updated build system

docker/x86_64/mingw64

@@ -269,6 +269,28 @@ RUN if [ -f "/3rd_party/libjpeg_turbo-${MY_LIBJPEG_TURBO_VERSION}.tar.gz" ]; the
       && rm -r libjpeg-turbo-${MY_LIBJPEG_TURBO_VERSION} \
     ; fi
 
+ARG LIBPNG_VERSION
+ENV MY_LIBPNG_VERSION=${LIBPNG_VERSION}
+RUN if [ -f "/3rd_party/libpng-v${MY_LIBPNG_VERSION}.tar.gz" ]; then \
+      tar xvzf /3rd_party/libpng-v${MY_LIBPNG_VERSION}.tar.gz \
+      && cd libpng-${MY_LIBPNG_VERSION} \
+      && mkdir _build \
+      && cd _build \
+      && cmake .. -DCMAKE_TOOLCHAIN_FILE=${MY_TOOLCHAIN_FILE_CMAKE} \
+        -DBUILD_SHARED_LIBS=ON \
+        -DBUILD_STATIC_LIBS=ON \
+        -DCMAKE_BUILD_TYPE=Release \
+        -DCMAKE_INSTALL_PREFIX=${MY_MINGW_DIR} \
+        -DPNG_SHARED=ON \
+        -DPNG_STATIC=ON \
+        -DPNG_TESTS=OFF \
+        -DPNG_TOOLS=OFF \
+      && make -j${MY_NUM_JOBS} \
+      && make install \
+      && cd ${MY_WORKDIR} \
+      && rm -r libpng-${MY_LIBPNG_VERSION} \
+    ; fi
+
 ARG FREETYPE2_VERSION
 ENV MY_FREETYPE2_VERSION=${FREETYPE2_VERSION}
 RUN if [ -f "/3rd_party/freetype-${MY_FREETYPE2_VERSION}.tar.gz" ]; then \