[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.

5 files changed, 13 insertions, 7 deletions

diff --git a/platform/darwin/image.mm b/platform/darwin/image.mm
index e7187366b9..854b9157f8 100644
--- a/platform/darwin/image.mm
+++ b/platform/darwin/image.mm
@@ -10,7 +10,7 @@
 
 namespace mbgl {
 
-std::string encodePNG(const UnassociatedImage& src) {
+std::string encodePNG(const PremultipliedImage& src) {
     CGDataProviderRef provider = CGDataProviderCreateWithData(NULL, src.data.get(), src.size(), NULL);
     if (!provider) {
         return "";
@@ -23,7 +23,7 @@ std::string encodePNG(const UnassociatedImage& src) {
     }
 
     CGImageRef image = CGImageCreate(src.width, src.height, 8, 32, 4 * src.width, color_space,
-        kCGBitmapByteOrderDefault | kCGImageAlphaLast, provider, NULL, false,
+        kCGBitmapByteOrderDefault | kCGImageAlphaPremultipliedLast, provider, NULL, false,
         kCGRenderingIntentDefault);
     if (!image) {
         CGColorSpaceRelease(color_space);
diff --git a/platform/default/headless_view.cpp b/platform/default/headless_view.cpp
index d96b3ffcd1..d6fd892700 100644
--- a/platform/default/headless_view.cpp
+++ b/platform/default/headless_view.cpp
@@ -167,13 +167,13 @@ void HeadlessView::resize(const uint16_t width, const uint16_t height) {
     needsResize = true;
 }
 
-UnassociatedImage HeadlessView::readStillImage() {
+PremultipliedImage HeadlessView::readStillImage() {
     assert(isActive());
 
     const unsigned int w = dimensions[0] * pixelRatio;
     const unsigned int h = dimensions[1] * pixelRatio;
 
-    UnassociatedImage image { w, h };
+    PremultipliedImage image { w, h };
     MBGL_CHECK_ERROR(glReadPixels(0, 0, w, h, GL_RGBA, GL_UNSIGNED_BYTE, image.data.get()));
 
     const int stride = image.stride();
diff --git a/platform/default/image.cpp b/platform/default/image.cpp
index dc28c68ef9..bf8071af5c 100644
--- a/platform/default/image.cpp
+++ b/platform/default/image.cpp
@@ -1,5 +1,6 @@
 #include <mbgl/util/image.hpp>
 #include <mbgl/util/string.hpp>
+#include <mbgl/util/premultiply.hpp>
 
 #include <png.h>
 
@@ -19,7 +20,12 @@ const static bool png_version_check = []() {
 #pragma GCC diagnostic pop
 namespace mbgl {
 
-std::string encodePNG(const UnassociatedImage& src) {
+std::string encodePNG(const PremultipliedImage& pre) {
+    PremultipliedImage copy { pre.width, pre.height };
+    std::copy(pre.data.get(), pre.data.get() + pre.size(), copy.data.get());
+
+    UnassociatedImage src = util::unpremultiply(std::move(copy));
+
     png_voidp error_ptr = 0;
     png_structp png_ptr = png_create_write_struct(PNG_LIBPNG_VER_STRING, error_ptr, NULL, NULL);
     if (!png_ptr) {
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.