Add scaling. (#10)

Closes #6.

lib/src/buffer.dart

@@ -12,6 +12,7 @@ part 'buffer/map.dart';
 part 'buffer/pixels_float.dart';
 part 'buffer/pixels_int.dart';
 part 'buffer/pixels.dart';
+part 'buffer/scaled.dart';
 
 /// A 2-dimensional _view_ of pixel data [T] in memory.
 ///
@@ -171,6 +172,30 @@ abstract base mixin class Buffer<T extends Object?> {
     return _ClippedBuffer(this, result);
   }
 
+  /// Returns a lazy buffer that scales the buffer by the given factor.
+  ///
+  /// The returned buffer will have the same dimensions as the original buffer
+  /// multiplied by the scale factor. The scale factor must be greater than 0.
+  ///
+  /// ## Example
+  ///
+  /// ```dart
+  /// final buffer = IntPixels(2, 2, data: Uint32List.fromList([
+  ///   abgr8888.red, abgr8888.green,
+  ///   abgr8888.blue, abgr8888.magenta,
+  /// ]));
+  ///
+  /// final scaled = buffer.mapScaled(2);
+  /// print(scaled.data); // [0xFFFF0000, 0xFFFF0000, 0xFF00FF00, 0xFF00FF00, 0xFF0000FF, 0xFF0000FF, 0xFFFF00FF, 0xFFFF00FF]
+  /// ```
+  Buffer<T> mapScaled(int scale) {
+    RangeError.checkNotNegative(scale, 'scale');
+    if (scale == 1) {
+      return this;
+    }
+    return _ScaledBuffer(this, scale);
+  }
+
   /// Returns a lazy iterable of pixels in the buffer from [start] to [end].
   ///
   /// The returned iterable will contain all pixels in the buffer that are

lib/src/buffer/scaled.dart

@@ -0,0 +1,26 @@
+part of '../buffer.dart';
+
+final class _ScaledBuffer<T> extends _Buffer<T> {
+  const _ScaledBuffer(super._source, this._scale);
+  final int _scale;
+
+  @override
+  Iterable<T> get data {
+    return Iterable.generate(length, (i) {
+      final pos = Pos(i % width, i ~/ width);
+      return getUnsafe(pos);
+    });
+  }
+
+  @override
+  T getUnsafe(Pos pos) {
+    final sourcePos = pos ~/ _scale;
+    return _source.getUnsafe(sourcePos);
+  }
+
+  @override
+  int get width => _source.width * _scale;
+
+  @override
+  int get height => _source.height * _scale;
+}

test/buffer_test.dart

@@ -116,6 +116,40 @@ void main() {
     ).throws<ArgumentError>();
   });
 
+  test('mapScaled', () {
+    final buffer = IntPixels(
+      2,
+      2,
+      data: Uint32List.fromList([
+        abgr8888.red,
+        abgr8888.green,
+        abgr8888.blue,
+        abgr8888.cyan,
+      ]),
+    );
+    final scaled = buffer.mapScaled(2);
+    check(scaled.width).equals(4);
+    check(scaled.height).equals(4);
+    check(scaled.data).deepEquals([
+      abgr8888.red,
+      abgr8888.red,
+      abgr8888.green,
+      abgr8888.green,
+      abgr8888.red,
+      abgr8888.red,
+      abgr8888.green,
+      abgr8888.green,
+      abgr8888.blue,
+      abgr8888.blue,
+      abgr8888.cyan,
+      abgr8888.cyan,
+      abgr8888.blue,
+      abgr8888.blue,
+      abgr8888.cyan,
+      abgr8888.cyan,
+    ]);
+  });
+
   group('compare', () {
     test('different width returns difference = 1.0', () {
       final a = IntPixels(2, 2);

test/golden_test.dart

@@ -159,4 +159,38 @@ void main() {
       uncompressedPngEncoder.convert(output),
     );
   });
+
+  test('blit with embedded font and scaling', () {
+    // We are going to write the word "PXL" in the terminal8x8Font.
+    // The font is stored in code page 437 tile order.
+    final $P = Pos(00, 5) * 8;
+    final $X = Pos(08, 5) * 8;
+    final $L = Pos(12, 4) * 8;
+
+    final output = IntPixels(24 * 4, 8 * 4)..fill(abgr8888.black);
+    final scaled = terminal8x8Font.mapScaled(4);
+
+    output.blit(
+      scaled,
+      target: Pos(00, 00),
+      source: Rect.fromWH(8 * 4, 8 * 4, offset: $P * 4),
+    );
+
+    output.blit(
+      scaled,
+      target: Pos(08 * 4, 00),
+      source: Rect.fromWH(8 * 4, 8 * 4, offset: $X * 4),
+    );
+
+    output.blit(
+      scaled,
+      target: Pos(16 * 4, 00),
+      source: Rect.fromWH(8 * 4, 8 * 4, offset: $L * 4),
+    );
+
+    checkOrUpdateGolden(
+      'blit_with_embedded_font_and_scaling',
+      uncompressedPngEncoder.convert(output),
+    );
+  });
 }