Real-Time Code Preview: See Your Flutter CustomPainter Code Instantly

One of the most powerful features of Flutter Shape Builder is the real-time code preview. As you draw, move, resize, or style shapes on the canvas, the corresponding Flutter Dart code updates instantly in the sidebar panel. There is no "generate" button to click — the code is always live and always in sync.

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How it works

The code preview panel is located in the sidebar on the right side of the editor. It shows the generated Dart code for all shapes currently on the canvas. Every action you take is immediately reflected:

• Draw a new shape → new path and paint code appears

• Move a shape → coordinate values update

• Change fill color → Color() value updates

• Resize or rotate → dimensions and transform values update

• Delete a shape → its code block is removed

• Reorder layers → paint call order changes

This tight feedback loop means you always know exactly what your Flutter code looks like — no surprises when you paste it into your project.

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Syntax highlighting

The code preview uses syntax highlighting powered by React Syntax Highlighter with a dark theme optimized for the editor's color scheme. The highlighting covers:

• Dart keywords (final, class, void, override)

• Type names (Path, Paint, Canvas, Color)

• String and number literals

• Method calls and property access

• Comments

Code is displayed in Fira Code monospace font for readability, matching what you would see in VS Code or Android Studio.

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Copy to clipboard

Click the copy button to copy the entire generated code to your clipboard in one click. Paste it directly into your Flutter project's .dart file and it compiles immediately. No formatting fixes or manual edits required.

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Pre-export validation

Before you copy, Flutter Shape Builder runs an automatic validation pass and displays any warnings directly in the sidebar:

• Unsupported features — alerts you if your design uses features like SVG Arcs that don't have a direct Flutter equivalent

• Empty shapes — warns if a shape has no path data

• Rendering issues — flags potential problems that could cause unexpected behavior at runtime

Validation warnings appear as non-blocking notices — you can still export the code, but the warnings help you make an informed decision about whether to adjust your design first.

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Export format options

The code preview panel lets you switch between three export formats:

Switching between formats updates the preview instantly — you can quickly compare what each option looks like.

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What the live preview looks like

Here is a simplified example of what you see in the code preview panel as you draw a filled diamond shape:

class MyShapePainter extends CustomPainter {
  @override
  void paint(Canvas canvas, Size size) {
    final paint_0 = Paint()
      ..color = Color(0xFF6366F1)
      ..style = PaintingStyle.fill;

    final path_0 = Path();
    path_0.moveTo(200.0, 50.0);
    path_0.lineTo(350.0, 175.0);
    path_0.lineTo(200.0, 300.0);
    path_0.lineTo(50.0, 175.0);
    path_0.close();

    canvas.drawPath(path_0, paint_0);
  }

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

Every pixel you drag, every color you change — this code updates in real time.

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Why real-time preview matters

Eliminates the guessing game

Traditional CustomPainter development is a cycle of: write code → hot reload → check result → adjust → repeat. With real-time preview, you see the code and the visual result simultaneously.

Builds intuition for Flutter paths

Watching how your visual edits translate to moveTo, lineTo, cubicTo, and close calls is one of the fastest ways to learn the Flutter Path API.

Catches problems early

Validation warnings appear as you work, not after you have already pasted the code into your project. Fix issues while you are still in the design phase.

Speeds up iteration

Change a shape, see the code update, copy it. The entire design-to-code cycle takes seconds instead of minutes.

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See your code update in real time

Open the editor and start drawing. Your Flutter code appears instantly in the sidebar.

Open the Editor →

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