_output_dpi(struct libfonts_output *output, const char *edid)
 {
+	struct libfonts_transformation invtrans;
 	int width, height;
 	char width1, width2, height1, height2;
 	double x[2], y[2];
@@ -12,7 +77,7 @@ libfonts_get_output_dpi(struct libfonts_output *output, const char *edid)
 	if (edid) {
 		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;
 
@@ -36,8 +101,14 @@ libfonts_get_output_dpi(struct libfonts_output *output, const char *edid)
 		output->dpi_y = (double)output->unrotated_output_height / (double)height * 2.54;
 	}
 
-	transform(&x[0], &y[0], 0, 0, &output->output_transformation);
-	transform(&x[1], &y[1], output->dpi_x, output->dpi_y, &output->output_transformation);
+	if (!invert(&invtrans, &output->output_transformation)) {
+		output->dpi_x = 0;
+		output->dpi_y = 0;
+		return 0;
+	}
+
+	transform(&x[0], &y[0], 0, 0, &invtrans);
+	transform(&x[1], &y[1], output->dpi_x, output->dpi_y, &invtrans);
 
 	output->dpi_x = x[1] > x[0] ? x[1] - x[0] : x[0] - x[1];
 	output->dpi_y = y[1] > y[0] ? y[1] - y[0] : y[0] - y[1];