Added Surface.writePNG()

Sources/Cairo/SurfacePNG.swift

@@ -16,6 +16,22 @@ public extension Surface {
 
         cairo_surface_write_to_png(internalPointer, path)
     }
+
+    public func writePNG() throws -> Data {
+
+        let dataProvider = PNGDataProvider()
+
+        let unmanaged = Unmanaged.passUnretained(dataProvider)
+
+        let pointer = unmanaged.toOpaque()
+
+        if let error = cairo_surface_write_to_png_stream(internalPointer, pngWrite, pointer).toError() {
+
+            throw error
+        }
+
+        return dataProvider.data
+    }
 }
 
 public extension Surface.Image {
@@ -43,33 +59,40 @@ public extension Surface.Image {
 
 // MARK: - Supporting Types
 
-fileprivate extension Surface.Image {
+fileprivate extension Surface {
 
     final class PNGDataProvider {
 
-        let data: Data
-        private(set) var position: Int
+        private(set) var data: Data
+        private(set) var readPosition: Int = 0
 
-        init(data: Data) {
+        init(data: Data = Data()) {
             self.data = data
-            self.position = 0
         }
 
         @inline(__always)
         func copyBytes(to pointer: UnsafeMutablePointer<UInt8>, length: Int) -> cairo_status_t {
 
             var size = length
 
-            if (position + size) > data.count {
+            if (readPosition + size) > data.count {
 
-                size = data.count - position;
+                size = data.count - readPosition;
             }
 
-            let byteRange = Range<Data.Index>(position ..< position + size)
+            let byteRange = Range<Data.Index>(readPosition ..< readPosition + size)
 
             let _ = data.copyBytes(to: pointer, from: byteRange)
 
-            position += size
+            readPosition += size
+
+            return CAIRO_STATUS_SUCCESS
+        }
+
+        @inline(__always)
+        func copyBytes(from pointer: UnsafePointer<UInt8>, length: Int) -> cairo_status_t {
+
+            data.append(pointer, count: length)
 
             return CAIRO_STATUS_SUCCESS
         }
@@ -81,9 +104,19 @@ fileprivate extension Surface.Image {
 @_silgen_name("_cairo_swift_png_read_data")
 private func pngRead(_ closure: UnsafeMutableRawPointer?, _ data: UnsafeMutablePointer<UInt8>?, _ length: UInt32) -> cairo_status_t {
 
-    let unmanaged = Unmanaged<Surface.Image.PNGDataProvider>.fromOpaque(closure!)
+    let unmanaged = Unmanaged<Surface.PNGDataProvider>.fromOpaque(closure!)
 
     let dataProvider = unmanaged.takeUnretainedValue()
 
     return dataProvider.copyBytes(to: data!, length: Int(length))
 }
+
+@_silgen_name("_cairo_swift_png_write_data")
+private func pngWrite(_ closure: UnsafeMutableRawPointer?, _ data: UnsafePointer<UInt8>?, _ length: UInt32) -> cairo_status_t {
+
+    let unmanaged = Unmanaged<Surface.PNGDataProvider>.fromOpaque(closure!)
+
+    let dataProvider = unmanaged.takeUnretainedValue()
+
+    return dataProvider.copyBytes(from: data!, length: Int(length))
+}