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Comment:TIP529: worded next insights: property functions and new call functions
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SHA3-256: 5376cf14bcade356d5d24145567d55d2af5cdef96528b6b6a567d95985836811
User & Date: oehhar 2018-12-18 17:07:33.738
Context
2019-01-01
17:05
Added TIP 531, with apologies to Shannon Noe for taking so long to get this in check-in: 04c80b80d0 user: dkf tags: trunk
2018-12-18
17:07
TIP529: worded next insights: property functions and new call functions check-in: 5376cf14bc user: oehhar tags: trunk
2018-12-17
04:40
Added 530 to index.md check-in: f4f9d9861e user: leon tags: trunk
Changes
Unified Diff Ignore Whitespace Patch
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Any current contents is lost.

The write file commands uses any dict keys it knows.
Any unknown dict keys are ignored.

## C interface
















































Two new stub table functions are added:

    Tcl_Obj * Tk_PhotoGetMetadata(Tk_PhotoHandle handle)

    void Tk_PhotoSetMetadata(Tk_PhotoHandle handle, Tcl_Obj *metadata)

This works well for image read. The function "Tk_PhotoSetMetadata" is called within the image read function.

But it is not suitable for image write, as the required photo handle is not passed into the write functions:

    static int CommonWriteGIF(Tcl_Interp *interp,
            const char *fileName,
            WriteBytesFunc *writeProc,
            Tcl_Obj *format,
            Tk_PhotoImageBlock *blockPtr);

In consequence, the write function should be extended by the metadata object pointer.

# Implementation

The current implementation is only a sketch in my brain.
I hope, that an image handler can set the options after reading and a binary extension of the image handlers is not necessary.
Nevertheless, I don't know jet.

Any help and comments are appreciated.
I am realy a novice here.

Implementation may start soon with the tag tip-529-image-metadata.

# Rejected alternatives



# Copyright

This document has been placed in the public domain.








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Any current contents is lost.

The write file commands uses any dict keys it knows.
Any unknown dict keys are ignored.

## C interface

The current C interface for drivers and other programs is not sufficient to support the metadata dict.

A new extensible interface is envisaged with:

   *   a pair of functions to get or set all options of the image.
   *   a new driver interface to basically only pass the command.
   *   and a compatibility layer to the current driver interface

There are currently functions to access the raster data (Tk_PhotoGetImage, Tk_PhotoPutBlock).
The other properties (-file, -data, -format, -gamma) are not exposed.

A new interface may also be used for other image formats like svg where the image data consists of the rastered image, the image data and metadata.
In this case, an image save operation might even not use the raster data but only metadata and image data.

### image property get and set functions

Two new stub table functions are added:

    Tcl_Obj * Tk_PhotoGetOption(Tk_PhotoHandle handle, char *OptionName)

    void Tk_PhotoSetOption(Tk_PhotoHandle handle, char *OptionName, Tcl_Obj *optionValue)

### Revised image driver commands

The new command interface only passes the image handle. Any required data may be accquired by the get/set functions. Also, access to the raster data is done by the raster access functions.

The current registration function is
    Tk_CreatePhotoImageFormat()

...


# Implementation

The current implementation is only a sketch in my brain.
I hope, that an image handler can set the options after reading and a binary extension of the image handlers is not necessary.
Nevertheless, I don't know jet.

Any help and comments are appreciated.
I am realy a novice here.

Implementation may start soon with the tag tip-529-image-metadata.

# Rejected alternatives

## C interface: only use metadata dict get and set functions

Two new stub table functions are added:

    Tcl_Obj * Tk_PhotoGetMetadata(Tk_PhotoHandle handle)

    void Tk_PhotoSetMetadata(Tk_PhotoHandle handle, Tcl_Obj *metadata)

This works well for image read. The function "Tk_PhotoSetMetadata" is called within the image read function.

But it is not suitable for image write, as the required photo handle is not passed into the write functions:

    static int CommonWriteGIF(Tcl_Interp *interp,
            const char *fileName,
            WriteBytesFunc *writeProc,
            Tcl_Obj *format,
            Tk_PhotoImageBlock *blockPtr);

In consequence, the write function should be extended by the metadata object pointer.
















# Copyright

This document has been placed in the public domain.