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docs: add sections on options [skip-ci]

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Randy 2022-02-02 07:15:25 +01:00
parent 30a94e6226
commit e47826e7d9
3 changed files with 40 additions and 2 deletions
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8
docs/context.md
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@ -107,6 +107,8 @@ enum spng_option
SPNG_TEXT_COMPRESSION_STRATEGY,
SPNG_FILTER_CHOICE,
SPNG_CHUNK_COUNT_LIMIT,
SPNG_ENCODE_TO_BUFFER,
};
```
@ -221,9 +223,13 @@ int spng_set_option(spng_ctx *ctx, enum spng_option option, int value)
Set `option` to the specified `value`.
For details see [Decode options](decode.md#decode-options) and [Encode options](encode.md#encode-options).
# spng_get_option()
```c
int spng_get_option(spng_ctx *ctx, enum spng_option option, int *value)
```
Get the value for the specified `option`.
Get the value for the specified `option`.
For details see [Decode options](decode.md#decode-options) and [Encode options](encode.md#encode-options).

12
docs/decode.md
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@ -300,3 +300,15 @@ For the last row and subsequent calls the return value is `SPNG_EOI`.
If the image is not interlaced this function's behavior is identical to
`spng_decode_scanline()`.
# Decode options
| Option | Default value | Description |
|------------------------------|---------------|----------------------------------------------------------|
| `SPNG_KEEP_UNKNOWN_CHUNKS` | `0` | Set to keep or discard unknown chunks |
| `SPNG_IMG_COMPRESSION_LEVEL` | `-1` | May expose an estimate (0-9) after `spng_decode_image()` |
| `SPNG_IMG_WINDOW_BITS` | `15`* | Set zlib window bits used for image decompression |
| `SPNG_CHUNK_COUNT_LIMIT` | `1000` | Limit shared by both known and unknown chunks |
\* Option may be optimized if not set explicitly.
Options not listed here have no effect on decoders.

22
docs/encode.md
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@ -87,7 +87,8 @@ the internal buffer is freed by [spng_ctx_free()](context.md#spng_ctx_free).
The alpha channel is always [straight alpha](https://en.wikipedia.org/wiki/Alpha_compositing#Straight_versus_premultiplied),
premultiplied alpha is not supported.
Compression level and other options can be customized with [`spng_set_option()`]([context.md#spng_set_option]).
Compression level and other options can be customized with [`spng_set_option()`](context.md#spng_set_option),
see [Encode options](encode.md#encode-options) for all options.
Note that encoder options are optimized based on PNG format and compression level,
overriding other options such as filtering may disable some of these optimizations.
@ -182,3 +183,22 @@ If `SPNG_ENCODE_TO_BUFFER` is enabled via [spng_set_option()](context.md#spng_se
it must be called after [spng_encode_image()](encode.md#spng_encode_image) and the PNG must be finalized.
On success the buffer must be freed by the user.
# Encode options
| Option | Default value | Description |
|----------------------------------|---------------------------|-----------------------------------|
| `SPNG_IMG_COMPRESSION_LEVEL` | `Z_DEFAULT_COMPRESSION` | Set image compression level (0-9) |
| `SPNG_IMG_WINDOW_BITS` | `15`* | Set image zlib window bits (9-15) |
| `SPNG_IMG_MEM_LEVEL` | `8` | Set zlib `memLevel` for images |
| `SPNG_IMG_COMPRESSION_STRATEGY` | `Z_FILTERED`* | Set image compression strategy |
| `SPNG_TEXT_COMPRESSION_LEVEL` | `Z_DEFAULT_COMPRESSION` | Set text compression level (0-9) |
| `SPNG_TEXT_WINDOW_BITS` | `15` | Set text zlib window bits (9-15) |
| `SPNG_TEXT_MEM_LEVEL` | `8` | Set zlib `memLevel` for text |
| `SPNG_TEXT_COMPRESSION_STRATEGY` | `Z_DEFAULT_STRATEGY` | Set text compression strategy |
| `SPNG_FILTER_CHOICE` | `SPNG_FILTER_CHOICE_ALL`* | Configure or disable filtering |
| `SPNG_ENCODE_TO_BUFFER` | `0` | Encode to internal buffer |
\* Option may be optimized if not set explicitly.
Options not listed here have no effect on encoders.