Adds Swipe layout

examples/reference/layouts/Swipe.ipynb

@@ -0,0 +1,96 @@
+{
+ "cells": [
+  {
+   "cell_type": "code",
+   "execution_count": null,
+   "id": "ed7c1d01-d655-4878-a27d-c6d0e330097b",
+   "metadata": {},
+   "outputs": [],
+   "source": [
+    "import panel as pn\n",
+    "import pandas as pd\n",
+    "\n",
+    "pn.extension()"
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "id": "ea1bc3ca-f83c-48e5-8046-7a4341ed835d",
+   "metadata": {},
+   "source": [
+    "The `Swipe` layout enables you to quickly compare two panels layed out on top of each other with a part of the *before* panel shown on one side of a slider and a part of the *after* panel shown on the other side.\n",
+    "\n",
+    "#### Parameters:\n",
+    "\n",
+    "* **``objects``** (list): The before and after components to lay out.\n",
+    "* **``value``** (int): The percentage of the *after* panel shown. Default is 50.\n",
+    "\n",
+    "Styling-related parameters:\n",
+    "\n",
+    "* **``slider_width``** (int): The width of the slider in pixels. Default is 12.\n",
+    "* **``slider_color``** (str): The color of the slider. Default is 'black'.\n",
+    "\n",
+    "For further layout and styling-related parameters see the [customization user guide](../../user_guide/Customization.ipynb).\n",
+    "\n",
+    "---"
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "id": "5613561d-d483-45df-8cbb-366abbb96e79",
+   "metadata": {},
+   "source": [
+    "The `Swipe` layout accepts any two objects, which must have identical sizing options to work as intended.\n",
+    "\n",
+    "Here we compare two images of mean surface temperatures in 1945-1949 and temperatures between 2015-2019:"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": null,
+   "id": "07cdc635-9642-4335-9862-d8195dadade7",
+   "metadata": {},
+   "outputs": [],
+   "source": [
+    "gis_1880 = 'https://earthobservatory.nasa.gov/ContentWOC/images/globaltemp/global_gis_1945-1949.png'\n",
+    "gis_2015 = 'https://earthobservatory.nasa.gov/ContentWOC/images/globaltemp/global_gis_2015-2019.png'\n",
+    "\n",
+    "pn.Swipe(gis_1880, gis_2015)"
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "id": "9af72676-c50d-4c61-820d-048daf8872e9",
+   "metadata": {},
+   "source": [
+    "The layout can compare any type of component, e.g. here we will compare two violin plots:"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": null,
+   "id": "c6187cb3-21a1-4900-be93-02ce3e480ff4",
+   "metadata": {},
+   "outputs": [],
+   "source": [
+    "import hvplot.pandas\n",
+    "\n",
+    "penguins = pd.read_csv('https://datasets.holoviz.org/penguins/v1/penguins.csv')\n",
+    "\n",
+    "pn.Swipe(\n",
+    "    penguins[penguins.species=='Chinstrap'].hvplot.violin('bill_length_mm', color='#00cde1'),\n",
+    "    penguins[penguins.species=='Adelie'].hvplot.violin('bill_length_mm', color='#cd0000'),\n",
+    "    value=51\n",
+    ")"
+   ]
+  }
+ ],
+ "metadata": {
+  "language_info": {
+   "name": "python",
+   "pygments_lexer": "ipython3"
+  }
+ },
+ "nbformat": 4,
+ "nbformat_minor": 5
+}

panel/__init__.py

@@ -60,8 +60,8 @@
     _jupyter_server_extension_paths, cache, ipywidget, serve, state,
 )
 from .layout import (  # noqa
-    Accordion, Card, Column, FlexBox, GridBox, GridSpec, Row, Spacer, Tabs,
-    WidgetBox,
+    Accordion, Card, Column, FlexBox, GridBox, GridSpec, Row, Spacer, Swipe,
+    Tabs, WidgetBox,
 )
 from .pane import panel  # noqa
 from .param import Param  # noqa

panel/dist/css/swipe.css

@@ -0,0 +1,23 @@
+.swipe-container {
+    display: grid;
+    grid-template-columns: 1fr;
+    grid-template-rows: 1fr;
+}
+
+.swipe-container .outer {
+    grid-column: 1;
+    grid-row: 1;
+}
+
+.swipe-container .slider {
+  grid-row: 1;
+  grid-column: 1;
+  z-index: 1;
+  height: 100%;
+  cursor: move;
+}
+
+.swipe-container .inner {
+  width: 100%;
+  height: 100%;
+}

panel/layout/__init__.py

@@ -39,6 +39,7 @@
 from .spacer import (  # noqa
     Divider, HSpacer, Spacer, VSpacer,
 )
+from .swipe import Swipe  # noqa
 from .tabs import Tabs  # noqa
 
 __all__ = (

panel/layout/swipe.py

@@ -0,0 +1,139 @@
+"""
+The Swipe layout enables you to quickly compare two panels
+"""
+
+import param
+
+from ..reactive import ReactiveHTML
+from .base import ListLike
+
+
+class Swipe(ListLike, ReactiveHTML):
+    """
+    The Swipe layout enables you to quickly compare two panels layed
+    out on top of each other with a part of the *before* panel shown
+    on one side of a slider and a part of the *after* panel shown on
+    the other side.
+    """
+
+    objects = param.List(default=[], bounds=(0, 2), doc="""
+        The list of child objects that make up the layout.""", precedence=-1)
+
+    slider_width = param.Integer(default=5, bounds=(0, 25), doc="""
+        The width of the slider in pixels""")
+
+    slider_color = param.Color(default="black", doc="""
+        The color of the slider""")
+
+    value = param.Integer(50, bounds=(0, 100), doc="""
+        The percentage of the *after* panel to show.""")
+
+    _before = param.Parameter()
+
+    _after = param.Parameter()
+
+    _template = """
+    <div id="container" class="swipe-container">
+      <div id="before" class="outer">
+        <div id="before-inner" class="inner">${_before}</div>
+      </div>
+      <div id="after" class="outer" style="overflow: hidden;">
+        <div id="after-inner" class="inner">${_after}</div>
+      </div>
+      <div id="slider" class="slider" onmousedown="${script('drag')}"
+           style="background: ${slider_color}; width: ${slider_width}px;">
+      </div>
+    </div>
+    """
+
+    _scripts = {
+        'render': """
+          self.adjustSlider()
+        """,
+        'after_layout': """
+          self.value()
+        """,
+        'drag': """
+          function endDrag() {
+             document.removeEventListener('mouseup', endDrag);
+             document.removeEventListener('mousemove', handleDrag);
+           }
+           function handleDrag(e) {
+             e = e || window.event;
+             e.preventDefault();
+             current = e.clientX
+             start = view.el.getBoundingClientRect().left
+             value = parseInt(((current-start)/ container.clientWidth)*100)
+             data.value = Math.max(0, Math.min(value, 100))
+           }
+           let e = event || window.event;
+           e.preventDefault();
+           document.addEventListener('mouseup', endDrag);
+           document.addEventListener('mousemove', handleDrag);
+        """,
+        'value': """
+           before.style.clipPath = `polygon(0% 0%, calc(${data.value}% + 5px) 0%, calc(${data.value}% + 5px) 100%, 0% 100%)`
+           after.style.clipPath = `polygon(calc(${data.value}% + 5px) 0%, 100% 0%, 100% 100%, calc(${data.value}% + 5px) 100%)`
+           self.adjustSlider()
+        """,
+        'slider_width': "self.adjustSlider()",
+        'adjustSlider': """
+           halfWidth = parseInt(data.slider_width/2)
+           slider.style.marginLeft = `calc(${data.value}% + 5px - ${halfWidth}px)`
+        """
+    }
+
+    _stylesheets = ['css/swipe.css']
+
+    def __init__(self, *objects, **params):
+        if 'objects' in params and objects:
+            raise ValueError(
+                "Either supply objects as an positional argument or "
+                "as a keyword argument, not both."
+            )
+        from ..pane.base import panel
+        objects = params.pop('objects', objects)
+        if not objects:
+            objects = [None, None]
+        super().__init__(objects=[panel(obj) for obj in objects], **params)
+
+    @param.depends('objects', watch=True, on_init=True)
+    def _update_layout(self):
+        self._before = self.before
+        self._after = self.after
+
+    @property
+    def before(self):
+        return self[0] if len(self) else None
+
+    @before.setter
+    def before(self, before):
+        self[0] = before
+
+    @property
+    def after(self):
+        return self[1] if len(self) > 1 else None
+
+    @after.setter
+    def after(self, after):
+        self[1] = after
+
+    def select(self, selector=None):
+        """
+        Iterates over the Viewable and any potential children in the
+        applying the Selector.
+
+        Arguments
+        ---------
+        selector: type or callable or None
+          The selector allows selecting a subset of Viewables by
+          declaring a type or callable function to filter by.
+
+        Returns
+        -------
+        viewables: list(Viewable)
+        """
+        objects = super().select(selector)
+        for obj in self:
+            objects += obj.select(selector)
+        return objects

panel/tests/layout/test_swipe.py

@@ -0,0 +1,21 @@
+from panel.layout import Spacer, Swipe
+
+
+def test_swip_construct(document, comm):
+    before = Spacer(background="red", height=400, width=800)
+    after = Spacer(background="green", height=400, width=800)
+    swipe = Swipe(
+        before,
+        after,
+        value=20,
+        height=800,
+        slider_width=15,
+        slider_color="lightgray"
+    )
+
+    model = swipe.get_root(document, comm)
+
+    assert model.children == {
+        'before-inner': [before._models[model.ref['id']][0]],
+        'after-inner': [after._models[model.ref['id']][0]]
+    }