Docs 4.3

Notes/improving-deflate-compression-ratio.md

@@ -1,6 +1,6 @@
-# Improving *deflate* compression ratios
+# Improving DEFLATE compression ratios
 
-Version 4 of Swift *PNG* features a native Swift implementation of the *DEFLATE* and *INFLATE* algorithms, as described in the [rfc-1951](https://tools.ietf.org/html/rfc1951). *DEFLATE* implementations can vary widely in quality, with some implementations producing far better-optimized (higher compression ratio) output streams than others. So, just as it is important to ensure Swift *PNG*’s *INFLATE* procedure [is as fast as that of the *zlib* C library](../low-level-swift-optimization.md), it is also important to ensure Swift *PNG*’s *DEFLATE* output is as optimal as *zlib*’s. This readme documents some comparisons between Swift *PNG* and *libpng*/*zlib*, as well as choices of compression parameters in the framework at the time of writing.
+Version 4 of Swift *PNG* features a native Swift implementation of the *DEFLATE* and *INFLATE* algorithms, as described in the [rfc-1951](https://tools.ietf.org/html/rfc1951). *DEFLATE* implementations can vary widely in quality, with some implementations producing far better-optimized (higher compression ratio) output streams than others. So, just as it is important to ensure Swift *PNG*’s *INFLATE* procedure [is as fast as that of the *zlib* C library](https://swiftinit.org/articles/low-level-swift-optimization), it is also important to ensure Swift *PNG*’s *DEFLATE* output is as optimal as *zlib*’s. This readme documents some comparisons between Swift *PNG* and *libpng*/*zlib*, as well as choices of compression parameters in the framework at the time of writing.
 
 ## Methodology
 

README.md

@@ -13,34 +13,19 @@
 
 *Swift PNG* is a Foundation-less, cross-platform framework for decoding, inspecting, editing, and encoding PNG images. The framework is written in pure Swift, and will compile and provide consistent behavior on all Swift platforms. The library also comes with built-in file system support on linux, macOS, and Windows.
 
-Swift *PNG* is [available](LICENSE) under the [Mozilla Public License 2.0](https://www.mozilla.org/en-US/MPL/2.0/). The [example programs](examples/) are public domain and can be adapted freely.
+Swift *PNG* is [available](LICENSE) under the [Mozilla Public License 2.0](https://www.mozilla.org/en-US/MPL/2.0/). The [example programs](Snippets/) are public domain and can be adapted freely.
 
-## [tutorials and example programs](examples/)
+Swift *PNG*’s [documentation](https://swiftinit.org/docs/swift-png/png) is available on Swiftinit!
 
-1. [basic decoding](Snippets/BasicDecoding.swift) ([sources](Snippets/BasicDecoding.swift))
-2. [basic encoding](Snippets/BasicEncoding.swift) ([sources](Snippets/BasicEncoding.swift))
-3. [using indexed images](Snippets/Indexing.swift) ([sources](Snippets/Indexing.swift))
-4. [using iphone-optimized images](Snippets/iPhoneOptimized.swift) ([sources](Snippets/iPhoneOptimized.swift))
-5. [working with metadata](Snippets/ImageMetadata.swift) ([sources](Snippets/ImageMetadata.swift))
-6. [using in-memory images](Snippets/ImagesInMemory.swift) ([sources](Snippets/ImagesInMemory.swift))
-7. [online decoding](Snippets/OnlineDecoding.swift) ([sources](Snippets/OnlineDecoding.swift))
-8. [custom color targets](Snippets/CustomColor.swift) ([sources](Snippets/CustomColor.swift))
-
-## [api reference](https://tayloraswift.github.io/swift-png)
-
-* [**`PNG.PNG`**](https://tayloraswift.github.io/swift-png/PNG)
-* [**`PNG.LZ77`**](https://tayloraswift.github.io/swift-png/LZ77)
-* [**`PNG.System`**](https://tayloraswift.github.io/swift-png/System)
-
-## getting started
+## Getting started
 
 To use *Swift PNG* in a project, add this descriptor to the `dependencies` list in your `Package.swift` file:
 
 ```swift
 .package(url: "https://github.com/tayloraswift/swift-png", .exact("4.0.3"))
 ```
 
-## basic usage
+## Basic usage
 
 Decode an image:
 
@@ -72,52 +57,24 @@ func encode(png path:String, size:(x:Int, y:Int), pixels:[PNG.RGBA<UInt8>]) thro
 }
 ```
 
-## features
-
-- ***Powerful interfaces.*** *Swift PNG*’s expressive, strongly-typed APIs make working with PNG images easy for beginners and advanced users alike. If your code compiles, you’re already most of the way there. Power users can take advantage of [custom indexing](examples/#using-indexed-images), [manual decoding workflows](examples/#online-decoding), and [user-defined color targets](examples/#custom-color-targets).
-
-- ***Superior compression***. *Swift PNG* supports minimum cost path-based [*DEFLATE*](https://tools.ietf.org/html/rfc1951) optimization, which is why it offers four additional compression levels beyond what [*libpng*](http://www.libpng.org/pub/png/libpng.html) supports. *Swift PNG* outperforms *libpng* at its highest compression setting by [significant margins](benchmarks#compression-level-13) for almost all types of input images.
-
-- ***Competitive performance.*** *Swift PNG* offers [competitive performance](benchmarks/) compared to *libpng*. On appropriate CPU architectures, the *Swift PNG* encoder makes use of [hardware-accelerated hash tables](https://engineering.fb.com/2019/04/25/developer-tools/f14/) for even greater performance.
-
-- ***Pure Swift, all the way down.*** *Swift PNG* is powered by its own, native Swift *DEFLATE* implementation. It depends only on other Foundation-less, pure-Swift libraries, and therefore does not need to link Foundation. This also means the core components of *Swift PNG* work on any platform that Swift itself works on, and that *Swift PNG*’s performance [improves as the Swift compiler matures](benchmarks#performance-by-toolchain).
-
-- ***Batteries included.*** *Swift PNG* comes with [built-in color targets](https://tayloraswift.github.io/swift-png/PNG/Color/) with support for [premultiplied alpha](https://tayloraswift.github.io/swift-png/PNG/RGBA/premultiplied/). [Convolution](https://tayloraswift.github.io/swift-png/PNG/convolve(_:dereference:kernel:)/) and [deconvolution](https://tayloraswift.github.io/swift-png/PNG/deconvolve(_:reference:kernel:)/) helper functions make [implementing custom color targets](examples/#custom-color-targets) a breeze.
+## Features
 
-    On MacOS and Linux, *Swift PNG* has built-in file system support, allowing you to [compress](https://tayloraswift.github.io/swift-png/PNG/Image/compress(path:level:hint:)/) or [decompress](https://tayloraswift.github.io/swift-png/PNG/Image/decompress(path:)/) an image, given a filepath, in a single function call. Other platforms can take advantage of *Swift PNG*’s [protocol-oriented IO](https://tayloraswift.github.io/swift-png/PNG/Bytestream/) to implement their own data loading.
+- ***Powerful interfaces.*** *Swift PNG*’s expressive, strongly-typed APIs make working with PNG images easy for beginners and advanced users alike. If your code compiles, you’re already most of the way there. Power users can take advantage of [custom indexing](https://swiftinit.org/docs/swift-png/png/indexing), [manual decoding workflows](https://swiftinit.org/docs/swift-png/png/onlinedecoding), and [user-defined color targets](https://swiftinit.org/docs/swift-png/png/customcolor).
 
-- ***First-class iPhone optimization support.*** *Swift PNG* requires no custom setup or third-party plugins to handle [iPhone-optimized](examples/#using-iphone-optimized-images) PNG images. iPhone-optimized images just work, on all platforms. Reproduce [`pngcrush`](https://developer.apple.com/library/archive/qa/qa1681/_index.html)’s output with [bit width-aware alpha premultiplication](https://tayloraswift.github.io/swift-png/PNG/RGBA/premultiplied(as:)/), for seamless integration anywhere in your application stack.
+- ***Superior compression***. *Swift PNG* supports minimum cost path-based [*DEFLATE*](https://tools.ietf.org/html/rfc1951) optimization, which is why it offers four additional compression levels beyond what [*libpng*](http://www.libpng.org/pub/png/libpng.html) supports.
 
-- ***Comprehensive metadata support.*** *Swift PNG* can parse and validate all public PNG chunks, which are accessible as [strongly-typed metadata records](https://tayloraswift.github.io/swift-png/PNG/Metadata/).
+- ***Competitive performance.*** *Swift PNG* offers competitive performance compared to *libpng*. On appropriate CPU architectures, the *Swift PNG* encoder makes use of [hardware-accelerated hash tables](https://engineering.fb.com/2019/04/25/developer-tools/f14/) for even greater performance.
 
-- ***Modern error handling.*** *Swift PNG* has a fully stateless and Swift-native [error-handling system](https://tayloraswift.github.io/swift-png/PNG/Error/).
+- ***Pure Swift, all the way down.*** *Swift PNG* is powered by its own, native Swift *DEFLATE* implementation. It depends only on other Foundation-less, pure-Swift libraries, and therefore does not need to link Foundation. This also means the core components of *Swift PNG* work on any platform that Swift itself works on, and that *Swift PNG*’s performance improves as the Swift compiler matures.
 
-## infrastructure
+- ***Batteries included.*** *Swift PNG* comes with [built-in color targets](https://swiftinit.org/ptcl/swift-png/png/_pngcolor) with support for [premultiplied alpha](https://swiftinit.org/docs/swift-png/png/png/rgba.premultiplied). [Convolution](https://swiftinit.org/docs/swift-png/png/png.convolve(_:dereference:kernel:)?hash=O92V) and [deconvolution](https://swiftinit.org/docs/swift-png/png/png.deconvolve(_:as:depth:kernel:)?hash=2SQA0) helper functions make [implementing custom color targets](https://swiftinit.org/docs/swift-png/png/customcolor) a breeze.
 
-A list of build flags can be found [here](build.md). Project automation scripts live in the [`utils/`](utils/) directory, and are invoked as follows:
+- ***First-class iPhone optimization support.*** *Swift PNG* requires no custom setup or third-party plugins to handle [iPhone-optimized](https://swiftinit.org/docs/swift-png/png/iphoneoptimized) PNG images. iPhone-optimized images just work, on all platforms. Reproduce [`pngcrush`](https://developer.apple.com/library/archive/qa/qa1681/_index.html)’s output with [bit width-aware alpha premultiplication](https://swiftinit.org/docs/swift-png/png/png/rgba.premultiplied(as:)), for seamless integration anywhere in your application stack.
 
-- [**`utils/examples`**](utils/examples) `[-c/--configuration debug | release]`
+- ***Comprehensive metadata support.*** *Swift PNG* can parse and validate all public PNG chunks, which are accessible as [strongly-typed metadata records](https://swiftinit.org/docs/swift-png/png/png/metadata).
 
-    Builds and runs the example programs in the [`examples/`](examples/) directory. The `--configuration` argument specifies the Swift build mode to use.
-
-- [**`utils/benchmark`**](utils/benchmark) `[-t/--trials n0 n1 n2]` `[-s/--save]` `[-l/--load]`
-
-    Runs library performance and compression benchmarks, and generates a [performance report](benchmarks/).
-
-    The `--trials` argument specifies the number of trials to run, for decompression, compression, and historical toolchain benchmarks, respectively. The `--save` argument makes this script store benchmark measurements in cache files; the `--load` argument makes this script use cached measurements instead of re-running the benchmarks.
-
-- [**`utils/generate-documentation`**](utils/generate-documentation) `[-l/--local]`
-
-    Generates documentation pages for the library using [*Entrapta*](https://github.com/tayloraswift/entrapta). A [Github action](.github/workflows/docs.yml) invokes this script and deploys the output to the [*Swift PNG* API reference website](https://tayloraswift.github.io/swift-png) on every commit.
-
-The CI [runs](.github/workflows/build.yml) *Swift PNG*’s test suites with the following invocations:
-
-```bash
-swift run            PNGTests
-swift run -c release PNGIntegrationTests
-swift run -c release PNGCompressionTests
-```
+- ***Modern error handling.*** *Swift PNG* has a fully stateless and Swift-native [error-handling system](https://swiftinit.org/docs/swift-png/png/png/error).
 
-## see also
+## See also
 
 * [Swift *JPEG*](https://github.com/tayloraswift/jpeg)

Snippets/PNG/BasicEncoding.swift

@@ -1,6 +1,10 @@
+//  In this example code, we have loaded pixel data from a raw `.rgba` data file using the
+//  library’s [file system APIs](/PNG/System/File). As previously mentioned, these APIs are only
+//  available on MacOS and Linux.
+
+//  snippet.LOAD_RGBA
 import PNG
 
-/// https://commons.wikimedia.org/wiki/File:Photo_of_a_venetian_mask_in_a_studio_photo_session.jpg
 let path:String = "Sources/PNG/docs.docc/BasicEncoding/BasicEncoding"
 let size:(x:Int, y:Int) = (638, 425)
 
@@ -25,28 +29,38 @@ else
     fatalError("failed to open file '\(path).rgba'")
 }
 
+//  snippet.LAYOUT
+
 let layout:(rgb:PNG.Layout, v:PNG.Layout) =
 (
     rgb:    .init(format: .rgb8(palette: [], fill: nil, key: nil)),
     v:      .init(format:   .v8(             fill: nil, key: nil))
 )
 
+//  snippet.end
+
 do
 {
+    //  snippet.PACK_RGB
     let image:PNG.Image  = .init(packing: rgba, size: size, layout: layout.rgb)
+    //  snippet.COMPRESS_RGB
     try image.compress(path: "\(path)-color-rgb.png", level: 9)
-
+    //  snippet.COMPRESS_RGB_LEVELS
     for level:Int in [0, 4, 8, 13]
     {
         try image.compress(path: "\(path)-color-rgb@\(level).png", level: level)
     }
+    //  snippet.end
 }
 do
 {
+    //  snippet.SAVE_V
     let image:PNG.Image  = .init(packing: rgba, size: size, layout: layout.v)
     try image.compress(path: "\(path)-color-v.png", level: 9)
+    //  snippet.end
 }
 
+//  snippet.COMPUTE_LUMINANCE
 let luminance:[UInt8] = rgba.map
 {
     let r:Double = .init($0.r),
@@ -57,11 +71,15 @@ let luminance:[UInt8] = rgba.map
 }
 do
 {
+    //  snippet.SAVE_V_LUMINANCE
     let image:PNG.Image  = .init(packing: luminance, size: size, layout: layout.v)
     try image.compress(path: "\(path)-luminance-v.png", level: 9)
+    //  snippet.end
 }
 do
 {
+    //  snippet.SAVE_RGB_LUMINANCE
     let image:PNG.Image  = .init(packing: luminance, size: size, layout: layout.rgb)
     try image.compress(path: "\(path)-luminance-rgb.png", level: 9)
+    //  snippet.end
 }

Snippets/PNG/CustomColor.swift

@@ -1,23 +1,21 @@
 import PNG
 
-/// https://commons.wikimedia.org/wiki/File:Alice-in-Wonderland_by-David-Revoy_2010-07-21.jpg
-let path:String = "Sources/PNG/docs.docc/CustomColor/CustomColor"
-
+//  snippet.HSVA_TYPE
 struct HSVA
 {
     var h:UInt32
     var s:UInt16
     var v:UInt8
     var a:UInt8
-
+    //  snippet.end
     init(h:UInt32, s:UInt16, v:UInt8, a:UInt8)
     {
         self.h = h
         self.s = s
         self.v = v
         self.a = a
     }
-
+    //  snippet.HSVA_CONVERT_FROM_RGBA
     init(r:UInt8, g:UInt8, b:UInt8, a:UInt8)
     {
         let sorted:(min:UInt8, mid:UInt8, max:UInt8)
@@ -49,7 +47,7 @@ struct HSVA
         self.v = sorted.max
         self.a = a
     }
-
+    //  snippet.HSVA_CONVERT_TO_RGBA
     var rgba:PNG.RGBA<UInt8>
     {
         guard self.s > 0, self.v > 0
@@ -78,8 +76,9 @@ struct HSVA
         default: fatalError("unreachable")
         }
     }
+    //  snippet.end
 }
-
+//  snippet.HSVA_CONFORMANCE_SIGNATURES
 extension HSVA:PNG.Color
 {
     typealias Aggregate = (UInt8, UInt8, UInt8, UInt8)
@@ -89,6 +88,7 @@ extension HSVA:PNG.Color
         of format:PNG.Format,
         deindexer:([(r:UInt8, g:UInt8, b:UInt8, a:UInt8)]) -> (Int) -> Aggregate) -> [Self]
     {
+        //  snippet.HSVA_CONFORMANCE_INDEXED
         let depth:Int = format.pixel.depth
         switch format
         {
@@ -101,7 +101,7 @@ extension HSVA:PNG.Color
                 (c:(UInt8, UInt8, UInt8, UInt8)) in
                 .init(r: c.0, g: c.1, b: c.2, a: c.3)
             }
-
+        //  snippet.HSVA_CONFORMANCE_V
         case    .v1(fill: _, key: nil),
                 .v2(fill: _, key: nil),
                 .v4(fill: _, key: nil),
@@ -117,6 +117,7 @@ extension HSVA:PNG.Color
                 (v:UInt8, _) in
                 .init(h: 0, s: 0, v: v, a: .max)
             }
+        //  snippet.HSVA_CONFORMANCE_V_KEYED
         case    .v1(fill: _, key: let key?),
                 .v2(fill: _, key: let key?),
                 .v4(fill: _, key: let key?),
@@ -133,6 +134,7 @@ extension HSVA:PNG.Color
                 .init(h: 0, s: 0, v: v, a: k == key ? .min : .max)
             }
 
+        //  snippet.HSVA_CONFORMANCE_REST
         case    .va8(fill: _):
             return PNG.convolve(interleaved, of: UInt8.self, depth: depth)
             {
@@ -204,8 +206,10 @@ extension HSVA:PNG.Color
                 .init(r: c.0, g: c.1, b: c.2, a: c.3)
             }
         }
+        //  snippet.end
     }
 
+    //  snippet.HSVA_CONFORMANCE_PACK
     static
     func pack(_ pixels:[Self],
         as format:PNG.Format,
@@ -293,8 +297,12 @@ extension HSVA:PNG.Color
             }
         }
     }
+    //  snippet.end
 }
 
+//  snippet.LOAD_EXAMPLE
+let path:String = "Sources/PNG/docs.docc/CustomColor/CustomColor"
+
 guard
 let image:PNG.Image = try .decompress(path: "\(path).png")
 else
@@ -304,27 +312,28 @@ else
 
 let hsva:[HSVA] = image.unpack(as: HSVA.self)
 
+//  snippet.SAVE_HUE
 let hue:PNG.Image = .init(
     packing: hsva.map{ HSVA.init(h: $0.h, s: .max / 2, v: .max, a: $0.a) },
     size: image.size,
     layout: image.layout,
     metadata: image.metadata)
 try hue.compress(path: "\(path)-hue.png")
-
+//  snippet.SAVE_SATURATION
 let saturation:PNG.Image = .init(
     packing: hsva.map{ HSVA.init(h: 370000, s: $0.s, v: .max, a: $0.a) },
     size: image.size,
     layout: image.layout,
     metadata: image.metadata)
 try saturation.compress(path: "\(path)-saturation.png")
-
+//  snippet.SAVE_VALUE
 let value:PNG.Image = .init(
     packing: hsva.map{ HSVA.init(h: 0, s: 0, v: $0.v, a: $0.a) },
     size: image.size,
     layout: image.layout,
     metadata: image.metadata)
 try value.compress(path: "\(path)-value.png")
-
+//  snippet.SAVE_EXAMPLE
 let new:PNG.Image = .init(packing: hsva,
     size: image.size,
     layout: image.layout,

Snippets/PNG/ImageMetadata.swift

@@ -1,6 +1,8 @@
+//
+
+//  snippet.LOAD_EXAMPLE
 import PNG
 
-/// https://commons.wikimedia.org/wiki/File:Coat_of_arms_of_Siam.svg
 let path:String = "Sources/PNG/docs.docc/ImageMetadata/ImageMetadata"
 
 guard
@@ -10,6 +12,7 @@ else
     fatalError("failed to open file '\(path).png'")
 }
 
+//  snippet.INSPECT_CHUNKS
 if  let time:PNG.TimeModified = image.metadata.time
 {
     print(time)
@@ -23,13 +26,15 @@ if  let physicalDimensions:PNG.PhysicalDimensions = image.metadata.physicalDimen
     print(physicalDimensions)
 }
 
-//print(image.metadata)
+//  snippet.PRINT_CHUNKS
+print(image.metadata)
 
+//  snippet.MODIFY_CHUNKS
 image.metadata.time = .init(year: 1992, month: 8, day: 3, hour: 0, minute: 0, second: 0)
 
+//  snippet.SAVE_EXAMPLE
 try image.compress(path: "\(path)-newtime.png")
 
-
 if  let image:PNG.Image = try .decompress(path: "\(path)-newtime.png"),
     let time:PNG.TimeModified = image.metadata.time ?? nil
 {