Tk_CreateImageType(typePtr)
Tk_ImageType *typePtr
(in) Tk_CreateImageType is invoked to define a new kind of image. An image type corresponds to a particular value of the type argument for the image create command. There may exist any number of different image types, and new types may be defined dynamically by calling Tk_CreateImageType. For example, there might be one type for 2-color bitmaps, another for multi-color images, another for dithered images, another for video, and so on.
The code that implements a new image type is called an
image manager.
It consists of a collection of procedures plus three different
kinds of data structures.
The first data structure is a Tk_ImageType structure, which contains
the name of the image type and pointers to five procedures provided
by the image manager to deal with images of this type:
typedef struct Tk_ImageType {
char *name;
Tk_ImageCreateProc *createProc;
Tk_ImageGetProc *getProc;
Tk_ImageDisplayProc *displayProc;
Tk_ImageFreeProc *freeProc;
Tk_ImageDeleteProc *deleteProc;
} Tk_ImageType;
The fields of this structure will be described in later subsections
of this entry.
The second major data structure manipulated by an image manager is called an image master; it contains overall information about a particular image, such as the values of the configuration options specified in an image create command. There will usually be one of these structures for each invocation of the image create command.
The third data structure related to images is an image instance. There will usually be one of these structures for each usage of an image in a particular widget. It is possible for a single image to appear simultaneously in multiple widgets, or even multiple times in the same widget. Furthermore, different instances may be on different screens or displays. The image instance data structure describes things that may vary from instance to instance, such as colors and graphics contexts for redisplay. There is usually one instance structure for each -image option specified for a widget or canvas item.
The following subsections describe the fields of a Tk_ImageType in more detail.
typePtr->name provides a name for the image type. Once Tk_CreateImageType returns, this name may be used in image create commands to create images of the new type. If there already existed an image type by this name then the new image type replaces the old one.
If createProc encounters an error, it should leave an error message in interp->result and return TCL_ERROR; otherwise it should return TCL_OK.
createProc should call Tk_ImageChanged in order to set the size of the image and request an initial redisplay.
typePtr->getProc is invoked by Tk whenever a widget
calls Tk_GetImage to use a particular image.
This procedure must match the following prototype:
typedef ClientData Tk_ImageGetProc(
Tk_Window tkwin,
ClientData masterData);
The tkwin argument identifies the window in which the
image will be used and masterData is the value
returned by createProc when the image master was created.
getProc will usually create a data structure for the new
instance, including such things as the resources needed to
display the image in the given window.
getProc returns a one-word token for the instance, which
is typically the address of the instance data structure.
Tk will pass this value back to the image manager when invoking
its displayProc and freeProc procedures.
typePtr->displayProc is invoked by Tk whenever an image needs
to be displayed (i.e., whenever a widget calls Tk_RedrawImage).
displayProc must match the following prototype:
typedef void Tk_ImageDisplayProc(
ClientData instanceData,
Display *display,
Drawable drawable,
int imageX,
int imageY,
int width,
int height,
int drawableX,
int drawableY);
The instanceData will be the same as the value returned by
getProc when the instance was created.
display and drawable indicate where to display the
image; drawable may be a pixmap rather than
the window specified to getProc (this is usually the case,
since most widgets double-buffer their redisplay to get smoother
visual effects).
imageX, imageY, width, and height
identify the region of the image that must be redisplayed.
This region will always be within the size of the image
as specified in the most recent call to Tk_ImageChanged.
drawableX and drawableY indicate where in drawable
the image should be displayed; displayProc should display
the given region of the image so that point (imageX, imageY)
in the image appears at (drawableX, drawableY) in drawable.
typePtr->freeProc contains the address of a procedure that
Tk will invoke when an image instance is released (i.e., when
Tk_FreeImage is invoked).
This can happen, for example, when a widget is deleted or a image item
in a canvas is deleted, or when the image displayed in a widget or
canvas item is changed.
freeProc must match the following prototype:
typedef void Tk_ImageFreeProc(
ClientData instanceData,
Display *display);
The instanceData will be the same as the value returned by
getProc when the instance was created, and display
is the display containing the window for the instance.
freeProc should release any resources associated with the
image instance, since the instance will never be used again.
typePtr->deleteProc is a procedure that Tk invokes when an
image is being deleted (i.e. when the image delete command
is invoked).
Before invoking deleteProc Tk will invoke freeProc for
each of the image's instances.
deleteProc must match the following prototype:
typedef void Tk_ImageDeleteProc(
ClientData masterData);
The masterData argument will be the same as the value
stored in *masterDataPtr by createProc when the
image was created.
deleteProc should release any resources associated with
the image.