tetra/graphics/

mesh.rs

//! Functions and types relating to meshes and shape drawing.
//!
//! # Performance
//!
//! This module gives you very low level control over the geometry that you're rendering - while that's useful,
//! it requires you to be a bit more careful about performance than other areas of Tetra's API. Ensure that you
//! read the docs for the various buffer/mesh types to understand their performance characteristics before
//! using them.

pub use lyon_tessellation::path::builder::BorderRadii;

use std::rc::Rc;

use bytemuck::{Pod, Zeroable};
use lyon_tessellation::geom::euclid::Point2D;
use lyon_tessellation::math::{Angle, Box2D, Point, Vector};
use lyon_tessellation::path::{Polygon, Winding};
use lyon_tessellation::{
    BuffersBuilder, FillOptions, FillTessellator, FillVertex, FillVertexConstructor, StrokeOptions,
    StrokeTessellator, StrokeVertex, StrokeVertexConstructor, VertexBuffers,
};

use crate::graphics::{self, Color, DrawParams, Rectangle, Texture};
use crate::math::Vec2;
use crate::platform::{RawIndexBuffer, RawVertexBuffer};
use crate::Context;
use crate::{Result, TetraError};

/// An individual piece of vertex data.
#[repr(C)]
#[derive(Debug, Default, Copy, Clone, PartialEq)]
pub struct Vertex {
    /// The position of the vertex, in screen co-ordinates.
    ///
    /// The transform matrix will be applied to this value, followed by a projection
    /// from screen co-ordinates to device co-ordinates.
    pub position: Vec2<f32>,

    /// The texture co-ordinates that should be sampled for this vertex.
    ///
    /// Both the X and the Y should be between 0.0 and 1.0.
    pub uv: Vec2<f32>,

    /// The color of the vertex.
    ///
    /// This will be multiplied by the `color` of the `DrawParams` when drawing a
    /// mesh.
    pub color: Color,
}

impl Vertex {
    /// Creates a new vertex.
    pub fn new(position: Vec2<f32>, uv: Vec2<f32>, color: Color) -> Vertex {
        Vertex {
            position,
            uv,
            color,
        }
    }
}

// SAFETY: While the contract for `Pod` states that all fields should also be `Pod`,
// that isn't possible without upstream changes. All of the fields meet the
// *requirements* to be `Pod`, however, so this should not be unsound.
unsafe impl Pod for Vertex {}
unsafe impl Zeroable for Vertex {}

/// The expected usage of a GPU buffer.
///
/// The GPU may optionally use this to optimize data storage and access.
#[derive(Copy, Clone, Debug, PartialEq, Eq)]
pub enum BufferUsage {
    /// The buffer's data is not expected to change after creation.
    Static,

    /// The buffer's data is expected to change occasionally after creation.
    Dynamic,

    /// The buffer's data is expected to change every frame.
    Stream,
}

/// The ordering of the vertices in a piece of geometry.
#[derive(Copy, Clone, Debug, PartialEq, Eq)]
pub enum VertexWinding {
    /// The vertices are in clockwise order.
    Clockwise,

    /// The vertices are in counter-clockwise order.
    CounterClockwise,
}

impl VertexWinding {
    /// Returns the opposite winding, compared to `self`.
    pub fn flipped(self) -> VertexWinding {
        match self {
            VertexWinding::Clockwise => VertexWinding::CounterClockwise,
            VertexWinding::CounterClockwise => VertexWinding::Clockwise,
        }
    }
}

/// Vertex data, stored in GPU memory.
///
/// This data can be drawn to the screen via a [`Mesh`].
///
/// # Performance
///
/// When you create or modify a vertex buffer, you are effectively 'uploading' data to the GPU, which
/// can be relatively slow. You should try to minimize how often you do this - for example, if a piece
/// of geometry does not change from frame to frame, reuse the buffer instead of recreating it.
///
/// You can clone a vertex buffer cheaply, as it is a [reference-counted](https://doc.rust-lang.org/std/rc/struct.Rc.html)
/// handle to a GPU resource. However, this does mean that modifying a buffer (e.g.
/// calling `set_data`) will also affect any clones that exist of it.
///
#[derive(Clone, Debug, PartialEq)]
pub struct VertexBuffer {
    handle: Rc<RawVertexBuffer>,
}

impl VertexBuffer {
    /// Creates a new vertex buffer.
    ///
    /// The buffer will be created with the [`BufferUsage::Dynamic`] usage hint - this can
    /// be overridden via the [`with_usage`](Self::with_usage) constructor.
    ///
    /// # Errors
    ///
    /// * [`TetraError::PlatformError`] will be returned if the underlying
    ///   graphics API encounters an error.
    pub fn new(ctx: &mut Context, vertices: &[Vertex]) -> Result<VertexBuffer> {
        VertexBuffer::with_usage(ctx, vertices, BufferUsage::Dynamic)
    }

    /// Creates a new vertex buffer, with the specified usage hint.
    ///
    /// The GPU may optionally use the usage hint to optimize data storage and access.
    ///
    /// # Errors
    ///
    /// * [`TetraError::PlatformError`] will be returned if the underlying
    ///   graphics API encounters an error.
    pub fn with_usage(
        ctx: &mut Context,
        vertices: &[Vertex],
        usage: BufferUsage,
    ) -> Result<VertexBuffer> {
        let buffer = ctx.device.new_vertex_buffer(vertices.len(), usage)?;

        ctx.device.set_vertex_buffer_data(&buffer, vertices, 0);

        Ok(VertexBuffer {
            handle: Rc::new(buffer),
        })
    }

    /// Uploads new vertex data to the GPU.
    ///
    /// # Panics
    ///
    /// Panics if the offset is out of bounds.
    pub fn set_data(&self, ctx: &mut Context, vertices: &[Vertex], offset: usize) {
        ctx.device
            .set_vertex_buffer_data(&self.handle, vertices, offset);
    }

    /// Creates a mesh using this buffer.
    ///
    /// This is a shortcut for calling [`Mesh::new`].
    pub fn into_mesh(self) -> Mesh {
        Mesh::new(self)
    }
}

/// Index data, stored in GPU memory.
///
/// An index buffer can be used as part of a [`Mesh`], in order to describe which vertex data should be drawn,
/// and what order it should be drawn in.
///
/// For example, to draw a square with raw vertex data, you need to use six vertices (two triangles,
/// with three vertices each). This is inefficient, as two of those vertices are shared by the two
/// triangles! Using an index buffer, you can instruct the graphics card to use vertices
/// multiple times while constructing your square.
///
/// Index data is made up of [`u32`] values, each of which correspond to the zero-based index of a vertex.
/// For example, to get the mesh to draw the third vertex, then the first, then the second, you would
/// create an index buffer containing `[2, 0, 1]`.
///
/// # Performance
///
/// When you create or modify an index buffer, you are effectively 'uploading' data to the GPU, which
/// can be relatively slow. You should try to minimize how often you do this - for example, if a piece
/// of geometry does not change from frame to frame, reuse the buffer instead of recreating it.
///
/// You can clone an index buffer cheaply, as it is a [reference-counted](https://doc.rust-lang.org/std/rc/struct.Rc.html)
/// handle to a GPU resource. However, this does mean that modifying a buffer (e.g.
/// calling `set_data`) will also affect any clones that exist of it.
#[derive(Clone, Debug, PartialEq)]
pub struct IndexBuffer {
    handle: Rc<RawIndexBuffer>,
}

impl IndexBuffer {
    /// Creates a new index buffer.
    ///
    /// The buffer will be created with the [`BufferUsage::Dynamic`] usage hint - this can
    /// be overridden via the [`with_usage`](Self::with_usage) constructor.
    ///
    /// # Errors
    ///
    /// * [`TetraError::PlatformError`] will be returned if the underlying
    ///   graphics API encounters an error.
    pub fn new(ctx: &mut Context, indices: &[u32]) -> Result<IndexBuffer> {
        IndexBuffer::with_usage(ctx, indices, BufferUsage::Dynamic)
    }

    /// Creates a new index buffer, with the specified usage hint.
    ///
    /// The GPU may optionally use the usage hint to optimize data storage and access.
    ///
    /// # Errors
    ///
    /// * [`TetraError::PlatformError`] will be returned if the underlying
    ///   graphics API encounters an error.
    pub fn with_usage(
        ctx: &mut Context,
        indices: &[u32],
        usage: BufferUsage,
    ) -> Result<IndexBuffer> {
        let buffer = ctx.device.new_index_buffer(indices.len(), usage)?;

        ctx.device.set_index_buffer_data(&buffer, indices, 0);

        Ok(IndexBuffer {
            handle: Rc::new(buffer),
        })
    }

    /// Sends new index data to the GPU.
    ///
    /// # Panics
    ///
    /// Panics if the offset is out of bounds.
    pub fn set_data(&self, ctx: &mut Context, indices: &[u32], offset: usize) {
        ctx.device
            .set_index_buffer_data(&self.handle, indices, offset);
    }
}

#[derive(Copy, Clone, Debug)]
struct DrawRange {
    start: usize,
    count: usize,
}

/// Ways of drawing a shape.
#[derive(Copy, Clone, Debug)]
pub enum ShapeStyle {
    /// A filled shape.
    Fill,
    /// An outlined shape with the specified stroke width.
    Stroke(f32),
}

/// A 2D mesh that can be drawn to the screen.
///
/// A `Mesh` is a wrapper for a [`VertexBuffer`], which allows it to be drawn in combination with several
/// optional modifiers:
///
/// * A [`Texture`] that individual vertices can sample from.
/// * An [`IndexBuffer`] that can be used to modify the order/subset of vertices that are drawn.
/// * A winding order, which determines which side of the geometry is front-facing.
/// * A backface culling flag, which determines whether back-facing geometry should be drawn.
/// * A draw range, which can be used to draw subsections of the mesh.
///
/// Without a texture set, the mesh will be drawn in white - the `color` attribute on the [vertex data](Vertex) or
/// [`DrawParams`] can be used to change this.
///
/// # Performance
///
/// Creating or cloning a mesh is a very cheap operation, as they are effectively just bundles
/// of resources that live on the GPU (such as buffers and textures). However, creating or
/// modifying those underlying resources may be slow - make sure you read the docs for
/// each type to understand their performance characteristics.
///
/// Note that, unlike most rendering in Tetra, mesh rendering is *not* batched by default - each time you
/// draw the mesh will result in a seperate draw call.
///
/// # Examples
///
/// The [`mesh`](https://github.com/17cupsofcoffee/tetra/blob/main/examples/mesh.rs) example demonstrates
/// how to build and draw a simple mesh.
///
/// The [`shapes`](https://github.com/17cupsofcoffee/tetra/blob/main/examples/shapes.rs) example demonstrates
/// how to draw primitive shapes, both through the simplified API on `Mesh`, and the more powerful
/// [`GeometryBuilder`] API.  
#[derive(Clone, Debug)]
pub struct Mesh {
    vertex_buffer: VertexBuffer,
    index_buffer: Option<IndexBuffer>,
    texture: Option<Texture>,
    draw_range: Option<DrawRange>,
    winding: VertexWinding,
    backface_culling: bool,
}

impl Mesh {
    /// Creates a new mesh, using the provided vertex buffer.
    pub fn new(vertex_buffer: VertexBuffer) -> Mesh {
        Mesh {
            vertex_buffer,
            index_buffer: None,
            texture: None,
            draw_range: None,
            winding: VertexWinding::CounterClockwise,
            backface_culling: true,
        }
    }

    /// Creates a new mesh, using the provided vertex and index buffers.
    pub fn indexed(vertex_buffer: VertexBuffer, index_buffer: IndexBuffer) -> Mesh {
        Mesh {
            vertex_buffer,
            index_buffer: Some(index_buffer),
            texture: None,
            winding: VertexWinding::CounterClockwise,
            draw_range: None,
            backface_culling: true,
        }
    }

    /// Draws the mesh to the screen (or to a canvas, if one is enabled).
    pub fn draw<P>(&self, ctx: &mut Context, params: P)
    where
        P: Into<DrawParams>,
    {
        self.draw_instanced(ctx, 1, params);
    }

    /// Draws multiple instances of the mesh to the screen (or to a canvas,
    /// if one is enabled).
    ///
    /// You will need to use a custom [`Shader`](crate::graphics::Shader) in order to pass unique
    /// properties to each instance. Currently, the easiest way of doing this is via uniform
    /// arrays - however, there is a hardware-determined limit on how many uniform locations
    /// an individual shader can use, so this may not work if you're rendering a large
    /// number of objects.
    ///
    /// This should usually only be used for complex meshes - instancing can be inefficient
    /// for simple geometry (e.g. quads). That said, as with all things performance-related,
    /// benchmark it before coming to any conclusions!
    pub fn draw_instanced<P>(&self, ctx: &mut Context, instances: usize, params: P)
    where
        P: Into<DrawParams>,
    {
        graphics::flush(ctx);

        let texture = self
            .texture
            .as_ref()
            .unwrap_or(&ctx.graphics.default_texture);

        let shader = ctx
            .graphics
            .shader
            .as_ref()
            .unwrap_or(&ctx.graphics.default_shader);

        let params = params.into();
        let model_matrix = params.to_matrix();

        // TODO: Failing to apply the defaults should be handled more gracefully than this,
        // but we can't do that without breaking changes.
        let _ = shader.set_default_uniforms(
            &mut ctx.device,
            ctx.graphics.projection_matrix * ctx.graphics.transform_matrix * model_matrix,
            params.color,
        );

        ctx.device.cull_face(self.backface_culling);

        // Because canvas rendering is effectively done upside-down, the winding order is the opposite
        // of what you'd expect in that case.
        ctx.device.front_face(match &ctx.graphics.canvas {
            None => self.winding,
            Some(_) => self.winding.flipped(),
        });

        let (start, count) = match (self.draw_range, &self.index_buffer) {
            (Some(d), _) => (d.start, d.count),
            (_, Some(i)) => (0, i.handle.count()),
            (_, None) => (0, self.vertex_buffer.handle.count()),
        };

        ctx.device.draw_instanced(
            &self.vertex_buffer.handle,
            self.index_buffer.as_ref().map(|i| &*i.handle),
            &texture.data.handle,
            &shader.data.handle,
            start,
            count,
            instances,
        );
    }

    /// Gets a reference to the vertex buffer contained within this mesh.
    pub fn vertex_buffer(&self) -> &VertexBuffer {
        &self.vertex_buffer
    }

    /// Sets the vertex buffer that will be used when drawing the mesh.
    pub fn set_vertex_buffer(&mut self, vertex_buffer: VertexBuffer) {
        self.vertex_buffer = vertex_buffer;
    }

    /// Gets a reference to the index buffer contained within this mesh.
    ///
    /// Returns [`None`] if this mesh does not currently have an index buffer attatched.
    pub fn index_buffer(&self) -> Option<&IndexBuffer> {
        self.index_buffer.as_ref()
    }

    /// Sets the index buffer that will be used when drawing the mesh.
    pub fn set_index_buffer(&mut self, index_buffer: IndexBuffer) {
        self.index_buffer = Some(index_buffer);
    }

    /// Resets the mesh to no longer use indexed drawing.
    pub fn reset_index_buffer(&mut self) {
        self.index_buffer = None;
    }

    /// Gets a reference to the texture contained within this mesh.
    ///
    /// Returns [`None`] if this mesh does not currently have an texture attatched.
    pub fn texture(&self) -> Option<&Texture> {
        self.texture.as_ref()
    }

    /// Sets the texture that will be used when drawing the mesh.
    pub fn set_texture(&mut self, texture: Texture) {
        self.texture = Some(texture);
    }

    /// Resets the mesh to be untextured.
    pub fn reset_texture(&mut self) {
        self.texture = None;
    }

    /// Returns which winding order represents front-facing geometry in this mesh.
    ///
    /// Back-facing geometry will be culled (not rendered) by default, but
    /// this can be changed via [`set_backface_culling`](Self::set_backface_culling).
    ///
    /// The default winding order is counter-clockwise.
    pub fn front_face_winding(&self) -> VertexWinding {
        self.winding
    }

    /// Sets which winding order represents front-facing geometry in this mesh.
    ///
    /// Back-facing geometry will be culled (not rendered) by default, but
    /// this can be changed via [`set_backface_culling`](Self::set_backface_culling).
    ///
    /// The default winding order is counter-clockwise.
    pub fn set_front_face_winding(&mut self, winding: VertexWinding) {
        self.winding = winding;
    }

    /// Returns whether or not this mesh will cull (not render) back-facing geometry.
    ///
    /// By default, backface culling is enabled, counter-clockwise vertices are
    /// considered front-facing, and clockwise vertices are considered back-facing.
    /// This can be modified via [`set_backface_culling`](Self::set_backface_culling) and
    /// [`set_front_face_winding`](Self::set_front_face_winding).
    pub fn backface_culling(&self) -> bool {
        self.backface_culling
    }

    /// Sets whether or not this mesh will cull (not render) back-facing geometry.
    ///
    /// By default, backface culling is enabled, counter-clockwise vertices are
    /// considered front-facing, and clockwise vertices are considered back-facing.
    /// This can be modified via this function and [`set_front_face_winding`](Self::set_front_face_winding).
    pub fn set_backface_culling(&mut self, enabled: bool) {
        self.backface_culling = enabled;
    }

    /// Sets the range of vertices (or indices, if the mesh is indexed) that should be included
    /// when drawing this mesh.
    ///
    /// This can be useful if you have a large mesh but you only want to want to draw a
    /// subsection of it, or if you want to draw a mesh in multiple stages.
    pub fn set_draw_range(&mut self, start: usize, count: usize) {
        self.draw_range = Some(DrawRange { start, count });
    }

    /// Sets the mesh to include all of its data when drawing.
    pub fn reset_draw_range(&mut self) {
        self.draw_range = None;
    }
}

/// # Shape constructors
impl Mesh {
    /// Creates a new rectangle mesh.
    ///
    /// If you need to draw multiple shapes, consider using [`GeometryBuilder`] to generate a combined mesh
    /// instead.
    ///
    /// # Errors
    ///
    /// * [`TetraError::TessellationError`] will be returned if the shape
    ///   could not be turned into vertex data.
    /// * [`TetraError::PlatformError`] will be returned if the underlying
    ///   graphics API encounters an error.
    pub fn rectangle(ctx: &mut Context, style: ShapeStyle, rectangle: Rectangle) -> Result<Mesh> {
        GeometryBuilder::new()
            .rectangle(style, rectangle)?
            .build_mesh(ctx)
    }

    /// Creates a new rounded rectangle mesh.
    ///
    /// If you need to draw multiple shapes, consider using [`GeometryBuilder`] to generate a combined mesh
    /// instead.
    ///
    /// # Errors
    ///
    /// * [`TetraError::TessellationError`] will be returned if the shape
    ///   could not be turned into vertex data.
    /// * [`TetraError::PlatformError`] will be returned if the underlying
    ///   graphics API encounters an error.
    pub fn rounded_rectangle(
        ctx: &mut Context,
        style: ShapeStyle,
        rectangle: Rectangle,
        radii: BorderRadii,
    ) -> Result<Mesh> {
        GeometryBuilder::new()
            .rounded_rectangle(style, rectangle, radii)?
            .build_mesh(ctx)
    }

    /// Creates a new circle mesh.
    ///
    /// If you need to draw multiple shapes, consider using [`GeometryBuilder`] to generate a combined mesh
    /// instead.
    ///
    /// # Errors
    ///
    /// * [`TetraError::TessellationError`] will be returned if the shape
    ///   could not be turned into vertex data.
    /// * [`TetraError::PlatformError`] will be returned if the underlying
    ///   graphics API encounters an error.
    pub fn circle(
        ctx: &mut Context,
        style: ShapeStyle,
        center: Vec2<f32>,
        radius: f32,
    ) -> Result<Mesh> {
        GeometryBuilder::new()
            .circle(style, center, radius)?
            .build_mesh(ctx)
    }

    /// Creates a new ellipse mesh.
    ///
    /// If you need to draw multiple shapes, consider using [`GeometryBuilder`] to generate a combined mesh
    /// instead.
    ///
    /// # Errors
    ///
    /// * [`TetraError::TessellationError`] will be returned if the shape
    ///   could not be turned into vertex data.
    /// * [`TetraError::PlatformError`] will be returned if the underlying
    ///   graphics API encounters an error.
    pub fn ellipse(
        ctx: &mut Context,
        style: ShapeStyle,
        center: Vec2<f32>,
        radii: Vec2<f32>,
    ) -> Result<Mesh> {
        GeometryBuilder::new()
            .ellipse(style, center, radii)?
            .build_mesh(ctx)
    }

    /// Creates a new polygon mesh.
    ///
    /// If you need to draw multiple shapes, consider using [`GeometryBuilder`] to generate a combined mesh
    /// instead.
    ///
    /// # Errors
    ///
    /// * [`TetraError::TessellationError`] will be returned if the shape
    ///   could not be turned into vertex data.
    /// * [`TetraError::PlatformError`] will be returned if the underlying
    ///   graphics API encounters an error.
    pub fn polygon(ctx: &mut Context, style: ShapeStyle, points: &[Vec2<f32>]) -> Result<Mesh> {
        GeometryBuilder::new()
            .polygon(style, points)?
            .build_mesh(ctx)
    }

    /// Creates a new polyline mesh.
    ///
    /// If you need to draw multiple shapes, consider using [`GeometryBuilder`] to generate a combined mesh
    /// instead.
    ///
    /// # Errors
    ///
    /// * [`TetraError::TessellationError`] will be returned if the shape
    ///   could not be turned into vertex data.
    /// * [`TetraError::PlatformError`] will be returned if the underlying
    ///   graphics API encounters an error.
    pub fn polyline(ctx: &mut Context, stroke_width: f32, points: &[Vec2<f32>]) -> Result<Mesh> {
        GeometryBuilder::new()
            .polyline(stroke_width, points)?
            .build_mesh(ctx)
    }
}

impl From<VertexBuffer> for Mesh {
    fn from(buffer: VertexBuffer) -> Self {
        Mesh::new(buffer)
    }
}

fn to_box2d(rectangle: Rectangle) -> Box2D {
    Box2D::new(
        Point2D::new(rectangle.x, rectangle.y),
        Point2D::new(rectangle.right(), rectangle.bottom()),
    )
}

struct TetraVertexConstructor(Color);

impl FillVertexConstructor<Vertex> for TetraVertexConstructor {
    fn new_vertex(&mut self, vertex: FillVertex) -> Vertex {
        let position = vertex.position();

        Vertex::new(Vec2::new(position.x, position.y), Vec2::zero(), self.0)
    }
}

impl StrokeVertexConstructor<Vertex> for TetraVertexConstructor {
    fn new_vertex(&mut self, vertex: StrokeVertex) -> Vertex {
        let position = vertex.position();

        Vertex::new(Vec2::new(position.x, position.y), Vec2::zero(), self.0)
    }
}

/// A builder for creating primitive shape geometry, and associated buffers/meshes.
///
/// # Performance
///
/// `GeometryBuilder` stores the generated vertex and index data in a pair of `Vec`s. This means that creating
/// a new builder (as well as cloning an existing one) will allocate memory. Consider reusing a `GeometryBuilder`
/// if you need to reuse the generated data, or if you need to create new data every frame.
///
/// Creating buffers/meshes from the generated geometry is a fairly expensive operation. Try to avoid creating
/// lots of seperate buffers/meshes, and pack multiple shapes into the same buffers/mesh if
/// they don't move relative to each other.
///
/// # Examples
///
/// The [`shapes`](https://github.com/17cupsofcoffee/tetra/blob/main/examples/shapes.rs) example demonstrates
/// how to draw primitive shapes, both through the simplified API on [`Mesh`], and the more powerful
/// `GeometryBuilder` API.  
#[derive(Debug, Clone)]
pub struct GeometryBuilder {
    data: VertexBuffers<Vertex, u32>,
    color: Color,
}

impl GeometryBuilder {
    /// Creates a new empty geometry builder.
    pub fn new() -> GeometryBuilder {
        GeometryBuilder {
            data: VertexBuffers::new(),
            color: Color::WHITE,
        }
    }

    /// Adds a rectangle.
    ///
    /// # Errors
    ///
    /// * [`TetraError::TessellationError`] will be returned if the shape
    ///   could not be turned into vertex data.
    pub fn rectangle(
        &mut self,
        style: ShapeStyle,
        rectangle: Rectangle,
    ) -> Result<&mut GeometryBuilder> {
        let mut builder = BuffersBuilder::new(&mut self.data, TetraVertexConstructor(self.color));

        match style {
            ShapeStyle::Fill => {
                let options = FillOptions::default();
                let mut tessellator = FillTessellator::new();
                tessellator
                    .tessellate_rectangle(&to_box2d(rectangle), &options, &mut builder)
                    .map_err(TetraError::TessellationError)?;
            }

            ShapeStyle::Stroke(width) => {
                let options = StrokeOptions::default().with_line_width(width);
                let mut tessellator = StrokeTessellator::new();
                tessellator
                    .tessellate_rectangle(&to_box2d(rectangle), &options, &mut builder)
                    .map_err(TetraError::TessellationError)?;
            }
        }

        Ok(self)
    }

    /// Adds a rounded rectangle.
    ///
    /// # Errors
    ///
    /// * [`TetraError::TessellationError`] will be returned if the shape
    ///   could not be turned into vertex data.
    pub fn rounded_rectangle(
        &mut self,
        style: ShapeStyle,
        rectangle: Rectangle,
        radii: BorderRadii,
    ) -> Result<&mut GeometryBuilder> {
        let mut builder = BuffersBuilder::new(&mut self.data, TetraVertexConstructor(self.color));

        match style {
            ShapeStyle::Fill => {
                let options = FillOptions::default();
                let mut tessellator = FillTessellator::new();
                let mut builder = tessellator.builder(&options, &mut builder);
                builder.add_rounded_rectangle(&to_box2d(rectangle), &radii, Winding::Positive);
                builder.build().map_err(TetraError::TessellationError)?;
            }

            ShapeStyle::Stroke(width) => {
                let options = StrokeOptions::default().with_line_width(width);
                let mut tessellator = StrokeTessellator::new();
                let mut builder = tessellator.builder(&options, &mut builder);
                builder.add_rounded_rectangle(&to_box2d(rectangle), &radii, Winding::Positive);
                builder.build().map_err(TetraError::TessellationError)?;
            }
        }

        Ok(self)
    }

    /// Adds a circle.
    ///
    /// # Errors
    ///
    /// * [`TetraError::TessellationError`] will be returned if the shape
    ///   could not be turned into vertex data.
    pub fn circle(
        &mut self,
        style: ShapeStyle,
        center: Vec2<f32>,
        radius: f32,
    ) -> Result<&mut GeometryBuilder> {
        let mut builder = BuffersBuilder::new(&mut self.data, TetraVertexConstructor(self.color));

        match style {
            ShapeStyle::Fill => {
                let options = FillOptions::default();
                let mut tessellator = FillTessellator::new();

                tessellator
                    .tessellate_circle(
                        Point::new(center.x, center.y),
                        radius,
                        &options,
                        &mut builder,
                    )
                    .map_err(TetraError::TessellationError)?;
            }

            ShapeStyle::Stroke(width) => {
                let options = StrokeOptions::default().with_line_width(width);
                let mut tessellator = StrokeTessellator::new();

                tessellator
                    .tessellate_circle(
                        Point::new(center.x, center.y),
                        radius,
                        &options,
                        &mut builder,
                    )
                    .map_err(TetraError::TessellationError)?;
            }
        }

        Ok(self)
    }

    /// Adds an ellipse.
    ///
    /// # Errors
    ///
    /// * [`TetraError::TessellationError`] will be returned if the shape
    ///   could not be turned into vertex data.
    pub fn ellipse(
        &mut self,
        style: ShapeStyle,
        center: Vec2<f32>,
        radii: Vec2<f32>,
    ) -> Result<&mut GeometryBuilder> {
        let mut builder = BuffersBuilder::new(&mut self.data, TetraVertexConstructor(self.color));

        match style {
            ShapeStyle::Fill => {
                let options = FillOptions::default();
                let mut tessellator = FillTessellator::new();

                tessellator
                    .tessellate_ellipse(
                        Point::new(center.x, center.y),
                        Vector::new(radii.x, radii.y),
                        Angle::radians(0.0),
                        Winding::Positive,
                        &options,
                        &mut builder,
                    )
                    .map_err(TetraError::TessellationError)?;
            }

            ShapeStyle::Stroke(width) => {
                let options = StrokeOptions::default().with_line_width(width);
                let mut tessellator = StrokeTessellator::new();

                tessellator
                    .tessellate_ellipse(
                        Point::new(center.x, center.y),
                        Vector::new(radii.x, radii.y),
                        Angle::radians(0.0),
                        Winding::Positive,
                        &options,
                        &mut builder,
                    )
                    .map_err(TetraError::TessellationError)?;
            }
        }

        Ok(self)
    }

    /// Adds a polygon.
    ///
    /// # Errors
    ///
    /// * [`TetraError::TessellationError`] will be returned if the shape
    ///   could not be turned into vertex data.
    pub fn polygon(
        &mut self,
        style: ShapeStyle,
        points: &[Vec2<f32>],
    ) -> Result<&mut GeometryBuilder> {
        let mut builder = BuffersBuilder::new(&mut self.data, TetraVertexConstructor(self.color));

        let points: Vec<Point> = points
            .iter()
            .map(|point| Point::new(point.x, point.y))
            .collect();

        let polygon = Polygon {
            points: &points,
            closed: true,
        };

        match style {
            ShapeStyle::Fill => {
                let options = FillOptions::default();
                let mut tessellator = FillTessellator::new();

                tessellator
                    .tessellate_polygon(polygon, &options, &mut builder)
                    .map_err(TetraError::TessellationError)?;
            }

            ShapeStyle::Stroke(width) => {
                let options = StrokeOptions::default().with_line_width(width);
                let mut tessellator = StrokeTessellator::new();

                tessellator
                    .tessellate_polygon(polygon, &options, &mut builder)
                    .map_err(TetraError::TessellationError)?;
            }
        }

        Ok(self)
    }

    /// Adds a polyline.
    ///
    /// # Errors
    ///
    /// * [`TetraError::TessellationError`] will be returned if the shape
    ///   could not be turned into vertex data.
    pub fn polyline(
        &mut self,
        stroke_width: f32,
        points: &[Vec2<f32>],
    ) -> Result<&mut GeometryBuilder> {
        let mut builder = BuffersBuilder::new(&mut self.data, TetraVertexConstructor(self.color));

        let points: Vec<Point> = points
            .iter()
            .map(|point| Point::new(point.x, point.y))
            .collect();

        let polygon = Polygon {
            points: &points,
            closed: false,
        };

        let options = StrokeOptions::default().with_line_width(stroke_width);
        let mut tessellator = StrokeTessellator::new();

        tessellator
            .tessellate_polygon(polygon, &options, &mut builder)
            .map_err(TetraError::TessellationError)?;

        Ok(self)
    }

    /// Sets the color that will be used for subsequent shapes.
    ///
    /// You can also use [`DrawParams::color`](super::DrawParams) to tint an entire mesh -
    /// this method only needs to be used if you want to display multiple colors in a
    /// single piece of geometry.
    pub fn set_color(&mut self, color: Color) -> &mut GeometryBuilder {
        self.color = color;
        self
    }

    /// Clears the geometry builder's data.
    pub fn clear(&mut self) -> &mut GeometryBuilder {
        self.data.vertices.clear();
        self.data.indices.clear();

        self
    }

    /// Returns a view of the generated vertex data.
    pub fn vertices(&self) -> &[Vertex] {
        &self.data.vertices
    }

    /// Returns a view of the generated index data.
    pub fn indices(&self) -> &[u32] {
        &self.data.indices
    }

    /// Consumes the builder, returning the generated geometry.
    pub fn into_data(self) -> (Vec<Vertex>, Vec<u32>) {
        (self.data.vertices, self.data.indices)
    }

    /// Builds a vertex and index buffer from the generated geometry.
    ///
    /// This involves uploading the geometry to the GPU, and is a fairly expensive operation.
    ///
    /// # Errors
    ///
    /// * [`TetraError::PlatformError`] will be returned if the underlying
    ///   graphics API encounters an error.
    pub fn build_buffers(&self, ctx: &mut Context) -> Result<(VertexBuffer, IndexBuffer)> {
        Ok((
            VertexBuffer::new(ctx, &self.data.vertices)?,
            IndexBuffer::new(ctx, &self.data.indices)?,
        ))
    }

    /// Builds a mesh from the generated geometry.
    ///
    /// This involves uploading the geometry to the GPU, and is a fairly expensive operation.
    ///
    /// # Errors
    ///
    /// * [`TetraError::PlatformError`] will be returned if the underlying
    ///   graphics API encounters an error.
    pub fn build_mesh(&self, ctx: &mut Context) -> Result<Mesh> {
        let (vertex_buffer, index_buffer) = self.build_buffers(ctx)?;

        Ok(Mesh::indexed(vertex_buffer, index_buffer))
    }
}

impl Default for GeometryBuilder {
    fn default() -> Self {
        GeometryBuilder::new()
    }
}