Enable loading fonts from file

Author: nicklockwood

Help/text.md

@@ -140,5 +140,23 @@ fill text "Hello World"
 
 **Note:** Some fonts are inherently much more detailed than others, and may take a considerable time to generate. You may need to set the [detail](options.md#detail) option to a lower value for text than you would for other geometry.
 
+The font name you provide must match a font that is already installed on your system. If no matching fonts are found then an error will be raised. If you wish to load a font file directly, without installing it, you can pass the filename or path to the `font` command instead of the font name:
+
+```swift
+font "filename.ttf"
+```
+
+Only fonts with a ".ttf", ".otf" or ".ttc" file extension are supported. The extension is required, or the `font` parameter will be treated as a system font rather than a file. If a relative path or filename is used, it should be specified relative to the ShapeScript file that references it.
+
+The filename can be constructed dynamically by using the [text interpolation](text.md#interpolation) feature, which is sometimes useful if, for example, you have multiple font files with a common prefix or suffix:
+
+```swift
+for n in 1 to 5 {
+    texture "font" n ".ttf"
+    text "Hello, World!"
+    translate 0 -1 0
+}
+```
+
 ---
 [Index](index.md) | Next: [Builders](builders.md)

ShapeScript/EvaluationContext.swift

@@ -214,6 +214,45 @@ extension EvaluationContext {
         return url
     }
 
+    func resolveFont(_ name: String?) throws -> String? {
+        guard let name = name?
+            .trimmingCharacters(in: .whitespacesAndNewlines)
+            .replacingOccurrences(of: "\t", with: " ")
+            .replacingOccurrences(of: "  ", with: " ")
+        else {
+            return nil
+        }
+        #if canImport(CoreGraphics)
+        guard [".otf", ".ttf", ".ttc"].contains(where: {
+            name.lowercased().hasSuffix($0)
+        }) else {
+            guard CGFont(name as CFString) != nil else {
+                var options = [String]()
+                #if canImport(CoreText)
+                options += CTFontManagerCopyAvailablePostScriptNames() as? [String] ?? []
+                options += CTFontManagerCopyAvailableFontFamilyNames() as? [String] ?? []
+                #endif
+                throw RuntimeErrorType.unknownFont(name, options: options)
+            }
+            return name
+        }
+        let url = try resolveURL(for: name)
+        guard let dataProvider = CGDataProvider(url: url as CFURL) else {
+            throw RuntimeErrorType.fileNotFound(for: name, at: url)
+        }
+        #if canImport(CoreText)
+        guard let cgFont = CGFont(dataProvider),
+              CTFontManagerRegisterGraphicsFont(cgFont, nil)
+        else {
+            throw RuntimeErrorType.fileParsingError(for: name, at: url, message: "")
+        }
+        return cgFont.fullName as String?
+        #endif
+        #else
+        return name
+        #endif
+    }
+
     func importModel(at path: String) throws {
         let url = try resolveURL(for: path)
         let program: Program

ShapeScript/Interpreter.swift

@@ -1314,7 +1314,8 @@ extension Expression {
             }
         case .font where Value.tuple(values).isConvertible(to: .string):
             let name = Value.tuple(values).stringValue
-            return try RuntimeError.wrap(.string(validateFont(name)), at: parameters[0].range)
+            let range = parameters.first!.range.lowerBound ..< parameters.last!.range.upperBound
+            return try RuntimeError.wrap(.string(context.resolveFont(name)), at: range)
         case .paths:
             return try .tuple(values.enumerated().flatMap { i, value -> [Value] in
                 switch value {
@@ -1381,24 +1382,3 @@ extension Expression {
         }
     }
 }
-
-private func validateFont(_ name: String?) throws -> String? {
-    guard let name = name?
-        .trimmingCharacters(in: .whitespacesAndNewlines)
-        .replacingOccurrences(of: "\t", with: " ")
-        .replacingOccurrences(of: "  ", with: " ")
-    else {
-        return nil
-    }
-    #if canImport(CoreGraphics)
-    guard CGFont(name as CFString) != nil else {
-        var options = [String]()
-        #if canImport(CoreText)
-        options += CTFontManagerCopyAvailablePostScriptNames() as? [String] ?? []
-        options += CTFontManagerCopyAvailableFontFamilyNames() as? [String] ?? []
-        #endif
-        throw RuntimeErrorType.unknownFont(name, options: options)
-    }
-    #endif
-    return name
-}

ShapeScriptTests/EdgeOfTheGalaxyRegular-OVEa6.otf

@@ -1016,6 +1016,16 @@ class InterpreterTests: XCTestCase {
         #endif
     }
 
+    func testSetFontWithFile() throws {
+        #if canImport(CoreGraphics)
+        let program = try parse("font \"EdgeOfTheGalaxyRegular-OVEa6.otf\"")
+        let delegate = TestDelegate()
+        let context = EvaluationContext(source: program.source, delegate: delegate)
+        XCTAssertNoThrow(try program.evaluate(in: context))
+        XCTAssertEqual(context.font, "Edge of the Galaxy Regular")
+        #endif
+    }
+
     // MARK: Import
 
     func testImport() throws {