[core] Fix image type of Map::renderStill

It's a premultiplied image. This implies that we were misusing encodePNG
in most cases, as we were passing premultiplied pixels which were then
interpreted as unmultiplied. I changed encodePNG to accept premultipled
pixels, and unpremultiply in the implementations.

1 files changed, 1 insertions, 0 deletions

diff --git a/src/mbgl/util/premultiply.hpp b/src/mbgl/util/premultiply.hpp
index 9d9dcc6468..8d87c157c8 100644
--- a/src/mbgl/util/premultiply.hpp
+++ b/src/mbgl/util/premultiply.hpp
@@ -7,6 +7,7 @@ namespace mbgl {
 namespace util {
 
 PremultipliedImage premultiply(UnassociatedImage&&);
+UnassociatedImage unpremultiply(PremultipliedImage&&);
 
 }
 }