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//! Tools to help with generating vertex and index buffers.
//!
//! ## Overview
//!
//! While it would be possible for the tessellation algorithms to manually generate vertex
//! and index buffers with a certain layout, it would mean that most code using the tessellators
//! have to copy and convert all generated vertices in order to have their own vertex
//! layout, or de-interleaved vertex formats, which is a very common use-case.
//!
//! In order to flexibly and efficiently build geometry of various flavors, this module contains
//! a number of builder interfaces that centered around the idea of building vertex and index
//! buffers without having to know about the final vertex and index types.
//!
//! See:
//!
//! * [`GeometryBuilder`](trait.GeometryBuilder.html)
//! * [`FillGeometryBuilder`](trait.FillGeometryBuilder.html)
//! * [`StrokeGeometryBuilder`](trait.StrokeGeometryBuilder.html)
//!
//! The traits above are what the tessellators interface with. It is very common to push
//! vertices and indices into a pair of vectors, so to facilitate this pattern this module
//! also provides:
//!
//! * The struct [`VertexBuffers`](struct.VertexBuffers.html) is a simple pair of vectors of
//! indices and vertices (generic parameters).
//! * The struct [`BuffersBuilder`](struct.BuffersBuilder.html) which writes into a
//! [`VertexBuffers`](struct.VertexBuffers.html) and implements the various geometry
//! builder traits. It takes care of filling the buffers while producing vertices is
//! delegated to a vertex constructor.
//! * The traits [`FillVertexConstructor`](trait.FillVertexConstructor.html),
//! [`StrokeVertexConstructor`](trait.StrokeVertexConstructor.html) and
//! [`BuffersBuilder`](struct.BuffersBuilder.html) in order to generate any vertex type. In the
//! first example below, a struct `WithColor` implements the `FillVertexConstructor` trait in order to
//! create vertices composed of a 2d position and a color value from an input 2d position.
//! This separates the construction of vertex values from the assembly of the vertex buffers.
//! Another, simpler example of vertex constructor is the [`Positions`](struct.Positions.html)
//! constructor which just returns the vertex position untransformed.
//!
//! Geometry builders are a practical way to add one last step to the tessellation pipeline,
//! such as applying a transform or clipping the geometry.
//!
//! While this is module designed to facilitate the generation of vertex buffers and index
//! buffers, nothing prevents a given GeometryBuilder implementation to only generate a
//! vertex buffer without indices, or write into a completely different format.
//! These builder traits are at the end of the tessellation pipelines and are meant for
//! users of this crate to be able to adapt the output of the tessellators to their own
//! needs.
//!
//! ## Do I need to implement geometry builders or vertex constructors?
//!
//! If you only generate a vertex buffer and an index buffer (as a pair of standard `Vec`),
//! then the simplest option is to work with custom vertex constructors and use
//! `VertexBuffers` and `BuffersBuilder`.
//!
//! For more specific or elaborate use cases where control over where the vertices as written
//! is needed such as building de-interleaved vertex buffers or writing directly into a mapped
//! GPU buffer, implementing custom geometry builders is the right thing to do.
//!
//! Which of the vertex constructor or geometry builder traits to implement (fill/stroke/basic
//! variants), depends on which tessellators the builder or constructor will interface with.
//!
//! ## Examples
//!
//! ### Generating custom vertices
//!
//! The example below implements the `FillVertexConstructor` trait in order to use a custom
//! vertex type `MyVertex` (containing position and color), storing the tessellation in a
//! `VertexBuffers<MyVertex, u16>`, and tessellates two shapes with different colors.
//!
//! ```
//! extern crate lyon_tessellation as tess;
//! use tess::{FillVertexConstructor, VertexBuffers, BuffersBuilder, FillOptions, FillTessellator, FillVertex};
//! use tess::math::{Point, point};
//!
//! // Our custom vertex.
//! #[derive(Copy, Clone, Debug)]
//! pub struct MyVertex {
//! position: [f32; 2],
//! color: [f32; 4],
//! }
//!
//! // The vertex constructor. This is the object that will be used to create the custom
//! // vertices from the information provided by the tessellators.
//! struct WithColor([f32; 4]);
//!
//! impl FillVertexConstructor<MyVertex> for WithColor {
//! fn new_vertex(&mut self, vertex: FillVertex) -> MyVertex {
//! MyVertex {
//! position: vertex.position().to_array(),
//! color: self.0,
//! }
//! }
//! }
//!
//! fn main() {
//! let mut output: VertexBuffers<MyVertex, u16> = VertexBuffers::new();
//! let mut tessellator = FillTessellator::new();
//! // Tessellate a red and a green circle.
//! tessellator.tessellate_circle(
//! point(0.0, 0.0),
//! 10.0,
//! &FillOptions::tolerance(0.05),
//! &mut BuffersBuilder::new(
//! &mut output,
//! WithColor([1.0, 0.0, 0.0, 1.0])
//! ),
//! );
//! tessellator.tessellate_circle(
//! point(10.0, 0.0),
//! 5.0,
//! &FillOptions::tolerance(0.05),
//! &mut BuffersBuilder::new(
//! &mut output,
//! WithColor([0.0, 1.0, 0.0, 1.0])
//! ),
//! );
//!
//! println!(" -- {} vertices, {} indices", output.vertices.len(), output.indices.len());
//! }
//! ```
//!
//! ### Generating a completely custom output
//!
//! Using `VertexBuffers<T>` is convenient and probably fits a lot of use cases, but
//! what if we do not want to write the geometry in a pair of vectors?
//! Perhaps we want to write the geometry in a different data structure or directly
//! into gpu-accessible buffers mapped on the CPU?
//!
//! ```
//! extern crate lyon_tessellation as tess;
//! use tess::{StrokeTessellator, GeometryBuilder, StrokeGeometryBuilder, StrokeOptions, GeometryBuilderError, StrokeVertex, VertexId};
//! use tess::math::{Point, point};
//! use tess::path::polygon::Polygon;
//! use std::fmt::Debug;
//! use std::u32;
//!
//! // A geometry builder that writes the result of the tessellation to stdout instead
//! // of filling vertex and index buffers.
//! pub struct ToStdOut {
//! vertices: u32,
//! indices: u32,
//! }
//!
//! impl ToStdOut {
//! pub fn new() -> Self { ToStdOut { vertices: 0, indices: 0 } }
//! }
//!
//! impl GeometryBuilder for ToStdOut {
//! fn begin_geometry(&mut self) {
//! // Reset the vertex in index counters.
//! self.vertices = 0;
//! self.indices = 0;
//! println!(" -- begin geometry");
//! }
//!
//! fn add_triangle(&mut self, a: VertexId, b: VertexId, c: VertexId) {
//! println!("triangle ({}, {}, {})", a.offset(), b.offset(), c.offset());
//! self.indices += 3;
//! }
//!
//! fn abort_geometry(&mut self) {
//! println!(" -- oops!");
//! }
//! }
//!
//! impl StrokeGeometryBuilder for ToStdOut {
//! fn add_stroke_vertex(&mut self, vertex: StrokeVertex) -> Result<VertexId, GeometryBuilderError> {
//! println!("vertex {:?}", vertex.position());
//! if self.vertices >= u32::MAX {
//! return Err(GeometryBuilderError::TooManyVertices);
//! }
//! self.vertices += 1;
//! Ok(VertexId(self.vertices as u32 - 1))
//! }
//! }
//!
//! fn main() {
//! let mut output = ToStdOut::new();
//! let mut tessellator = StrokeTessellator::new();
//! tessellator.tessellate_polygon(
//! Polygon {
//! points: &[point(0.0, 0.0), point(10.0, 0.0), point(5.0, 5.0)],
//! closed: true,
//! },
//! &StrokeOptions::default(),
//! &mut output,
//! );
//! }
//! ```
//!
use crate::math::Point;
use crate::{FillVertex, Index, StrokeVertex, VertexId};
pub use crate::error::GeometryBuilderError;
use core::convert::From;
use core::ops::Add;
use alloc::vec::Vec;
/// An interface separating tessellators and other geometry generation algorithms from the
/// actual vertex construction.
///
/// Depending on which tessellator a geometry builder interfaces with, it also has to
/// implement one or several of the following traits (Which contain the hooks to generate
/// vertices):
/// - [`FillGeometryBuilder`](trait.FillGeometryBuilder.html)
/// - [`StrokeGeometryBuilder`](trait.StrokeGeometryBuilder.html)
///
/// See the [`geometry_builder`](index.html) module documentation for more detailed explanation.
pub trait GeometryBuilder {
/// Called at the beginning of a generation.
///
/// end_geometry must be called before begin_geometry is called again.
fn begin_geometry(&mut self) {}
/// Called at the end of a generation.
/// Returns the number of vertices and indices added since the last time begin_geometry was
/// called.
fn end_geometry(&mut self) {}
/// Insert a triangle made of vertices that were added after the last call to begin_geometry.
///
/// This method can only be called between begin_geometry and end_geometry.
fn add_triangle(&mut self, a: VertexId, b: VertexId, c: VertexId);
/// abort_geometry is called instead of end_geometry if an error occurred while producing
/// the geometry and we won't be able to finish.
///
/// The implementation is expected to discard the geometry that was generated since the last
/// time begin_geometry was called, and to remain in a usable state.
fn abort_geometry(&mut self) {}
}
/// A Geometry builder to interface with the [`FillTessellator`](../struct.FillTessellator.html).
///
/// Types implementing this trait must also implement the [`GeometryBuilder`](trait.GeometryBuilder.html) trait.
pub trait FillGeometryBuilder: GeometryBuilder {
/// Inserts a vertex, providing its position, and optionally a normal.
/// Returns a vertex id that is only valid between begin_geometry and end_geometry.
///
/// This method can only be called between begin_geometry and end_geometry.
fn add_fill_vertex(&mut self, vertex: FillVertex) -> Result<VertexId, GeometryBuilderError>;
}
/// A Geometry builder to interface with the [`StrokeTessellator`](../struct.StrokeTessellator.html).
///
/// Types implementing this trait must also implement the [`GeometryBuilder`](trait.GeometryBuilder.html) trait.
pub trait StrokeGeometryBuilder: GeometryBuilder {
/// Inserts a vertex, providing its position, and optionally a normal.
/// Returns a vertex id that is only valid between begin_geometry and end_geometry.
///
/// This method can only be called between begin_geometry and end_geometry.
fn add_stroke_vertex(&mut self, vertex: StrokeVertex)
-> Result<VertexId, GeometryBuilderError>;
}
/// Structure that holds the vertex and index data.
///
/// Usually written into though temporary `BuffersBuilder` objects.
#[derive(Clone, Debug, Default)]
#[cfg_attr(feature = "serialization", derive(Serialize, Deserialize))]
pub struct VertexBuffers<OutputVertex, OutputIndex> {
pub vertices: Vec<OutputVertex>,
pub indices: Vec<OutputIndex>,
}
impl<OutputVertex, OutputIndex> VertexBuffers<OutputVertex, OutputIndex> {
/// Constructor
pub fn new() -> Self {
VertexBuffers::with_capacity(512, 1024)
}
/// Constructor
pub fn with_capacity(num_vertices: usize, num_indices: usize) -> Self {
VertexBuffers {
vertices: Vec::with_capacity(num_vertices),
indices: Vec::with_capacity(num_indices),
}
}
}
/// A temporary view on a `VertexBuffers` object which facilitate the population of vertex and index
/// data.
///
/// `BuffersBuilders` record the vertex offset from when they are created so that algorithms using
/// them don't need to worry about offsetting indices if some geometry was added beforehand. This
/// means that from the point of view of a `BuffersBuilder` user, the first added vertex is at always
/// offset at the offset 0 and `VertexBuilder` takes care of translating indices adequately.
///
/// Often, algorithms are built to generate vertex positions without knowledge of eventual other
/// vertex vertex. The `VertexConstructor` does the translation from generic `Input` to `OutputVertex`.
/// If your logic generates the actual vertex type directly, you can use the `SimpleBuffersBuilder`
/// convenience typedef.
pub struct BuffersBuilder<'l, OutputVertex: 'l, OutputIndex: 'l, Ctor> {
buffers: &'l mut VertexBuffers<OutputVertex, OutputIndex>,
first_vertex: Index,
first_index: Index,
vertex_offset: Index,
vertex_constructor: Ctor,
}
impl<'l, OutputVertex: 'l, OutputIndex: 'l, Ctor>
BuffersBuilder<'l, OutputVertex, OutputIndex, Ctor>
{
pub fn new(buffers: &'l mut VertexBuffers<OutputVertex, OutputIndex>, ctor: Ctor) -> Self {
let first_vertex = buffers.vertices.len() as Index;
let first_index = buffers.indices.len() as Index;
BuffersBuilder {
buffers,
first_vertex,
first_index,
vertex_offset: 0,
vertex_constructor: ctor,
}
}
pub fn with_vertex_offset(mut self, offset: Index) -> Self {
self.vertex_offset = offset;
self
}
/// Consumes self and returns a builder with opposite triangle face winding.
pub fn with_inverted_winding(self) -> InvertWinding<Self> {
InvertWinding(self)
}
pub fn buffers<'a, 'b: 'a>(&'b self) -> &'a VertexBuffers<OutputVertex, OutputIndex> {
self.buffers
}
}
/// A wrapper for stroke and fill geometry builders that inverts the triangle face winding.
pub struct InvertWinding<B>(B);
impl<B: GeometryBuilder> GeometryBuilder for InvertWinding<B> {
fn begin_geometry(&mut self) {
self.0.begin_geometry();
}
fn end_geometry(&mut self) {
self.0.end_geometry()
}
fn add_triangle(&mut self, a: VertexId, b: VertexId, c: VertexId) {
// Invert the triangle winding by flipping b and c.
self.0.add_triangle(a, c, b);
}
fn abort_geometry(&mut self) {
self.0.abort_geometry();
}
}
impl<B: FillGeometryBuilder> FillGeometryBuilder for InvertWinding<B> {
#[inline]
fn add_fill_vertex(&mut self, vertex: FillVertex) -> Result<VertexId, GeometryBuilderError> {
self.0.add_fill_vertex(vertex)
}
}
impl<B: StrokeGeometryBuilder> StrokeGeometryBuilder for InvertWinding<B> {
#[inline]
fn add_stroke_vertex(
&mut self,
vertex: StrokeVertex,
) -> Result<VertexId, GeometryBuilderError> {
self.0.add_stroke_vertex(vertex)
}
}
/// A trait specifying how to create vertex values.
pub trait FillVertexConstructor<OutputVertex> {
fn new_vertex(&mut self, vertex: FillVertex) -> OutputVertex;
}
/// A trait specifying how to create vertex values.
pub trait StrokeVertexConstructor<OutputVertex> {
fn new_vertex(&mut self, vertex: StrokeVertex) -> OutputVertex;
}
/// A simple vertex constructor that just takes the position.
pub struct Positions;
impl FillVertexConstructor<Point> for Positions {
fn new_vertex(&mut self, vertex: FillVertex) -> Point {
vertex.position()
}
}
impl StrokeVertexConstructor<Point> for Positions {
fn new_vertex(&mut self, vertex: StrokeVertex) -> Point {
vertex.position()
}
}
impl<F, OutputVertex> FillVertexConstructor<OutputVertex> for F
where
F: Fn(FillVertex) -> OutputVertex,
{
fn new_vertex(&mut self, vertex: FillVertex) -> OutputVertex {
self(vertex)
}
}
impl<F, OutputVertex> StrokeVertexConstructor<OutputVertex> for F
where
F: Fn(StrokeVertex) -> OutputVertex,
{
fn new_vertex(&mut self, vertex: StrokeVertex) -> OutputVertex {
self(vertex)
}
}
/// A `BuffersBuilder` that takes the actual vertex type as input.
pub type SimpleBuffersBuilder<'l> = BuffersBuilder<'l, Point, u16, Positions>;
/// Creates a `SimpleBuffersBuilder`.
pub fn simple_builder(buffers: &mut VertexBuffers<Point, u16>) -> SimpleBuffersBuilder {
let first_vertex = buffers.vertices.len() as Index;
let first_index = buffers.indices.len() as Index;
BuffersBuilder {
buffers,
first_vertex,
first_index,
vertex_offset: 0,
vertex_constructor: Positions,
}
}
impl<'l, OutputVertex, OutputIndex, Ctor> GeometryBuilder
for BuffersBuilder<'l, OutputVertex, OutputIndex, Ctor>
where
OutputVertex: 'l,
OutputIndex: Add + From<VertexId> + MaxIndex,
{
fn begin_geometry(&mut self) {
self.first_vertex = self.buffers.vertices.len() as Index;
self.first_index = self.buffers.indices.len() as Index;
}
fn add_triangle(&mut self, a: VertexId, b: VertexId, c: VertexId) {
#[cfg(feature = "std")]
if a == b || a == c || b == c {
std::println!("bad triangle {a:?} {b:?} {c:?}");
}
debug_assert!(a != b);
debug_assert!(a != c);
debug_assert!(b != c);
debug_assert!(a != VertexId::INVALID);
debug_assert!(b != VertexId::INVALID);
debug_assert!(c != VertexId::INVALID);
self.buffers.indices.push((a + self.vertex_offset).into());
self.buffers.indices.push((b + self.vertex_offset).into());
self.buffers.indices.push((c + self.vertex_offset).into());
}
fn abort_geometry(&mut self) {
self.buffers.vertices.truncate(self.first_vertex as usize);
self.buffers.indices.truncate(self.first_index as usize);
}
}
impl<'l, OutputVertex, OutputIndex, Ctor> FillGeometryBuilder
for BuffersBuilder<'l, OutputVertex, OutputIndex, Ctor>
where
OutputVertex: 'l,
OutputIndex: Add + From<VertexId> + MaxIndex,
Ctor: FillVertexConstructor<OutputVertex>,
{
fn add_fill_vertex(&mut self, vertex: FillVertex) -> Result<VertexId, GeometryBuilderError> {
self.buffers
.vertices
.push(self.vertex_constructor.new_vertex(vertex));
let len = self.buffers.vertices.len();
if len > OutputIndex::MAX {
return Err(GeometryBuilderError::TooManyVertices);
}
Ok(VertexId((len - 1) as Index))
}
}
impl<'l, OutputVertex, OutputIndex, Ctor> StrokeGeometryBuilder
for BuffersBuilder<'l, OutputVertex, OutputIndex, Ctor>
where
OutputVertex: 'l,
OutputIndex: Add + From<VertexId> + MaxIndex,
Ctor: StrokeVertexConstructor<OutputVertex>,
{
fn add_stroke_vertex(&mut self, v: StrokeVertex) -> Result<VertexId, GeometryBuilderError> {
self.buffers
.vertices
.push(self.vertex_constructor.new_vertex(v));
let len = self.buffers.vertices.len();
if len > OutputIndex::MAX {
return Err(GeometryBuilderError::TooManyVertices);
}
Ok(VertexId((len - 1) as Index))
}
}
/// A geometry builder that does not output any geometry.
///
/// Mostly useful for testing.
pub struct NoOutput {
next_vertex: u32,
}
impl NoOutput {
pub fn new() -> Self {
NoOutput { next_vertex: 0 }
}
}
impl Default for NoOutput {
fn default() -> Self {
Self::new()
}
}
impl GeometryBuilder for NoOutput {
fn add_triangle(&mut self, a: VertexId, b: VertexId, c: VertexId) {
debug_assert!(a != b);
debug_assert!(a != c);
debug_assert!(b != c);
}
}
impl FillGeometryBuilder for NoOutput {
fn add_fill_vertex(&mut self, _vertex: FillVertex) -> Result<VertexId, GeometryBuilderError> {
if self.next_vertex == u32::MAX {
return Err(GeometryBuilderError::TooManyVertices);
}
self.next_vertex += 1;
Ok(VertexId(self.next_vertex - 1))
}
}
impl StrokeGeometryBuilder for NoOutput {
fn add_stroke_vertex(&mut self, _: StrokeVertex) -> Result<VertexId, GeometryBuilderError> {
if self.next_vertex == u32::MAX {
return Err(GeometryBuilderError::TooManyVertices);
}
self.next_vertex += 1;
Ok(VertexId(self.next_vertex - 1))
}
}
/// Provides the maximum value of an index.
///
/// This should be the maximum value representable by the index type up
/// to u32::MAX because the tessellators can't internally represent more
/// than u32::MAX indices.
pub trait MaxIndex {
const MAX: usize;
}
impl MaxIndex for u8 {
const MAX: usize = u8::MAX as usize;
}
impl MaxIndex for i8 {
const MAX: usize = i8::MAX as usize;
}
impl MaxIndex for u16 {
const MAX: usize = u16::MAX as usize;
}
impl MaxIndex for i16 {
const MAX: usize = i16::MAX as usize;
}
impl MaxIndex for u32 {
const MAX: usize = u32::MAX as usize;
}
impl MaxIndex for i32 {
const MAX: usize = i32::MAX as usize;
}
// The tessellators internally use u32 indices so we can't have more than u32::MAX
impl MaxIndex for u64 {
const MAX: usize = u32::MAX as usize;
}
impl MaxIndex for i64 {
const MAX: usize = u32::MAX as usize;
}
impl MaxIndex for usize {
const MAX: usize = u32::MAX as usize;
}
impl MaxIndex for isize {
const MAX: usize = u32::MAX as usize;
}