Add crystal native implementation of PNG support

BENCHMARKS.md

@@ -81,6 +81,8 @@ For these tests, with `template[n]`, `template = CrImage::OneMap.new(n, n)`
 | ------------------------------------ | -------- | ------- |
 |                              to_gray | 1.95ms   | 732kiB  |
 |               to_ppm(IO::Memory.new) | 6.9ms    | 4.01MiB |
+|libspng        to_png(IO::Memory.new) | 119.5ms  | 1.55MiB |
+|native crystal to_png(IO::Memory.new) | 117.86ms | 1.93MiB |
 |              to_jpeg(IO::Memory.new) | 10.24ms  | 1.2MiB  |
 |              to_webp(IO::Memory.new) | 213.93ms | 1.5MiB  |
 | to_webp(IO::Memory.new, lossy: true) | 38.07ms  | 1.45MiB |

README.md

@@ -25,16 +25,16 @@ All sample images used are from [Unsplash](https://unsplash.com/).
 CrImage supports the formats:
 * PPM
 * JPEG (requires `libturbojpeg`)
-* PNG (requirens `libspng`)
+* PNG (natively by default, or optionally through requires `libspng`)
 * WebP (requires `libwebp`)
 
 For the formats that require a linked library, they must be `require`d explicitly:
 
 ```crystal
 require "cr-image"
 require "cr-image/jpeg"
-require "cr-image/png"
 require "cr-image/webp"
+require "cr-image/png" # replaces native crystal with libspng
 
 # Or, alternatively
 require "cr-image/all_formats"

scripts/benchmark.cr

@@ -1,7 +1,8 @@
 #!/usr/bin/env -S crystal run --no-debug --release
 
 require "../src/cr-image"
-require "../src/all_formats"
+require "../src/webp"
+require "../src/jpeg"
 
 record Result, name : String, time : Float64, memory : Int64
 alias Color = CrImage::Color
@@ -156,6 +157,10 @@ results.clear
 
 results << benchmark { image.to_gray }
 results << benchmark { image.to_ppm(IO::Memory.new) }
+# NOTE: to get the benchmark for libspng, you need to:
+# require "../src/png"
+# Since the perf of both is so close, the default is for the native implementation
+results << benchmark { image.to_png(IO::Memory.new) }
 results << benchmark { image.to_jpeg(IO::Memory.new) }
 results << benchmark { image.to_webp(IO::Memory.new) }
 results << benchmark { image.to_webp(IO::Memory.new, lossy: true) }

shard.yml

@@ -4,6 +4,10 @@ version: 0.1.0
 authors:
   - Troy Sornson <[email protected]>
 
+dependencies:
+  png:
+    github: sleepinginsomniac/png
+
 development_dependencies:
   spectator:
     gitlab: arctic-fox/spectator

spec/cr-image/format/png_spec.cr

@@ -10,7 +10,7 @@ Spectator.describe CrImage::Format::PNG do
         io = IO::Memory.new
         image.to_png(io)
 
-        expect_digest(io.to_s).to eq "c9450089873a4bbe98a2aa54f1bea959915ba088"
+        expect_digest(io.to_s).to eq "8635306d7a0201533e8812ebf3671b9c2e31c4b0"
       end
     end
 
@@ -20,7 +20,7 @@ Spectator.describe CrImage::Format::PNG do
         io = IO::Memory.new
         image.to_png(io)
 
-        expect_digest(io.to_s).to eq "4cac53568704ac1617cd96313658559f22c1a24b"
+        expect_digest(io.to_s).to eq "4623c3074b418ca58a9c083297baa3fefaad8f1c"
       end
     end
   end

spec/spec_helper.cr

@@ -2,7 +2,6 @@ require "digest"
 require "spectator"
 require "../src/cr-image"
 require "../src/jpeg"
-require "../src/png"
 require "../src/webp"
 require "./helpers/**"
 

src/cr-image.cr

@@ -7,6 +7,7 @@ require "./cr-image/format/open"
 
 # Native crystal image format implementations
 require "./cr-image/format/ppm"
+require "./cr-image/format/png"
 
 # Require `image` first, and then subclasses of it
 require "./cr-image/image"

src/cr-image/format/png.cr

@@ -0,0 +1,82 @@
+require "png"
+
+# Provides methods to read from and write to PNG. Requires `libspng` to function.
+#
+# ```
+# image = File.open("image.png") { |file| CrImage::RGBAImage.from_png(file) }
+# File.open("other_image.png") { |file| image.to_png(file) }
+# ```
+# Alternatively, you can use the convenience methods in the `Open` and `Save` modules
+# to acheive the same thing:
+# ```
+# image = CrImage::RGBAImage.open("image.png")
+# image.save("other_image.png")
+# ```
+module CrImage::Format::PNG
+  {% CrImage::Format::SUPPORTED_FORMATS << {extension: ".png", method: "png"} %}
+
+  macro included
+    # Read `image_data` and PNG encoded bytes
+    def self.from_png(image_data : Bytes) : self
+      from_png(IO::Memory.new(image_data))
+    end
+
+    # Construct an Image by reading bytes from `io`
+    def self.from_png(io : IO) : self
+      png = ::PNG.read(io)
+
+      width = png.width.to_i32
+      height = png.height.to_i32
+
+      red = Array.new(width * height) { ChannelType::Red.default }
+      green = Array.new(width * height) { ChannelType::Green.default }
+      blue = Array.new(width * height) { ChannelType::Blue.default }
+      alpha = Array.new(width * height) { ChannelType::Alpha.default }
+
+      red_offset = 0
+      green_offset = 1
+      blue_offset = 2
+      alpha_offset = 3
+      jump = png.color_type.channels
+
+      case jump
+      when 1
+        red_offset = green_offset = blue_offset = 0
+        alpha_offset = -1
+      when 2
+        red_offset = green_offset = blue_offset = 0
+        alpha_offset = 1
+      when 3
+        alpha_offset = -1
+      end
+
+      (width * height).times do |index|
+        png.data[index * jump]
+        red.unsafe_put(index, png.data[index * jump + red_offset])
+        green.unsafe_put(index, png.data[index * jump + green_offset])
+        blue.unsafe_put(index, png.data[index * jump + blue_offset])
+        if alpha_offset > -1
+          alpha.unsafe_put(index, png.data[index * jump + alpha_offset])
+        end
+      end
+
+      new(red, green, blue, alpha, width, height)
+    end
+  end
+
+  # Output the image as PNG to `io`
+  def to_png(io : IO) : Nil
+    bytes = Bytes.new(size * 4)
+    idx = 0
+    (size * 4).times.step(4).each do |index|
+      bytes.unsafe_put(index, red[idx])
+      bytes.unsafe_put(index + 1, green[idx])
+      bytes.unsafe_put(index + 2, blue[idx])
+      bytes.unsafe_put(index + 3, alpha[idx])
+      idx += 1
+    end
+    canvas = ::PNG::Canvas.new(::PNG::Header.new(width.to_u32, height.to_u32, color_type: ::PNG::ColorType::TrueColorAlpha), bytes)
+
+    ::PNG.write(io, canvas)
+  end
+end

src/cr-image/image.cr

@@ -11,6 +11,7 @@ abstract class CrImage::Image
 
   macro inherited
     include Format::PPM
+    include Format::PNG
 
     include Operation::BilinearResize
     include Operation::BoxBlur