The Metal return type from main() diverges from the SkSL source, so we
patch it in the Metal code generator. This CL improves the patching
process in multiple ways:
- A `return` statement from a fragment processor main() is rewritten to:
return *_out;
- A `return` statement from a vertex processor main() is rewritten to:
return (_out->sk_Position.y = -_out->sk_Position.y, *_out);
- We avoid emitting a duplicate `return *_out;` statement if we can
determine that main() already ends in a return statement. This is
harmless either way so it doesn't necessarily catch everything. (e.g.
it doesn't detect an if/else which returns at the end of both blocks.)
Also added a unit test which returns from the middle of a vertex shader,
since we didn't test this anywhere and we need to verify that
sk_Position.y will be negated. (This didn't work properly before.)
Change-Id: I14cf18375894fc712fa6c6466df3888ebaeba7c8
Bug: skia:10903
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/339636
Reviewed-by: Ethan Nicholas <ethannicholas@google.com>
Commit-Queue: John Stiles <johnstiles@google.com>
Auto-Submit: John Stiles <johnstiles@google.com>
