Add option to remove alpha channel from the generated image

Sources/SVGConverter/SVGConverter.swift

@@ -28,12 +28,18 @@ struct SVGConverter: AsyncParsableCommand {
     @Flag(name: .customLong("no-svg-fix"), help: "Set this to true if you do not want this tool to automatically add a viewBox attribute if it is possible. Without viewBox the svg cannot be resized, but it can still be converted at its natural size")
     var preventMissingViewBoxFix: Bool = false
 
+    @Flag(name: .customLong("no-alpha-channel"), help: "When present the generated image will not contain an alpha channel")
+    var withoutAlphaChannel: Bool = false
+
     @Flag(help: "Setting this to true prevent any output in standard error output")
     var quiet: Bool = false
 
     func run() async throws {
         let svgData = try Data(contentsOf: inputPath)
-        let configuration = SVGRenderer.Configuration(allowFixingMissingViewBox: !preventMissingViewBoxFix)
+        let configuration = SVGRenderer.Configuration(
+            allowFixingMissingViewBox: !preventMissingViewBoxFix,
+            removePNGAlphaChannel: withoutAlphaChannel
+        )
         let renderer = await SVGRenderer(
             configuration: configuration,
             warningHandler: quiet ? nil : logWarning

Sources/SVGConverterCore/Internal/Utils/CGImage+Utils.swift

@@ -0,0 +1,27 @@
+//
+//  CGImage+Utils.swift
+//
+//
+//  Created by Alexandre Podlewski on 07/04/2022.
+//
+
+import CoreGraphics
+
+extension CGImage {
+    func removingAlphaChannel() -> CGImage? {
+        let cgBitmapInfo = CGBitmapInfo(rawValue: CGImageAlphaInfo.noneSkipLast.rawValue)
+
+        let cgContext = CGContext(
+            data: nil,
+            width: width,
+            height: height,
+            bitsPerComponent: bitsPerComponent,
+            bytesPerRow: 0,
+            space: CGColorSpace(name: CGColorSpace.sRGB)!,
+            bitmapInfo: cgBitmapInfo.rawValue
+        )
+        cgContext?.draw(self, in: CGRect(origin: .zero, size: CGSize(width: width, height: height)))
+
+        return cgContext?.makeImage()
+    }
+}

Sources/SVGConverterCore/Internal/WebViewSVGRenderer.swift

@@ -20,6 +20,17 @@ private extension SVGRenderingWarnings {
 @available(macOS 10.15, *)
 final class WebViewSVGRenderer: WKWebView, WKNavigationDelegate {
 
+    // MARK: - Public structures
+
+    struct Options: OptionSet {
+        let rawValue: Int
+
+        /// This option stop the renderer to try adding a viewBox attribute to svg that are lacking of it. Without viewBox the renderer is unable to resize the svg image.
+        static let preventViewBoxFix = Options(rawValue: 1<<0)
+        /// Tells the renderer to remove the alpha channel from the PNG image data
+        static let removePNGAlphaChannel = Options(rawValue: 1<<1)
+    }
+
     // MARK: - Public typealias
 
     typealias WarningHandler = (SVGRenderingWarnings) -> Void
@@ -30,7 +41,7 @@ final class WebViewSVGRenderer: WKWebView, WKNavigationDelegate {
 
     // MARK: - Private Properties
 
-    private let allowFixingMissingViewBox: Bool
+    private let options: Options
     private var completion: ((Result<Data, Error>) -> Void)?
     private var isRendering = false
     private var inPixelSize: CGSize = .zero
@@ -41,16 +52,16 @@ final class WebViewSVGRenderer: WKWebView, WKNavigationDelegate {
     /// An SVG renderer using a WebView to render the SVG
     /// - Parameter allowFixingMissingViewBox: allow the renderer to try adding a viewBox attribute to svg that are lacking of it.
     /// Without viewBox the renderer is unable to resize the svg image.
-    init(allowFixingMissingViewBox: Bool = true) {
-        self.allowFixingMissingViewBox = allowFixingMissingViewBox
+    init(options: Options = []) {
+        self.options = options
         super.init(frame: .zero, configuration: WebViewSVGRenderer.rendererConfiguration)
         navigationDelegate = self
         setValue(false, forKey: "drawsBackground")
     }
 
     @available(*, unavailable)
     required init?(coder: NSCoder) {
-        self.allowFixingMissingViewBox = true
+        self.options = []
         fatalError("init(coder:) has not been implemented")
     }
 
@@ -130,7 +141,15 @@ final class WebViewSVGRenderer: WKWebView, WKNavigationDelegate {
                 else {
                     throw SVGRenderingError.cgImageConversionFailed
                 }
-                let rep = NSBitmapImageRep(cgImage: resizedCGImage)
+                let rep: NSBitmapImageRep
+                if self.options.contains(.removePNGAlphaChannel) {
+                    guard let transformedImage = resizedCGImage.removingAlphaChannel() else {
+                        throw SVGRenderingError.alphaChannelRemovalFailed
+                    }
+                    rep = NSBitmapImageRep(cgImage: transformedImage)
+                } else {
+                    rep = NSBitmapImageRep(cgImage: resizedCGImage)
+                }
                 rep.size = self.inPixelSize
                 guard let data = rep.representation(using: .png, properties: [:]) else {
                     throw SVGRenderingError.pngImageConversionFailed
@@ -155,7 +174,7 @@ final class WebViewSVGRenderer: WKWebView, WKNavigationDelegate {
 
         if svgElement.attribute(forName: "viewBox") == nil {
             if
-                allowFixingMissingViewBox,
+                !options.contains(.preventViewBoxFix),
                 let width = svgElement.attribute(forName: "width")?.stringValue.flatMap(Double.init),
                 let height = svgElement.attribute(forName: "height")?.stringValue.flatMap(Double.init)
             {

Sources/SVGConverterCore/SVGRenderer.swift

@@ -24,10 +24,17 @@ public final class SVGRenderer {
         /// When at true, if there is no viewBox attribute in the SVG and the svg has a width and an height, it will add a viewBox attribute with the value `"0 0 width height"`
         public var allowFixingMissingViewBox: Bool
 
+        /// When this is true the renderer will produce an image without alpha channel
+        public var removePNGAlphaChannel: Bool
+
         /// Create a configuration for SVGRenderer
         /// - Parameter allowFixingMissingViewBox: Controls wether or not the renderer will try to add viewBox attribute to SVG without one
-        public init(allowFixingMissingViewBox: Bool = true) {
+        public init(
+            allowFixingMissingViewBox: Bool = true,
+            removePNGAlphaChannel: Bool = false
+        ) {
             self.allowFixingMissingViewBox = allowFixingMissingViewBox
+            self.removePNGAlphaChannel = removePNGAlphaChannel
         }
     }
 
@@ -53,7 +60,15 @@ public final class SVGRenderer {
         configuration: Configuration = Configuration(),
         warningHandler: WarningHandler? = nil
     ) {
-        self.renderer = WebViewSVGRenderer(allowFixingMissingViewBox: configuration.allowFixingMissingViewBox)
+
+        var options: WebViewSVGRenderer.Options = []
+        if !configuration.allowFixingMissingViewBox {
+            options.insert(.preventViewBoxFix)
+        }
+        if configuration.removePNGAlphaChannel {
+            options.insert(.removePNGAlphaChannel)
+        }
+        self.renderer = WebViewSVGRenderer(options: options)
 
         self.warningHandler = warningHandler
         self.renderer.warningHandler = warningHandler

Sources/SVGConverterCore/SVGRenderingError.swift

@@ -11,6 +11,7 @@ public enum SVGRenderingError: Error {
     case renderingAlreadyInProgress
     case invalidSVGData
     case cgImageConversionFailed
+    case alphaChannelRemovalFailed
     case pngImageConversionFailed
     case invalidState
 }
@@ -27,6 +28,8 @@ public extension SVGRenderingError {
             return "The SVG data is malformed"
         case .cgImageConversionFailed:
             return "Internal error, conversion to cgImage failed"
+        case .alphaChannelRemovalFailed:
+            return "Internal error, failed to remove alpha channel from the generated image"
         case .pngImageConversionFailed:
             return "Internal error, getting png representation from cgImage failed"
         case .invalidState: