GCC, stringification, and inline GLSL?

问题:

I'd like to declare GLSL shader strings inline using macro stringification:

#define STRINGIFY(A)  #A
const GLchar* vert = STRINGIFY(
#version 120\n
attribute vec2 position;
void main()
{
    gl_Position = vec4( position, 0.0, 1.0 );
}
);

This builds and runs fine using VS2010 but fails to compile on gcc with:

error: invalid preprocessing directive #version

Is there a way to use stringification like this in a portable manner?

I'm trying to avoid per-line quotes:

const GLchar* vert = 
"#version 120\n"
"attribute vec2 position;"
"void main()"
"{"
"    gl_Position = vec4( position, 0.0, 1.0 );"
"}"
;

...and/or line continuation:

const GLchar* vert = "\
#version 120\n                                 \
attribute vec2 position;                       \
void main()                                    \
{                                              \
    gl_Position = vec4( position, 0.0, 1.0 );  \
}                                              \
";

回答1:

Unfortunately, having preprocessor directives in the argument of a macro is undefined, so you can't do this directly. But as long as none of your shaders need preprocessor directives other than #version, you could do something like:

#define GLSL(version, shader)  "#version " #version "\n" #shader

const GLchar* vert = GLSL(120,
    attribute vec2 position;
    void main()
    {
        gl_Position = vec4( position, 0.0, 1.0 );
    }
);

回答2:

Can you use C++11? If so you could use raw string literals:

const GLchar* vert = R"END(
#version 120
attribute vec2 position;
void main()
{
    gl_Position = vec4( position, 0.0, 1.0 );
}
)END";

No need for escapes or explicit newlines. These strings start with an R (or r). You need a delimiter (I chose END) between the quote and the first parenthesis to escape parenthesis which you have in the code snippet.

回答3:

The problem is due to gcc preprocessing macros meant for GLSL. Using standard stringify and escaping preprocessor directives with new lines in GLSL code worked for me.

#define STRINGIFY(A)  #A

const GLchar* vert = STRINGIFY(

\n#version 120\n
\n#define MY_MACRO 999\n

attribute vec2 position;
void main()
{
    gl_Position = vec4( position, 0.0, 1.0 );
}
);

回答4:

To achieve this purpose I used sed. I have seperate files with GLSL which I edit (with proper syntax highlighting), and in the same time GLSL in inlined in C++. Not very cross platform, but with msys it works under windows.

In C++ code:

const GLchar* vert = 
#include "shader_processed.vert"
;

In Makefile:

shader_processed.vert: shader.vert
    sed -f shader.sed shader.vert > shader_processed.vert

programm: shader_processed.vert main.cpp
    g++ ...

shader.sed

s|\\|\\\\|g
s|"|\\"|g
s|$|\\n"|g
s|^|"|g