glew-cmake/auto/src/glew_gl.c

/* ------------------------------------------------------------------------- */

/*
 * GLEW, just like OpenGL or GLU, does not rely on the standard C library.
 * These functions implement the functionality required in this file.
 */

static GLuint _glewStrLen (const GLubyte *s)
{
  GLuint i=0;
  while (s+i != NULL && s[i] != '\0') i++;
  return i;
}

static GLuint _glewStrCLen (const GLubyte *s, GLubyte c)
{
  GLuint i=0;
  while (s+i != NULL && s[i] != '\0' && s[i] != c) i++;
  return i;
}

static GLboolean _glewStrSame (const GLubyte *a, const GLubyte *b, GLuint n)
{
  GLuint i=0;
  while (i < n && a+i != NULL && b+i != NULL && a[i] == b[i]) i++;
  return i == n;
}

/* 
 * Search for name in the extensions string. Use of strstr()
 * is not sufficient because extension names can be prefixes of
 * other extension names. Could use strtok() but the constant
 * string returned by glGetString might be in read-only memory.
 */
GLboolean glewGetExtension (const GLubyte *name)
{    
  GLubyte *p, *end;
  GLuint len = _glewStrLen(name);
  p = (GLubyte*)glGetString(GL_EXTENSIONS);
  if (0 == p) return GL_FALSE;
  end = p + _glewStrLen(p);
  while (p < end)
  {
    GLuint n = _glewStrCLen(p, ' ');
    if (len == n && _glewStrSame(name, p, n)) return GL_TRUE;
    p += n+1;
  }
  return GL_FALSE;
}

/* ------------------------------------------------------------------------- */

static GLuint _glewInit ()
{
  const GLubyte* s;
  GLuint i;
  /* query opengl version */
  s = glGetString(GL_VERSION);
  if (!s) return GLEW_ERROR_NO_GL_VERSION;
  i = _glewStrCLen(s, '.')+1;
  if (s+i == NULL || s[i] < '1')
  {
    return GLEW_ERROR_GL_VERSION_10_ONLY;
  }
  else
  {
    if (s[3] >= '5')
    {
      GLEW_VERSION_1_1 = GL_TRUE;
      GLEW_VERSION_1_2 = GL_TRUE;
      GLEW_VERSION_1_3 = GL_TRUE;
      GLEW_VERSION_1_4 = GL_TRUE;
      GLEW_VERSION_1_5 = GL_TRUE;
    }
    if (s[2] == '4')
    {
      GLEW_VERSION_1_1 = GL_TRUE;
      GLEW_VERSION_1_2 = GL_TRUE;
      GLEW_VERSION_1_3 = GL_TRUE;
      GLEW_VERSION_1_4 = GL_TRUE;
    }
    if (s[2] == '3')
    {
      GLEW_VERSION_1_1 = GL_TRUE;
      GLEW_VERSION_1_2 = GL_TRUE;
      GLEW_VERSION_1_3 = GL_TRUE;
    }
    if (s[2] == '2')
    {
      GLEW_VERSION_1_1 = GL_TRUE;
      GLEW_VERSION_1_2 = GL_TRUE;
    }
    if (s[2] < '2')
    {
      GLEW_VERSION_1_1 = GL_TRUE;
    }
  }
  /* initialize extensions */