Document how to find Halide from a pip installation (#8411)

README.md

@@ -53,6 +53,15 @@ Currently, we provide wheels for: Windows x86-64, macOS x86-64, macOS arm64, and
 Linux x86-64. The Linux wheels are built for manylinux_2_28, which makes them
 broadly compatible (Debian 10, Ubuntu 18.10, Fedora 29).
 
+*For C++ usage of the pip package:* On Linux and macOS, CMake's `find_package`
+command should find Halide as long as you're in the same virtual environment you
+installed it in. On Windows, you will need to add the virtual environment root
+directory to `CMAKE_PREFIX_PATH`. This can be done by running
+`set CMAKE_PREFIX_PATH=%VIRTUAL_ENV%` in `cmd`.
+
+Other build systems can find the Halide root path by running `python -c 
+"import halide; print(halide.install_dir())"`.
+
 ## Homebrew
 
 Alternatively, if you use macOS, you can install Halide via

doc/HalideCMakePackage.md

@@ -71,14 +71,18 @@ vendor-specific extensions to C++. This is not necessary to simply use Halide,
 but we do not allow such extensions in the Halide repo.
 
 Finally, we use [`find_package`][find_package] to locate Halide on your system.
-If Halide is not globally installed, you will need to add the root of the Halide
-installation directory to [`CMAKE_PREFIX_PATH`][cmake_prefix_path] at the CMake
-command line.
+When using the pip package on Linux and macOS, CMake's `find_package`
+command should find Halide as long as you're in the same virtual environment you
+installed it in. On Windows, you will need to add the virtual environment root
+directory to [`CMAKE_PREFIX_PATH`][cmake_prefix_path]:
 
 ```shell
-$ cmake -G Ninja -S . -B build -DCMAKE_BUILD_TYPE=Release -DCMAKE_PREFIX_PATH="/path/to/Halide-install"
+$ cmake -G Ninja -S . -B build -DCMAKE_BUILD_TYPE=Release -DCMAKE_PREFIX_PATH=%VIRTUAL_ENV%
 ```
 
+If `find_package` cannot find Halide, set `CMAKE_PREFIX_PATH` to the Halide
+installation directory.
+
 ## JIT mode
 
 To use Halide in JIT mode (like the [tutorials][halide-tutorials] do, for

python_bindings/src/halide/__init__.py

@@ -11,7 +11,15 @@ def patch_dll_dirs():
 del patch_dll_dirs
 
 from .halide_ import *
+# noinspection PyUnresolvedReferences
 from .halide_ import _, _0, _1, _2, _3, _4, _5, _6, _7, _8, _9
+
+
+def install_dir():
+    import os
+    return os.path.dirname(__file__)
+
+
 from ._generator_helpers import (
     _create_python_generator,
     _generatorcontext_enter,