FIX: Image.renderText() in Xcode 12 beta 5

Sources/SwiftGD/Image.swift

@@ -118,21 +118,28 @@ public class Image {
     public func renderText(
         _ text: String, from: Point, fontList: [String], color: Color, size: Double, angle: Angle = .zero
     ) -> (upperLeft: Point, upperRight: Point, lowerRight: Point, lowerLeft: Point) {
+        /// Notes on `gdImageStringFT`:
+        /// - it returns an Tuple of empty `Point`s if there is nothing to render or no valid fonts
+        /// - `gdImageStringFT` accepts a semicolon delimited list of fonts.
+        /// - `gdImageStringFT` expects pointers to `text` and `fontList` values
+        guard !text.isEmpty,
+              !fontList.isEmpty,
+              var textCChar = text.cString(using: .utf8),
+              var joinedFonts = fontList.joined(separator: ";").cString(using: .utf8) else {
+                  return (upperLeft: .zero, upperRight: .zero, lowerRight: .zero, lowerLeft: .zero)
+        }
         let red = Int32(color.redComponent * 255.0)
         let green = Int32(color.greenComponent * 255.0)
         let blue = Int32(color.blueComponent * 255.0)
         let alpha = 127 - Int32(color.alphaComponent * 127.0)
         let internalColor = gdImageColorAllocateAlpha(internalImage, red, green, blue, alpha)
         defer { gdImageColorDeallocate(internalImage, internalColor) }
 
-        // `gdImageStringFT` accepts a semicolon delimited list of fonts.
-        let fontList = fontList.joined(separator: ";")
-
         // `gdImageStringFT` returns the text bounding box, specified as four
         // points in the following order:
-        // lower left, lower right, upper right, and upper left corner.
+        // upper left, upper right, lower right, and lower left corner.
         var boundingBox: [Int32] = .init(repeating: .zero, count: 8)
-        gdImageStringFT(internalImage, &boundingBox, internalColor, fontList, size, -angle.radians, Int32(from.x), Int32(from.y), text)
+        gdImageStringFT(internalImage, &boundingBox, internalColor, &joinedFonts, size, -angle.radians, Int32(from.x), Int32(from.y), &textCChar)
 
         let lowerLeft = Point(x: boundingBox[0], y: boundingBox[1])
         let lowerRight = Point(x: boundingBox[2], y: boundingBox[3])

Tests/SwiftGDTests/ImageTests.swift

@@ -0,0 +1,67 @@
+import XCTest
+@testable import SwiftGD
+
+class TestImage: XCTestCase {
+    /// Trying to create a list that *should* have at least
+    /// one font for most Swift-compatible platforms.
+    /// NOTE: Tests might fail on platforms that don’t have
+    /// one of these fonts installed. E.g.: Docker images
+    internal static let fontList = [
+        "SFCompact",
+        "ArialMT",
+        "Arial",
+        "Roboto",
+        "Ubuntu",
+        "Noto",
+        "Noto Sans",
+        "SSTPro-Roman"
+    ]
+
+    func testRenderText() throws {
+        guard let image = Image(width: 640, height: 480) else {
+            throw Error.invalidImage(reason: "Could not initialize image")
+        }
+        let basepoint = Point(x: 320, y: 240)
+        let renderBounds = image.renderText(
+            "SwiftGD",
+            from: basepoint,
+            fontList: Self.fontList,
+            color: .red,
+            size: 50,
+            angle: .degrees(-15)
+        )
+
+        XCTAssertFalse(try isEmptyBounds(for: renderBounds), "When text is rendered, it returns NON-zero Points")
+    }
+
+    func testRenderEmptyText() throws {
+        guard let image = Image(width: 640, height: 480) else {
+            throw Error.invalidImage(reason: "Could not initialize image")
+        }
+        let renderBounds = image.renderText("", from: .zero, fontList: ["Arial", "Ubuntu", "Roboto"], color: .black, size: 18.0)
+
+        XCTAssertTrue(try isEmptyBounds(for: renderBounds), "Empty `text` values return tuple of zero-value Points")
+    }
+
+    func testRenderEmptyFontList() throws {
+        guard let image = Image(width: 640, height: 480) else {
+            throw Error.invalidImage(reason: "Could not create image")
+        }
+        let renderBounds = image.renderText("Hello, World", from: .zero, fontList: [], color: .white, size: 18.0)
+
+        XCTAssertTrue(try isEmptyBounds(for: renderBounds), "Empty fontLists return tuple of zero-value Points")
+    }
+}
+
+extension TestImage {
+    private func isEmptyBounds(for resultValues: (upperLeft: Point, upperRight: Point, lowerRight: Point, lowerLeft: Point)) throws -> Bool {
+        return [
+            resultValues.upperLeft,
+            resultValues.upperRight,
+            resultValues.lowerRight,
+            resultValues.lowerLeft
+        ].allSatisfy {
+            $0 == .zero
+        }
+    }
+}