Added support for relative positioning of gradient fills. Addressed some PR feedback.

8 files changed, 182 insertions, 54 deletions

diff --git a/examples/modern_art/src/main.rs b/examples/modern_art/src/main.rs
index 0601fc44..362e4ad1 100644
--- a/examples/modern_art/src/main.rs
+++ b/examples/modern_art/src/main.rs
@@ -1,5 +1,5 @@
 use iced::widget::canvas::{
-    self, fill, Cache, Canvas, Cursor, Fill, Frame, Geometry, Gradient,
+    self, Cache, Canvas, Cursor, Frame, Geometry, Gradient, Position, Location
 };
 use iced::{
     executor, Application, Color, Command, Element, Length, Point, Rectangle,
@@ -76,6 +76,20 @@ impl<Message> canvas::Program<Message> for ModernArt {
     }
 }
 
+fn random_direction() -> Location {
+    match thread_rng().gen_range(0..8) {
+        0 => Location::TopLeft,
+        1 => Location::Top,
+        2 => Location::TopRight,
+        3 => Location::Right,
+        4 => Location::BottomRight,
+        5 => Location::Bottom,
+        6 => Location::BottomLeft,
+        7 => Location::Left,
+        _ => Location::TopLeft
+    }
+}
+
 fn generate_box(frame: &mut Frame, bounds: Size) -> bool {
     let solid = rand::random::<bool>();
 
@@ -87,8 +101,13 @@ fn generate_box(frame: &mut Frame, bounds: Size) -> bool {
         )
     };
 
-    let gradient = |top_left: Point, bottom_right: Point| -> Gradient {
-        let mut builder = Gradient::linear(top_left, bottom_right);
+    let gradient = |top_left: Point, size: Size| -> Gradient {
+        let mut builder = Gradient::linear(Position::Relative {
+            top_left,
+            size,
+            start: random_direction(),
+            end: random_direction()
+        });
         let stops = thread_rng().gen_range(1..15u32);
 
         let mut i = 0;
@@ -114,25 +133,13 @@ fn generate_box(frame: &mut Frame, bounds: Size) -> bool {
         frame.fill_rectangle(
             top_left,
             size,
-            Fill {
-                style: fill::Style::Solid(random_color()),
-                ..Default::default()
-            },
+            random_color(),
         );
     } else {
         frame.fill_rectangle(
             top_left,
             size,
-            Fill {
-                style: fill::Style::Gradient(&gradient(
-                    top_left,
-                    Point::new(
-                        top_left.x + size.width,
-                        top_left.y + size.height,
-                    ),
-                )),
-                ..Default::default()
-            },
+            &gradient(top_left, size),
         );
     };
 
diff --git a/examples/solar_system/src/main.rs b/examples/solar_system/src/main.rs
index 6f38f480..9200391b 100644
--- a/examples/solar_system/src/main.rs
+++ b/examples/solar_system/src/main.rs
@@ -19,6 +19,7 @@ use iced::{
 };
 
 use std::time::Instant;
+use crate::canvas::Position;
 
 pub fn main() -> iced::Result {
     SolarSystem::run(Settings {
@@ -202,8 +203,10 @@ impl<Message> canvas::Program<Message> for State {
                 let earth = Path::circle(Point::ORIGIN, Self::EARTH_RADIUS);
 
                 let earth_fill = Gradient::linear(
-                    Point::new(-Self::EARTH_RADIUS, 0.0),
-                    Point::new(Self::EARTH_RADIUS, 0.0),
+                    Position::Absolute {
+                        start: Point::new(-Self::EARTH_RADIUS, 0.0),
+                        end: Point::new(Self::EARTH_RADIUS, 0.0)
+                    }
                 )
                 .add_stop(0.2, Color::from_rgb(0.15, 0.50, 1.0))
                 .add_stop(0.8, Color::from_rgb(0.0, 0.20, 0.47))
diff --git a/glow/src/shader/common/gradient.frag b/glow/src/shader/common/gradient.frag
index ade9c4a1..3c701af7 100644
--- a/glow/src/shader/common/gradient.frag
+++ b/glow/src/shader/common/gradient.frag
@@ -45,6 +45,9 @@ void main() {
             fragColor = color_stops[0];
         } else if (coord_offset > color_stops[color_stops_size - 1].x) {
             fragColor = color_stops[color_stops_size - 2];
+        } else {
+            //This use case can happen if a gradient's start & end position are the same
+            fragColor = vec4(0.0, 0.0, 0.0, 0.0);
         }
     }
 }
diff --git a/graphics/src/gradient.rs b/graphics/src/gradient.rs
index d785fb2a..e1984854 100644
--- a/graphics/src/gradient.rs
+++ b/graphics/src/gradient.rs
@@ -1,9 +1,10 @@
 //! For creating a Gradient.
 mod linear;
 
-pub use crate::gradient::linear::Linear;
+pub use crate::gradient::linear::{Linear, Position, Location};
 use crate::widget::canvas::frame::Transform;
-use crate::{Point, Color};
+use crate::Color;
+use crate::widget::canvas::{Fill, fill};
 
 #[derive(Debug, Clone, PartialEq)]
 /// A fill which transitions colors progressively along a direction, either linearly, radially (TBD),
@@ -25,18 +26,27 @@ pub struct ColorStop {
 
 impl Gradient {
     /// Creates a new linear [`linear::Builder`].
-    pub fn linear(start: Point, end: Point) -> linear::Builder {
-        linear::Builder::new(start, end)
+    pub fn linear(position: impl Into<Position>) -> linear::Builder {
+        linear::Builder::new(position.into())
     }
 
     /// Modifies the start & end stops of the gradient to have a proper transform value.
     pub(crate) fn transform(mut self, transform: &Transform) -> Self {
         match &mut self {
             Gradient::Linear(linear) => {
-                linear.start = transform.apply_to(linear.start);
-                linear.end = transform.apply_to(linear.end);
+                linear.start = transform.transform_point(linear.start);
+                linear.end = transform.transform_point(linear.end);
             }
         }
         self
     }
 }
+
+impl<'a> Into<Fill<'a>> for &'a Gradient {
+    fn into(self) -> Fill<'a> {
+        Fill {
+            style: fill::Style::Gradient(self),
+            .. Default::default()
+        }
+    }
+}
diff --git a/graphics/src/gradient/linear.rs b/graphics/src/gradient/linear.rs
index 6bf69b43..a9cfd55d 100644
--- a/graphics/src/gradient/linear.rs
+++ b/graphics/src/gradient/linear.rs
@@ -1,7 +1,6 @@
 //! Linear gradient builder & definition.
-
 use crate::gradient::{ColorStop, Gradient};
-use crate::{Color, Point};
+use crate::{Color, Point, Size};
 
 /// A linear gradient that can be used in the style of [`super::Fill`] or [`super::Stroke`].
 #[derive(Debug, Clone, PartialEq)]
@@ -14,18 +13,115 @@ pub struct Linear {
     pub color_stops: Vec<ColorStop>,
 }
 
+#[derive(Debug)]
+/// The position of the gradient within its bounds.
+pub enum Position {
+    /// The gradient will be positioned with respect to two points.
+    Absolute {
+        /// The starting point of the gradient.
+        start: Point,
+        /// The ending point of the gradient.
+        end: Point,
+    },
+    /// The gradient will be positioned relative to the provided bounds.
+    Relative {
+        /// The top left position of the bounds.
+        top_left: Point,
+        /// The width & height of the bounds.
+        size: Size,
+        /// The start [Location] of the gradient.
+        start: Location,
+        /// The end [Location] of the gradient.
+        end: Location,
+    },
+}
+
+impl Into<Position> for (Point, Point) {
+    fn into(self) -> Position {
+        Position::Absolute {
+            start: self.0,
+            end: self.1,
+        }
+    }
+}
+
+#[derive(Debug)]
+/// The location of a relatively-positioned gradient.
+pub enum Location {
+    /// Top left.
+    TopLeft,
+    /// Top.
+    Top,
+    /// Top right.
+    TopRight,
+    /// Right.
+    Right,
+    /// Bottom right.
+    BottomRight,
+    /// Bottom.
+    Bottom,
+    /// Bottom left.
+    BottomLeft,
+    /// Left.
+    Left,
+}
+
+impl Location {
+    fn to_absolute(&self, top_left: Point, size: Size) -> Point {
+        match self {
+            Location::TopLeft => top_left,
+            Location::Top => {
+                Point::new(top_left.x + size.width / 2.0, top_left.y)
+            }
+            Location::TopRight => {
+                Point::new(top_left.x + size.width, top_left.y)
+            }
+            Location::Right => Point::new(
+                top_left.x + size.width,
+                top_left.y + size.height / 2.0,
+            ),
+            Location::BottomRight => {
+                Point::new(top_left.x + size.width, top_left.y + size.height)
+            }
+            Location::Bottom => Point::new(
+                top_left.x + size.width / 2.0,
+                top_left.y + size.height,
+            ),
+            Location::BottomLeft => {
+                Point::new(top_left.x, top_left.y + size.height)
+            }
+            Location::Left => {
+                Point::new(top_left.x, top_left.y + size.height / 2.0)
+            }
+        }
+    }
+}
+
 /// A [`Linear`] builder.
 #[derive(Debug)]
 pub struct Builder {
     start: Point,
     end: Point,
-    stops: Vec<(f32, Color)>,
+    stops: Vec<ColorStop>,
     valid: bool,
 }
 
 impl Builder {
     /// Creates a new [`Builder`].
-    pub fn new(start: Point, end: Point) -> Self {
+    pub fn new(position: Position) -> Self {
+        let (start, end) = match position {
+            Position::Absolute { start, end } => (start, end),
+            Position::Relative {
+                top_left,
+                size,
+                start,
+                end,
+            } => (
+                start.to_absolute(top_left, size),
+                end.to_absolute(top_left, size),
+            ),
+        };
+
         Self {
             start,
             end,
@@ -36,37 +132,47 @@ impl Builder {
 
     /// Adds a new stop, defined by an offset and a color, to the gradient.
     ///
-    /// `offset` must be between `0.0` and `1.0`.
+    /// `offset` must be between `0.0` and `1.0` or the gradient cannot be built.
+    ///
+    /// Note: when using the [Glow] backend, any color stop added after the 16th
+    /// will not be displayed.
+    ///
+    /// On [backend::Wgpu] backend this limitation does not exist (technical limit is 524,288 stops).
     pub fn add_stop(mut self, offset: f32, color: Color) -> Self {
-        if !(0.0..=1.0).contains(&offset) {
+        if offset.is_finite() && (0.0..=1.0).contains(&offset) {
+            match self.stops.binary_search_by(|stop| {
+                stop.offset.partial_cmp(&offset).unwrap()
+            }) {
+                Ok(_) => {
+                    //the offset already exists in the gradient
+                    self.valid = false;
+                }
+                Err(index) => {
+                    self.stops.insert(index, ColorStop { offset, color })
+                }
+            }
+        } else {
             self.valid = false;
         }
-
-        //TODO: can sort on insert here
-        self.stops.push((offset, color));
         self
     }
 
     /// Builds the linear [`Gradient`] of this [`Builder`].
     ///
-    /// Returns `None` if no stops were added to the builder or
+    /// Returns `Err` if no stops were added to the builder or
     /// if stops not between 0.0 and 1.0 were added.
-    pub fn build(self) -> Option<Gradient> {
+    pub fn build(self) -> Result<Gradient, &'static str> {
         if self.stops.is_empty() || !self.valid {
-            return None;
+            return Err("Valid gradient conditions: \
+            1) Must contain at least one color stop. \
+             2) Every color stop offset must be unique. \
+             3) Every color stop must be within the range of 0.0..=1.0");
         }
 
-        let mut stops: Vec<ColorStop> = self.stops.clone().into_iter().map(|f| ColorStop {
-            offset: f.0,
-            color: f.1
-        }).collect();
-
-        stops.sort_by(|a, b| a.offset.partial_cmp(&b.offset).unwrap());
-
-        Some(Gradient::Linear(Linear {
+        Ok(Gradient::Linear(Linear {
             start: self.start,
             end: self.end,
-            color_stops: stops
+            color_stops: self.stops,
         }))
     }
 }
diff --git a/graphics/src/primitive.rs b/graphics/src/primitive.rs
index 10c86ad2..5cb0ef23 100644
--- a/graphics/src/primitive.rs
+++ b/graphics/src/primitive.rs
@@ -2,11 +2,10 @@ use iced_native::image;
 use iced_native::svg;
 use iced_native::{Background, Color, Font, Rectangle, Size, Vector};
 
-use crate::{alignment, layer};
+use crate::{alignment, layer::mesh};
 use crate::triangle;
 
 use std::sync::Arc;
-use layer::mesh;
 
 /// A rendering primitive.
 #[derive(Debug, Clone)]
diff --git a/graphics/src/widget/canvas.rs b/graphics/src/widget/canvas.rs
index fe0f618f..ea8af8c2 100644
--- a/graphics/src/widget/canvas.rs
+++ b/graphics/src/widget/canvas.rs
@@ -28,7 +28,7 @@ pub use stroke::{LineCap, LineDash, LineJoin, Stroke};
 pub use text::Text;
 
 use crate::{Backend, Primitive, Renderer};
-pub use crate::gradient::Gradient;
+pub use crate::gradient::{Gradient, Position, Location};
 
 use iced_native::layout::{self, Layout};
 use iced_native::mouse;
diff --git a/graphics/src/widget/canvas/frame.rs b/graphics/src/widget/canvas/frame.rs
index ccba840a..6dd0d06a 100644
--- a/graphics/src/widget/canvas/frame.rs
+++ b/graphics/src/widget/canvas/frame.rs
@@ -1,4 +1,4 @@
-use lyon::geom::euclid::Vector2D;
+use lyon::geom::euclid::Point2D;
 use std::borrow::Cow;
 
 use iced_native::{Point, Rectangle, Size, Vector};
@@ -38,11 +38,11 @@ pub(crate) struct Transform {
 
 impl Transform {
     /// Transforms the given [Point] by the transformation matrix.
-    pub(crate) fn apply_to(&self, mut point: Point) -> Point {
+    pub(crate) fn transform_point(&self, mut point: Point) -> Point {
         let transformed =
-            self.raw.transform_vector(Vector2D::new(point.x, point.y));
-        point.x = transformed.x + self.raw.m31;
-        point.y = transformed.y + self.raw.m32;
+            self.raw.transform_point(Point2D::new(point.x, point.y));
+        point.x = transformed.x;
+        point.y = transformed.y;
         point
     }
 }