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digitalmars.D.learn - std.zlib odd behavior

reply solidstate1991 <laszloszeremi outlook.com> writes:
https://github.com/ZILtoid1991/dimage/blob/master/source/dimage/png.d

It seems that after a certain point, it doesn't add more data to 
the compression stream, flushing doesn't help.
Mar 04 2019
next sibling parent reply Adam D. Ruppe <destructionator gmail.com> writes:
On Tuesday, 5 March 2019 at 01:43:42 UTC, solidstate1991 wrote:

 https://github.com/ZILtoid1991/dimage/blob/master/source/dimage/png.d

 It seems that after a certain point, it doesn't add more data 
 to the compression stream, flushing doesn't help.


I haven't found the bug in your code yet, but one thing I suspect 
from my experience is you might be reusing a buffer. std.zlib 
actually stores pointers internally across function calls, so if 
you are trying to compress a stream, you are liable to get 
corruption.

(std.zlib is very bad code, frankly.)

I don't know for sure though, my brain is in the compiler 
tonight...
Mar 04 2019
parent reply solidstate1991 <laszloszeremi outlook.com> writes:
On Tuesday, 5 March 2019 at 02:19:26 UTC, Adam D. Ruppe wrote:

 I haven't found the bug in your code yet, but one thing I 
 suspect from my experience is you might be reusing a buffer. 
 std.zlib actually stores pointers internally across function 
 calls, so if you are trying to compress a stream, you are 
 liable to get corruption.

 (std.zlib is very bad code, frankly.)

 I don't know for sure though, my brain is in the compiler 
 tonight...


Thanks, it seems I'll have to write my own solution for this, and 
I really dislike the way streaming compression works in C. I've 
spotted some other bugs regarding my PNG implementation, but 
those were unrelated and didn't improve the compression issues.
Mar 05 2019
parent solidstate1991 <laszloszeremi outlook.com> writes:
On Wednesday, 6 March 2019 at 01:50:16 UTC, solidstate1991 wrote:

 Thanks, it seems I'll have to write my own solution for this, 
 and I really dislike the way streaming compression works in C. 
 I've spotted some other bugs regarding my PNG implementation, 
 but those were unrelated and didn't improve the compression 
 issues.


I was finally able to tame the beast, now I can load and save PNG 
files. Now I probably have issues with standardization, which 
will require me to read up on the topic, since my output isn't 
liked by IrfanView, and many other applications.
May 20 2019
prev sibling parent Kagamin <spam here.lot> writes:
On Tuesday, 5 March 2019 at 01:43:42 UTC, solidstate1991 wrote:

 https://github.com/ZILtoid1991/dimage/blob/master/source/dimage/png.d

 It seems that after a certain point, it doesn't add more data 
 to the compression stream, flushing doesn't help.


What do you mean by "doesn't add"?

ubyte[] slice = pos < imageData.length ? imageData[pos..(pos + 
pitch)] : imageData[pos..$];
This can't possibly work. You slice past the end of array.
Mar 05 2019