gstate: Track whether the combination of ctm * device is identity.

In the fairly common condition that both the ctm and the device
transforms are identity, the function overhead of calling the matrix
multiplication on the point overwhelmingly dominates.

1 files changed, 16 insertions, 2 deletions

diff --git a/src/cairo-gstate.c b/src/cairo-gstate.c
index 119bc0792..f7a32aec3 100644
--- a/src/cairo-gstate.c
+++ b/src/cairo-gstate.c
@@ -105,6 +105,7 @@ _cairo_gstate_init (cairo_gstate_t  *gstate,
     gstate->parent_target = NULL;
     gstate->original_target = cairo_surface_reference (target);
 
+    gstate->is_identity = _cairo_matrix_is_identity (&gstate->target->device_transform);
     cairo_matrix_init_identity (&gstate->ctm);
     gstate->ctm_inverse = gstate->ctm;
     gstate->source_ctm_inverse = gstate->ctm;
@@ -170,6 +171,7 @@ _cairo_gstate_init_copy (cairo_gstate_t *gstate, cairo_gstate_t *other)
     gstate->parent_target = NULL;
     gstate->original_target = cairo_surface_reference (other->original_target);
 
+    gstate->is_identity = other->is_identity;
     gstate->ctm = other->ctm;
     gstate->ctm_inverse = other->ctm_inverse;
     gstate->source_ctm_inverse = other->source_ctm_inverse;
@@ -306,6 +308,7 @@ _cairo_gstate_redirect_target (cairo_gstate_t *gstate, cairo_surface_t *child)
     /* Now set up our new target; we overwrite gstate->target directly,
      * since its ref is now owned by gstate->parent_target */
     gstate->target = cairo_surface_reference (child);
+    gstate->is_identity &= _cairo_matrix_is_identity (&child->device_transform);
 
     /* The clip is in surface backend coordinates for the previous target;
      * translate it into the child's backend coordinates. */
@@ -608,6 +611,7 @@ _cairo_gstate_translate (cairo_gstate_t *gstate, double tx, double ty)
 
     cairo_matrix_init_translate (&tmp, tx, ty);
     cairo_matrix_multiply (&gstate->ctm, &tmp, &gstate->ctm);
+    gstate->is_identity = FALSE;
 
     /* paranoid check against gradual numerical instability */
     if (! _cairo_matrix_is_invertible (&gstate->ctm))
@@ -633,6 +637,7 @@ _cairo_gstate_scale (cairo_gstate_t *gstate, double sx, double sy)
 
     cairo_matrix_init_scale (&tmp, sx, sy);
     cairo_matrix_multiply (&gstate->ctm, &tmp, &gstate->ctm);
+    gstate->is_identity = FALSE;
 
     /* paranoid check against gradual numerical instability */
     if (! _cairo_matrix_is_invertible (&gstate->ctm))
@@ -659,6 +664,7 @@ _cairo_gstate_rotate (cairo_gstate_t *gstate, double angle)
 
     cairo_matrix_init_rotate (&tmp, angle);
     cairo_matrix_multiply (&gstate->ctm, &tmp, &gstate->ctm);
+    gstate->is_identity = FALSE;
 
     /* paranoid check against gradual numerical instability */
     if (! _cairo_matrix_is_invertible (&gstate->ctm))
@@ -692,6 +698,7 @@ _cairo_gstate_transform (cairo_gstate_t	      *gstate,
 
     cairo_matrix_multiply (&gstate->ctm, matrix, &gstate->ctm);
     cairo_matrix_multiply (&gstate->ctm_inverse, &gstate->ctm_inverse, &tmp);
+    gstate->is_identity = FALSE;
 
     /* paranoid check against gradual numerical instability */
     if (! _cairo_matrix_is_invertible (&gstate->ctm))
@@ -712,12 +719,18 @@ _cairo_gstate_set_matrix (cairo_gstate_t       *gstate,
     if (! _cairo_matrix_is_invertible (matrix))
 	return _cairo_error (CAIRO_STATUS_INVALID_MATRIX);
 
+    if (_cairo_matrix_is_identity (matrix)) {
+	_cairo_gstate_identity_matrix (gstate);
+	return CAIRO_STATUS_SUCCESS;
+    }
+
     _cairo_gstate_unset_scaled_font (gstate);
 
     gstate->ctm = *matrix;
     gstate->ctm_inverse = *matrix;
     status = cairo_matrix_invert (&gstate->ctm_inverse);
     assert (status == CAIRO_STATUS_SUCCESS);
+    gstate->is_identity = FALSE;
 
     return CAIRO_STATUS_SUCCESS;
 }
@@ -732,6 +745,7 @@ _cairo_gstate_identity_matrix (cairo_gstate_t *gstate)
 
     cairo_matrix_init_identity (&gstate->ctm);
     cairo_matrix_init_identity (&gstate->ctm_inverse);
+    gstate->is_identity = _cairo_matrix_is_identity (&gstate->target->device_transform);
 }
 
 void
@@ -761,14 +775,14 @@ _cairo_gstate_device_to_user_distance (cairo_gstate_t *gstate,
 }
 
 void
-_cairo_gstate_user_to_backend (cairo_gstate_t *gstate, double *x, double *y)
+_do_cairo_gstate_user_to_backend (cairo_gstate_t *gstate, double *x, double *y)
 {
     cairo_matrix_transform_point (&gstate->ctm, x, y);
     cairo_matrix_transform_point (&gstate->target->device_transform, x, y);
 }
 
 void
-_cairo_gstate_backend_to_user (cairo_gstate_t *gstate, double *x, double *y)
+_do_cairo_gstate_backend_to_user (cairo_gstate_t *gstate, double *x, double *y)
 {
     cairo_matrix_transform_point (&gstate->target->device_transform_inverse, x, y);
     cairo_matrix_transform_point (&gstate->ctm_inverse, x, y);