Check-in [4f351811b4]

The image create and file load functions recreate the metadata dict.
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.