readme: Document some preprocessor definitions used by vkd3d.

Approved-by: Giovanni Mascellani (@giomasce)
Approved-by: Henri Verbeet (@hverbeet)
Merge-Request: https://gitlab.winehq.org/wine/vkd3d/-/merge_requests/1139

README

@@ -19,10 +19,9 @@ available or is not recent (>= 3.21), then you can build Wine with `make
 tools/widl/widl' to avoid building all of Wine. You can then point vkd3d's
 configure at that widl binary with `WIDL="/path/to/widl"'.
 
-For release builds, you may want to define NDEBUG. If you do not need debug log
+For release builds, you may want to disable debug log messages defining
-messages, you may also consider VKD3D_NO_TRACE_MESSAGES and
+preprocessor macros VKD3D_NO_TRACE_MESSAGES and VKD3D_NO_DEBUG_MESSAGES.
-VKD3D_NO_DEBUG_MESSAGES. For example, you can pass `CPPFLAGS="-DNDEBUG
+See the `Preprocessor definitions' section below for more details.
--DVKD3D_NO_TRACE_MESSAGES"' to configure.
 
 ================
 Developing vkd3d
@@ -50,8 +49,8 @@ Environment variables
 =====================
 
 Most of the environment variables used by vkd3d are for debugging purposes. The
-environment variables are not considered a part of API and might be changed or
+environment variables are not considered a stable interface and might be changed
-removed in the future versions of vkd3d.
+or removed in future versions of vkd3d.
 
 Some of debug variables are lists of elements. Elements must be separated by
 commas or semicolons.
@@ -116,6 +115,48 @@ code for adding DXBC checksums, so the official release should be installed
 from:
 https://github.com/microsoft/DirectXShaderCompiler/releases
 
+========================
+Preprocessor definitions
+========================
+
+A number of preprocessor definitions can be used at compilation time to control
+the behaviour of the generated binary. You can pass something like
+`CPPFLAGS="-DVKD3D_VAR1 -DVKD3D_VAR2"' to the configure script. The preprocessor
+variables are not considered a stable interface and might be changed or removed
+in future versions of vkd3d.
+
+ * VKD3D_NO_TRACE_MESSAGES - do not emit trace messages in the debug log; this
+   can be useful in release builds to reduce the size of the binary and make it
+   slightly faster.
+
+ * VKD3D_NO_DEBUG_MESSAGES - do not emit warn and fixme messages in the debug
+   log; this will further optimise the binary, but may omit messages that could
+   help debug problems with vkd3d.
+
+ * VKD3D_NO_ERROR_MESSAGES - do not emit error messages; this will optimise the
+   binary even more, but may omit very important messages, so it is not
+   recommended in most circumstances.
+
+ * VKD3D_ABORT_ON_ERR - abort the process as soon as an error message is
+   emitted; this can be useful for developers to make error conditions as
+   conspicuous as possible.
+
+ * VKD3D_SHADER_UNSUPPORTED_DXIL - enable DXIL (DirectX Intermediate Language)
+   support in vkd3d-shader, which is disabled by default because it is not
+   considered ready for release yet. Please note that this feature is not
+   currently supported, and it might change in a non-compatible way before it is
+   released.
+
+ * VKD3D_SHADER_UNSUPPORTED_GLSL - enable GLSL (GL Shading Language) support in
+   vkd3d-shader, which is disabled by default because it is not considered ready
+   for release yet. Please note that this feature is not currently supported,
+   and it might change in a non-compatible way before it is released.
+
+ * VKD3D_SHADER_UNSUPPORTED_MSL - enable MSL (Metal Shading Language) support in
+   vkd3d-shader, which is disabled by default because it is not considered ready
+   for release yet. Please note that this feature is not currently supported,
+   and it might change in a non-compatible way before it is released.
+
 ============================
 Testing with the Agility SDK
 ============================