src/element/mod.rs

/*!
    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 is a pending drawing operation on a drawing backend with pixel-based coordinate

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

    ```rust
    use std::iter::{Once, once};
    use plotters::element::{PointCollection, Drawable};
    use plotters_backend::{BackendCoord, DrawingErrorKind, BackendStyle};
    use plotters::style::IntoTextStyle;
    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 Point = &'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,
            _: (u32, u32),
        ) -> Result<(), DrawingErrorKind<DB::ErrorType>> {
            let pos = pos.next().unwrap();
            backend.draw_rect(pos, (pos.0 + 10, pos.1 + 12), &RED, false)?;
            let text_style = &("sans-serif", 20).into_text_style(&backend.get_size()).color(&RED);
            backend.draw_text("X", text_style, pos)
        }
    }

    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(())
    }
    ```
      ![](https://plotters-rs.github.io/plotters-doc-data/element-0.png)

      ## 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 element, 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:
    ```rust
    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 = ("sans-serif", 20).into();
        root.draw(&(EmptyElement::at((200, 200))
                + Text::new("X", (0, 0), &"sans-serif".into_font().resize(20.0).color(&RED))
                + Rectangle::new([(0,0), (10, 12)], &RED)
        ))?;
        Ok(())
    }
    ```
    ![](https://plotters-rs.github.io/plotters-doc-data/element-1.png)

    ## 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 heterogynous, which means
    the iterator should be able to holds elements in different type.
    For example, a point series with cross 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 external 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 dynamic element wrapper.

    For example, the following code counts the number of factors of integer and mark all prime numbers in cross.
    ```rust
    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(())
    }
    ```
    ![](https://plotters-rs.github.io/plotters-doc-data/element-3.png)
*/
use plotters_backend::{BackendCoord, DrawingBackend, DrawingErrorKind};
use std::borrow::Borrow;

mod basic_shapes;
pub use basic_shapes::*;

mod text;
pub use text::*;

mod points;
pub use points::*;

mod composable;
pub use composable::{ComposedElement, EmptyElement};

#[cfg(feature = "candlestick")]
mod candlestick;
#[cfg(feature = "candlestick")]
pub use candlestick::CandleStick;

#[cfg(feature = "errorbar")]
mod errorbar;
#[cfg(feature = "errorbar")]
pub use errorbar::{ErrorBar, ErrorBarOrientH, ErrorBarOrientV};

#[cfg(feature = "boxplot")]
mod boxplot;
#[cfg(feature = "boxplot")]
pub use boxplot::Boxplot;

#[cfg(feature = "bitmap_backend")]
mod image;
#[cfg(feature = "bitmap_backend")]
pub use self::image::BitMapElement;

mod dynelem;
pub use dynelem::{DynElement, IntoDynElement};

/// A type which is logically a collection of points, under any given coordinate system.
/// Note: Ideally, a point collection trait should be any type of which coordinate elements can be
/// iterated. This is similar to `iter` method of many collection types in std.
///
/// ```ignore
/// trait PointCollection<Coord> {
///     type PointIter<'a> : Iterator<Item = &'a Coord>;
///     fn iter(&self) -> PointIter<'a>;
/// }
/// ```
///
/// However,
/// [Generic Associated Types](https://github.com/rust-lang/rfcs/blob/master/text/1598-generic_associated_types.md)
/// is far away from stablize.
/// So currently we have the following workaround:
///
/// Instead of implement the PointCollection trait on the element type itself, it implements on the
/// reference to the element. By doing so, we now have a well-defined lifetime for the iterator.
///
/// In addition, for some element, the coordinate is computed on the fly, thus we can't hard-code
/// the iterator's return type is `&'a Coord`.
/// `Borrow` trait seems to strict in this case, since we don't need the order and hash
/// preservation properties at this point. However, `AsRef` doesn't work with `Coord`
///
/// This workaround also leads overly strict lifetime bound on `ChartContext::draw_series`.
///
/// TODO: Once GAT is ready on stable Rust, we should simplify the design.
///
pub trait PointCollection<'a, Coord> {
    /// The item in point iterator
    type Point: Borrow<Coord> + 'a;

    /// The point iterator
    type IntoIter: IntoIterator<Item = Self::Point>;

    /// framework to do the coordinate mapping
    fn point_iter(self) -> Self::IntoIter;
}
/// The trait indicates we are able to draw it on a drawing area
pub trait Drawable<DB: DrawingBackend> {
    /// Actually draws the element. The key points is already translated into the
    /// image coordinate and can be used by DC directly
    fn draw<I: Iterator<Item = BackendCoord>>(
        &self,
        pos: I,
        backend: &mut DB,
        parent_dim: (u32, u32),
    ) -> Result<(), DrawingErrorKind<DB::ErrorType>>;
}