download_and_compile.sh: only install dependencies for selected components

For instance, don't attempt to install TerraGear dependencies unless
TERRAGEAR is in WHATTOBUILD. This should significantly reduce the number
of packages downloaded by the first use of download_and_compile.sh that
doesn't have -pn in the options.

We may get reports of missing dependencies for some components as a side
effect of this change; we'll just have to add the missing dependencies
wherever they are required (this can happen if, for instance, some
particular dependency was so far listed in the comments only as a
TERRAGEAR dependency, but was actually required by *another component*
such as FGFS). Incorrect dependency information needs to be fixed,
that's all there is to it.

download_and_compile.sh

@@ -603,18 +603,34 @@ if [[ "$DOWNLOAD_PACKAGES" = "y" ]]; then
   # Minimum
   PKG=(build-essential cmake git)
   _mandatory_pkg_alternative libcurl4-openssl-dev libcurl4-gnutls-dev
-  # cmake
+
+  # CMake
+  if _elementIn "CMAKE" "${WHATTOBUILD[@]}"; then
     PKG+=(libarchive-dev libbz2-dev libexpat1-dev libjsoncpp-dev liblzma-dev
           libncurses5-dev procps zlib1g-dev)
-  # TG
+  fi
+
+  # TerraGear
+  if _elementIn "TERRAGEAR" "${WHATTOBUILD[@]}"; then
     PKG+=(libcgal-dev libgdal-dev libtiff5-dev)
-  # TGGUI/OpenRTI
+  fi
+
+  # TerraGear GUI and OpenRTI
+  if _elementIn "TERRAGEARGUI" "${WHATTOBUILD[@]}" || \
+     _elementIn "OPENRTI" "${WHATTOBUILD[@]}"; then
     PKG+=(libqt4-dev)
-  # SG/FG
+  fi
+
+  # SimGear and FlightGear
+  if _elementIn "SIMGEAR" "${WHATTOBUILD[@]}" || \
+     _elementIn "FGFS" "${WHATTOBUILD[@]}"; then
     PKG+=(zlib1g-dev freeglut3-dev libglew-dev libboost-dev)
     _mandatory_pkg_alternative libopenscenegraph-3.4-dev libopenscenegraph-dev \
                                'libopenscenegraph-[0-9]+\.[0-9]+-dev'
-  # FG
+  fi
+
+  # FlightGear
+  if _elementIn "FGFS" "${WHATTOBUILD[@]}"; then
     PKG+=(libopenal-dev libudev-dev libdbus-1-dev libplib-dev)
     _mandatory_pkg_alternative libpng-dev libpng12-dev libpng16-dev
     # CppUnit is shipped with the FG sources, but if installed via the distro
@@ -641,12 +657,23 @@ if [[ "$DOWNLOAD_PACKAGES" = "y" ]]; then
     PKG+=(fluid libbz2-dev libfltk1.3-dev libxi-dev libxmu-dev)
     # FGAdmin
     PKG+=(libxinerama-dev libjpeg-dev libxft-dev)
-  # ATC-Pie
+  fi
+
+  # ATC-pie
+  if _elementIn "ATCPIE" "${WHATTOBUILD[@]}"; then
     PKG+=(python3-pyqt5 python3-pyqt5.qtmultimedia libqt5multimedia5-plugins)
-  # FGo
+  fi
+
+  # FGo!
+  if _elementIn "FGO" "${WHATTOBUILD[@]}"; then
     PKG+=(python-tk)
-  # FGx (FGx is not compatible with Qt5, however we have installed Qt5 by default)
+  fi
-  #PKG+=(libqt5xmlpatterns5-dev libqt5webkit5-dev)
+
+  # if _elementIn "FGX" "${WHATTOBUILD[@]}"; then
+  #   FGx (FGx is not compatible with Qt5, however we have installed Qt5 by
+  #   default)
+  #   PKG+=(libqt5xmlpatterns5-dev libqt5webkit5-dev)
+  # fi
 
   _aptInstall "${PKG[@]}"
 else