An outline of the common steps found in all the examples.
1) For a given projeciton, use its default projection builder , make changes to the scale, translation .. etc, then call build() to construct a projector.
```rust
let projector = Stereographic::<f64>::builder()
.scale_set(100_f64)
.translate_set(&Coord {
x: 300_f64,
y: 300_f64,
})
.clip_angle(90_f64)
.precision_set(&10_f64)
.build();
````
2) Construct a PathBuilder
A Path is a collection of nodes where each step on the path transforms the geometry object.
An object is then streamed along the path. The endpoints are special path nodes which hold the result of a calculation. A variey of endpoint are available Area, Centroid, Length which can be use to compute statistics about polygons or lines. These examples only show endpoints that render to a HTML canvas element or a SVG path element.
When rendering to a HTML canvas the endpoint holds Path2D "rendering conext"
```rust
// Construct a PathBuilder linked to Path2d
// rendering context.
let path2d = Path2d::new()?;
let endpoint = PathBuilder::new(path2d);
let pb = PathBuilder::new(endpoint);
let path = pb.build();
```
When generating a SVG image, the endpint holds a string value from which a PATH element can be constructed.
```rust
let pb = PathBuilder::pathstring();
let path = pb.build();
```
3) Please see the different examples, but the common next step is to
construct a PathBuilder object and then to stream a geometry object into it :-
```rust
// 'countries' is a geometry extratced from
// a world map json file.
path.stream(&countries)
```
Running the examples
Requirements:
To view an example application either create a devleopment build, or construct a static-web site as follows
Start And Run A Development Build
console
git clone https://github.com/martinfrances107/rust_d3_geo.git
cd rust_d3_geo/examples/ring/
npm install
npm run start
The last command "npm run start" will automatically open your default browser at http:://localhost::8080
Performance: Building A Static Site
Much better performance can be acheived by bulding a static web site and viewing that directly. At the expense of longer build times the RUST protions of the code a build using the "--release" tags
console
git clone https://github.com/martinfrances107/rust_d3_geo.git
cd rust_d3_geo/examples/ring
npm install
npm run build
npm run serve
Benchmarking
The github respoitory associated with crate has two "profile targets" and two "benches"
which can be used to to spot bottlnecks in the code.
The benches are Criterion.rs based micro benchmarks.
See also rustd3geo_voronoi
uses this library, and that project contains a benchmark which contains an exact port of a benchmark in d3-geo-voronoi.
Based on that benchmark rust is 31% faster, or permits a 37% increase in throughput.
Flamegraph
A profile_target is binary that outputs a HTML page containing a SVG image showing the globe with graticule markings.
A flamegraph can be created with the following
bash
cd profile_target
sudo CARGO_PROFILE_RELEASE_DEBUG=true cargo flamegraph
The complexity of rendering 240 countries/polygons provides a good view in memory allocation issues.
Coding Standard
- Idomatic RUST, as defined by cargo clippy where possible.
No booleans as arguments to functions/methods, use two state enums instead.
See "Reflect" as an example.
rust
pub trait ReflectSet {
/// f64 or f32.
type T;
/// Set the projection builder to invert the x-coordinate.
fn reflect_x_set(&mut self, reflect: Reflect) -> &mut Self;
/// Set the projection builder to invert the y-coordinate.
fn reflect_y_set(&mut self, reflect: Reflect) -> &mut Self;
}
This allow for a clearer statement of intent :-
```rust
builder.reflectyset(Reflect::Flipped);
```
"Type-Driven API Design" is the
preferred way of constructing state machines.
In the example below, when assembling a stream pipeline, connect() can only be called
when the state is "Unconnected". The output type's STATE is "Connected\
rust
impl StreamTransformRadians<Unconnected> {
#[inline]
/// Connect this node to the next element in the pipeline.
pub const fn connect<EP, SINK, T>(self, sink: SINK) -> StreamTransformRadians<Connected<SINK>>
where
SINK: Clone,
{
StreamTransformRadians(Connected { sink })
}
}
The "Stream" trait is only implemented when the STATE is "Connected\
Future 2.0 upgrades
Version 1.0 is stable.
"Semantic Versioning" guidelines :-
- Increment the major number when a breaking change occurs.
- Increment the minor number when a new feature is added, @deprecated notes added to outdated functions,
- Increment the patch number for tighly focused security fixes.
Future Work.
Architecture discussion
There is an aspect of the design that needs review. It related to the best way to implement a doubly-linked list which has cross links between nodes.
The clipping algorithm in clip/rejoin/mod.rs needs to be refactored.
see The intersection Problem.
Test coverage in that area is high so the algortihms is working but the data structures make extensive use of vectors ( heap objects ) containng references to other heap objects Vec<Options<Rc<RefCell<_Intersection_>>>> which is not performant.
A full discusion can be found here
Unimplemented sections of the library
Support for a custom projection is not yet supported.
For an example of this see the test labelled "projection.fitExtent(…) custom projection"
