Spectrogram

FFT processing and CustomPainter rendering.

Pipeline

RingBuffer → FftProcessor → SpectrogramPainter → Canvas

FftProcessor

• Windowed FFT (Hann window) via the fftea package
• Converts complex spectrum to normalized dB magnitudes [0.0, 1.0]
• Configurable dB range (floor/ceiling) and FFT size

SpectrogramPainter (CustomPainter)

Uses a synchronous canvas-shift rendering strategy:

1. Draw previous spectrogram image shifted left by N columns
2. Draw new columns as colored rectangles on the right edge
3. Picture.toImageSync produces a GPU-backed ui.Image
4. Single drawImageRect composites to the main canvas

This avoids async decodeImageFromPixels which caused frozen spectrograms.

Color Maps

Pre-computed 256-entry ARGB lookup tables:

• Viridis — perceptually uniform, color-blind friendly (default)
• Magma — dark-to-bright purple/orange
• Inferno — dark black to vivid yellow
• Grayscale — simple luminance ramp
• BirdNET — custom brand blue palette

SpectrogramWidget

Bridges the audio ring buffer, FFT, and painter into a Flutter widget:

• Ticker drives animation at up to 60 fps
• RepaintBoundary isolates repaints from the widget tree
• Supports optional log amplitude scaling and frequency axis labels