Add support for grids

This support is basic so far, and only for continuous views for now.

The user can choose how many grid points they wish to use for each axis
(defaults to 3 each), and the colour of the grid lines (defaults to a
grey colour).

Author: simonrw

examples/with_grid.rs

@@ -0,0 +1,16 @@
+extern crate plotlib;
+
+use plotlib::grid::Grid;
+use plotlib::style::Line;
+use plotlib::view::View;
+
+fn main() {
+    let l1 = plotlib::line::Line::new(&[(0., 1.), (2., 1.5), (3., 1.2), (4., 1.1)])
+        .style(plotlib::line::Style::new().colour("burlywood"));
+    let grid = Grid::new(3, 8);
+    let mut v = plotlib::view::ContinuousView::new().add(&l1);
+    v.add_grid(grid);
+    plotlib::page::Page::single(&v)
+        .save("line.svg")
+        .expect("saving svg");
+}

src/grid.rs

@@ -0,0 +1,21 @@
+pub struct Grid {
+    pub nx: u32,
+    pub ny: u32,
+    pub color: String,
+}
+
+impl Default for Grid {
+    fn default() -> Self {
+        Grid::new(3, 3)
+    }
+}
+
+impl Grid {
+    pub fn new(nx: u32, ny: u32) -> Grid {
+        Grid {
+            nx,
+            ny,
+            color: "darkgrey".to_owned(),
+        }
+    }
+}

src/lib.rs

@@ -88,6 +88,7 @@ pub mod barchart;
 pub mod boxplot;
 mod errors;
 pub mod function;
+pub mod grid;
 pub mod histogram;
 pub mod line;
 pub mod scatter;

src/svg_render.rs

@@ -4,6 +4,7 @@ use svg::node;
 use svg::Node;
 
 use crate::axis;
+use crate::grid::Grid;
 use crate::histogram;
 use crate::style;
 use crate::utils;
@@ -14,14 +15,34 @@ fn value_to_face_offset(value: f64, axis: &axis::ContinuousAxis, face_size: f64)
     (face_size * (value - axis.min())) / range
 }
 
+fn vertical_line<S>(xpos: f64, ymin: f64, ymax: f64, color: S) -> node::element::Line
+where
+    S: AsRef<str>,
+{
+    node::element::Line::new()
+        .set("x1", xpos)
+        .set("x2", xpos)
+        .set("y1", ymin)
+        .set("y2", ymax)
+        .set("stroke", color.as_ref())
+        .set("stroke-width", 1)
+}
+
+fn horizontal_line<S>(ypos: f64, xmin: f64, xmax: f64, color: S) -> node::element::Line
+where
+    S: AsRef<str>,
+{
+    node::element::Line::new()
+        .set("x1", xmin)
+        .set("x2", xmax)
+        .set("y1", ypos)
+        .set("y2", ypos)
+        .set("stroke", color.as_ref())
+        .set("stroke-width", 1)
+}
+
 pub fn draw_x_axis(a: &axis::ContinuousAxis, face_width: f64) -> node::element::Group {
-    let axis_line = node::element::Line::new()
-        .set("x1", 0)
-        .set("y1", 0)
-        .set("x2", face_width)
-        .set("y2", 0)
-        .set("stroke", "black")
-        .set("stroke-width", 1);
+    let axis_line = horizontal_line(0.0, 0.0, face_width, "black");
 
     let mut ticks = node::element::Group::new();
     let mut labels = node::element::Group::new();
@@ -61,13 +82,7 @@ pub fn draw_x_axis(a: &axis::ContinuousAxis, face_width: f64) -> node::element::
 }
 
 pub fn draw_y_axis(a: &axis::ContinuousAxis, face_height: f64) -> node::element::Group {
-    let axis_line = node::element::Line::new()
-        .set("x1", 0)
-        .set("y1", 0)
-        .set("x2", 0)
-        .set("y2", -face_height)
-        .set("stroke", "black")
-        .set("stroke-0", 1);
+    let axis_line = vertical_line(0.0, 0.0, -face_height, "black");
 
     let mut ticks = node::element::Group::new();
     let mut labels = node::element::Group::new();
@@ -101,7 +116,8 @@ pub fn draw_y_axis(a: &axis::ContinuousAxis, face_height: f64) -> node::element:
         .set(
             "transform",
             format!("rotate(-90 {} {})", -30, -(face_height / 2.)),
-        ).add(node::Text::new(a.get_label()));
+        )
+        .add(node::Text::new(a.get_label()));
 
     node::element::Group::new()
         .add(ticks)
@@ -214,7 +230,8 @@ where
                         .set(
                             "stroke",
                             style.get_colour().clone().unwrap_or_else(|| "".into()),
-                        ).set("stroke-width", 2)
+                        )
+                        .set("stroke-width", 2)
                         .set("d", path),
                 );
             }
@@ -253,7 +270,8 @@ where
                     .get_fill()
                     .clone()
                     .unwrap_or_else(|| "burlywood".into()),
-            ).set("stroke", "black");
+            )
+            .set("stroke", "black");
         group.append(rect);
     }
 
@@ -298,7 +316,8 @@ where
             .set(
                 "stroke",
                 style.get_colour().clone().unwrap_or_else(|| "".into()),
-            ).set("stroke-width", style.get_width().clone().unwrap_or(2.))
+            )
+            .set("stroke-width", style.get_width().clone().unwrap_or(2.))
             .set("d", path),
     );
 
@@ -344,7 +363,8 @@ where
                     .get_fill()
                     .clone()
                     .unwrap_or_else(|| "burlywood".into()),
-            ).set("stroke", "black"),
+            )
+            .set("stroke", "black"),
     );
 
     let mid_line = -value_to_face_offset(median, y_axis, face_height);
@@ -421,12 +441,37 @@ where
                     .get_fill()
                     .clone()
                     .unwrap_or_else(|| "burlywood".into()),
-            ).set("stroke", "black"),
+            )
+            .set("stroke", "black"),
     );
 
     group
 }
 
+pub(crate) fn draw_grid(grid: &Grid, face_width: f64, face_height: f64) -> node::element::Group {
+    let (xmin, xmax) = (0f64, face_width);
+    let (ymin, ymax) = (0f64, face_height);
+
+    let x_step = (xmax - xmin) / f64::from(grid.nx);
+    let y_step = (ymax - ymin) / f64::from(grid.ny);
+
+    let mut lines = node::element::Group::new();
+
+    for iy in 0..=grid.ny {
+        let y = f64::from(iy) * y_step + ymin;
+        let line = horizontal_line(-y, 0.0, face_width, grid.color.as_str());
+        lines = lines.add(line);
+    }
+
+    for ix in 0..=grid.nx {
+        let x = f64::from(ix) * x_step + xmin;
+        let line = vertical_line(x, 0.0, -face_height, grid.color.as_str());
+        lines = lines.add(line);
+    }
+
+    lines
+}
+
 #[cfg(test)]
 mod tests {
     use super::*;

src/view.rs

@@ -14,13 +14,16 @@ use svg::Node;
 
 use crate::axis;
 use crate::errors::Result;
+use crate::grid::Grid;
 use crate::representation::{CategoricalRepresentation, ContinuousRepresentation};
 use crate::svg_render;
 use crate::text_render;
 
 pub trait View {
     fn to_svg(&self, face_width: f64, face_height: f64) -> Result<svg::node::element::Group>;
     fn to_text(&self, face_width: u32, face_height: u32) -> Result<String>;
+    fn add_grid(&mut self, grid: Grid);
+    fn grid<'a>(&'a self) -> &'a Option<Grid>;
 }
 
 /// Standard 1-dimensional view with a continuous x-axis
@@ -31,6 +34,7 @@ pub struct ContinuousView<'a> {
     y_range: Option<axis::Range>,
     x_label: Option<String>,
     y_label: Option<String>,
+    grid: Option<Grid>,
 }
 
 impl<'a> ContinuousView<'a> {
@@ -44,6 +48,7 @@ impl<'a> ContinuousView<'a> {
             y_range: None,
             x_label: None,
             y_label: None,
+            grid: None,
         }
     }
 
@@ -164,6 +169,11 @@ impl<'a> View for ContinuousView<'a> {
         // Add in the axes
         view_group.append(svg_render::draw_x_axis(&x_axis, face_width));
         view_group.append(svg_render::draw_y_axis(&y_axis, face_height));
+
+        if let Some(grid) = &self.grid {
+            view_group.append(svg_render::draw_grid(grid, face_width, face_height));
+        }
+
         Ok(view_group)
     }
 
@@ -212,6 +222,14 @@ impl<'a> View for ContinuousView<'a> {
 
         Ok(view_string)
     }
+
+    fn add_grid(&mut self, grid: Grid) {
+        self.grid = Some(grid)
+    }
+
+    fn grid(&self) -> &Option<Grid> {
+        &self.grid
+    }
 }
 
 /// A view with categorical entries along the x-axis and continuous values along the y-axis
@@ -222,6 +240,7 @@ pub struct CategoricalView<'a> {
     y_range: Option<axis::Range>,
     x_label: Option<String>,
     y_label: Option<String>,
+    grid: Option<Grid>,
 }
 
 impl<'a> CategoricalView<'a> {
@@ -235,6 +254,7 @@ impl<'a> CategoricalView<'a> {
             y_range: None,
             x_label: None,
             y_label: None,
+            grid: None,
         }
     }
 
@@ -355,6 +375,14 @@ impl<'a> View for CategoricalView<'a> {
     fn to_text(&self, _face_width: u32, _face_height: u32) -> Result<String> {
         Ok("".into())
     }
+
+    fn add_grid(&mut self, grid: Grid) {
+        self.grid = Some(grid);
+    }
+
+    fn grid(&self) -> &Option<Grid> {
+        &self.grid
+    }
 }
 
 /*pub struct AnyView<'a> {