Added defaults file to properly configure the build when no env vars are set (prebuild)

Author: Simon Hofmann

install/defaults.js

@@ -0,0 +1,37 @@
+const opencvBuild = require(`@nut-tree/opencv-build-${process.platform}`)
+const { resolvePath } = require('../lib/commons')
+const fs = require('fs')
+
+const libDir = resolvePath(opencvBuild.opencvLibDir);
+
+if (!fs.existsSync(libDir)) {
+  throw new Error("library dir does not exist: " + libDir);
+}
+
+const libsFoundInDir = opencvBuild.getLibs(libDir).filter(lib => lib.libPath);
+
+if (!libsFoundInDir.length) {
+  throw new Error("No OpenCV libraries found in lib dir: " + libDir);
+}
+
+const defines = libsFoundInDir.map(
+  lib => `OPENCV4NODEJS_FOUND_LIBRARY_${lib.opencvModule.toUpperCase()}`
+);
+
+const inc = [
+  resolvePath(opencvBuild.opencvInclude),
+  resolvePath(opencvBuild.opencv4Include)
+];
+
+const libs = opencvBuild.isWin()
+  ? libsFoundInDir.map(lib => resolvePath(lib.libPath))
+  : // dynamically link libs if not on windows
+    ["-L" + libDir]
+      .concat(libsFoundInDir.map(lib => "-lopencv_" + lib.opencvModule))
+      .concat("-Wl,-rpath," + libDir);
+
+module.exports = {
+    OPENCV4NODEJS_LIBRARIES: () => libs.join("\n"),
+    OPENCV4NODEJS_INCLUDES: () => inc.join("\n"),
+    OPENCV4NODEJS_DEFINES: () => defines.join("\n")
+}