allow additional triplet options/flags for script mode; update readme

README.md

@@ -21,7 +21,7 @@ vcpkg_add_package(fmt)
 ...
 ```
 
-### What it does & intended use
+## What it does & intended use
 * fetch *vcpkg* & build if required
 * provide *"numeric"* or semantic versioning of *vcpkg* itself
 * enable the *vcpkg*-*CMake* toolchain
@@ -30,22 +30,32 @@ vcpkg_add_package(fmt)
 
 Intention of this script is to provide rapid setup and integration for *vcpkg* to kickstart your *C++* development on **(mainly) new** projects. Secondary use-case is sharing and reliable builds of projects by persons unfamiliar with *CMake* and managing dependencies for *C++* projects.
 
-#### `vcpkg_add_package()`
-This wrapper around `vcpkg install` makes the use of *vcpkg* completely transparent and is intended for the **setup and prototyping phase** of your project, allowing to focus on your code and not getting distracted by dependency management.
+## using `vcpkg_add_package()`
+This wrapper around `vcpkg install` makes the use of *vcpkg* completely transparent and is intended for the **setup and prototyping phase** of your project, allowing to focus on your build and not getting distracted by setting up package management systems.
 
 What it does more, is **generating a `vcpkg.json`-manifest** in your build directory, *to be used at a later stage* of your project to pin dependencies!
 > **📌 CMake 3.19 or later is required for automatic manifest generation!**
 
 ## using `vcpkg.json`-manifests
 When a `vcpkg.json` manifest file is present, all packages from this manifest will be installed. Per default, `manifests` and `versions` features are enabled. **Using manifests is (at time of writing) still considered *experimental*. Using versioning and the `versions`-key may currently require a newer *vcpkg* version than tagged as latest release! Check the [official resources](https://github.com/microsoft/vcpkg) for the state of manifest use! The `edge`-version supports versioning, as per the examples.**
 
-To transition to manifests from `vcpkg_add_package()` calls, use the auto-generated manifest in your build directory.
+> **ℹ To transition to manifests from `vcpkg_add_package()` calls, use the *auto-generated manifest in your build directory*.**
 
-### manifests and container layer caching
-To make use of the manifest to setup your dependencies independently of you project, use following recipe:
+### manifests, CMake scripting mode & container layer caching
+`vcpkg.cmake` can be called in *CMake* scripting mode to bootstrap *vcpkg* and install dependencies from a manifest. Allowing you to separate dependency installation and configuration of your project. This is mainly useful in building containers and not fetching and rebuilding all dependencies on every new build.
+```shell
+cmake -DVCPKG_PARENT_DIR=<path-to-build-directory> -P <path-to>/vcpkg.cmake
+```
+* **Set your build directory** using `-DVCPKG_PARENT_DIR=<path-to-build-directory>` (directory will be created if not exists)
+* Set your *vcpkg* version as outlined below in ***vcpkg* versions** (`-DVCPKG_VERSION=<version>`)
+* `VCPKG_TARGET_TRIPLET`/`VCPKG_DEFAULT_TRIPLET` CMake variables will set `ENV{VCPKG_DEFAULT_TRIPLET}`
+* `VCPKG_HOST_TRIPLET`/`VCPKG_DEFAULT_HOST_TRIPLET` CMake variables will set `ENV{VCPKG_DEFAULT_HOST_TRIPLET}`
+
+As no *CMake* configuration step is performed, *vcpkgs* own toolchain integration does not execute its magic itself, so be careful to set your target triplets accordingly.
+
+#### container recipe
 * `ADD` `vcpkg.json`-manifest to your project root inside the container
 * `ADD` your copy of `vcpkg.cmake` to your container
-* create your build directory
 * run `cmake -DVCPKG_PARENT_DIR=<path-to-build-directory> -DVCPKG_VERSION=<desired-vcpkg-version> -DVCPKG_DEFAULT_TRIPLET=<triplet> -P <path-to>/vcpkg.cmake` in your project root
 
 

vcpkg.cmake

@@ -2,7 +2,7 @@
 # License, v. 2.0. If a copy of the MPL was not distributed with this
 # file, You can obtain one at https://mozilla.org/MPL/2.0/.
 #
-# Copyright (C) 2021, Arne Wendt
+# Copyright (C) 2022, Arne Wendt
 #
 
 # vcpkg examples use 3.0.0, assuming this as minimum version for vcpkg cmake toolchain
@@ -58,9 +58,15 @@ function(vcpkg_init)
 
     # for use in scripting mode
     if(CMAKE_SCRIPT_MODE_FILE)
+        if(VCPKG_TARGET_TRIPLET)
+            set(ENV{VCPKG_DEFAULT_TRIPLET} "${VCPKG_DEFAULT_TRIPLET}")
+        endif()
         if(VCPKG_DEFAULT_TRIPLET)
             set(ENV{VCPKG_DEFAULT_TRIPLET} "${VCPKG_DEFAULT_TRIPLET}")
         endif()
+        if(VCPKG_HOST_TRIPLET)
+            set(ENV{VCPKG_DEFAULT_HOST_TRIPLET} "${VCPKG_DEFAULT_HOST_TRIPLET}")
+        endif()
         if(VCPKG_DEFAULT_HOST_TRIPLET)
             set(ENV{VCPKG_DEFAULT_HOST_TRIPLET} "${VCPKG_DEFAULT_HOST_TRIPLET}")
         endif()