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Flutter Mobile Development · Ders

Canvas API'si: Yollar, Boyamalar ve Gölgelendiriciler

Canvas temel öğelerini ve Paint yapılandırmasını kullanarak şekiller, renk geçişleri ve çizgiler çizin.

Canvas API'si: Yollar, Boyamalar ve Gölgelendiriciler, CoddyKit'te ücretsiz bir Flutter Mobile Development dersidir. Bu, 4 dersinin 1. dersidir. Aşağıdan dersin tamamını ücretsiz okuyabilir, sonra tarayıcıda yerleşik kod editörü ve 7/24 yapay zeka koçu ile uygulamalı olarak pratik yapabilirsin. Bu, Flutter Mobile Development öğrenme yolunun bir parçasıdır ve ilerlemeniz web ve CoddyKit uygulaması arasında senkronize olur. Flutter Mobile Development kursu toplamda 4 dersten oluşur.

Bu dersin bazı bölümleri henüz çevrilmemiş olup İngilizce olarak gösterilmektedir.

Meet the Canvas

When you build a CustomPainter, Flutter hands you two things in paint(): a Canvas and a Size.

  • Canvas is your drawing surface. It exposes primitives like drawRect, drawCircle, drawPath, and drawLine.
  • Size tells you how big the area is, so you can scale your drawing to fit any device.

Every draw call needs a Paint object that describes how to draw: color, stroke vs fill, width, and more.

void paint(Canvas canvas, Size size) {
  final paint = Paint()..color = const Color(0xFF2196F3);
  canvas.drawRect(
    Rect.fromLTWH(0, 0, size.width, size.height),
    paint,
  );
}

The Paint Object

A Paint is a bundle of styling options. The most important fields are:

  • color — the color used to draw.
  • style — PaintingStyle.fill (solid interior) or PaintingStyle.stroke (outline only).
  • strokeWidth — line thickness when stroking.
  • isAntiAlias — smooth edges, on by default.

Flutter idiom uses the cascade operator .. to configure a freshly created Paint in one expression.

final fill = Paint()
  ..color = const Color(0xFFE91E63)
  ..style = PaintingStyle.fill;

final outline = Paint()
  ..color = const Color(0xFF000000)
  ..style = PaintingStyle.stroke
  ..strokeWidth = 4.0;

Drawing Basic Shapes

The Canvas offers ready-made primitives so you do not always need a path:

  • drawRect(Rect, Paint) — axis-aligned rectangle.
  • drawRRect(RRect, Paint) — rounded rectangle.
  • drawCircle(Offset center, double radius, Paint)
  • drawOval(Rect, Paint) — fills the bounding rect with an ellipse.

Coordinates start at (0,0) in the top-left corner; x grows right, y grows down.

void paint(Canvas canvas, Size size) {
  final p = Paint()..color = const Color(0xFF4CAF50);
  final center = Offset(size.width / 2, size.height / 2);

  canvas.drawCircle(center, 40, p);
  canvas.drawRRect(
    RRect.fromRectAndRadius(
      Rect.fromLTWH(10, 10, 80, 50),
      const Radius.circular(12),
    ),
    p,
  );
}

Strokes: Caps, Joins, and Width

When style is PaintingStyle.stroke, several properties shape the line:

  • strokeWidth — thickness in logical pixels.
  • strokeCap — how line ends look: butt, round, or square.
  • strokeJoin — how corners connect: miter, round, or bevel.

Round caps and joins are common for friendly, smooth chart and signature drawing.

final stroke = Paint()
  ..color = const Color(0xFF9C27B0)
  ..style = PaintingStyle.stroke
  ..strokeWidth = 6.0
  ..strokeCap = StrokeCap.round
  ..strokeJoin = StrokeJoin.round;

// canvas.drawLine(Offset(10, 10), Offset(120, 60), stroke);

Building a Path

A Path describes an arbitrary outline made of line and curve segments. The core methods are:

  • moveTo(x, y) — lift the pen and start a new subpath.
  • lineTo(x, y) — draw a straight segment.
  • quadraticBezierTo / cubicTo — curved segments.
  • close() — connect back to the subpath start.

Draw the finished path with canvas.drawPath(path, paint).

void paint(Canvas canvas, Size size) {
  final path = Path()
    ..moveTo(size.width / 2, 0)
    ..lineTo(size.width, size.height)
    ..lineTo(0, size.height)
    ..close();

  final paint = Paint()..color = const Color(0xFFFF5722);
  canvas.drawPath(path, paint);
}

Curves with Bezier Segments

Smooth shapes come from Bezier curves. The most common is the quadratic Bezier, which uses one control point.

  • quadraticBezierTo(cpx, cpy, x, y) bends the line toward the control point (cpx, cpy) on its way to the end point (x, y).
  • cubicTo(c1x, c1y, c2x, c2y, x, y) uses two control points for S-curves.

These power wave dividers, chart lines, and speech-bubble tails.

void paint(Canvas canvas, Size size) {
  final wave = Path()
    ..moveTo(0, size.height * 0.5)
    ..quadraticBezierTo(
      size.width * 0.25, size.height * 0.2,
      size.width * 0.5, size.height * 0.5,
    )
    ..quadraticBezierTo(
      size.width * 0.75, size.height * 0.8,
      size.width, size.height * 0.5,
    );

  final paint = Paint()
    ..color = const Color(0xFF00BCD4)
    ..style = PaintingStyle.stroke
    ..strokeWidth = 3;
  canvas.drawPath(wave, paint);
}

Plain Dart: Computing Points

Canvas math is just geometry. Before you draw, you often compute coordinates with plain Dart. Here we generate evenly spaced points along a sine wave — the same values you would feed into path.lineTo.

This logic is framework-free, so you can unit-test it without rendering anything.

import 'dart:math';

List<Point<double>> wavePoints(double width, double height, int n) {
  final pts = <Point<double>>[];
  for (var i = 0; i <= n; i++) {
    final x = width * i / n;
    final y = height / 2 + sin(i / n * 2 * pi) * height / 4;
    pts.add(Point(x, y));
  }
  return pts;
}

void main() {
  final pts = wavePoints(200, 100, 4);
  for (final p in pts) {
    print('(${p.x.toStringAsFixed(1)}, ${p.y.toStringAsFixed(1)})');
  }
}

Shaders: Linear Gradients

A shader fills a shape with more than a flat color. The most common is a linear gradient. You build it with ui.Gradient.linear and assign it to paint.shader.

  • from / to are the start and end Offsets of the gradient line.
  • colors lists the gradient stops, blended along that line.

Once shader is set, the paint's color is ignored for fills.

import 'dart:ui' as ui;

Paint gradientPaint(Size size) {
  return Paint()
    ..shader = ui.Gradient.linear(
      Offset.zero,
      Offset(size.width, size.height),
      const [Color(0xFF2196F3), Color(0xFF9C27B0)],
    );
}

Radial and Sweep Gradients

Beyond linear, Flutter offers two more gradient shaders:

  • Radial — ui.Gradient.radial(center, radius, colors) blends outward from a center point, great for glows and spotlights.
  • Sweep — ui.Gradient.sweep(center, colors) rotates colors around a center, ideal for circular progress and color wheels.

You can add an optional stops list (0.0 to 1.0) to control exactly where each color sits.

import 'dart:ui' as ui;

Paint glow(Offset center) {
  return Paint()
    ..shader = ui.Gradient.radial(
      center,
      60,
      const [Color(0xFFFFEB3B), Color(0x00FFEB3B)],
      const [0.0, 1.0],
    );
}

Putting It Together in a Painter

A real CustomPainter combines paths, paints, and shaders. Remember two overrides:

  • paint(canvas, size) — do the drawing.
  • shouldRepaint(old) — return true only when inputs changed, so Flutter avoids needless repaints.

This snippet draws a gradient-filled rounded card with a stroked border.

class CardPainter extends CustomPainter {
  @override
  void paint(Canvas canvas, Size size) {
    final rect = Rect.fromLTWH(0, 0, size.width, size.height);
    final rrect = RRect.fromRectAndRadius(rect, const Radius.circular(16));

    final fill = Paint()
      ..shader = ui.Gradient.linear(
        rect.topLeft, rect.bottomRight,
        const [Color(0xFF42A5F5), Color(0xFF7E57C2)],
      );
    canvas.drawRRect(rrect, fill);

    final border = Paint()
      ..style = PaintingStyle.stroke
      ..strokeWidth = 2
      ..color = const Color(0x33000000);
    canvas.drawRRect(rrect, border);
  }

  @override
  bool shouldRepaint(CardPainter oldDelegate) => false;
}

Save, Restore, and Transforms

The Canvas keeps a stack of transforms and clips. Use it to draw rotated or scaled content without permanently changing state:

  • canvas.save() pushes the current matrix.
  • canvas.translate / rotate / scale modify it.
  • canvas.restore() pops back to where you were.

Always pair every save() with a restore(), or later draws will inherit the transform.

void paint(Canvas canvas, Size size) {
  final p = Paint()..color = const Color(0xFF3F51B5);
  canvas.save();
  canvas.translate(size.width / 2, size.height / 2);
  canvas.rotate(0.785398); // 45 degrees in radians
  canvas.drawRect(
    const Rect.fromLTWH(-30, -30, 60, 60),
    p,
  );
  canvas.restore();
}

Quick Check

Test your understanding of the Paint configuration.

Recap

You now command the Canvas API:

  • Paint controls how you draw: color, style (fill vs stroke), strokeWidth, caps, and joins.
  • Primitives like drawRect, drawRRect, and drawCircle handle common shapes; Path with moveTo, lineTo, and Bezier curves handles anything custom.
  • Shaders (Gradient.linear, radial, sweep) fill or stroke with gradients and override the flat color.
  • save/restore isolates transforms, and shouldRepaint keeps rendering efficient.

With these building blocks you can draw charts, custom controls, and rich decorations entirely in Dart.

Sıkça Sorulan Sorular

“Canvas API'si: Yollar, Boyamalar ve Gölgelendiriciler” dersi ücretsiz mi?

Evet — “Canvas API'si: Yollar, Boyamalar ve Gölgelendiriciler” dersin tüm metni burada web'de ücretsiz olarak okunabilir. Etkileşimli olarak pratik yapmak (yerleşik kod editörü ve 7/24 yapay zeka koçu) ve Flutter Mobile Development kursunun geri kalanını açmak için CoddyKit PRO'ya yükselt. Flutter Mobile Development kursu toplamda 4 dersten oluşur.

“Canvas API'si: Yollar, Boyamalar ve Gölgelendiriciler” dersinde ne öğreneceğim?

Canvas temel öğelerini ve Paint yapılandırmasını kullanarak şekiller, renk geçişleri ve çizgiler çizin. Flutter Mobile Development ile uygulamalı kodu tarayıcıda doğrudan çalıştırarak pratik yaparsın ve 7/24 yapay zeka koçu dersi çalışırken sorularını yanıtlar.

Flutter Mobile Development öğrenmeye başlamak için deneyim gerekli mi?

Önceden deneyim gerekmez. CoddyKit'te Flutter Mobile Development, başlangıçtan ileri seviyeye kadar yapılandırıldığı için buradan başlayabilir veya başından başlayıp kendi hızında ilerleme yapabilirsin. Bu, 4 dersinin 1. dersidir.

“Canvas API'si: Yollar, Boyamalar ve Gölgelendiriciler” dersi ne kadar sürer?

Çoğu CoddyKit dersi yaklaşık 5–10 dakika sürer. Her biri kısa ve etkileşimli olduğu için sabit ilerleme yaparsın ve web ile uygulama arasında tam olarak bıraktığın yerden devam edebilirsin.

Bu Flutter Mobile Development dersinde kod yazıp çalıştırabilir miyim?

Evet. Her Flutter Mobile Development dersi yerleşik bir kod editörü içerir, bu sayede tarayıcıda gerçek kod yazıp çalıştırabilir ve anlık yapay zeka geri bildirimi alırsın — yerel kurulum gerekli değildir.

Bu kursun tüm dersleri

  1. Canvas API'si: Yollar, Boyamalar ve Gölgelendiriciler
  2. Etkileşimli Özel Grafik Bileşeni Oluşturma
  3. Kırpma, Karışım Kipleri ve Katman Birleştirme
  4. Vuruş Testi ve Yeniden Çizim Optimizasyonu
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