[cairo] JPEG support patch

[Vladimir Vukicevic]

Hmm.. there already is a surface_pattern, and surfaces can have 
arbitrary data attached to them.  It seems like the pdf backend can just 
check for some well-known compressed_data_key data to be set on the 
surface, that would be a struct that looks like:

struct compressed_image_data {
   char *type; // "image/jpeg"
   unsigned long data_length;
   unsigned char *data;
};

(or whatever -- maybe a getter function so that the data doesn't have to 
stay in memory, etc.)

If it finds one of those and recognizes the type, it can embed the image 
data directly.  I don't understand why doing this would require adding 
any API to cairo itself (other than the image data struct/global key) -- 
certainly there could be helper libraries that would simplify the image 
loading process, but other than that, it would just be a few changes to 
the PDF backend using already existing infrastructure...

     - Vlad

Bill Spitzak wrote:
> You are right, cairo would not require DevIL, only the image_pattern 
> types. Although if the pdf surface was able to recognize the jpeg 
> image_pattern, it may mean the pdf surface would end up depending on DevIL.
> 
> Even if this was done, I think cairo should be able to *write* a png 
> file without requiring DevIL, just libpng. But it may not be able to 
> read a png without it.
> 
> Vladimir Vukicevic wrote:
>> Bill Spitzak wrote:
>>> Actually DevIL is the library I was thinking of when I was trying to 
>>> make a proposal for a new cairo pattern t.
>>>
>>> Perhaps Cairo can just require DevIL.
>>
>> What purpose would there be to having Cairo require DevIL, rather than 
>> just having there be a middle layer shim library that can use DevIL to 
>> load data into cairo surfaces/cairo patterns?  There isn't anything 
>> preventing you from creating cairo_image_pattern_create() on top of 
>> existing public cairo APIs from another library.  I wouldn't call it 
>> cairo_ to avoid confusion, but something similar.
>>
>>    - Vlad
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