Graph example not writing to a file, but to a buffer not "working"

[manuelarte]

Hi, I would like to run the example of the graphs but instead of writing to a file, get the buffer so I can send the image. This is what I changed

use plotters::prelude::*;

const OUT_FILE_NAME: &str = "plotters-doc-data/sample.png";

fn main() -> Result<Vec<u8>, Box<dyn std::error::Error>> {
    let width = 1024;
    let height = 768;
    let mut buffer = vec![0; (width as usize) * (height as usize) * 3];
    {
      let root_area =
                  BitMapBackend::with_buffer(&mut buffer, (width , height )).into_drawing_area();
  
      root_area.fill(&WHITE)?;
  
      let root_area = root_area.titled("Image Title", ("sans-serif", 60))?;
  
      let (upper, lower) = root_area.split_vertically(512);
  
      let x_axis = (-3.4f32..3.4).step(0.1);
  
      let mut cc = ChartBuilder::on(&upper)
          .margin(5)
          .set_all_label_area_size(50)
          .caption("Sine and Cosine", ("sans-serif", 40))
          .build_cartesian_2d(-3.4f32..3.4, -1.2f32..1.2f32)?;
  
      cc.configure_mesh()
          .x_labels(20)
          .y_labels(10)
          .disable_mesh()
          .x_label_formatter(&|v| format!("{:.1}", v))
          .y_label_formatter(&|v| format!("{:.1}", v))
          .draw()?;
  
      cc.draw_series(LineSeries::new(x_axis.values().map(|x| (x, x.sin())), &RED))?
          .label("Sine")
          .legend(|(x, y)| PathElement::new(vec![(x, y), (x + 20, y)], RED));
  
      cc.draw_series(LineSeries::new(
          x_axis.values().map(|x| (x, x.cos())),
          &BLUE,
      ))?
      .label("Cosine")
      .legend(|(x, y)| PathElement::new(vec![(x, y), (x + 20, y)], BLUE));
  
      cc.configure_series_labels().border_style(BLACK).draw()?;
  
      /*
      // It's possible to use a existing pointing element
       cc.draw_series(PointSeries::<_, _, Circle<_>>::new(
          (-3.0f32..2.1f32).step(1.0).values().map(|x| (x, x.sin())),
          5,
          Into::<ShapeStyle>::into(&RGBColor(255,0,0)).filled(),
      ))?;*/
  
      // Otherwise you can use a function to construct your pointing element yourself
      cc.draw_series(PointSeries::of_element(
          (-3.0f32..2.1f32).step(1.0).values().map(|x| (x, x.sin())),
          5,
          ShapeStyle::from(&RED).filled(),
          &|coord, size, style| {
              EmptyElement::at(coord)
                  + Circle::new((0, 0), size, style)
                  + Text::new(format!("{:?}", coord), (0, 15), ("sans-serif", 15))
          },
      ))?;
  
      let drawing_areas = lower.split_evenly((1, 2));
  
      for (drawing_area, idx) in drawing_areas.iter().zip(1..) {
          let mut cc = ChartBuilder::on(drawing_area)
              .x_label_area_size(30)
              .y_label_area_size(30)
              .margin_right(20)
              .caption(format!("y = x^{}", 1 + 2 * idx), ("sans-serif", 40))
              .build_cartesian_2d(-1f32..1f32, -1f32..1f32)?;
          cc.configure_mesh()
              .x_labels(5)
              .y_labels(3)
              .max_light_lines(4)
              .draw()?;
  
          cc.draw_series(LineSeries::new(
              (-1f32..1f32)
                  .step(0.01)
                  .values()
                  .map(|x| (x, x.powf(idx as f32 * 2.0 + 1.0))),
              &BLUE,
          ))?;
      }
  
      // To avoid the IO failure being ignored silently, we manually call the present function
      root_area.present().expect("Unable to write result to file, please make sure 'plotters-doc-data' dir exists under current dir");
    }
    Ok(buffer)
}
#[test]
fn entry_point() {
    let buffer = main().unwrap()
    let image = image::RgbImage::from_raw(input.width, input.height, buffer.clone()).unwrap();
    let path = format!("{}/{}", OUT_DIRECTORY, "graphs.png".to_string());
    image.save(&Path::new(path.as_str()))?;
    println!("Result has been saved to {}", OUT_DIRECTORY);
}

But I get a weird image (with the graphs overlapping), not the graphs, any idea what I am doing wrong? I have very similar code with the histogram and it works.