Re: [PATCH 1/2] stkutil: convert img to xpm

[Denis Kenzior <denkenz@gmail.com>]

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Hi Kristen,

On 07/23/2010 04:39 PM, Kristen Carlson Accardi wrote:
> On Fri, 23 Jul 2010 16:03:16 -0500
> Denis Kenzior <denkenz@gmail.com> wrote:
> 
>> Hi Kristen,
>>
>> On 07/23/2010 03:52 PM, Kristen Carlson Accardi wrote:
>>> On Fri, 23 Jul 2010 15:03:59 -0500
>>> Denis Kenzior <denkenz@gmail.com> wrote:
>>>>
>>>> This also brings up another point.  You're assuming that the caller is
>>>> appending the CLUT right after the image data and massaging the clut
>>>> offset appropriately.  This is a really bad idea since the caller will
>>>> have to do some significant pre-processing.
>>>>
>>>> You can handle this in one of two ways:
>>>>
>>>> 1. Assume the calling logic will read the entire image file before
>>>> calling this function.  In this case, modifying the signature as follows
>>>> might be a good idea:
>>>>
>>>> char *stk_image_to_xpm(const unsigned char *file,
>>>> 			unsigned short file_len,
>>>> 			enum stk_img_scheme scheme,
>>>> 			unsigned short img_offset,
>>>> 			unsigned short img_len);
>>>>
>>>> 2. Assume the calling logic is clever and will optimize reading of the
>>>> file, including peeking into the image header to determine the where the
>>>> CLUT is located and reading it.  In this case you can either reuse the
>>>> signature from 1 above, or come up with something else.
>>>>
>>>> Remember, reading from the SIM is extremely slow, so any and all clever
>>>> optimization tricks are definitely wanted.
>>>
>>> So, is it likely given normal usage that we'll access an image a single
>>> image at a time, or is it more likely that we'll access a bunch of images
>>> all at once?  It may be better to read an entire image data file (with
>>> multiple images) and keep it cached if we are likely to immediately
>>> need the other images.  In which case I'd be inclined to just pass
>>> in the entire data image file and the offset like you have above.  If 
>>> we are only likely to use a single image for any given length of time,
>>> then it seems better to have the caller be smart and pass us the clut.
>>
>> The problem is we just don't know, so we have to assume the worst case.
>>  Anything that minimizes the number of reads is a good thing (TM).
>>
>> For instance, you might have couple of dozen images from EFimg dispersed
>> among multiple EFiidf files.  Each EFiidf file might be 65K in length,
>> but EFimg files might only refer to about 10k from all of them.
>>
>> It is perfectly OK for EFiidf to contain mostly garbage (e.g. for future
>> updates, installation of new SIM Toolkit applications on the SIM +
>> associated image data, etc)  So you simply can't assume any sort of
>> packing or efficient storage use.
>>
>> In this case, a clever algorithm that minimizes the number of SIM
>> fetches is needed.
>>
>> Regards,
>> -Denis
> 
> If that is the case then I propose we assume a smart algorithm fetched
> our data for us and change the signature to something like this:
> 
> unsigned char *stk_image_to_xpm(const unsigned char *image_body,
> 				enum stk_image_scheme scheme,
> 				unsigned int height,
> 				unsigned int width, unsigned int ncolors,
> 				const unsigned char *clut);
> 
> We would assume that the caller has done all the sanity checking on
> the file and handed us a clut of appropriate size as well.

You sure you want unsigned char * as the return and not char *?

Also, you might want to change unsigned ints to unsigned chars.  The
image size and CLUT size can never be more than 256.

Regards,
-Denis