More uiControl work.

doc/controls.md

@@ -18,7 +18,7 @@ uint32_t uiControlType(void);
 
 `uiControl` is an opaque type that describes a control.
 
-`uiControlType()` is the type identifier of a `uiControl` as passed to `uiControlCheckType()`. You rarely need to call this directly; the `uiControl()` conversion macro does this for you.
+`uiControlType()` is the type identifier of a `uiControl` as passed to `uiCheckControlType()`. You rarely need to call this directly; the `uiControl()` conversion macro does this for you.
 
 ### `uiControlVtable`
 
@@ -36,6 +36,32 @@ Each method takes at least two parameters. The first, `c`, is the `uiControl` it
 
 Each method is named for the `uiControl` function that it implements. As such, details on how to implement these methods are documented alongside those functions. For instance, instructions on implementing `Free()` are given under the documentation for `uiControlFree()`. The only exception is `Init()`, which is discussed under `uiNewControl()` below.
 
+### `uiRegisterControlType()`
+
+```c
+uint32_t uiRegisterControlType(uiControlVtable *vtable, uiControlOSVtable *osVtable, size_t implDataSize);
+```
+
+`uiRegisterControlType()` registers a new `uiControl` type with the given vtables and returns its ID as passed to `uiNewControl()`. `implDataSize` is the size of the implementation data struct that is created by `uiNewControl()`.
+
+`uiControlVtable` describes the functions of a `uiControl` common between platforms, and is discussed on this page. `uiControlOSVtable` describes functionst hat vary from OS to OS, and are described in the respective OS-specific uiControl implementation pages.
+
+It is a programmer error to specify `NULL` for either vtable. An `implDataSize` of 0 is legal; the implementation data pointer will be `NULL`. This is not particularly useful, however. It is also a programmer error to specify `NULL` for any of the methods in either vtable — that is, all methods are required.
+
+### `uiCheckControlType()`
+
+```c
+void *uiCheckControlType(void *c, uint32_t type);
+```
+
+`uiCheckControlType()` checks whether `c` is a `uiControl`, and if so, whether it is of the type specified by `type`. If `c` is `NULL`, or if either of the above conditions is false, a programmer error is raised. If the conditions are met, the function returns `c` unchanged.
+
+This function is intended to be used to implement a macro that converts an arbitrary `uiControl` pointer into a specific type. For instance, `uiButton` exposes its type ID as a function `uiButtonType()`, and provides the macro `uiButton()` that does the actual conversion as so:
+
+```c
+#define uiButton(c) ((uiButton *) uiCheckControlType((c), uiButtonType()))
+```
+
 ### `uiNewControl()`
 
 ```c

ui.h

@@ -63,6 +63,7 @@ uiprivExtern void uiEventSetHandlerBlocked(uiEvent *e, int id, bool blocked);
 
 typedef struct uiControl uiControl;
 typedef struct uiControlVtable uiControlVtable;
+typedef struct uiControlOSVtable uiControlOSVtable;
 
 uiprivExtern uint32_t uiControlType(void);
 #define uiControl(obj) ((uiControl *) uiCheckControlType((obj), uiControlType()))
@@ -72,6 +73,9 @@ struct uiControlVtable {
 	void (*Free)(uiControl *c, void *implData);
 };
 
+uiprivExtern uint32_t uiRegisterControlType(uiControlVtable *vtable, uiControlOSVtable *osVtable, size_t implDataSize);
+uiprivExtern void *uiCheckControlType(void *c, uint32_t type);
+
 uiprivExtern uiControl *uiNewControl(uint32_t type, void *initData);
 uiprivExtern void uiControlFree(uiControl *c);