[Mesa-dev] [PATCH] TransformFeedback: Assign transform feedback varying slots in linker.

[Marek Olšák]

Hi Dan,

I have written this function to parse expressions of the form
"name[x]" for parsing the list of transform feedback varyings with
indexing. It's good enough to pass the piglit tests, but I am not sure
whether it's good enough for GLSL 1.3. I use this code to query
locations of indexed varyings, particularly "gl_TexCoord[1]" in one of
my tests. Feel free to use this code.

My question to the others is whether this is the way it should be
done, or whether there is a better way. Thanks.

Marek


#include <cmath>

#ifndef Elements
#define Elements(x) (sizeof(x)/sizeof(*(x)))
#endif

struct tfeedback_decl {
   char name[1024];
   bool is_array;
   unsigned array_index;
};

/* This expects expressions of the form "var" and "var[i]",
 * where i is a literal.
 *
 * We don't have to be pedantic about what is a valid GLSL variable name,
 * because any variable with an invalid name can't exist in the IR anyway. */
static bool parse_tfeedback_decl(const char *input,
                                 struct tfeedback_decl *decl)
{
   unsigned name_index = 0;

   decl->is_array = false;

   /* Parse the variable name. */
   while (*input &&
          ((*input > 'a' && *input < 'z') ||
           (*input > 'A' && *input < 'Z') ||
           (*input > '0' && *input < '9') ||
           *input == '_') &&
          name_index < Elements(decl->name)-1) {
      decl->name[name_index++] = *input;
      input++;
   }
   decl->name[name_index++] = 0;

   if (!*input) {
      return true;
   }

   /* Parse the array index. */
   if (*input == '[') {
      input++;

      if (*input && *input >= '0' && *input <= '9' &&
          sscanf(input, "%u", &decl->array_index) == 1) {
         decl->is_array = true;
         input += (unsigned)(log(decl->array_index)/log(10)) + 1;

         if (*input && *input == ']') {
            input++;
            if (!*input) {
               return true;
            }
         }
      }
   }

   return false;
}