metal_shader_fx

Physically-based metallic border shine effects for Flutter widgets. Features a full Cook-Torrance microfacet BRDF adapted for UI border rings — the same math used in game engines and 3D renderers, now running on your buttons, toggles, and text fields.

Button	Toggle	Text Field

Features

• Cook-Torrance BRDF — GGX normal distribution, Schlick Fresnel, Smith G masking-shadowing
• Thin-film interference — per-channel (R/G/B wavelength) spectral color separation simulating anodized aluminum
• Anisotropic highlights — configurable brush direction and stretch for brushed metal looks
• Energy conservation — running budget prevents physically impossible over-brightening
• Dual-lobe environment map — key + fill light simulating studio 3-point lighting
• Corner caustics with bloom — light concentration at rounded corners with soft radial glow
• Inverse-square falloff — far side of the border dims naturally
• 5-frequency micro-scratch shimmer — non-harmonic sine layers eliminate digital repetition
• Radial cross-section lighting — convex torus profile with bright crown and shadow bevel

Widgets

Widget	Description
MetalToggleCard	Toggle switch card with animated metallic thumb
MetallicBorderButton	Button with metallic border shine
MetallicBorderTextField	Text field with metallic border that intensifies on focus

Installation

dependencies:
  metal_shader_fx: ^0.1.3

Quick Start

import 'package:metal_shader_fx/metal_shader_fx.dart';

// Toggle
MetalToggleCard(
  value: _enabled,
  onChanged: (v) => setState(() => _enabled = v),
  accentColor: const Color(0xFFE3AA00),
);

// Button
MetallicBorderButton(
  text: 'Continue',
  color: const Color(0xFF55267E),
  onPressed: () => print('tapped'),
);

// Text field
MetallicBorderTextField(
  controller: _controller,
  hintText: 'Enter your email',
  color: const Color(0xFFE3AA00),
  onChanged: (value) => print(value),
);

Material Presets

Use built-in presets or create your own:

// Polished chrome — mirror-like, no anodization
MetallicBorderButton(
  text: 'Chrome',
  color: Colors.blue,
  onPressed: () {},
  material: const MetalMaterialConfig.chrome(),
);

// Brushed stainless steel
material: const MetalMaterialConfig.brushedSteel()

// Heavy anodized aluminum — strong iridescence
material: const MetalMaterialConfig.anodized()

// Gold — warm, high reflectance
material: const MetalMaterialConfig.gold()

// Custom
material: const MetalMaterialConfig(
  roughness: 0.10,      // 0 = mirror, 1 = diffuse
  f0: 0.92,             // Fresnel base reflectance
  filmThickness: 0.5,   // thin-film iridescence strength
  anisotropy: 0.4,      // brush direction stretch
  brushAngle: 1.57,     // vertical brushing (π/2)
)

MetalMaterialConfig Properties

Property	Default	Description
roughness	0.15	GGX α (0 = mirror, 1 = diffuse)
f0	0.88	Base Fresnel reflectance
filmThickness	0.38	Thin-film oxide layer (0 = bare, 1 = max iridescence)
anisotropy	0.30	Directional stretch (0 = isotropic, 1 = fully anisotropic)
brushAngle	0.0	Brush direction in radians
lightDistance	3.0	Virtual light distance (affects falloff)
distanceFalloffStrength	0.25	Inverse-square falloff intensity
ggxTailSteps	6	GGX sub-segments (more = smoother, costlier)
ringWidth	per-widget	Border ring stroke width
shineDuration	per-widget	Full rotation cycle duration

Widget API Reference

MetalToggleCard

Property	Type	Default	Description
value	bool	required	Toggle state
onChanged	ValueChanged<bool>	required	State change callback
accentColor	Color	required	Shine tint color
width	double?	stretches	Card width
height	double	142	Card height
enabledLabel	String	'Enabled'	On-state text
disabledLabel	String	'Disabled'	Off-state text
toggleWidth	double	170	Toggle track width
toggleHeight	double	92	Toggle track height
thumbSize	double	74	Thumb diameter
material	MetalMaterialConfig	default	Physics config

MetallicBorderButton

Property	Type	Default	Description
text	String?	—	Button label
child	Widget?	—	Custom content (overrides text)
color	Color	required	Button color and shine tint
onPressed	VoidCallback?	—	Tap callback
onLongPress	VoidCallback?	—	Long-press callback
width	double?	content-sized	Fixed width
height	double	64	Button height
borderRadius	double	22	Corner radius
enabled	bool	true	Enable/disable
textStyle	TextStyle?	white/18/w600	Label style
material	MetalMaterialConfig	default	Physics config

MetallicBorderTextField

Property	Type	Default	Description
controller	TextEditingController?	auto-created	Text controller
color	Color	required	Shine tint color
hintText	String?	—	Hint text
labelText	String?	—	Label text
onChanged	ValueChanged<String>?	—	Text change callback
onSubmitted	ValueChanged<String>?	—	Submit callback
onFocusChanged	ValueChanged<bool>?	—	Focus change callback
onTap	VoidCallback?	—	Tap callback
width	double?	stretches	Fixed width
height	double	64	Field height
borderRadius	double	22	Corner radius
enabled	bool	true	Enable/disable
obscureText	bool	false	Password mode
maxLines	int	1	Max lines
maxLength	int?	—	Max text length
keyboardType	TextInputType?	—	Keyboard type
textInputAction	TextInputAction?	—	Input action
inputFormatters	List<TextInputFormatter>?	—	Input restrictions
prefixIcon	Widget?	—	Prefix icon
suffixIcon	Widget?	—	Suffix icon
focusNode	FocusNode?	auto-created	External focus node
material	MetalMaterialConfig	default	Physics config

Advanced: Using the Painter Directly

For custom widgets, use PhysicalMetalShinePainter in any CustomPaint:

CustomPaint(
  foregroundPainter: PhysicalMetalShinePainter(
    rotation: _animationController.value * 3.14159 * 2,
    energy: 1.0,
    tint: Colors.amber,
    borderRadius: 16,
    ringWidth: 3.0,
    isCircle: false,
    material: const MetalMaterialConfig.gold(),
  ),
  child: YourWidget(),
)

Shoutout

Shoutout to @aligrids for sparking the idea.

License

MIT