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.so man.macros

.TH Tk_CreateImageType 3 8.0 Tk "Tk Library Procedures"

.BS

.SH NAME

Tk_CreateImageType, Tk_GetImageMasterData \- define new kind of image

.SH SYNOPSIS

.nf

\fB#include \fR

.sp

\fBTk_CreateImageType\fR(\fItypePtr\fR)

ClientData

.sp

.VS

\fBTk_GetImageMasterData\fR(\fIinterp, name, typePtrPtr\fR)

.SH ARGUMENTS

.AS Tk_ImageType *typePtrPtr

.AP Tk_ImageType *typePtr in

Structure that defines the new type of image.

Must be static: a

pointer to this structure is retained by the image code.

.AP Tcl_Interp *interp in

Interpreter in which image was created.

.AP char *name in

Name of existing image.

.AP Tk_ImageType **typePtrPtr out

Points to word in which to store a pointer to type information for

the given image, if it exists.

.VE

.BE

.SH DESCRIPTION

.PP

\fBTk_CreateImageType\fR is invoked to define a new kind of image.

An image type corresponds to a particular value of the \fItype\fR

argument for the \fBimage create\fR command.  There may exist

any number of different image types, and new types may be defined

dynamically by calling \fBTk_CreateImageType\fR.

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.

.PP

The code that implements a new image type is called an

\fIimage manager\fR.

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:

.CS

typedef struct Tk_ImageType {

        char *\fIname\fR;

        Tk_ImageCreateProc *\fIcreateProc\fR;

        Tk_ImageGetProc *\fIgetProc\fR;

        Tk_ImageDisplayProc *\fIdisplayProc\fR;

        Tk_ImageFreeProc *\fIfreeProc\fR;

        Tk_ImageDeleteProc *\fIdeleteProc\fR;

} Tk_ImageType;

.CE

The fields of this structure will be described in later subsections

of this entry.

.PP

The second major data structure manipulated by an image manager

is called an \fIimage master\fR;  it contains overall information

about a particular image, such as the values of the configuration

options specified in an \fBimage create\fR command.

There will usually be one of these structures for each

invocation of the \fBimage create\fR command.

.PP

The third data structure related to images is an \fIimage instance\fR.

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 \fB\-image\fR

option specified for a widget or canvas item.

.PP

The following subsections describe the fields of a Tk_ImageType

in more detail.

.SH NAME

.PP

\fItypePtr->name\fR provides a name for the image type.

Once \fBTk_CreateImageType\fR returns, this name may be used

in \fBimage create\fR 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.

.SH CREATEPROC

\fItypePtr->createProc\fR provides the address of a procedure for

Tk to call whenever \fBimage create\fR is invoked to create

an image of the new type.

\fItypePtr->createProc\fR must match the following prototype:

.CS

typedef int Tk_ImageCreateProc(

        Tcl_Interp *\fIinterp\fR,

        char *\fIname\fR,

        int \fIargc\fR,

        char **\fIargv\fR,

        Tk_ImageType *\fItypePtr\fR,

        Tk_ImageMaster \fImaster\fR,

        ClientData *\fImasterDataPtr\fR);

.CE

The \fIinterp\fR argument is the interpreter in which the \fBimage\fR

command was invoked, and \fIname\fR is the name for the new image,

which was either specified explicitly in the \fBimage\fR command

or generated automatically by the \fBimage\fR command.

The \fIargc\fR and \fIargv\fR arguments describe all the configuration

options for the new image (everything after the name argument to

\fBimage\fR).

The \fImaster\fR argument is a token that refers to Tk's information

about this image;  the image manager must return this token to

Tk when invoking the \fBTk_ImageChanged\fR procedure.

Typically \fIcreateProc\fR will parse \fIargc\fR and \fIargv\fR

and create an image master data structure for the new image.

\fIcreateProc\fR may store an arbitrary one-word value at

*\fImasterDataPtr\fR, which will be passed back to the

image manager when other callbacks are invoked.

Typically the value is a pointer to the master data

structure for the image.

.PP

If \fIcreateProc\fR encounters an error, it should leave an error

message in \fIinterp->result\fR and return \fBTCL_ERROR\fR;  otherwise

it should return \fBTCL_OK\fR.

.PP

\fIcreateProc\fR should call \fBTk_ImageChanged\fR in order to set the

size of the image and request an initial redisplay.

.SH GETPROC

.PP

\fItypePtr->getProc\fR is invoked by Tk whenever a widget

calls \fBTk_GetImage\fR to use a particular image.

This procedure must match the following prototype:

.CS

typedef ClientData Tk_ImageGetProc(

        Tk_Window \fItkwin\fR,

        ClientData \fImasterData\fR);

.CE

The \fItkwin\fR argument identifies the window in which the

image will be used and \fImasterData\fR is the value

returned by \fIcreateProc\fR when the image master was created.

\fIgetProc\fR 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.

\fIgetProc\fR 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 \fIdisplayProc\fR and \fIfreeProc\fR procedures.

.SH DISPLAYPROC

.PP

\fItypePtr->displayProc\fR is invoked by Tk whenever an image needs

to be displayed (i.e., whenever a widget calls \fBTk_RedrawImage\fR).

\fIdisplayProc\fR must match the following prototype:

.CS

typedef void Tk_ImageDisplayProc(

        ClientData \fIinstanceData\fR,

        Display *\fIdisplay\fR,

        Drawable \fIdrawable\fR,

        int \fIimageX\fR,

        int \fIimageY\fR,

        int \fIwidth\fR,

        int \fIheight\fR,

        int \fIdrawableX\fR,

        int \fIdrawableY\fR);

.CE

The \fIinstanceData\fR will be the same as the value returned by

\fIgetProc\fR when the instance was created.

\fIdisplay\fR and \fIdrawable\fR indicate where to display the

image;  \fIdrawable\fR may be a pixmap rather than

the window specified to \fIgetProc\fR (this is usually the case,

since most widgets double-buffer their redisplay to get smoother

visual effects).

\fIimageX\fR, \fIimageY\fR, \fIwidth\fR, and \fIheight\fR

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 \fBTk_ImageChanged\fR.

\fIdrawableX\fR and \fIdrawableY\fR indicate where in \fIdrawable\fR

the image should be displayed;  \fIdisplayProc\fR should display

the given region of the image so that point (\fIimageX\fR, \fIimageY\fR)

in the image appears at (\fIdrawableX\fR, \fIdrawableY\fR) in \fIdrawable\fR.

.SH FREEPROC

.PP

\fItypePtr->freeProc\fR contains the address of a procedure that

Tk will invoke when an image instance is released (i.e., when

\fBTk_FreeImage\fR 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.

\fIfreeProc\fR must match the following prototype:

.CS

typedef void Tk_ImageFreeProc(

        ClientData \fIinstanceData\fR,

        Display *\fIdisplay\fR);

.CE

The \fIinstanceData\fR will be the same as the value returned by

\fIgetProc\fR when the instance was created, and \fIdisplay\fR

is the display containing the window for the instance.

\fIfreeProc\fR should release any resources associated with the

image instance, since the instance will never be used again.

.SH DELETEPROC

.PP

\fItypePtr->deleteProc\fR is a procedure that Tk invokes when an

image is being deleted (i.e. when the \fBimage delete\fR command

is invoked).

Before invoking \fIdeleteProc\fR Tk will invoke \fIfreeProc\fR for

each of the image's instances.

\fIdeleteProc\fR must match the following prototype:

.CS

typedef void Tk_ImageDeleteProc(

        ClientData \fImasterData\fR);

.CE

The \fImasterData\fR argument will be the same as the value

stored in \fI*masterDataPtr\fR by \fIcreateProc\fR when the

image was created.

\fIdeleteProc\fR should release any resources associated with

the image.

.SH TK_GETIMAGEMASTERDATA

.VS

.PP

The procedure \fBTk_GetImageMasterData\fR may be invoked to retrieve

information about an image.  For example, an image manager can use this

procedure to locate its image master data for an image.

If there exists an image named \fIname\fR

in the interpreter given by \fIinterp\fR, then \fI*typePtrPtr\fR is

filled in with type information for the image (the \fItypePtr\fR value

passed to \fBTk_CreateImageType\fR when the image type was registered)

and the return value is the ClientData value returned by the

\fIcreateProc\fR when the image was created (this is typically a

pointer to the image master data structure).  If no such image exists

then NULL is returned and NULL is stored at \fI*typePtrPtr\fR.

.VE

.SH "SEE ALSO"

Tk_ImageChanged, Tk_GetImage, Tk_FreeImage, Tk_RedrawImage, Tk_SizeOfImage

.SH KEYWORDS

image manager, image type, instance, master