[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, 4 insertions, 32 deletions

diff --git a/test/fixtures/util.cpp b/test/fixtures/util.cpp
index aa6371a4c7..ebd530eaac 100644
--- a/test/fixtures/util.cpp
+++ b/test/fixtures/util.cpp
@@ -85,45 +85,17 @@ uint64_t crc64(const std::string& str) {
     return crc64(str.data(), str.size());
 }
 
-UnassociatedImage unpremultiply(const PremultipliedImage& src) {
-    UnassociatedImage dst { src.width, src.height };
-    std::copy(src.data.get(), src.data.get() + src.size(), dst.data.get());
-
-    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);
-}
-
 void checkImage(const std::string& base,
-                const UnassociatedImage& actual,
+                const PremultipliedImage& actual,
                 double imageThreshold,
                 double pixelThreshold) {
-    // TODO: the pixels produced by Map::renderStill are probably actually premultiplied,
-    // but Map::renderStill produces an UnassociatedImage. This probably should be fixed;
-    // here we just hack around it by copying the pixels to a PremultipliedImage (and
-    // un-premultiplying them when updating expected.png, since encodePNG wants
-    // un-premultiplied pixels).
-    PremultipliedImage actualActual { actual.width, actual.height };
-    std::copy(actual.data.get(), actual.data.get() + actual.size(), actualActual.data.get());
-
     if (getenv("UPDATE")) {
-        util::write_file(base + "/expected.png", encodePNG(unpremultiply(actualActual)));
+        util::write_file(base + "/expected.png", encodePNG(actual));
         return;
     }
 
     PremultipliedImage expected = decodeImage(util::read_file(base + "/expected.png"));
-    UnassociatedImage diff { expected.width, expected.height };
+    PremultipliedImage diff { expected.width, expected.height };
 
     ASSERT_EQ(expected.width, actual.width);
     ASSERT_EQ(expected.height, actual.height);
diff --git a/test/fixtures/util.hpp b/test/fixtures/util.hpp
index b369979e9c..16edfbace3 100644
--- a/test/fixtures/util.hpp
+++ b/test/fixtures/util.hpp
@@ -25,7 +25,7 @@ uint64_t crc64(const char*, size_t);
 uint64_t crc64(const std::string&);
 
 void checkImage(const std::string& base,
-                const UnassociatedImage& actual,
+                const PremultipliedImage& actual,
                 double imageThreshold = 0,
                 double pixelThreshold = 0);