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Merge pull request #17 from jangko/devel 

update readme.md
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# nimPNG
Portable Network Graphics Encoder and Decoder written in Nim store lossless image with good compression
# nimPNG (PNG + APNG)
Portable Network Graphics Encoder and Decoder written in Nim store lossless image with good compression.
Since version 0.2.0 also support Animated PNG!
[![Build Status][badge-nimpng-travisci]][nimpng-travisci]
@ -96,21 +97,32 @@ pixels are stored as raw bytes using Nim's string as container:
Since version 0.2.0, nimPNG provides support for [Animated PNG](https://wiki.mozilla.org/APNG_Specification).
Both decoder and encoder recognize/generate APNG chunks correctly: acTL, fcTL, fdAT.
Decoded frames is provided as is, the dimension and coordinate offset might be different with default frame.
No alpha blending or other blending method performed.
It is up to the application to do proper in-memory rendering before displaying the animation.
Don't ask how to do it, any decent graphics rendering library have their own set of API to do alpha blending and
offset rendering. In the future nimPNG might be shipped with simple frame rendering utility for common cases.
Right now nimPNG is just a PNG encoder/decoder.
### Decoding
```Nim
#let png = loadPNG32("image.png")
# or
#let png = loadPNG("image.png", LCT_RGBA, 8)
# or
#let png = decodePNG32(raw_bytes)
```
The usual loadPNG and decodePNG can decode both unanimated and animated PNG.
png.width, png.height, png.data works as usual. If the decoded PNG is an APNG, png.data will contains default frame.
Animation frames can be accessible via png.frames. If it is not an APNG, png.frames will be nil.
`png.width`, `png.height`, `png.data` works as usual. If the decoded PNG is an APNG, `png.data` will contains default frame.
Animation frames can be accessible via `png.frames`. If it is not an APNG, `png.frames` will be nil.
### Encoding
Under construction
[nimpng-travisci]: https://travis-ci.org/jangko/nimPNG
[badge-nimpng-travisci]: https://travis-ci.org/jangko/nimPNG.svg?branch=master