Add `ImagePane` widget

2 files changed, 410 insertions, 0 deletions

diff --git a/native/src/widget.rs b/native/src/widget.rs
index 4453145b..23194545 100644
--- a/native/src/widget.rs
+++ b/native/src/widget.rs
@@ -25,6 +25,7 @@ pub mod checkbox;
 pub mod column;
 pub mod container;
 pub mod image;
+pub mod image_pane;
 pub mod pane_grid;
 pub mod progress_bar;
 pub mod radio;
@@ -47,6 +48,8 @@ pub use container::Container;
 #[doc(no_inline)]
 pub use image::Image;
 #[doc(no_inline)]
+pub use image_pane::ImagePane;
+#[doc(no_inline)]
 pub use pane_grid::PaneGrid;
 #[doc(no_inline)]
 pub use progress_bar::ProgressBar;
diff --git a/native/src/widget/image_pane.rs b/native/src/widget/image_pane.rs
new file mode 100644
index 00000000..4d07f228
--- /dev/null
+++ b/native/src/widget/image_pane.rs
@@ -0,0 +1,407 @@
+//! Zoom and pan on an image.
+use crate::{
+    image,
+    input::{self, mouse},
+    layout, Clipboard, Element, Event, Hasher, Layout, Length, Point,
+    Rectangle, Size, Widget,
+};
+
+use std::{f32, hash::Hash, u32};
+
+/// A widget that can display an image with the ability to zoom in/out and pan.
+#[allow(missing_debug_implementations)]
+pub struct ImagePane<'a> {
+    state: &'a mut State,
+    padding: u16,
+    width: Length,
+    height: Length,
+    max_width: u32,
+    max_height: u32,
+    handle: image::Handle,
+}
+
+impl<'a> ImagePane<'a> {
+    /// Creates a new [`ImagePane`] with the given [`State`] and [`Handle`].
+    ///
+    /// [`ImagePane`]: struct.ImagePane.html
+    /// [`State`]: struct.State.html
+    /// [`Handle`]: ../image/struct.Handle.html
+    pub fn new(state: &'a mut State, handle: image::Handle) -> Self {
+        ImagePane {
+            state,
+            padding: 0,
+            width: Length::Shrink,
+            height: Length::Shrink,
+            max_width: u32::MAX,
+            max_height: u32::MAX,
+            handle,
+        }
+    }
+
+    /// Sets the padding of the [`ImagePane`].
+    ///
+    /// [`ImagePane`]: struct.ImagePane.html
+    pub fn padding(mut self, units: u16) -> Self {
+        self.padding = units;
+        self
+    }
+
+    /// Sets the width of the [`ImagePane`].
+    ///
+    /// [`ImagePane`]: struct.ImagePane.html
+    pub fn width(mut self, width: Length) -> Self {
+        self.width = width;
+        self
+    }
+
+    /// Sets the height of the [`ImagePane`].
+    ///
+    /// [`ImagePane`]: struct.ImagePane.html
+    pub fn height(mut self, height: Length) -> Self {
+        self.height = height;
+        self
+    }
+
+    /// Sets the max width of the [`ImagePane`].
+    ///
+    /// [`ImagePane`]: struct.ImagePane.html
+    pub fn max_width(mut self, max_width: u32) -> Self {
+        self.max_width = max_width;
+        self
+    }
+
+    /// Sets the max height of the [`ImagePane`].
+    ///
+    /// [`ImagePane`]: struct.ImagePane.html
+    pub fn max_height(mut self, max_height: u32) -> Self {
+        self.max_height = max_height;
+        self
+    }
+}
+
+impl<'a, Message, Renderer> Widget<Message, Renderer> for ImagePane<'a>
+where
+    Renderer: self::Renderer + image::Renderer,
+{
+    fn width(&self) -> Length {
+        self.width
+    }
+
+    fn height(&self) -> Length {
+        self.height
+    }
+
+    fn layout(
+        &self,
+        _renderer: &Renderer,
+        limits: &layout::Limits,
+    ) -> layout::Node {
+        let padding = f32::from(self.padding);
+
+        let limits = limits
+            .max_width(self.max_width)
+            .max_height(self.max_height)
+            .width(self.width)
+            .height(self.height)
+            .pad(padding);
+
+        let size = limits.resolve(Size::INFINITY);
+
+        layout::Node::new(size)
+    }
+
+    fn on_event(
+        &mut self,
+        event: Event,
+        layout: Layout<'_>,
+        cursor_position: Point,
+        _messages: &mut Vec<Message>,
+        renderer: &Renderer,
+        _clipboard: Option<&dyn Clipboard>,
+    ) {
+        let bounds = layout.bounds();
+        let is_mouse_over = bounds.contains(cursor_position);
+
+        let image_bounds = {
+            let (width, height) = renderer.dimensions(&self.handle);
+
+            let dimensions = if let Some(scale) = self.state.scale {
+                (width as f32 * scale, height as f32 * scale)
+            } else {
+                let dimensions = (width as f32, height as f32);
+
+                let width_scale = bounds.width / dimensions.0;
+                let height_scale = bounds.height / dimensions.1;
+
+                let scale = width_scale.min(height_scale);
+
+                if scale < 1.0 {
+                    (dimensions.0 * scale, dimensions.1 * scale)
+                } else {
+                    (dimensions.0, dimensions.1)
+                }
+            };
+
+            Rectangle {
+                x: bounds.x,
+                y: bounds.y,
+                width: dimensions.0,
+                height: dimensions.1,
+            }
+        };
+
+        if is_mouse_over {
+            match event {
+                Event::Mouse(mouse::Event::WheelScrolled { delta }) => {
+                    match delta {
+                        mouse::ScrollDelta::Lines { y, .. } => {
+                            // TODO: Configurable step and limits
+                            if y > 0.0 {
+                                self.state.scale = Some(
+                                    (self.state.scale.unwrap_or(1.0) + 0.25)
+                                        .min(10.0),
+                                );
+                            } else {
+                                self.state.scale = Some(
+                                    (self.state.scale.unwrap_or(1.0) - 0.25)
+                                        .max(0.25),
+                                );
+                            }
+                        }
+                        mouse::ScrollDelta::Pixels { y, .. } => {
+                            // TODO: Configurable step and limits
+                            if y > 0.0 {
+                                self.state.scale = Some(
+                                    (self.state.scale.unwrap_or(1.0) + 0.25)
+                                        .min(10.0),
+                                );
+                            } else {
+                                self.state.scale = Some(
+                                    (self.state.scale.unwrap_or(1.0) - 0.25)
+                                        .max(0.25),
+                                );
+                            }
+                        }
+                    }
+                }
+                Event::Mouse(mouse::Event::Input { button, state }) => {
+                    if button == mouse::Button::Left {
+                        match state {
+                            input::ButtonState::Pressed => {
+                                self.state.starting_cursor_pos = Some((
+                                    cursor_position.x,
+                                    cursor_position.y,
+                                ));
+
+                                self.state.starting_offset =
+                                    self.state.current_offset;
+                            }
+                            input::ButtonState::Released => {
+                                self.state.starting_cursor_pos = None
+                            }
+                        }
+                    }
+                }
+                Event::Mouse(mouse::Event::CursorMoved { x, y }) => {
+                    if self.state.is_cursor_clicked() {
+                        self.state.pan(x, y, bounds, image_bounds);
+                    }
+                }
+                _ => {}
+            }
+        } else if let Event::Mouse(mouse::Event::Input { button, state }) =
+            event
+        {
+            if button == mouse::Button::Left
+                && state == input::ButtonState::Released
+            {
+                self.state.starting_cursor_pos = None;
+            }
+        }
+    }
+
+    fn draw(
+        &self,
+        renderer: &mut Renderer,
+        _defaults: &Renderer::Defaults,
+        layout: Layout<'_>,
+        cursor_position: Point,
+    ) -> Renderer::Output {
+        let bounds = layout.bounds();
+
+        let image_bounds = {
+            let (width, height) = renderer.dimensions(&self.handle);
+
+            let dimensions = if let Some(scale) = self.state.scale {
+                (width as f32 * scale, height as f32 * scale)
+            } else {
+                let dimensions = (width as f32, height as f32);
+
+                let width_scale = bounds.width / dimensions.0;
+                let height_scale = bounds.height / dimensions.1;
+
+                let scale = width_scale.min(height_scale);
+
+                if scale < 1.0 {
+                    (dimensions.0 * scale, dimensions.1 * scale)
+                } else {
+                    (dimensions.0, dimensions.1)
+                }
+            };
+
+            Rectangle {
+                x: bounds.x,
+                y: bounds.y,
+                width: dimensions.0,
+                height: dimensions.1,
+            }
+        };
+
+        let offset = self.state.offset(bounds, image_bounds);
+
+        let is_mouse_over = bounds.contains(cursor_position);
+
+        self::Renderer::draw(
+            renderer,
+            &self.state,
+            bounds,
+            image_bounds,
+            offset,
+            self.handle.clone(),
+            is_mouse_over,
+        )
+    }
+
+    fn hash_layout(&self, state: &mut Hasher) {
+        struct Marker;
+        std::any::TypeId::of::<Marker>().hash(state);
+
+        self.width.hash(state);
+        self.height.hash(state);
+        self.max_width.hash(state);
+        self.max_height.hash(state);
+        self.padding.hash(state);
+
+        self.handle.hash(state);
+    }
+}
+
+/// The local state of an [`ImagePane`].
+///
+/// [`ImagePane`]: struct.ImagePane.html
+#[derive(Debug, Clone, Copy, Default)]
+pub struct State {
+    scale: Option<f32>,
+    starting_offset: (f32, f32),
+    current_offset: (f32, f32),
+    starting_cursor_pos: Option<(f32, f32)>,
+}
+
+impl State {
+    /// Creates a new [`State`] with the scrollbar located at the top.
+    ///
+    /// [`State`]: struct.State.html
+    pub fn new() -> Self {
+        State::default()
+    }
+
+    /// Apply a panning offset to the current [`State`], given the bounds of
+    /// the [`ImagePane`] and its image.
+    ///
+    /// [`ImagePane`]: struct.ImagePane.html
+    /// [`State`]: struct.State.html
+    fn pan(
+        &mut self,
+        x: f32,
+        y: f32,
+        bounds: Rectangle,
+        image_bounds: Rectangle,
+    ) {
+        let delta_x = x - self.starting_cursor_pos.unwrap().0;
+        let delta_y = y - self.starting_cursor_pos.unwrap().1;
+
+        if bounds.width < image_bounds.width {
+            self.current_offset.0 = (self.starting_offset.0 - delta_x)
+                .max(0.0)
+                .min((image_bounds.width - bounds.width) as f32);
+        }
+
+        if bounds.height < image_bounds.height {
+            self.current_offset.1 = (self.starting_offset.1 - delta_y)
+                .max(0.0)
+                .min((image_bounds.height - bounds.height) as f32);
+        }
+    }
+
+    /// Returns the current clipping offset of the [`State`], given the bounds
+    /// of the [`ImagePane`] and its contents.
+    ///
+    /// [`ImagePane`]: struct.ImagePane.html
+    /// [`State`]: struct.State.html
+    fn offset(&self, bounds: Rectangle, image_bounds: Rectangle) -> (u32, u32) {
+        let hidden_width = ((image_bounds.width - bounds.width) as f32)
+            .max(0.0)
+            .round() as u32;
+
+        let hidden_height = ((image_bounds.height - bounds.height) as f32)
+            .max(0.0)
+            .round() as u32;
+
+        (
+            (self.current_offset.0).min(hidden_width as f32) as u32,
+            (self.current_offset.1).min(hidden_height as f32) as u32,
+        )
+    }
+
+    /// Returns if the left mouse button is still held down since clicking inside
+    /// the [`ImagePane`].
+    ///
+    /// [`ImagePane`]: struct.ImagePane.html
+    /// [`State`]: struct.State.html
+    pub fn is_cursor_clicked(&self) -> bool {
+        self.starting_cursor_pos.is_some()
+    }
+}
+
+/// The renderer of an [`ImagePane`].
+///
+/// Your [renderer] will need to implement this trait before being
+/// able to use a [`ImagePane`] in your user interface.
+///
+/// [`ImagePane`]: struct.ImagePane.html
+/// [renderer]: ../../renderer/index.html
+pub trait Renderer: crate::Renderer + Sized {
+    /// Draws the [`ImagePane`].
+    ///
+    /// It receives:
+    /// - the [`State`] of the [`ImagePane`]
+    /// - the bounds of the [`ImagePane`] widget
+    /// - the bounds of the scaled [`ImagePane`] image
+    /// - the clipping x,y offset
+    /// - the [`Handle`] to the underlying image
+    /// - whether the mouse is over the [`ImagePane`] or not
+    ///
+    /// [`ImagePane`]: struct.ImagePane.html
+    /// [`State`]: struct.State.html
+    /// [`Handle`]: ../image/struct.Handle.html
+    fn draw(
+        &mut self,
+        state: &State,
+        bounds: Rectangle,
+        image_bounds: Rectangle,
+        offset: (u32, u32),
+        handle: image::Handle,
+        is_mouse_over: bool,
+    ) -> Self::Output;
+}
+
+impl<'a, Message, Renderer> From<ImagePane<'a>>
+    for Element<'a, Message, Renderer>
+where
+    Renderer: 'a + self::Renderer + image::Renderer,
+    Message: 'a,
+{
+    fn from(image_pane: ImagePane<'a>) -> Element<'a, Message, Renderer> {
+        Element::new(image_pane)
+    }
+}