Implement composable, type-safe renderer fallback

3 files changed, 234 insertions, 276 deletions

diff --git a/wgpu/src/backend.rs b/wgpu/src/backend.rs
index 09ddbe4d..924aacf1 100644
--- a/wgpu/src/backend.rs
+++ b/wgpu/src/backend.rs
@@ -397,3 +397,12 @@ impl backend::Svg for Backend {
         self.image_pipeline.viewport_dimensions(handle)
     }
 }
+
+#[cfg(feature = "geometry")]
+impl crate::graphics::geometry::Backend for Backend {
+    type Frame = crate::geometry::Frame;
+
+    fn new_frame(&self, size: Size) -> Self::Frame {
+        crate::geometry::Frame::new(size)
+    }
+}
diff --git a/wgpu/src/geometry.rs b/wgpu/src/geometry.rs
index f4e0fbda..4f6b67b1 100644
--- a/wgpu/src/geometry.rs
+++ b/wgpu/src/geometry.rs
@@ -6,7 +6,7 @@ use crate::core::{
 use crate::graphics::color;
 use crate::graphics::geometry::fill::{self, Fill};
 use crate::graphics::geometry::{
-    LineCap, LineDash, LineJoin, Path, Stroke, Style, Text,
+    self, LineCap, LineDash, LineJoin, Path, Stroke, Style, Text,
 };
 use crate::graphics::gradient::{self, Gradient};
 use crate::graphics::mesh::{self, Mesh};
@@ -14,6 +14,7 @@ use crate::primitive::{self, Primitive};
 
 use lyon::geom::euclid;
 use lyon::tessellation;
+
 use std::borrow::Cow;
 
 /// A frame for drawing some geometry.
@@ -27,191 +28,87 @@ pub struct Frame {
     stroke_tessellator: tessellation::StrokeTessellator,
 }
 
-enum Buffer {
-    Solid(tessellation::VertexBuffers<mesh::SolidVertex2D, u32>),
-    Gradient(tessellation::VertexBuffers<mesh::GradientVertex2D, u32>),
-}
-
-struct BufferStack {
-    stack: Vec<Buffer>,
-}
-
-impl BufferStack {
-    fn new() -> Self {
-        Self { stack: Vec::new() }
-    }
-
-    fn get_mut(&mut self, style: &Style) -> &mut Buffer {
-        match style {
-            Style::Solid(_) => match self.stack.last() {
-                Some(Buffer::Solid(_)) => {}
-                _ => {
-                    self.stack.push(Buffer::Solid(
-                        tessellation::VertexBuffers::new(),
-                    ));
-                }
-            },
-            Style::Gradient(_) => match self.stack.last() {
-                Some(Buffer::Gradient(_)) => {}
-                _ => {
-                    self.stack.push(Buffer::Gradient(
-                        tessellation::VertexBuffers::new(),
-                    ));
-                }
+impl Frame {
+    /// Creates a new [`Frame`] with the given [`Size`].
+    pub fn new(size: Size) -> Frame {
+        Frame {
+            size,
+            buffers: BufferStack::new(),
+            primitives: Vec::new(),
+            transforms: Transforms {
+                previous: Vec::new(),
+                current: Transform(lyon::math::Transform::identity()),
             },
+            fill_tessellator: tessellation::FillTessellator::new(),
+            stroke_tessellator: tessellation::StrokeTessellator::new(),
         }
-
-        self.stack.last_mut().unwrap()
     }
 
-    fn get_fill<'a>(
-        &'a mut self,
-        style: &Style,
-    ) -> Box<dyn tessellation::FillGeometryBuilder + 'a> {
-        match (style, self.get_mut(style)) {
-            (Style::Solid(color), Buffer::Solid(buffer)) => {
-                Box::new(tessellation::BuffersBuilder::new(
-                    buffer,
-                    TriangleVertex2DBuilder(color::pack(*color)),
-                ))
-            }
-            (Style::Gradient(gradient), Buffer::Gradient(buffer)) => {
-                Box::new(tessellation::BuffersBuilder::new(
-                    buffer,
-                    GradientVertex2DBuilder {
-                        gradient: gradient.pack(),
-                    },
-                ))
+    fn into_primitives(mut self) -> Vec<Primitive> {
+        for buffer in self.buffers.stack {
+            match buffer {
+                Buffer::Solid(buffer) => {
+                    if !buffer.indices.is_empty() {
+                        self.primitives.push(Primitive::Custom(
+                            primitive::Custom::Mesh(Mesh::Solid {
+                                buffers: mesh::Indexed {
+                                    vertices: buffer.vertices,
+                                    indices: buffer.indices,
+                                },
+                                size: self.size,
+                            }),
+                        ));
+                    }
+                }
+                Buffer::Gradient(buffer) => {
+                    if !buffer.indices.is_empty() {
+                        self.primitives.push(Primitive::Custom(
+                            primitive::Custom::Mesh(Mesh::Gradient {
+                                buffers: mesh::Indexed {
+                                    vertices: buffer.vertices,
+                                    indices: buffer.indices,
+                                },
+                                size: self.size,
+                            }),
+                        ));
+                    }
+                }
             }
-            _ => unreachable!(),
         }
-    }
 
-    fn get_stroke<'a>(
-        &'a mut self,
-        style: &Style,
-    ) -> Box<dyn tessellation::StrokeGeometryBuilder + 'a> {
-        match (style, self.get_mut(style)) {
-            (Style::Solid(color), Buffer::Solid(buffer)) => {
-                Box::new(tessellation::BuffersBuilder::new(
-                    buffer,
-                    TriangleVertex2DBuilder(color::pack(*color)),
-                ))
-            }
-            (Style::Gradient(gradient), Buffer::Gradient(buffer)) => {
-                Box::new(tessellation::BuffersBuilder::new(
-                    buffer,
-                    GradientVertex2DBuilder {
-                        gradient: gradient.pack(),
-                    },
-                ))
-            }
-            _ => unreachable!(),
-        }
+        self.primitives
     }
 }
 
-#[derive(Debug)]
-struct Transforms {
-    previous: Vec<Transform>,
-    current: Transform,
-}
-
-#[derive(Debug, Clone, Copy)]
-struct Transform(lyon::math::Transform);
-
-impl Transform {
-    fn is_identity(&self) -> bool {
-        self.0 == lyon::math::Transform::identity()
-    }
-
-    fn is_scale_translation(&self) -> bool {
-        self.0.m12.abs() < 2.0 * f32::EPSILON
-            && self.0.m21.abs() < 2.0 * f32::EPSILON
-    }
-
-    fn scale(&self) -> (f32, f32) {
-        (self.0.m11, self.0.m22)
-    }
+impl geometry::Frame for Frame {
+    type Geometry = Primitive;
 
-    fn transform_point(&self, point: Point) -> Point {
-        let transformed = self
-            .0
-            .transform_point(euclid::Point2D::new(point.x, point.y));
-
-        Point {
-            x: transformed.x,
-            y: transformed.y,
-        }
-    }
-
-    fn transform_style(&self, style: Style) -> Style {
-        match style {
-            Style::Solid(color) => Style::Solid(color),
-            Style::Gradient(gradient) => {
-                Style::Gradient(self.transform_gradient(gradient))
-            }
-        }
-    }
-
-    fn transform_gradient(&self, mut gradient: Gradient) -> Gradient {
-        match &mut gradient {
-            Gradient::Linear(linear) => {
-                linear.start = self.transform_point(linear.start);
-                linear.end = self.transform_point(linear.end);
-            }
-        }
-
-        gradient
-    }
-}
-
-impl Frame {
     /// Creates a new empty [`Frame`] with the given dimensions.
     ///
     /// The default coordinate system of a [`Frame`] has its origin at the
     /// top-left corner of its bounds.
-    pub fn new(size: Size) -> Frame {
-        Frame {
-            size,
-            buffers: BufferStack::new(),
-            primitives: Vec::new(),
-            transforms: Transforms {
-                previous: Vec::new(),
-                current: Transform(lyon::math::Transform::identity()),
-            },
-            fill_tessellator: tessellation::FillTessellator::new(),
-            stroke_tessellator: tessellation::StrokeTessellator::new(),
-        }
-    }
 
-    /// Returns the width of the [`Frame`].
     #[inline]
-    pub fn width(&self) -> f32 {
+    fn width(&self) -> f32 {
         self.size.width
     }
 
-    /// Returns the height of the [`Frame`].
     #[inline]
-    pub fn height(&self) -> f32 {
+    fn height(&self) -> f32 {
         self.size.height
     }
 
-    /// Returns the dimensions of the [`Frame`].
     #[inline]
-    pub fn size(&self) -> Size {
+    fn size(&self) -> Size {
         self.size
     }
 
-    /// Returns the coordinate of the center of the [`Frame`].
     #[inline]
-    pub fn center(&self) -> Point {
+    fn center(&self) -> Point {
         Point::new(self.size.width / 2.0, self.size.height / 2.0)
     }
 
-    /// Draws the given [`Path`] on the [`Frame`] by filling it with the
-    /// provided style.
-    pub fn fill(&mut self, path: &Path, fill: impl Into<Fill>) {
+    fn fill(&mut self, path: &Path, fill: impl Into<Fill>) {
         let Fill { style, rule } = fill.into();
 
         let mut buffer = self
@@ -239,9 +136,7 @@ impl Frame {
         .expect("Tessellate path.");
     }
 
-    /// Draws an axis-aligned rectangle given its top-left corner coordinate and
-    /// its `Size` on the [`Frame`] by filling it with the provided style.
-    pub fn fill_rectangle(
+    fn fill_rectangle(
         &mut self,
         top_left: Point,
         size: Size,
@@ -276,9 +171,7 @@ impl Frame {
             .expect("Fill rectangle");
     }
 
-    /// Draws the stroke of the given [`Path`] on the [`Frame`] with the
-    /// provided style.
-    pub fn stroke<'a>(&mut self, path: &Path, stroke: impl Into<Stroke<'a>>) {
+    fn stroke<'a>(&mut self, path: &Path, stroke: impl Into<Stroke<'a>>) {
         let stroke = stroke.into();
 
         let mut buffer = self
@@ -315,20 +208,7 @@ impl Frame {
         .expect("Stroke path");
     }
 
-    /// Draws the characters of the given [`Text`] on the [`Frame`], filling
-    /// them with the given color.
-    ///
-    /// __Warning:__ Text currently does not work well with rotations and scale
-    /// transforms! The position will be correctly transformed, but the
-    /// resulting glyphs will not be rotated or scaled properly.
-    ///
-    /// Additionally, all text will be rendered on top of all the layers of
-    /// a `Canvas`. Therefore, it is currently only meant to be used for
-    /// overlays, which is the most common use case.
-    ///
-    /// Support for vectorial text is planned, and should address all these
-    /// limitations.
-    pub fn fill_text(&mut self, text: impl Into<Text>) {
+    fn fill_text(&mut self, text: impl Into<Text>) {
         let text = text.into();
 
         let (scale_x, scale_y) = self.transforms.current.scale();
@@ -384,57 +264,55 @@ impl Frame {
         }
     }
 
-    /// Stores the current transform of the [`Frame`] and executes the given
-    /// drawing operations, restoring the transform afterwards.
-    ///
-    /// This method is useful to compose transforms and perform drawing
-    /// operations in different coordinate systems.
     #[inline]
-    pub fn with_save<R>(&mut self, f: impl FnOnce(&mut Frame) -> R) -> R {
-        self.push_transform();
-
-        let result = f(self);
-
-        self.pop_transform();
-
-        result
+    fn translate(&mut self, translation: Vector) {
+        self.transforms.current.0 =
+            self.transforms
+                .current
+                .0
+                .pre_translate(lyon::math::Vector::new(
+                    translation.x,
+                    translation.y,
+                ));
     }
 
-    /// Pushes the current transform in the transform stack.
-    pub fn push_transform(&mut self) {
-        self.transforms.previous.push(self.transforms.current);
+    #[inline]
+    fn rotate(&mut self, angle: impl Into<Radians>) {
+        self.transforms.current.0 = self
+            .transforms
+            .current
+            .0
+            .pre_rotate(lyon::math::Angle::radians(angle.into().0));
     }
 
-    /// Pops a transform from the transform stack and sets it as the current transform.
-    pub fn pop_transform(&mut self) {
-        self.transforms.current = self.transforms.previous.pop().unwrap();
+    #[inline]
+    fn scale(&mut self, scale: impl Into<f32>) {
+        let scale = scale.into();
+
+        self.scale_nonuniform(Vector { x: scale, y: scale });
     }
 
-    /// Executes the given drawing operations within a [`Rectangle`] region,
-    /// clipping any geometry that overflows its bounds. Any transformations
-    /// performed are local to the provided closure.
-    ///
-    /// This method is useful to perform drawing operations that need to be
-    /// clipped.
     #[inline]
-    pub fn with_clip<R>(
-        &mut self,
-        region: Rectangle,
-        f: impl FnOnce(&mut Frame) -> R,
-    ) -> R {
-        let mut frame = Frame::new(region.size());
+    fn scale_nonuniform(&mut self, scale: impl Into<Vector>) {
+        let scale = scale.into();
 
-        let result = f(&mut frame);
+        self.transforms.current.0 =
+            self.transforms.current.0.pre_scale(scale.x, scale.y);
+    }
 
-        let origin = Point::new(region.x, region.y);
+    fn push_transform(&mut self) {
+        self.transforms.previous.push(self.transforms.current);
+    }
 
-        self.clip(frame, origin);
+    fn pop_transform(&mut self) {
+        self.transforms.current = self.transforms.previous.pop().unwrap();
+    }
 
-        result
+    fn draft(&mut self, size: Size) -> Frame {
+        Frame::new(size)
     }
 
-    /// Draws the clipped contents of the given [`Frame`] with origin at the given [`Point`].
-    pub fn clip(&mut self, frame: Frame, at: Point) {
+    fn paste(&mut self, frame: Frame, at: Point) {
         let size = frame.size();
         let primitives = frame.into_primitives();
         let transformation = Transformation::translate(at.x, at.y);
@@ -461,90 +339,153 @@ impl Frame {
             ],
         });
     }
+}
+impl From<Frame> for Primitive {
+    fn from(frame: Frame) -> Self {
+        Self::Group {
+            primitives: frame.into_primitives(),
+        }
+    }
+}
 
-    /// Applies a translation to the current transform of the [`Frame`].
-    #[inline]
-    pub fn translate(&mut self, translation: Vector) {
-        self.transforms.current.0 =
-            self.transforms
-                .current
-                .0
-                .pre_translate(lyon::math::Vector::new(
-                    translation.x,
-                    translation.y,
-                ));
+enum Buffer {
+    Solid(tessellation::VertexBuffers<mesh::SolidVertex2D, u32>),
+    Gradient(tessellation::VertexBuffers<mesh::GradientVertex2D, u32>),
+}
+
+struct BufferStack {
+    stack: Vec<Buffer>,
+}
+
+impl BufferStack {
+    fn new() -> Self {
+        Self { stack: Vec::new() }
     }
 
-    /// Applies a rotation in radians to the current transform of the [`Frame`].
-    #[inline]
-    pub fn rotate(&mut self, angle: impl Into<Radians>) {
-        self.transforms.current.0 = self
-            .transforms
-            .current
-            .0
-            .pre_rotate(lyon::math::Angle::radians(angle.into().0));
+    fn get_mut(&mut self, style: &Style) -> &mut Buffer {
+        match style {
+            Style::Solid(_) => match self.stack.last() {
+                Some(Buffer::Solid(_)) => {}
+                _ => {
+                    self.stack.push(Buffer::Solid(
+                        tessellation::VertexBuffers::new(),
+                    ));
+                }
+            },
+            Style::Gradient(_) => match self.stack.last() {
+                Some(Buffer::Gradient(_)) => {}
+                _ => {
+                    self.stack.push(Buffer::Gradient(
+                        tessellation::VertexBuffers::new(),
+                    ));
+                }
+            },
+        }
+
+        self.stack.last_mut().unwrap()
     }
 
-    /// Applies a uniform scaling to the current transform of the [`Frame`].
-    #[inline]
-    pub fn scale(&mut self, scale: impl Into<f32>) {
-        let scale = scale.into();
+    fn get_fill<'a>(
+        &'a mut self,
+        style: &Style,
+    ) -> Box<dyn tessellation::FillGeometryBuilder + 'a> {
+        match (style, self.get_mut(style)) {
+            (Style::Solid(color), Buffer::Solid(buffer)) => {
+                Box::new(tessellation::BuffersBuilder::new(
+                    buffer,
+                    TriangleVertex2DBuilder(color::pack(*color)),
+                ))
+            }
+            (Style::Gradient(gradient), Buffer::Gradient(buffer)) => {
+                Box::new(tessellation::BuffersBuilder::new(
+                    buffer,
+                    GradientVertex2DBuilder {
+                        gradient: gradient.pack(),
+                    },
+                ))
+            }
+            _ => unreachable!(),
+        }
+    }
 
-        self.scale_nonuniform(Vector { x: scale, y: scale });
+    fn get_stroke<'a>(
+        &'a mut self,
+        style: &Style,
+    ) -> Box<dyn tessellation::StrokeGeometryBuilder + 'a> {
+        match (style, self.get_mut(style)) {
+            (Style::Solid(color), Buffer::Solid(buffer)) => {
+                Box::new(tessellation::BuffersBuilder::new(
+                    buffer,
+                    TriangleVertex2DBuilder(color::pack(*color)),
+                ))
+            }
+            (Style::Gradient(gradient), Buffer::Gradient(buffer)) => {
+                Box::new(tessellation::BuffersBuilder::new(
+                    buffer,
+                    GradientVertex2DBuilder {
+                        gradient: gradient.pack(),
+                    },
+                ))
+            }
+            _ => unreachable!(),
+        }
     }
+}
 
-    /// Applies a non-uniform scaling to the current transform of the [`Frame`].
-    #[inline]
-    pub fn scale_nonuniform(&mut self, scale: impl Into<Vector>) {
-        let scale = scale.into();
+#[derive(Debug)]
+struct Transforms {
+    previous: Vec<Transform>,
+    current: Transform,
+}
 
-        self.transforms.current.0 =
-            self.transforms.current.0.pre_scale(scale.x, scale.y);
+#[derive(Debug, Clone, Copy)]
+struct Transform(lyon::math::Transform);
+
+impl Transform {
+    fn is_identity(&self) -> bool {
+        self.0 == lyon::math::Transform::identity()
     }
 
-    /// Produces the [`Primitive`] representing everything drawn on the [`Frame`].
-    pub fn into_primitive(self) -> Primitive {
-        Primitive::Group {
-            primitives: self.into_primitives(),
+    fn is_scale_translation(&self) -> bool {
+        self.0.m12.abs() < 2.0 * f32::EPSILON
+            && self.0.m21.abs() < 2.0 * f32::EPSILON
+    }
+
+    fn scale(&self) -> (f32, f32) {
+        (self.0.m11, self.0.m22)
+    }
+
+    fn transform_point(&self, point: Point) -> Point {
+        let transformed = self
+            .0
+            .transform_point(euclid::Point2D::new(point.x, point.y));
+
+        Point {
+            x: transformed.x,
+            y: transformed.y,
         }
     }
 
-    fn into_primitives(mut self) -> Vec<Primitive> {
-        for buffer in self.buffers.stack {
-            match buffer {
-                Buffer::Solid(buffer) => {
-                    if !buffer.indices.is_empty() {
-                        self.primitives.push(Primitive::Custom(
-                            primitive::Custom::Mesh(Mesh::Solid {
-                                buffers: mesh::Indexed {
-                                    vertices: buffer.vertices,
-                                    indices: buffer.indices,
-                                },
-                                size: self.size,
-                            }),
-                        ));
-                    }
-                }
-                Buffer::Gradient(buffer) => {
-                    if !buffer.indices.is_empty() {
-                        self.primitives.push(Primitive::Custom(
-                            primitive::Custom::Mesh(Mesh::Gradient {
-                                buffers: mesh::Indexed {
-                                    vertices: buffer.vertices,
-                                    indices: buffer.indices,
-                                },
-                                size: self.size,
-                            }),
-                        ));
-                    }
-                }
+    fn transform_style(&self, style: Style) -> Style {
+        match style {
+            Style::Solid(color) => Style::Solid(color),
+            Style::Gradient(gradient) => {
+                Style::Gradient(self.transform_gradient(gradient))
             }
         }
+    }
 
-        self.primitives
+    fn transform_gradient(&self, mut gradient: Gradient) -> Gradient {
+        match &mut gradient {
+            Gradient::Linear(linear) => {
+                linear.start = self.transform_point(linear.start);
+                linear.end = self.transform_point(linear.end);
+            }
+        }
+
+        gradient
     }
 }
-
 struct GradientVertex2DBuilder {
     gradient: gradient::Packed,
 }
diff --git a/wgpu/src/primitive.rs b/wgpu/src/primitive.rs
index fff927ea..ee9af93c 100644
--- a/wgpu/src/primitive.rs
+++ b/wgpu/src/primitive.rs
@@ -28,3 +28,11 @@ impl Damage for Custom {
         }
     }
 }
+
+impl TryFrom<Mesh> for Custom {
+    type Error = &'static str;
+
+    fn try_from(mesh: Mesh) -> Result<Self, Self::Error> {
+        Ok(Custom::Mesh(mesh))
+    }
+}