Wrong expansion order with nested macros

[slapin]

When trying ifdefs in shaders found that these do not work, so the examples for preprocessor use are incorrect.
I found that if preprocessor_defines FOO`` used, one have to use #if FOOnot#ifdef FOO``` or else
syntax errors are reported.

line 1: Expecting a macro name after #ifdef, got: `1'

[paroj]

works fine here:

ogre/Samples/Media/PBR/pbr-vert.glsl

Line 14 in f629d22

#ifdef HAS_NORMALS

[slapin]

Nah, it is just much less flexible and does not behave similar to normal cpp.
The problem I was getting was because I had ifdef inside OGRE_UNIFORMS macro:

OGRE_UNIFORMS(
#ifdef FOO
uniform vec4 foo;
#endif
uniform vec4 bar;
)

if I replace this construct with

#ifdef FOO
OGRE_UNIFORMS(
uniform vec4 foo;
uniform vec4 bar;
)
#else
OGRE_UNIFORMS(
uniform vec4 bar;
)
#endif

It seems to work. However if I use #if instead of #ifdef, it works both ways but macro have to be always defned to 0 or 1. Probably that is because it uses glsl implementation's cpp instead of Ogre's one in this case.

[paroj]

the issue is that our CPreprocessor will first expand the OGRE_UNIFORMS argument, replacing FOO=1, before evaluating the ifdef.

Adding to know issues for now, as there is an easy workaround.

For investigating this, start here:

ogre/RenderSystems/GLSupport/src/GLSL/OgreGLSLPreprocessor.cpp

Line 414 in f629d22

CPreprocessor::Token CPreprocessor::ExpandMacro (const Token &iToken)