From a8aec7875aaf6c8d8d4ed37ce74705988b73e9c1 Mon Sep 17 00:00:00 2001
From: Robin Watts <robin.watts@artifex.com>
Date: Mon, 30 Sep 2013 16:45:15 +0100
Subject: Bug 694526: Spot non-invertable matrices and bale before stroking

The bug fix added in the previous commit fails to work in this
case (hang-9527.pdf) because the matrix is not invertible and
hence the clipping rectangle ends up infinite. Spot this case
here and return early.
---
 include/mupdf/fitz/math.h | 14 ++++++++++++++
 source/fitz/draw-path.c   |  3 ++-
 source/fitz/geometry.c    | 19 +++++++++++++++++++
 3 files changed, 35 insertions(+), 1 deletion(-)

diff --git a/include/mupdf/fitz/math.h b/include/mupdf/fitz/math.h
index 1d542964..387f73a4 100644
--- a/include/mupdf/fitz/math.h
+++ b/include/mupdf/fitz/math.h
@@ -399,6 +399,20 @@ fz_matrix *fz_pre_translate(fz_matrix *m, float tx, float ty);
 */
 fz_matrix *fz_invert_matrix(fz_matrix *inverse, const fz_matrix *matrix);
 
+/*
+	fz_try_invert_matrix: Attempt to create an inverse matrix.
+
+	inverse: Place to store inverse matrix.
+
+	matrix: Matrix to invert. A degenerate matrix, where the
+	determinant is equal to zero, can not be inverted.
+
+	Returns 1 if matrix is degenerate (singular), or 0 otherwise.
+
+	Does not throw exceptions.
+*/
+ int fz_try_invert_matrix(fz_matrix *inverse, const fz_matrix *matrix);
+
 /*
 	fz_is_rectilinear: Check if a transformation is rectilinear.
 
diff --git a/source/fitz/draw-path.c b/source/fitz/draw-path.c
index 6fa6191d..b33ea8b4 100644
--- a/source/fitz/draw-path.c
+++ b/source/fitz/draw-path.c
@@ -971,7 +971,8 @@ fz_flatten_dash_path(fz_gel *gel, fz_path *path, const fz_stroke_state *stroke,
 	for (i = 0; i < stroke->dash_len; i++)
 		phase_len += stroke->dash_list[i];
 	fz_gel_scissor(gel, &s.rect);
-	fz_invert_matrix(&inv, ctm);
+	if (fz_try_invert_matrix(&inv, ctm))
+		return;
 	fz_transform_rect(&s.rect, &inv);
 	s.rect.x0 -= linewidth;
 	s.rect.x1 += linewidth;
diff --git a/source/fitz/geometry.c b/source/fitz/geometry.c
index 81450246..c7c3d198 100644
--- a/source/fitz/geometry.c
+++ b/source/fitz/geometry.c
@@ -213,6 +213,25 @@ fz_invert_matrix(fz_matrix *dst, const fz_matrix *src)
 	return dst;
 }
 
+int
+fz_try_invert_matrix(fz_matrix *dst, const fz_matrix *src)
+{
+	/* Be careful to cope with dst == src */
+	float a = src->a;
+	float det = a * src->d - src->b * src->c;
+	if (det >= -FLT_EPSILON && det <= FLT_EPSILON)
+		return 1;
+	det = 1 / det;
+	dst->a = src->d * det;
+	dst->b = -src->b * det;
+	dst->c = -src->c * det;
+	dst->d = a * det;
+	a = -src->e * dst->a - src->f * dst->c;
+	dst->f = -src->e * dst->b - src->f * dst->d;
+	dst->e = a;
+	return 0;
+}
+
 int
 fz_is_rectilinear(const fz_matrix *m)
 {
-- 
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