byre/mac/Sources/Byre/Render.swift

import SwiftUI

#if os(macOS)
@MainActor
func renderDiagram(html: Bool) -> Int32 {
    FontSize.stored = false
    let source = String(decoding: FileHandle.standardInput.readDataToEndOfFile(), as: UTF8.self)
    let layout: BoxLayout
    switch cachedBoxLayout(source) {
    case .success(let l):
        layout = l
    case .failure(let error):
        FileHandle.standardError.write(Data(error.reason.utf8))
        return 1
    }
    if html {
        FileHandle.standardOutput.write(Data(diagramHTML(layout).utf8))
        return 0
    }
    guard let png = diagramCGImage(layout).flatMap({ NSBitmapImageRep(cgImage: $0).representation(using: .png, properties: [:]) }) else {
        FileHandle.standardError.write(Data("diagram didn't render".utf8))
        return 1
    }
    FileHandle.standardOutput.write(png)
    return 0
}
#endif

@MainActor
func diagramCGImage(_ layout: BoxLayout) -> CGImage? {
    let content = BoxCanvas(layout: layout)
        .frame(width: layout.size.width, height: layout.size.height)
        .padding(16)
        .background(Palette.bg)
        .environment(\.colorScheme, .light)
    let renderer = ImageRenderer(content: content)
    renderer.scale = 2
    var image: CGImage?
    #if os(macOS)
    NSAppearance(named: .aqua)!.performAsCurrentDrawingAppearance {
        image = renderer.cgImage
    }
    #else
    UITraitCollection(userInterfaceStyle: .light).performAsCurrent {
        image = renderer.cgImage
    }
    #endif
    return image
}