libui/doc/controls.md

Controls

Overview

TODO

Reference

uiControl

typedef struct uiControl uiControl;
uint32_t uiControlType(void);
#define uiControl(obj) ((uiControl *) uiCheckControlType((obj), uiControlType()))

uiControl is an opaque type that describes a control.

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. A control type identifier of 0 is always invalid; this can be used to initialize the variables that hold the returned identifiers from uiRegisterControlType().

uiControlVtable

typedef struct uiControlVtable uiControlVtable;
struct uiControlVtable {
	size_t Size;
	bool (*Init)(uiControl *c, void *implData, void *initData);
	void (*Free)(uiControl *c, void *implData);
	void (*ParentChanging)(uiControl *c, void *implData, uiControl *oldParent);
	void (*ParentChanged)(uiControl *c, void *implData, uiControl *newParent);
};

uiControlVtable describes the set of functions that control implementations need to implement. When registering your control type, you pass this in as a parameter to uiRegisterControlType(). Each method here is required.

You are responsible for allocating and initializing this struct. To do so, you simply zero the memory for this struct and set its Size field to sizeof (uiControlVtable). (TODO put this in a common place)

Each method takes at least two parameters. The first, c, is the uiControl itself. The second, implData, is the implementation data pointer; it is the same as the pointer returned by uiControlImplData(c), and is provided here as a convenience.

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()

uint32_t uiRegisterControlType(const char *name, const uiControlVtable *vtable, const 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().

Each type has a name, passed in the name parameter. The type name is only used for debugging and error reporting purposes. The type name should be a standard C string using the system encoding (TODO proper terminology), rather than a UTF-8 string as with the rest of libui. The type name is copied into libui-internal memory; the name pointer passed to uiRegisterControlType() is not used after it returns. It is a programmer error to specify NULL for name. (TODO anything else? Empty string? Duplicate name?) (TODO reserved name rules)

uiControlVtable describes the functions of a uiControl common between platforms, and is discussed above. uiControlOSVtable describes functionst hat vary from OS to OS, and are described in the respective OS-specific uiControl implementation pages. The two vtables are copied into libui-internal memory; the vtable pointers passed to uiRegisterControlType() are not used after it returns.

It is a programmer error to specify NULL for either vtable. It is also a programmer error to specify NULL for any of the methods in either vtable — that is, all methods are required. It is also a programmer error to pass the wrong value to the Size field of either vtable.

An implDataSize of 0 is legal; the implementation data pointer will be NULL. This is not particularly useful, however.

uiCheckControlType()

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:

#define uiButton(c) ((uiButton *) uiCheckControlType((c), uiButtonType()))

(TODO document passing uiControlType() to this, or even make doing so unnecessary)

uiNewControl()

uiControl *uiNewControl(uint32_t type, void *initData);

uiNewControl() creates a new uiControl of the given type.

This function is meant for control implementations to use in the implementation of dedicated creation functions; for instance, uiNewButton() calls uiNewControl(), passing in the appropriate values for initData. initData is, in turn, passed to the control's Init() method, and its format is generally internal to the control. Normal users should not call this function.

It is a programmer error to pass an invalid value for either type or initData.

For control implementations: This function allocates both the uiControl and the memory for the implementation data, and then passes both of these allocations as well as the value of initData into your Init() method. Before calling Init(), libui will clear the implData memory, as with memset(0). Return false from the Init() method if initData is invalid; if it is valid, initialize the control and return true. To discourage direct use of uiNewControl(), you should generally not allow initData to be NULL, even if there are no parameters. Do not return false for any other reason, including other forms of initialization failures; see Error handling for details on what to do instead. TODO is this whole spiel about the return value even necessary? shouldn't the outer library be responsible for handling errors instead?

uiControlFree()

void uiControlFree(uiControl *c);

uiControlFree() frees the given control.

If c has children, those children are also freed. It is a programmer error to free a control that is itself a child of another control.

It is a programmer error to specify NULL for c.

For control implementations: This function calls your vtable's Free() method. Parameter validity checks are already performed. Your Free() should call uiControlFree() on all your control's children and free dynamically allocated memory that is part of your implementation data. Once your Free() method returns, libui will take care of freeing the implementation data memory block itself.

uiControlSetParent()

uiprivExtern void uiControlSetParent(uiControl *c, uiControl *parent);

uiControlSetParent() marks parent as the parent of c. parent may be NULL, in which case the control has no parent.

This function is used by the implementation of a container control to actually establish a parent-child relationship from libui's point of view. This function is only intended to be called by control implementations. You should not call it directly; instead, use the methods provided by your container control to add children.

This function can only be used to set the parent of an unparented control or to remove its parent. It may not be used to change the parent of an already parented control. It is a programmer error to set the parent of a control that already has a parent to something other than NULL (even if to the same parent), or to set the parent of a control with no parent to NULL. (The idea here is to reinforce the concept of container implementations being responsible for setting their children properly, not the user.)

It is a programmer error to pass NULL for c. (TODO non-uiControl for either c or parent?)

It is a programmer error to introduce a cycle when changing the parent of a control. By extension, it is a programmer error to make a control its own parent.

TODO top-levels and parenting

For control implementations: You would call this when adding a control to your container, preferably before actually doing any internal bookkeeping. Likewise, call this when removing a child, preferably after doing any internal bookkeeping.

The child will receive a call to its ParentChanging() method before the actual change happens, and a call to ParentChanged() afterward, receiving the old and new parent, respectively, as an argument. This is where OS-specific parenting code would go; specific instructions can be found in each OS's uiControl implementation page.

TODO do things this way to avoid needing to check if reparenting from a container implementation, or do that manually each time? we used to have uiControlVerifySetParent()... TODO I forgot what this meant

uiControlImplData()

void *uiControlImplData(uiControl *c);

uiControlImplData() returns the pointer to the implementation data for c. The returned pointer is valid for the lifetime of c.

This function is meant to be used by control implementations only. There is in general no guarantee as to the size or format of this pointer. Normal users should not call uiControlImplData().

It is a programmer error to pass NULL for c. (TODO non-uiControl?)