drawGrid.swift

#!/usr/bin/swift

/*
 * Command line script that draws an evenly spaced grid over an image and labels each grid square.
 */

import Foundation

// Function to run a shell command and capture the output
func runShellCommand(_ command: String, printCommand: Bool) -> Int32 {
    
    if (printCommand) {
        print("RUNNING SHELL COMMAND:\n\(command)")
    }
    
    let process = Process()
    process.launchPath = "/bin/zsh"
    process.arguments = ["-c", command]

    let pipe = Pipe()
    process.standardOutput = pipe
    process.launch()

    _ = pipe.fileHandleForReading.readDataToEndOfFile()
    return process.terminationStatus
}

func A1Z26(_ digit: Int) -> String {
    guard digit >= 1 && digit <= 26 else {
        return "?"
    }
    let asciiValue = UInt8(digit - 1) + UInt8(Character("A").asciiValue!)
    return String(UnicodeScalar(asciiValue))
}

guard runShellCommand("which convert", printCommand: false) == 0 else {
    print("This script is dependent on the `convert` tool. You can install this by running `brew install imagemagick`.")
    exit(1)
}

guard CommandLine.arguments.count == 6 else {
    print("Usage: \(CommandLine.arguments[0]) <inputImagePath> <imageWidth> <imageHeight> <horizontalSlices> <verticalSlices>")
    exit(1)
}

let inputFileURL = URL(fileURLWithPath: CommandLine.arguments[1])
guard inputFileURL.isFileURL else {
    print("Invalid input file path.")
    exit(1)
}
guard let imageWidth = Int(CommandLine.arguments[2]), imageWidth > 0 else {
    print("Invalid image width.")
    exit(1)
}
guard let imageHeight = Int(CommandLine.arguments[3]), imageHeight > 0 else {
    print("Invalid image height.")
    exit(1)
}
guard let horizontalSlices = Int(CommandLine.arguments[4]), horizontalSlices > 0 else {
    print("Invalid horizontal slices.")
    exit(1)
}
guard let verticalSlices = Int(CommandLine.arguments[5]), verticalSlices > 0 else {
    print("Invalid vertical slices.")
    exit(1)
}

let outputFileNameWithSuffix = inputFileURL.deletingPathExtension().lastPathComponent + "_grid"
let outputFileURL = inputFileURL.deletingLastPathComponent().appendingPathComponent(outputFileNameWithSuffix).appendingPathExtension(inputFileURL.pathExtension)

let textSize = 24
var drawInstructions = ""
let horizontalSliceSize = Float(imageWidth) / Float(horizontalSlices)
let verticalSliceSize = Float(imageHeight) / Float(verticalSlices)
for i in 0..<horizontalSlices {
    let x = Int(horizontalSliceSize * Float(i))
    drawInstructions += "-draw 'line \(x),0 \(x),\(imageHeight)' "
    
    for j in 0..<verticalSlices {
        let y = Int(verticalSliceSize * Float(j))
        drawInstructions += "-draw \"text \(x),\(y+textSize) '\(A1Z26(j+1))\(i+1)'\" "
    }
}
for i in 1..<verticalSlices {
    let y = Int(verticalSliceSize * Float(i))
    drawInstructions += "-draw 'line 0,\(y) \(imageWidth),\(y)' "
}

_ = runShellCommand("convert \(inputFileURL.path) -fill none -stroke red -pointsize \(textSize) \(drawInstructions)\(outputFileURL.path)", printCommand: true)