gaffer.cmd : Set PXR_USD_WINDOWS_DLL_PATH

If this variable is set, USD will not add the entries from `PATH` to the
Python binary search paths. We set it to an empty string because the
`Gaffer` module adds the proper binary path and our intention here is
only to prevent USD from adding `PATH` entries.

Changes.md

@@ -19,6 +19,7 @@ Improvements
 - EditScope : Added summaries of set membership edits in the NodeEditor.
 - LightEditor : Mute and solo columns now accurately reflect the presence of the `light:mute` attribute (for the Mute column) and membership in the `soloLights` set (for the Solo column) for all scene locations, not just for lights.
 - RenderPassEditor : The currently active render pass can now be unset by double clicking on its green dot in the "Active" column.
+- Launch : The Windows launch script now sets the `PXR_USD_WINDOWS_DLL_PATH` environment variable to an empty string if it is not already set. This prevents USD from adding all entries from `PATH` to the Python binary search paths and ensures our USD binaries are found instead of potentially other installations.
 
 Fixes
 -----

bin/gaffer.cmd

@@ -19,6 +19,10 @@ call :prependToPath "%GAFFER_ROOT%\ops" IECORE_OP_PATHS
 
 call :prependToPath "%GAFFER_ROOT%\resources\IECoreUSD" PXR_PLUGINPATH_NAME
 call :prependToPath "%GAFFER_ROOT%\materialX" PXR_MTLX_STDLIB_SEARCH_PATHS
+rem Prevent USD from adding entries from `PATH` to Python binary search paths.
+if "%PXR_USD_WINDOWS_DLL_PATH%" EQU "" (
+	set PXR_USD_WINDOWS_DLL_PATH=""
+)
 
 call :prependToPath "%USERPROFILE%\gaffer\opPresets;%GAFFER_ROOT%\opPresets" IECORE_OP_PRESET_PATHS
 call :prependToPath "%USERPROFILE%\gaffer\procedurals;%GAFFER_ROOT%\procedurals" IECORE_PROCEDURAL_PATHS