[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.

2 files changed, 2 insertions, 2 deletions

diff --git a/platform/node/src/node_map.cpp b/platform/node/src/node_map.cpp
index 0ce7d9398b..d4c551d666 100644
--- a/platform/node/src/node_map.cpp
+++ b/platform/node/src/node_map.cpp
@@ -300,7 +300,7 @@ void NodeMap::startRender(std::unique_ptr<NodeMap::RenderOptions> options) {
     map->setBearing(options->bearing);
     map->setPitch(options->pitch);
 
-    map->renderStill([this](const std::exception_ptr eptr, mbgl::UnassociatedImage&& result) {
+    map->renderStill([this](const std::exception_ptr eptr, mbgl::PremultipliedImage&& result) {
         if (eptr) {
             error = std::move(eptr);
             uv_async_send(async);
diff --git a/platform/node/src/node_map.hpp b/platform/node/src/node_map.hpp
index 455d38e957..23cd3c9fab 100644
--- a/platform/node/src/node_map.hpp
+++ b/platform/node/src/node_map.hpp
@@ -49,7 +49,7 @@ public:
     std::unique_ptr<mbgl::Map> map;
 
     std::exception_ptr error;
-    mbgl::UnassociatedImage image;
+    mbgl::PremultipliedImage image;
     std::unique_ptr<Nan::Callback> callback;
 
     // Async for delivering the notifications of render completion.