opencv: don't download during configure

OpenCV downloads data files during the CMake configure phase, which
is bad because fetching should only happen in do_fetch (and if proxies
are needed, won't be set in do_configure).

The recipe attempts to solve this already by having the repositories in
SRC_URI and moving the files to the correct place before do_configure().
However they are written to ${B} which is then wiped in do_configure so
they're not used.

The OpenCV download logic has a download cache with specially formatted
filenames, so take the downloaded files and populate the cache.

Signed-off-by: Ross Burton <ross.burton@intel.com>
Signed-off-by: Khem Raj <raj.khem@gmail.com>

meta-oe/recipes-support/opencv/opencv_4.1.0.bb

@@ -51,10 +51,28 @@ PV = "4.1.0"
 
 S = "${WORKDIR}/git"
 
+# OpenCV wants to download more files during configure.  We download these in
+# do_fetch and construct a source cache in the format it expects
+OPENCV_DLDIR = "${WORKDIR}/downloads"
+
 do_unpack_extra() {
     tar xzf ${WORKDIR}/ipp/ippicv/${IPP_FILENAME} -C ${WORKDIR}
-    cp ${WORKDIR}/vgg/*.i ${WORKDIR}/contrib/modules/xfeatures2d/src
-    cp ${WORKDIR}/boostdesc/*.i ${WORKDIR}/contrib/modules/xfeatures2d/src
+
+    md5() {
+        # Return the MD5 of $1
+        echo $(md5sum $1 | cut -d' ' -f1)
+    }
+    cache() {
+        TAG=$1
+        shift
+        mkdir --parents ${OPENCV_DLDIR}/$TAG
+        for F in $*; do
+            DEST=${OPENCV_DLDIR}/$TAG/$(md5 $F)-$(basename $F)
+            test -e $DEST || ln -s $F $DEST
+        done
+    }
+    cache xfeatures2d/boostdesc ${WORKDIR}/boostdesc/*.i
+    cache xfeatures2d/vgg ${WORKDIR}/vgg/*.i
 }
 addtask unpack_extra after do_unpack before do_patch
 
@@ -65,6 +83,7 @@ EXTRA_OECMAKE = "-DOPENCV_EXTRA_MODULES_PATH=${WORKDIR}/contrib/modules \
     -DOPENCV_ICV_HASH=${IPP_MD5} \
     -DIPPROOT=${WORKDIR}/ippicv_lnx \
     -DOPENCV_GENERATE_PKGCONFIG=ON \
+    -DOPENCV_DOWNLOAD_PATH=${OPENCV_DLDIR} \
     ${@bb.utils.contains("TARGET_CC_ARCH", "-msse3", "-DENABLE_SSE=1 -DENABLE_SSE2=1 -DENABLE_SSE3=1 -DENABLE_SSSE3=1", "", d)} \
     ${@bb.utils.contains("TARGET_CC_ARCH", "-msse4.1", "-DENABLE_SSE=1 -DENABLE_SSE2=1 -DENABLE_SSE3=1 -DENABLE_SSSE3=1 -DENABLE_SSE41=1", "", d)} \
     ${@bb.utils.contains("TARGET_CC_ARCH", "-msse4.2", "-DENABLE_SSE=1 -DENABLE_SSE2=1 -DENABLE_SSE3=1 -DENABLE_SSSE3=1 -DENABLE_SSE41=1 -DENABLE_SSE42=1", "", d)} \