[gtk/wip/baedert/gl-rework: 1/3] GskTransform: Compute sin/deg of 90deg rotations manually

[Timm Bäder <baedert src gnome org>]

commit 6803be0aaeb0e8f12baa03c75ec92b0c8ab140ea
Author: Timm Bäder <mail baedert org>
Date:   Thu Dec 19 12:30:08 2019 +0100

    GskTransform: Compute sin/deg of 90deg rotations manually
    
    Otherwise we might end up with inaccuracies, e.g. when
    gsk_transform_transform_bounds()'ing bounds.

 gsk/gsktransform.c | 32 ++++++++++++++++++++++++++++----
 1 file changed, 28 insertions(+), 4 deletions(-)
---
diff --git a/gsk/gsktransform.c b/gsk/gsktransform.c
index 330342b5e7..b8e0d681ff 100644
--- a/gsk/gsktransform.c
+++ b/gsk/gsktransform.c
@@ -690,11 +690,35 @@ gsk_rotate_transform_to_matrix (GskTransform      *transform,
                                 graphene_matrix_t *out_matrix)
 {
   GskRotateTransform *self = (GskRotateTransform *) transform;
-  float rad, c, s;
+  float c, s;
+
+  if (self->angle == 90.0)
+    {
+      c = 0.0;
+      s = 1.0;
+    }
+  else if (self->angle == 180.0)
+    {
+      c = -1.0;
+      s = 0.0;
+    }
+  else if (self->angle == 270.0)
+    {
+      c = 0.0;
+      s = -1.0;
+    }
+  else if (self->angle == 0.0)
+    {
+      c = 1.0;
+      s = 0.0;
+    }
+  else
+    {
+      const float rad = self->angle * M_PI / 180.f;
+      c = cosf (rad);
+      s = sinf (rad);
+    }
 
-  rad = self->angle * M_PI / 180.f;
-  c = cosf (rad);
-  s = sinf (rad);
   graphene_matrix_init_from_2d (out_matrix,
                                 c, s,
                                 -s, c,