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authorJosé Fonseca <jrfonseca@tungstengraphics.com>2008-05-01 21:52:05 +0900
committerJosé Fonseca <jrfonseca@tungstengraphics.com>2008-05-01 22:32:49 +0900
commit073bb94a4150d7b3c78ea5420383cb7ed8f97566 (patch)
treee54976c5279b49eefa6e02927b0f56f6f1ca28bc /src/gallium/README.portability
parentc6fadd9fade40e3397f56fdbfa2325861799e49c (diff)
Add Brian's explanation for inheritance in C.
Diffstat (limited to 'src/gallium/README.portability')
-rw-r--r--src/gallium/README.portability65
1 files changed, 65 insertions, 0 deletions
diff --git a/src/gallium/README.portability b/src/gallium/README.portability
index ab0c1978476..18a97f449b4 100644
--- a/src/gallium/README.portability
+++ b/src/gallium/README.portability
@@ -24,6 +24,7 @@ headers in general, should stricly follow these guidelines to ensure
* Don't use variable number of macro arguments. Use static inline functions
instead.
+* Don't use C99 features.
= Standard Library =
@@ -42,3 +43,67 @@ portable way.
* Use the functions/macros in p_debug.h.
* Don't include assert.h, call abort, printf, etc.
+
+
+= Code Style =
+
+== Inherantice in C ==
+
+The main thing we do is mimic inheritance by structure containment.
+
+Here's a silly made-up example:
+
+/* base class */
+struct buffer
+{
+ int size;
+ void (*validate)(struct buffer *buf);
+};
+
+/* sub-class of bufffer */
+struct texture_buffer
+{
+ struct buffer base; /* the base class, MUST COME FIRST! */
+ int format;
+ int width, height;
+};
+
+
+Then, we'll typically have cast-wrapper functions to convert base-class
+pointers to sub-class pointers where needed:
+
+static inline struct vertex_buffer *vertex_buffer(struct buffer *buf)
+{
+ return (struct vertex_buffer *) buf;
+}
+
+
+To create/init a sub-classed object:
+
+struct buffer *create_texture_buffer(int w, int h, int format)
+{
+ struct texture_buffer *t = malloc(sizeof(*t));
+ t->format = format;
+ t->width = w;
+ t->height = h;
+ t->base.size = w * h;
+ t->base.validate = tex_validate;
+ return &t->base;
+}
+
+Example sub-class method:
+
+void tex_validate(struct buffer *buf)
+{
+ struct texture_buffer *tb = texture_buffer(buf);
+ assert(tb->format);
+ assert(tb->width);
+ assert(tb->height);
+}
+
+
+Note that we typically do not use typedefs to make "class names"; we use
+'struct whatever' everywhere.
+
+Gallium's pipe_context and the subclassed psb_context, etc are prime examples
+of this. There's also many examples in Mesa and the Mesa state tracker.