Change {x,y}_device_offset values to a device_transform matrix.

This is a step toward allowing device scaling in addition to device offsets.
So far, the scale values are still always 1.0 so only the translation is
actually being used. But most of the code is in place for doing scaling as
well and it just needs to be hooked up.

There are some fragile parts in this code, all of which involve using the
translation without the scale, (so grep for device_transform.x0 or
device_transform->x0). Some of these are likely bugs that will hopefully
be obvious once we start using the scale. Others are OK if only because
we 'know' that we aren't ever setting device scaling on a surface that
has a device offset (we only set device scaling on surfaces we create
internally and we don't export device scaling to the user).

All of these fragile parts in the code have been marked with comments of
the form: XXX: FRAGILE.

1 files changed, 8 insertions, 0 deletions

diff --git a/src/cairo-matrix.c b/src/cairo-matrix.c
index a3ab6aa0..ffaae605 100644
--- a/src/cairo-matrix.c
+++ b/src/cairo-matrix.c
@@ -529,6 +529,14 @@ _cairo_matrix_compute_scale_factors (const cairo_matrix_t *matrix,
 }
 
 cairo_bool_t
+_cairo_matrix_is_identity (const cairo_matrix_t *matrix)
+{
+    return (matrix->xx == 1.0 && matrix->yx == 0.0 &&
+	    matrix->xy == 0.0 && matrix->yy == 1.0 &&
+	    matrix->x0 == 0.0 && matrix->y0 == 0.0);
+}
+
+cairo_bool_t
 _cairo_matrix_is_integer_translation(const cairo_matrix_t *m,
 				     int *itx, int *ity)
 {