[graphics] add CGContext extensions

Package.resolved

@@ -6,7 +6,7 @@
       "location" : "https://github.com/honghaoz/ChouTi",
       "state" : {
         "branch" : "develop",
-        "revision" : "db4e47dbe69db57806049b7a99284809a03b573a"
+        "revision" : "43251518cd40350ffa0ac60c3a14c1e5cf0b9858"
       }
     }
   ],

Project.xcworkspace/xcshareddata/swiftpm/Package.resolved

@@ -6,7 +6,7 @@
       "location" : "https://github.com/honghaoz/ChouTi",
       "state" : {
         "branch" : "develop",
-        "revision" : "db4e47dbe69db57806049b7a99284809a03b573a"
+        "revision" : "43251518cd40350ffa0ac60c3a14c1e5cf0b9858"
       }
     }
   ],

Sources/ChouTiUI/Universal/CoreGraphics/CGContext+Extensions.swift

@@ -0,0 +1,113 @@
+//
+//  CGContext+Extensions.swift
+//  ChouTiUI
+//
+//  Created by Honghao Zhang on 1/14/22.
+//  Copyright © 2020 Honghao Zhang.
+//
+//  MIT License
+//
+//  Copyright (c) 2020 Honghao Zhang (github.com/honghaoz)
+//
+//  Permission is hereby granted, free of charge, to any person obtaining a copy
+//  of this software and associated documentation files (the "Software"), to
+//  deal in the Software without restriction, including without limitation the
+//  rights to use, copy, modify, merge, publish, distribute, sublicense, and/or
+//  sell copies of the Software, and to permit persons to whom the Software is
+//  furnished to do so, subject to the following conditions:
+//
+//  The above copyright notice and this permission notice shall be included in
+//  all copies or substantial portions of the Software.
+//
+//  THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+//  IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+//  FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+//  AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+//  LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
+//  FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS
+//  IN THE SOFTWARE.
+//
+
+#if canImport(AppKit)
+import AppKit
+#endif
+
+#if canImport(UIKit)
+import UIKit
+#endif
+
+import CoreGraphics
+
+public extension CGContext {
+
+  /// Returns the current drawing context.
+  @inlinable
+  @inline(__always)
+  static var current: CGContext? {
+    #if os(macOS)
+    return NSGraphicsContext.current?.cgContext
+    #else
+    return UIGraphicsGetCurrentContext()
+    #endif
+
+    /// https://github.com/shaps80/GraphicsRenderer/blob/master/GraphicsRenderer/Classes/Platforms.swift
+  }
+
+  /// Flips the context's coordinate system vertically.
+  ///
+  /// - Parameter height: The height of the context to flip.
+  func flipCoordinatesVertically(height: CGFloat) {
+    translateBy(x: 0.0, y: height)
+    scaleBy(x: 1.0, y: -1.0)
+
+    /// https://stackoverflow.com/questions/506622/cgcontextdrawimage-draws-image-upside-down-when-passed-uiimage-cgimage
+    ///
+    /// Useful when drawing CGImage on context.
+  }
+
+  // Deprecated: The below implementation is not reliable.
+  //
+  /// Get the height of the context.
+  // private func getContextHeight() -> CGFloat {
+  //   let contextHeight = self.height
+  //   if contextHeight > 0 {
+  //     return CGFloat(contextHeight)
+  //   } else {
+  //     // got zero height, the context is not a bitmap context
+  //     // fallback to use the clip path to get the height
+  //     saveGState()
+  //
+  //     resetClip()
+  //     let height = boundingBoxOfClipPath.size.height
+  //
+  //     restoreGState()
+  //
+  //     return height
+  //   }
+  // }
+
+  /// Executes drawing operations within a saved graphics state.
+  ///
+  /// Example:
+  /// ```swift
+  /// context.onPushedGraphicsState { context in
+  ///   context.setFillColor(UIColor.red.cgColor)
+  ///   context.fill(CGRect(x: 0, y: 0, width: 100, height: 100))
+  /// }
+  /// ```
+  ///
+  /// - Parameter draw: A closure that performs drawing operations on the context.
+  @inlinable
+  @inline(__always)
+  func onPushedGraphicsState(_ draw: (_ context: CGContext) throws -> Void) rethrows {
+    saveGState()
+    try draw(self)
+    restoreGState()
+  }
+}
+
+/// NSView Drawing Issue on macOS Big Sur.md
+/// https://gist.github.com/lukaskubanek/9a61ac71dc0db8bb04db2028f2635779
+
+/// Cocoa Drawing Guide
+/// https://developer.apple.com/library/archive/documentation/Cocoa/Conceptual/CocoaDrawingGuide/Introduction/Introduction.html#//apple_ref/doc/uid/TP40003290-CH201-SW1