Revert "Revert WebP support due to broken builds"

This reverts commit 6709bdcacd5a45a10b554f3f225206c9494e5e43.

There was an issue with the script that removes '-lwebp' from WebP
linker flags, since we're statically linking. This is now fixed.

3 files changed, 45 insertions, 3 deletions

diff --git a/platform/default/image.cpp b/platform/default/image.cpp
index bf8071af5c..71fb5414b3 100644
--- a/platform/default/image.cpp
+++ b/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);
         }
     }
diff --git a/platform/default/webp_reader.cpp b/platform/default/webp_reader.cpp
new file mode 100644
index 0000000000..37d23da110
--- /dev/null
+++ b/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
diff --git a/platform/linux/scripts/configure.sh b/platform/linux/scripts/configure.sh
index e824376804..8510d83bdc 100644
--- a/platform/linux/scripts/configure.sh
+++ b/platform/linux/scripts/configure.sh
@@ -15,6 +15,7 @@ VARIANT_VERSION=1.0
 RAPIDJSON_VERSION=1.0.2
 GTEST_VERSION=1.7.0
 PIXELMATCH_VERSION=0.9.0
+WEBP_VERSION=0.5.0
 
 function print_opengl_flags {
     CONFIG+="    'opengl_cflags%': $(quote_flags $(pkg-config gl x11 --cflags)),"$LN