Add support for extra traces

examples/threshold_contour.py

@@ -0,0 +1,66 @@
+"""
+An example demonstrating adding traces.
+
+This shows a volume with a contour overlaid on top. The `extra_traces`
+property is used to add scatter traces that represent the contour.
+"""
+
+import dash
+import dash_html_components as html
+import dash_core_components as dcc
+from dash.dependencies import Input, Output
+from dash_slicer import VolumeSlicer
+import imageio
+from skimage import measure
+
+
+app = dash.Dash(__name__, update_title=None)
+server = app.server
+
+vol = imageio.volread("imageio:stent.npz")
+mi, ma = vol.min(), vol.max()
+slicer = VolumeSlicer(app, vol)
+
+
+app.layout = html.Div(
+    [
+        slicer.graph,
+        slicer.slider,
+        dcc.Slider(
+            id="level-slider",
+            min=mi,
+            max=ma,
+            step=1,
+            value=mi + 0.2 * (ma - mi),
+        ),
+        *slicer.stores,
+    ]
+)
+
+
+@app.callback(
+    Output(slicer.extra_traces.id, "data"),
+    [Input("level-slider", "value"), Input(slicer.state.id, "data")],
+)
+def apply_levels(level, state):
+    if not state:
+        return dash.no_update
+    slice = vol[state["index"]]
+    contours = measure.find_contours(slice, level)
+    traces = []
+    for contour in contours:
+        traces.append(
+            {
+                "type": "scatter",
+                "mode": "lines",
+                "line": {"color": "cyan", "width": 3},
+                "x": contour[:, 1],
+                "y": contour[:, 0],
+            }
+        )
+    return traces
+
+
+if __name__ == "__main__":
+    # Note: dev_tools_props_check negatively affects the performance of VolumeSlicer
+    app.run_server(debug=True, dev_tools_props_check=False)