src/gallium/README.portability

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