1 files changed, 29 insertions, 6 deletions
diff --git a/src/mbgl/util/premultiply.cpp b/src/mbgl/util/premultiply.cpp
index 3ee5a1e129..8a62012251 100644
--- a/src/mbgl/util/premultiply.cpp
+++ b/src/mbgl/util/premultiply.cpp
@@ -6,14 +6,14 @@ namespace mbgl {
 namespace util {
 
 PremultipliedImage premultiply(UnassociatedImage&& src) {
-   PremultipliedImage dst;
+    PremultipliedImage dst;
 
-   dst.width = src.width;
-   dst.height = src.height;
-   dst.data = std::move(src.data);
+    dst.width = src.width;
+    dst.height = src.height;
+    dst.data = std::move(src.data);
 
-   uint8_t* data = dst.data.get();
-   for (size_t i = 0; i < dst.size(); i += 4) {
+    uint8_t* data = dst.data.get();
+    for (size_t i = 0; i < dst.size(); i += 4) {
         uint8_t& r = data[i + 0];
         uint8_t& g = data[i + 1];
         uint8_t& b = data[i + 2];
@@ -26,5 +26,28 @@ PremultipliedImage premultiply(UnassociatedImage&& src) {
     return std::move(dst);
 }
 
+UnassociatedImage unpremultiply(PremultipliedImage&& src) {
+    UnassociatedImage dst;
+
+    dst.width = src.width;
+    dst.height = src.height;
+    dst.data = std::move(src.data);
+
+    uint8_t* data = dst.data.get();
+    for (size_t i = 0; i < dst.size(); i += 4) {
+        uint8_t& r = data[i + 0];
+        uint8_t& g = data[i + 1];
+        uint8_t& b = data[i + 2];
+        uint8_t& a = data[i + 3];
+        if (a) {
+            r = (255 * r + (a / 2)) / a;
+            g = (255 * g + (a / 2)) / a;
+            b = (255 * b + (a / 2)) / a;
+        }
+    }
+
+    return std::move(dst);
+}
+
 }
 }