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

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,
         }))
     }
 }