[linux] Added WebP tile support

- Android support is currently disabled due to a libwebp build issue.
- iOS and OS X support will appear after the next Mapbox iOS SDK release.

Related: #https://github.com/mapbox/mapbox-gl-native/issues/2354

gyp/platform-linux.gypi

@@ -17,6 +17,7 @@
         '../platform/default/application_root.cpp',
         '../platform/default/thread.cpp',
         '../platform/default/image.cpp',
+        '../platform/default/webp_reader.cpp',
         '../platform/default/png_reader.cpp',
         '../platform/default/jpeg_reader.cpp',
         '../platform/default/timer.cpp',

include/mbgl/util/image.hpp

@@ -21,6 +21,11 @@ public:
           height(h),
           data(std::make_unique<uint8_t[]>(size())) {}
 
+    Image(size_t w, size_t h, std::unique_ptr<uint8_t[]> data_)
+        : width(w),
+          height(h),
+          data(std::move(data_)) {}
+
     size_t stride() const { return width * 4; }
     size_t size() const { return width * height * 4; }
 

platform/default/image.cpp

@@ -70,6 +70,10 @@ std::string encodePNG(const PremultipliedImage& pre) {
     return result;
 }
 
+#if !defined(__ANDROID__) && !defined(__APPLE__)
+PremultipliedImage decodeWebP(const uint8_t*, size_t);
+#endif // !defined(__ANDROID__) && !defined(__APPLE__)
+
 PremultipliedImage decodePNG(const uint8_t*, size_t);
 PremultipliedImage decodeJPEG(const uint8_t*, size_t);
 
@@ -77,16 +81,26 @@ PremultipliedImage decodeImage(const std::string& string) {
     const uint8_t* data = reinterpret_cast<const uint8_t*>(string.data());
     const size_t size = string.size();
 
+#if !defined(__ANDROID__) && !defined(__APPLE__)
+    if (size >= 12) {
+        uint32_t riff_magic = (data[0] << 24) | (data[1] << 16) | (data[2] << 8) | data[3];
+        uint32_t webp_magic = (data[8] << 24) | (data[9] << 16) | (data[10] << 8) | data[11];
+        if (riff_magic == 0x52494646 && webp_magic == 0x57454250) {
+            return decodeWebP(data, size);
+        }
+    }
+#endif // !defined(__ANDROID__) && !defined(__APPLE__)
+
     if (size >= 4) {
-        unsigned int magic = (data[0] << 24) | (data[1] << 16) | (data[2] << 8) | data[3];
+        uint32_t magic = (data[0] << 24) | (data[1] << 16) | (data[2] << 8) | data[3];
         if (magic == 0x89504E47U) {
             return decodePNG(data, size);
         }
     }
 
     if (size >= 2) {
-        unsigned int magic = ((data[0] << 8) | data[1]) & 0xffff;
-        if (magic == 0xffd8) {
+        uint16_t magic = ((data[0] << 8) | data[1]) & 0xffff;
+        if (magic == 0xFFD8) {
             return decodeJPEG(data, size);
         }
     }

platform/default/webp_reader.cpp

@@ -0,0 +1,27 @@
+#include <mbgl/util/image.hpp>
+#include <mbgl/util/premultiply.hpp>
+#include <mbgl/platform/log.hpp>
+
+extern "C"
+{
+#include <webp/decode.h>
+}
+
+namespace mbgl {
+
+PremultipliedImage decodeWebP(const uint8_t* data, size_t size) {
+    int width = 0, height = 0;
+    if (WebPGetInfo(data, size, &width, &height) == 0) {
+        throw std::runtime_error("failed to retrieve WebP basic header information");
+    }
+
+    std::unique_ptr<uint8_t[]> webp(WebPDecodeRGBA(data, size, &width, &height));
+    if (!webp) {
+        throw std::runtime_error("failed to decode WebP data");
+    }
+
+    UnassociatedImage image { size_t(width), size_t(height), std::move(webp) };
+    return util::premultiply(std::move(image));
+}
+
+} // namespace mbgl

test/miscellaneous/image.cpp

@@ -78,6 +78,14 @@ TEST(Image, JPEGTile) {
     EXPECT_EQ(256, image.height);
 }
 
+#if !defined(__ANDROID__) && !defined(__APPLE__)
+TEST(Image, WebPTile) {
+    PremultipliedImage image = decodeImage(util::read_file("test/fixtures/image/tile.webp"));
+    EXPECT_EQ(256, image.width);
+    EXPECT_EQ(256, image.height);
+}
+#endif // !defined(__ANDROID__) && !defined(__APPLE__)
+
 TEST(Image, Premultiply) {
     UnassociatedImage rgba { 1, 1 };
     rgba.data[0] = 255;