[−][src]Module plotters::element

Defines the drawing elements, the high-level drawing unit in Plotters drawing system

Introduction

An element is the drawing unit for Plotter's high-level drawing API. Different from low-level drawing API, an element is a logic unit of component in the image. There are few built-in elements, including Circle, Pixel, Rectangle, Path, Text, etc.

All element can be drawn onto the drawing area using API DrawingArea::draw(...). Plotters use "iterator of elements" as the abstraction of any type of plot.

Implementing your own element

You can also define your own element, CandleStick is a good sample of implementing complex element. There are two trait required for an element:

PointCollection - the struct should be able to return an iterator of key-points under guest coordinate
Drawable - the struct should be able to use performe drawing on a drawing backend with pixel-based coordinate

An example of element that draws a red "X" in a red rectangle onto the backend:

use std::iter::{Once, once};
use plotters::element::{PointCollection, Drawable};
use plotters::drawing::backend::{BackendCoord, DrawingErrorKind};
use plotters::prelude::*;

// Any example drawing a red X
struct RedBoxedX((i32, i32));

// For any reference to RedX, we can convert it into an iterator of points
impl <'a> PointCollection<'a, (i32, i32)> for &'a RedBoxedX {
    type Borrow = &'a (i32, i32);
    type IntoIter = Once<&'a (i32, i32)>;
    fn point_iter(self) -> Self::IntoIter {
        once(&self.0)
    }
}

// How to actually draw this element
impl <DB:DrawingBackend> Drawable<DB> for RedBoxedX {
    fn draw<I:Iterator<Item = BackendCoord>>(
        &self,
        mut pos: I,
        backend: &mut DB
    ) -> Result<(), DrawingErrorKind<DB::ErrorType>> {
        let pos = pos.next().unwrap();
        backend.draw_rect(pos, (pos.0 + 10, pos.1 + 12), &Red.to_rgba(), false)?;
        backend.draw_text("X", &("Arial", 20).into(), pos, &Red.to_rgba())
    }
}

fn main() -> Result<(), Box<dyn std::error::Error>> {
    let root = BitMapBackend::new(
        "plotters-doc-data/element-0.png",
        (640, 480)
    ).into_drawing_area();
    root.draw(&RedBoxedX((200, 200)))?;
    Ok(())
}

Composable Elements

You also have an convenient way to build an element that isn't built into the Plotters library by combining existing elements into a logic group. To build an composable elemnet, you need to use an logic empty element that draws nothing to the backend but denotes the relative zero point of the logical group. Any element defined with pixel based offset coordinate can be added into the group later using the + operator.

For example, the red boxed X element can be implemented with Composable element in the following way:

use plotters::prelude::*;
fn main() -> Result<(), Box<dyn std::error::Error>> {
    let root = BitMapBackend::new(
        "plotters-doc-data/element-1.png",
        (640, 480)
    ).into_drawing_area();
    let font:FontDesc = ("Arial", 20).into();
    root.draw(&(EmptyElement::at((200, 200))
            + Text::new("X", (0, 0), &"Arial".into_font().resize(20.0).color(&Red))
            + Rectangle::new([(0,0), (10, 12)], &Red)
    ))?;
    Ok(())
}

Dynamic Elements

By default, Plotters uses static dispatch for all the elements and series. For example, the ChartContext::draw_series method accepts an iterator of T where type T implements all the traits a element should implement. Although, we can use the series of composable element for complex series drawing. But sometimes, we still want to make the series heterogyous, which means the iterator should be able to holds elements in different type. For example, a point series with corss and circle. This requires the dynamically dispatched elements. In plotters, all the elements can be converted into DynElement, the dynamic dispatch container for all elements (include exernal implemented ones). Plotters automatically implements IntoDynElement for all elements, by doing so, any dynamic element should have into_dyn function which would wrap the element into a dynmanic element wrapper.

For example, the following code counts the number of factors of integer and mark all prime numbers in cross.

use plotters::prelude::*;
fn num_of_factor(n: i32) -> i32 {
    let mut ret = 2;
    for i in 2..n {
        if i * i > n {
            break;
        }

        if n % i == 0 {
            if i * i != n {
                ret += 2;
            } else {
                ret += 1;
            }
        }
    }
    return ret;
}
fn main() -> Result<(), Box<dyn std::error::Error>> {
    let root =
        BitMapBackend::new("plotters-doc-data/element-3.png", (640, 480))
        .into_drawing_area();
    root.fill(&White)?;
    let mut chart = ChartBuilder::on(&root)
        .x_label_area_size(40)
        .y_label_area_size(40)
        .margin(5)
        .build_ranged(0..50, 0..10)?;

    chart
        .configure_mesh()
        .disable_x_mesh()
        .disable_y_mesh()
        .draw()?;

    chart.draw_series((0..50).map(|x| {
        let center = (x, num_of_factor(x));
        // Although the arms of if statement has different types,
        // but they can be placed into a dynamic element wrapper,
        // by doing so, the type is unified.
        if center.1 == 2 {
            Cross::new(center, 4, Into::<ShapeStyle>::into(&Red).filled()).into_dyn()
        } else {
            Circle::new(center, 4, Into::<ShapeStyle>::into(&Green).filled()).into_dyn()
        }
    }))?;

    Ok(())
}

Structs

CandleStick	The candelstick data point element
Circle	A circle element
ComposedElement	The composed element which has at least two components
Cross	Describe a cross
DynElement	The container for a dynamically dispatched element
EmptyElement	An empty composibable element, which is the start point of an ad-hoc composible element
MultiLineText	An multi-line text element. The `Text` element allows only signle line text and the `MultiLineText` supports drawing multiple lines
Path	An element of a series of connected lines
Pixel	An element of a single pixel
Rectangle	A rectangle element
Text	A single line text element. This can be owned or borrowed string, dependeneds on `String` or `str` moved into.

Traits

Drawable	The trait indicates we are able to draw it on a drawing area
IntoDynElement	The trait that makes the conversion from the statically dispatched element to the dynamically dispatched element
PointCollection	A type which is logically a collection of points, under any given coordinate system
PointElement	The element that used to describe a point