src/gallium/README.portability

   1               CROSS-PLATFORM PORTABILITY GUIDELINES FOR GALLIUM3D
   2
   3
   4 = General Considerations =
   5
   6 The state tracker and winsys driver support a rather limited number of
   7 platforms. However, the pipe drivers are meant to run in a wide number of
   8 platforms. Hence the pipe drivers, the auxiliary modules, and all public
   9 headers in general, should strictly follow these guidelines to ensure
  10
  11
  12 = Compiler Support =
  13
  14 * Include the p_compiler.h.
  15
  16 * Don't use the 'inline' keyword, use the INLINE macro in p_compiler.h instead.
  17
  18 * Cast explicitly when converting to integer types of smaller sizes.
  19
  20 * Cast explicitly when converting between float, double and integral types.
  21
  22 * Don't use named struct initializers.
  23
  24 * Don't use variable number of macro arguments. Use static inline functions
  25 instead.
  26
  27 * Don't use C99 features.
  28
  29 = Standard Library =
  30
  31 * Avoid including standard library headers. Most standard library functions are
  32 not available in Windows Kernel Mode. Use the appropriate p_*.h include.
  33
  34 == Memory Allocation ==
  35
  36 * Use MALLOC, CALLOC, FREE instead of the malloc, calloc, free functions.
  37
  38 * Use align_pointer() function defined in p_util.h for aligning pointers in a
  39 portable way.
  40
  41 == Debugging ==
  42
  43 * Use the functions/macros in p_debug.h.
  44
  45 * Don't include assert.h, call abort, printf, etc.
  46
  47
  48 = Code Style =
  49
  50 == Inherantice in C ==
  51
  52 The main thing we do is mimic inheritance by structure containment.
  53
  54 Here's a silly made-up example:
  55
  56 /* base class */
  57 struct buffer
  58 {
  59   int size;
  60   void (*validate)(struct buffer *buf);
  61 };
  62
  63 /* sub-class of bufffer */
  64 struct texture_buffer
  65 {
  66   struct buffer base;  /* the base class, MUST COME FIRST! */
  67   int format;
  68   int width, height;
  69 };
  70
  71
  72 Then, we'll typically have cast-wrapper functions to convert base-class
  73 pointers to sub-class pointers where needed:
  74
  75 static inline struct vertex_buffer *vertex_buffer(struct buffer *buf)
  76 {
  77   return (struct vertex_buffer *) buf;
  78 }
  79
  80
  81 To create/init a sub-classed object:
  82
  83 struct buffer *create_texture_buffer(int w, int h, int format)
  84 {
  85   struct texture_buffer *t = malloc(sizeof(*t));
  86   t->format = format;
  87   t->width = w;
  88   t->height = h;
  89   t->base.size = w * h;
  90   t->base.validate = tex_validate;
  91   return &t->base;
  92 }
  93
  94 Example sub-class method:
  95
  96 void tex_validate(struct buffer *buf)
  97 {
  98   struct texture_buffer *tb = texture_buffer(buf);
  99   assert(tb->format);
 100   assert(tb->width);
 101   assert(tb->height);
 102 }
 103
 104
 105 Note that we typically do not use typedefs to make "class names"; we use
 106 'struct whatever' everywhere.
 107
 108 Gallium's pipe_context and the subclassed psb_context, etc are prime examples
 109 of this.  There's also many examples in Mesa and the Mesa state tracker.