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Made the spectrometer a bit smoother

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JorySeverijnse 2026-01-18 20:29:53 +01:00
parent 837be94e1c
commit 85434e84f2
1 changed files with 178 additions and 397 deletions
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src/render.rs
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@ -1,201 +1,92 @@
//! Frame rendering module. //! Frame rendering module.
//!
//! Contains all the logic for drawing oscilloscope visualizations.
use crate::audio::AudioData; use crate::audio::AudioData;
use crate::video::VideoEncoder; use crate::video::VideoEncoder;
use anyhow::{anyhow, Result}; use anyhow::{anyhow, Result};
use image::ImageBuffer; use image::ImageBuffer;
use rustfft::{num_complex::Complex, FftPlanner}; use rustfft::{num_complex::Complex, FftPlanner};
use std::cell::RefCell;
/// Render mode for the oscilloscope visualization. // --- Constants ---
#[derive(Debug, Clone, Copy, clap::ValueEnum)] const FFT_SIZE: usize = 2048;
pub enum RenderMode { const MIN_FREQ: f32 = 20.0;
/// Both channels merged into a single waveform const MAX_FREQ: f32 = 20000.0;
Combined, const FREQ_BOOST_FACTOR: f32 = 5.0;
/// Left channel on top, Right channel on bottom const DYNAMIC_RANGE_SCALE: f32 = 20.0;
Separate, const NOISE_FLOOR: f32 = 0.05;
/// Left and Right on top row, XY on bottom const SMOOTH_RISE: f32 = 0.6; // How quickly bars rise
All, const SMOOTH_FALL: f32 = 0.3; // How quickly bars fall (gravity)
/// Frequency spectrum display (spectrometer)
Spectrometer, thread_local! {
static FFT_PLANNER: RefCell<FftPlanner<f32>> = RefCell::new(FftPlanner::new());
static HANN_WINDOW: Vec<f32> = (0..FFT_SIZE)
.map(|i| 0.5 * (1.0 - (2.0 * std::f32::consts::PI * i as f32 / (FFT_SIZE - 1) as f32).cos()))
.collect();
}
#[derive(Debug, Clone, Copy, clap::ValueEnum, PartialEq, Eq)]
pub enum RenderMode {
Combined, Separate, All, Spectrometer,
} }
/// Rendering options for the visualization.
#[derive(Debug, Clone)] #[derive(Debug, Clone)]
pub struct RenderOptions { pub struct RenderOptions {
pub width: u32, pub width: u32, pub height: u32, pub fps: u32,
pub height: u32,
pub fps: u32,
pub mode: RenderMode, pub mode: RenderMode,
pub left_color: image::Rgb<u8>, pub left_color: image::Rgb<u8>, pub right_color: image::Rgb<u8>, pub xy_color: image::Rgb<u8>,
pub right_color: image::Rgb<u8>,
pub xy_color: image::Rgb<u8>,
pub background: image::Rgb<u8>, pub background: image::Rgb<u8>,
pub show_grid: bool, pub show_grid: bool, pub line_thickness: u32,
pub line_thickness: u32,
} }
/// Draw a line between two points using Bresenham's algorithm. fn compute_raw_bars(spectrum: &[f32], num_bars: usize, sample_rate: u32) -> Vec<f32> {
pub fn draw_line(
buffer: &mut ImageBuffer<image::Rgb<u8>, Vec<u8>>,
x0: i32,
y0: i32,
x1: i32,
y1: i32,
color: image::Rgb<u8>,
) {
let dx = (x1 - x0).abs();
let dy = -(y1 - y0).abs();
let mut x = x0;
let mut y = y0;
let sx = if x0 < x1 { 1 } else { -1 };
let sy = if y0 < y1 { 1 } else { -1 };
let mut err = dx + dy;
loop {
if x >= 0 && x < buffer.width() as i32 && y >= 0 && y < buffer.height() as i32 {
buffer.put_pixel(x as u32, y as u32, color);
}
if x == x1 && y == y1 {
break;
}
let e2 = 2 * err;
if e2 >= dy {
err += dy;
x += sx;
}
if e2 <= dx {
err += dx;
y += sy;
}
}
}
/// Draw grid lines (graticule).
fn draw_graticule(
buffer: &mut ImageBuffer<image::Rgb<u8>, Vec<u8>>,
primary_color: image::Rgb<u8>,
) {
let (width, height) = buffer.dimensions();
for x in 0..width {
buffer.put_pixel(x, height / 2, primary_color);
}
for y in 0..height {
buffer.put_pixel(width / 2, y, primary_color);
}
}
/// Parse RGB hex color string.
pub fn parse_rgb_hex(hex: &str) -> Result<image::Rgb<u8>> {
let hex = hex.trim_start_matches('#');
if hex.len() != 6 {
return Err(anyhow!("Invalid RGB hex: {}", hex));
}
let r = u8::from_str_radix(&hex[0..2], 16).map_err(|_| anyhow!("Invalid red component: {}", &hex[0..2]))?;
let g = u8::from_str_radix(&hex[2..4], 16).map_err(|_| anyhow!("Invalid green component: {}", &hex[2..4]))?;
let b = u8::from_str_radix(&hex[4..6], 16).map_err(|_| anyhow!("Invalid blue component: {}", &hex[4..6]))?;
Ok(image::Rgb([r, g, b]))
}
/// Compute frequency spectrum from audio samples using FFT.
fn compute_spectrum(audio_data: &AudioData, start_sample: usize) -> Vec<f32> {
// Use a larger FFT size for better frequency resolution, especially in the bass
let fft_size = 2048;
let mut planner = FftPlanner::new();
let fft = planner.plan_fft_forward(fft_size);
// Collect audio samples for this window
let mut buffer: Vec<Complex<f32>> = (0..fft_size)
.map(|i| {
let sample_idx = start_sample + i;
if sample_idx < audio_data.left_channel.len() {
// Sum channels for mono analysis
let sample = audio_data.left_channel[sample_idx] + audio_data.right_channel[sample_idx];
Complex::new(sample, 0.0)
} else {
Complex::new(0.0, 0.0)
}
})
.collect();
// Apply Hann window
for (i, sample) in buffer.iter_mut().enumerate() {
let window = 0.5 * (1.0 - (2.0 * std::f32::consts::PI * i as f32 / (fft_size - 1) as f32).cos());
sample.re *= window;
sample.im *= window;
}
fft.process(&mut buffer);
let nyquist_bin = fft_size / 2;
// Normalize and skip DC
let spectrum: Vec<f32> = buffer[1..nyquist_bin]
.iter()
.map(|c| c.norm() / (fft_size as f32))
.collect();
spectrum
}
/// Draw the spectrometer bars with logarithmic frequency mapping.
fn draw_spectrometer(
buffer: &mut ImageBuffer<image::Rgb<u8>, Vec<u8>>,
spectrum: &[f32],
x_offset: u32,
y_offset: u32,
width: u32,
height: u32,
num_bars: usize,
color: image::Rgb<u8>,
sample_rate: u32,
) {
// Constants for logarithmic frequency mapping
const MIN_FREQ: f32 = 20.0;
const MAX_FREQ: f32 = 20000.0;
const FREQ_BOOST_FACTOR: f32 = 5.0;
const DYNAMIC_RANGE_SCALE: f32 = 20.0;
const NOISE_FLOOR: f32 = 0.05;
const BAR_SPACING: u32 = 1;
let bar_width = (width - (num_bars as u32 - 1) * BAR_SPACING) / num_bars as u32;
let bar_width = bar_width.max(1);
let nyquist = sample_rate as f32 / 2.0; let nyquist = sample_rate as f32 / 2.0;
let mut bars = vec![0.0; num_bars];
for i in 0..num_bars { for i in 0..num_bars {
// Calculate frequency range for this bar (logarithmic)
let f_start = MIN_FREQ * (MAX_FREQ / MIN_FREQ).powf(i as f32 / num_bars as f32); let f_start = MIN_FREQ * (MAX_FREQ / MIN_FREQ).powf(i as f32 / num_bars as f32);
let f_end = MIN_FREQ * (MAX_FREQ / MIN_FREQ).powf((i + 1) as f32 / num_bars as f32); let f_end = MIN_FREQ * (MAX_FREQ / MIN_FREQ).powf((i + 1) as f32 / num_bars as f32);
let bin_start = (f_start / nyquist * spectrum.len() as f32).floor() as usize;
// Map frequencies to FFT bin indices let bin_end = (f_end / nyquist * spectrum.len() as f32).ceil() as usize;
let bin_start = (f_start / nyquist * spectrum.len() as f32) as usize;
let bin_end = (f_end / nyquist * spectrum.len() as f32) as usize;
let bin_end = bin_end.max(bin_start + 1).min(spectrum.len()); let bin_end = bin_end.max(bin_start + 1).min(spectrum.len());
// Aggregate magnitude in this frequency range
let mut magnitude = 0.0f32; let mut magnitude = 0.0f32;
if bin_start < spectrum.len() { if bin_start < spectrum.len() {
magnitude = spectrum[bin_start..bin_end].iter().fold(0.0f32, |acc, &x| acc.max(x)); for k in bin_start..bin_end { magnitude = magnitude.max(spectrum[k]); }
} }
// Apply frequency-dependent boost (higher frequencies are naturally quieter)
let freq_factor = 1.0 + (f_start / MAX_FREQ) * FREQ_BOOST_FACTOR; let freq_factor = 1.0 + (f_start / MAX_FREQ) * FREQ_BOOST_FACTOR;
let mut val = magnitude * freq_factor; let mut val = (magnitude * freq_factor * DYNAMIC_RANGE_SCALE).sqrt().min(1.0);
// Dynamic range compression/scaling
val = (val * DYNAMIC_RANGE_SCALE).sqrt().min(1.0);
// Noise floor
if val < NOISE_FLOOR { val = 0.0; } if val < NOISE_FLOOR { val = 0.0; }
bars[i] = val;
}
bars
}
fn smooth_bars(raw_bars: &mut Vec<Vec<f32>>) {
if raw_bars.is_empty() { return; }
let num_bars = raw_bars[0].len();
let mut prev_bars = vec![0.0; num_bars];
for frame_bars in raw_bars.iter_mut() {
for i in 0..num_bars {
let current_val = frame_bars[i];
let prev_val = prev_bars[i];
let factor = if current_val > prev_val { SMOOTH_RISE } else { SMOOTH_FALL };
let smoothed_val = prev_val * (1.0 - factor) + current_val * factor;
frame_bars[i] = smoothed_val;
prev_bars[i] = smoothed_val;
}
}
}
fn render_smoothed_bars(
buffer: &mut ImageBuffer<image::Rgb<u8>, Vec<u8>>,
bars: &[f32],
x_offset: u32, y_offset: u32, width: u32, height: u32, color: image::Rgb<u8>,
) {
const BAR_SPACING: u32 = 1;
let num_bars = bars.len();
let bar_width = (width.saturating_sub((num_bars as u32 - 1) * BAR_SPACING)) / num_bars as u32;
let bar_width = bar_width.max(1);
for (i, &val) in bars.iter().enumerate() {
let bar_height = (val * height as f32) as u32; let bar_height = (val * height as f32) as u32;
let x = x_offset + i as u32 * (bar_width + BAR_SPACING); let x = x_offset + i as u32 * (bar_width + BAR_SPACING);
for y in 0..bar_height { for y in 0..bar_height {
let pixel_y = y_offset + height - 1 - y; let pixel_y = y_offset + height - 1 - y;
for dx in 0..bar_width { for dx in 0..bar_width {
@ -208,245 +99,135 @@ fn draw_spectrometer(
} }
} }
/// Draw a single frame of the visualization.
pub fn draw_frame(
audio_data: &AudioData,
start_sample: usize,
samples_per_frame: usize,
options: &RenderOptions,
) -> ImageBuffer<image::Rgb<u8>, Vec<u8>> {
let width = options.width;
let height = options.height;
let mut buffer = ImageBuffer::new(width, height);
for pixel in buffer.pixels_mut() {
*pixel = options.background;
}
if options.show_grid {
draw_graticule(&mut buffer, options.left_color);
}
let end_sample = std::cmp::min(start_sample + samples_per_frame, audio_data.left_channel.len());
match options.mode {
RenderMode::Combined => {
let samples_per_pixel = samples_per_frame as f32 / width as f32;
let center_y = height / 2;
let mut prev_y = center_y as i32;
for x in 0..width {
let sample_index = start_sample + (x as f32 * samples_per_pixel) as usize;
if sample_index >= audio_data.left_channel.len() {
break;
}
let sample = (audio_data.left_channel[sample_index]
+ audio_data.right_channel[sample_index])
/ 2.0;
let y = center_y as i32 - (sample * (height as f32 * 0.4)) as i32;
draw_line(&mut buffer, x as i32, prev_y, x as i32, y, options.left_color);
prev_y = y;
}
}
RenderMode::Separate => {
let half_height = height / 2;
let samples_per_pixel = samples_per_frame as f32 / width as f32;
let left_center_y = half_height / 2;
let mut prev_y = left_center_y as i32;
for x in 0..width {
let sample_index = start_sample + (x as f32 * samples_per_pixel) as usize;
if sample_index >= audio_data.left_channel.len() {
break;
}
let sample = audio_data.left_channel[sample_index];
let y = left_center_y as i32 - (sample * (half_height as f32 * 0.35)) as i32;
draw_line(&mut buffer, x as i32, prev_y, x as i32, y, options.left_color);
prev_y = y;
}
let right_center_y = half_height + half_height / 2;
let mut prev_y_right = right_center_y as i32;
for x in 0..width {
let sample_index = start_sample + (x as f32 * samples_per_pixel) as usize;
if sample_index >= audio_data.right_channel.len() {
break;
}
let sample = audio_data.right_channel[sample_index];
let y = right_center_y as i32 - (sample * (half_height as f32 * 0.35)) as i32;
draw_line(&mut buffer, x as i32, prev_y_right, x as i32, y, options.right_color);
prev_y_right = y;
}
for x in 0..width {
buffer.put_pixel(x, half_height, image::Rgb([40, 40, 40]));
}
}
RenderMode::All => {
let half_height = height / 2;
let half_width = width / 2;
let quarter_width = width / 4;
let samples_per_pixel = samples_per_frame as f32 / quarter_width as f32;
// Top-left: Left channel waveform
let left_center_y = half_height / 2;
let mut prev_y = left_center_y as i32;
for x in 0..half_width {
let sample_index = start_sample + (x as f32 * samples_per_pixel) as usize;
if sample_index >= audio_data.left_channel.len() {
break;
}
let sample = audio_data.left_channel[sample_index];
let y = left_center_y as i32 - (sample * (half_height as f32 * 0.35)) as i32;
draw_line(&mut buffer, x as i32, prev_y, x as i32, y, options.left_color);
prev_y = y;
}
// Top-right: Right channel waveform
let right_center_y = half_height / 2;
let mut prev_y_right = right_center_y as i32;
for x in 0..half_width {
let sample_index = start_sample + (x as f32 * samples_per_pixel) as usize;
if sample_index >= audio_data.right_channel.len() {
break;
}
let sample = audio_data.right_channel[sample_index];
let y = right_center_y as i32 - (sample * (half_height as f32 * 0.35)) as i32;
draw_line(
&mut buffer,
(half_width + x) as i32,
prev_y_right,
(half_width + x) as i32,
y,
options.right_color,
);
prev_y_right = y;
}
// Bottom-left: XY pattern
let xy_center_x = half_width / 2;
let xy_center_y = half_height + half_height / 2;
let xy_scale = std::cmp::min(half_width, half_height) as f32 * 0.35;
let xy_samples = (end_sample - start_sample).min(samples_per_frame);
let mut prev_x = xy_center_x as i32 + (audio_data.left_channel[start_sample] * xy_scale) as i32;
let mut prev_y_xy = xy_center_y as i32
- (audio_data.right_channel[start_sample] * xy_scale) as i32;
for i in 1..xy_samples {
let sample_idx = start_sample + i;
if sample_idx >= audio_data.left_channel.len() {
break;
}
let x = xy_center_x as i32
+ (audio_data.left_channel[sample_idx] * xy_scale) as i32;
let y = xy_center_y as i32
- (audio_data.right_channel[sample_idx] * xy_scale) as i32;
draw_line(&mut buffer, prev_x, prev_y_xy, x, y, options.xy_color);
prev_x = x;
prev_y_xy = y;
}
// Bottom-right: Spectrometer
let spec_width = half_width;
let spec_height = half_height;
let spec_x_offset = half_width;
let spec_y_offset = half_height;
let spectrum = compute_spectrum(audio_data, start_sample);
draw_spectrometer(
&mut buffer,
&spectrum,
spec_x_offset,
spec_y_offset,
spec_width,
spec_height,
32,
options.left_color,
audio_data.sample_rate,
);
// Draw grid lines separating quadrants
for x in 0..width {
buffer.put_pixel(x, half_height, image::Rgb([40, 40, 40]));
}
for y in 0..height {
buffer.put_pixel(half_width, y, image::Rgb([40, 40, 40]));
}
}
RenderMode::Spectrometer => {
let spectrum = compute_spectrum(audio_data, start_sample);
draw_spectrometer(
&mut buffer,
&spectrum,
0,
0,
width,
height,
64,
options.left_color,
audio_data.sample_rate,
);
}
}
buffer
}
pub fn stream_frames( pub fn stream_frames(
audio_data: &AudioData, audio_data: &AudioData, options: &RenderOptions, encoder: &mut VideoEncoder,
options: &RenderOptions,
encoder: &mut VideoEncoder,
progress_callback: &(impl Fn(f64, usize, usize) + Send + Sync), progress_callback: &(impl Fn(f64, usize, usize) + Send + Sync),
) -> Result<()> { ) -> Result<()> {
let total_samples = audio_data.left_channel.len(); let total_samples = audio_data.left_channel.len();
let samples_per_frame = (audio_data.sample_rate / options.fps) as usize; let samples_per_frame = (audio_data.sample_rate / options.fps) as usize;
let total_frames = ((audio_data.duration * options.fps as f64) as usize).max(1); let total_frames = ((audio_data.duration * options.fps as f64) as usize).max(1);
let num_threads = rayon::current_num_threads();
let chunk_size = num_threads * 2;
use rayon::prelude::*; use rayon::prelude::*;
println!("Pass 1/3: Analyzing spectrum...");
let num_bars = if options.mode == RenderMode::Spectrometer { 64 } else { 32 };
let mut all_raw_bars = if matches!(options.mode, RenderMode::Spectrometer | RenderMode::All) {
(0..total_frames).into_par_iter().map(|frame_idx| {
let start_sample = (frame_idx * samples_per_frame).min(total_samples.saturating_sub(1));
let mut buffer: Vec<Complex<f32>> = (0..FFT_SIZE).map(|i| {
if let Some(sample) = audio_data.left_channel.get(start_sample + i) {
Complex::new(sample + audio_data.right_channel[start_sample + i], 0.0)
} else { Complex::new(0.0, 0.0) }
}).collect();
HANN_WINDOW.with(|win| {
for (sample, &w) in buffer.iter_mut().zip(win.iter()) { sample.re *= w; }
});
let fft = FFT_PLANNER.with(|p| p.borrow_mut().plan_fft_forward(FFT_SIZE));
fft.process(&mut buffer);
let spectrum: Vec<f32> = buffer[1..FFT_SIZE / 2].iter().map(|c| c.norm() / FFT_SIZE as f32).collect();
compute_raw_bars(&spectrum, num_bars, audio_data.sample_rate)
}).collect()
} else { Vec::new() };
println!("Pass 2/3: Smoothing data...");
if !all_raw_bars.is_empty() { smooth_bars(&mut all_raw_bars); }
println!("Pass 3/3: Rendering and encoding frames...");
let chunk_size = rayon::current_num_threads() * 2;
for chunk_start in (0..total_frames).step_by(chunk_size) { for chunk_start in (0..total_frames).step_by(chunk_size) {
let chunk_end = (chunk_start + chunk_size).min(total_frames); let chunk_end = (chunk_start + chunk_size).min(total_frames);
let frame_indices: Vec<usize> = (chunk_start..chunk_end).collect(); let frames: Vec<Result<Vec<u8>>> = (chunk_start..chunk_end).into_par_iter().map(|frame_idx| {
let start_sample = (frame_idx * samples_per_frame).min(total_samples.saturating_sub(1));
let frames: Vec<Result<Vec<u8>>> = frame_indices let smoothed_bars = if all_raw_bars.is_empty() { None } else { Some(all_raw_bars[frame_idx].as_slice()) };
.par_iter() Ok(draw_frame(audio_data, start_sample, samples_per_frame, options, smoothed_bars).into_raw())
.map(|&frame_idx| { }).collect();
let start_sample = std::cmp::min( for frame in frames { encoder.write_frame(&frame?)?; }
frame_idx * samples_per_frame, progress_callback(chunk_end as f64 / total_frames as f64 * 100.0, chunk_end, total_frames);
total_samples.saturating_sub(1),
);
let frame = draw_frame(audio_data, start_sample, samples_per_frame, options);
Ok(frame.into_raw())
})
.collect();
for frame_result in frames {
let frame_data = frame_result?;
encoder.write_frame(&frame_data)?;
} }
let current = chunk_end;
progress_callback(
current as f64 / total_frames as f64 * 100.0,
current,
total_frames,
);
}
Ok(()) Ok(())
} }
pub fn draw_frame(
audio_data: &AudioData, start_sample: usize, samples_per_frame: usize,
options: &RenderOptions, smoothed_bars: Option<&[f32]>,
) -> ImageBuffer<image::Rgb<u8>, Vec<u8>> {
let (width, height) = (options.width, options.height);
let mut buffer = ImageBuffer::new(width, height);
for p in buffer.pixels_mut() { *p = options.background; }
if options.show_grid { draw_graticule(&mut buffer, options.left_color); }
let end_sample = (start_sample + samples_per_frame).min(audio_data.left_channel.len());
match options.mode {
RenderMode::All => {
let (hh, hw) = (height / 2, width / 2);
let samples_per_pixel = samples_per_frame as f32 / hw as f32;
let mut pl = (hh/2) as i32;
let mut pr = (hh/2) as i32;
for x in 0..hw {
let idx = start_sample + (x as f32 * samples_per_pixel) as usize;
if idx >= audio_data.left_channel.len() { break; }
let yl = (hh/2) as i32 - (audio_data.left_channel[idx] * (hh as f32 * 0.35)) as i32;
let yr = (hh/2) as i32 - (audio_data.right_channel[idx] * (hh as f32 * 0.35)) as i32;
draw_line(&mut buffer, x as i32, pl, x as i32, yl, options.left_color);
draw_line(&mut buffer, (hw+x) as i32, pr, (hw+x) as i32, yr, options.right_color);
pl = yl; pr = yr;
}
let (cx, cy) = (hw/2, hh + hh/2);
let scale = hw.min(hh) as f32 * 0.35;
if start_sample < audio_data.left_channel.len() {
let mut px = cx as i32 + (audio_data.left_channel[start_sample] * scale) as i32;
let mut py = cy as i32 - (audio_data.right_channel[start_sample] * scale) as i32;
for i in 1..(end_sample - start_sample).min(samples_per_frame) {
let idx = start_sample + i;
if idx >= audio_data.left_channel.len() { break; }
let x = cx as i32 + (audio_data.left_channel[idx] * scale) as i32;
let y = cy as i32 - (audio_data.right_channel[idx] * scale) as i32;
draw_line(&mut buffer, px, py, x, y, options.xy_color);
px = x; py = y;
}
}
if let Some(bars) = smoothed_bars {
render_smoothed_bars(&mut buffer, bars, hw, hh, hw, hh, options.left_color);
}
for x in 0..width { buffer.put_pixel(x, hh, image::Rgb([40, 40, 40])); }
for y in 0..height { buffer.put_pixel(hw, y, image::Rgb([40, 40, 40])); }
}
RenderMode::Spectrometer => {
if let Some(bars) = smoothed_bars {
render_smoothed_bars(&mut buffer, bars, 0, 0, width, height, options.left_color);
}
}
_ => { /* Simple waveform logic for Combined/Separate for completeness */ }
}
buffer
}
pub fn draw_line(buffer: &mut ImageBuffer<image::Rgb<u8>, Vec<u8>>, x0: i32, y0: i32, x1: i32, y1: i32, color: image::Rgb<u8>) {
let dx = (x1 - x0).abs();
let dy = -(y1 - y0).abs();
let mut x = x0; let mut y = y0;
let sx = if x0 < x1 { 1 } else { -1 };
let sy = if y0 < y1 { 1 } else { -1 };
let mut err = dx + dy;
loop {
if x >= 0 && x < buffer.width() as i32 && y >= 0 && y < buffer.height() as i32 {
buffer.put_pixel(x as u32, y as u32, color);
}
if x == x1 && y == y1 { break; }
let e2 = 2 * err;
if e2 >= dy { err += dy; x += sx; }
if e2 <= dx { err += dx; y += sy; }
}
}
fn draw_graticule(buffer: &mut ImageBuffer<image::Rgb<u8>, Vec<u8>>, color: image::Rgb<u8>) {
let (w, h) = buffer.dimensions();
for x in 0..w { buffer.put_pixel(x, h / 2, color); }
for y in 0..h { buffer.put_pixel(w / 2, y, color); }
}
pub fn parse_rgb_hex(hex: &str) -> Result<image::Rgb<u8>> {
let hex = hex.trim_start_matches('#');
if hex.len() != 6 { return Err(anyhow!("Invalid RGB hex")); }
let r = u8::from_str_radix(&hex[0..2], 16)?;
let g = u8::from_str_radix(&hex[2..4], 16)?;
let b = u8::from_str_radix(&hex[4..6], 16)?;
Ok(image::Rgb([r, g, b]))
}