feat(ImageMarchingCubes): Added 2D image or slice contouring

A new isocontouring algorithm for 2D images or a zslice from a
volume has been added. Multiple contours are supported, and merging
intersection points along edges may be enabled or disabled.

Sources/Common/DataModel/ImplicitBoolean/index.js

@@ -19,6 +19,18 @@ function vtkImplicitBoolean(publicAPI, model) {
   // Set our className
   model.classHierarchy.push('vtkImplicitBoolean');
 
+  publicAPI.getMTime = () => {
+    let mTime = model.superClass.getMTime();
+    if (!model.functions || model.functions.length <= 0) {
+      return mTime;
+    }
+
+    for (let i = 0; i < model.functions.length; ++i) {
+      mTime = Math.max(mTime, model.functions[i].getMTime());
+    }
+    return mTime;
+  };
+
   publicAPI.getOperationAsString = () => macro.enumToString(Operation, model.operation);
 
   publicAPI.setOperationToUnion = () => publicAPI.setOperation(0);

Sources/Filters/General/ImageMarchingSquares/api.md

@@ -0,0 +1,24 @@
+## Introduction
+
+vtkImageMarchingSquares - isocontour an image (or slice from a volume)
+
+Given a specified contour value, generate isolines using the
+Marching Squares algorithm (the 2D version of the 3D Marching Cubes
+algorithm).
+
+## Public API
+
+### contourValues
+
+Set/Get an array of isocontour values.
+
+### sliceNumber
+
+Set/Get the k-slice number of the input volume. By default the
+sliceNumber = 0.
+
+### mergePoints
+
+As lines forming the isolines are generated, indicate whether
+conincident points are to be merged. Merging produces connected polylines
+at the cost of additional memory and computation.

Sources/Filters/General/ImageMarchingSquares/caseTable.js

@@ -0,0 +1,48 @@
+// ----------------------------------------------------------------------------
+// Marching squares case functions (using lines to generate the 2D tessellation).
+// For each case, a list of edge ids that form the triangles. A -1 marks the
+// end of the list of edges. Edges are taken three at a time to generate
+// triangle points.
+// ----------------------------------------------------------------------------
+const MARCHING_SQUARES_CASES = [
+  [-1, -1, -1, -1, -1], /* 0 */
+  [0, 3, -1, -1, -1], /* 1 */
+  [1, 0, -1, -1, -1], /* 2 */
+  [1, 3, -1, -1, -1], /* 3 */
+  [2, 1, -1, -1, -1], /* 4 */
+  [0, 3, 2, 1, -1], /* 5 */
+  [2, 0, -1, -1, -1], /* 6 */
+  [2, 3, -1, -1, -1], /* 7 */
+  [3, 2, -1, -1, -1], /* 8 */
+  [0, 2, -1, -1, -1], /* 9 */
+  [1, 0, 3, 2, -1], /* 10 */
+  [1, 2, -1, -1, -1], /* 11 */
+  [3, 1, -1, -1, -1], /* 12 */
+  [0, 1, -1, -1, -1], /* 13 */
+  [3, 0, -1, -1, -1], /* 14 */
+  [-1, -1, -1, -1, -1], /* 15 */
+];
+
+const EDGES = [
+  [0, 1],
+  [1, 3],
+  [2, 3],
+  [0, 2],
+];
+
+function getCase(index) {
+  return MARCHING_SQUARES_CASES[index];
+}
+
+// Define the four edges of the pixel by the following pairs of vertices
+function getEdge(eid) {
+  return EDGES[eid];
+}
+
+// ----------------------------------------------------------------------------
+// Static API
+// ----------------------------------------------------------------------------
+export default {
+  getCase,
+  getEdge,
+};

Sources/Filters/General/ImageMarchingSquares/example/controller.html

@@ -0,0 +1,20 @@
+<table>
+  <tr>
+    <td>Volume resolution</td>
+    <td>
+      <input class='volumeResolution' type="range" min="10" max="100" step="1" value="50" />
+    </td>
+  </tr>
+  <tr>
+    <td>Radius</td>
+    <td>
+      <input class='sphereRadius' type="range" min="0.01" max="1.0" step="0.01" value="0.025" />
+    </td>
+  </tr>
+  <tr>
+    <td>Merge Points</td>
+    <td>
+      <input class='mergePoints' type="checkbox" unchecked />
+    </td>
+  </tr>
+</table>

Sources/Filters/General/ImageMarchingSquares/example/index.js

@@ -0,0 +1,110 @@
+import 'vtk.js/Sources/favicon';
+
+import vtkActor                   from 'vtk.js/Sources/Rendering/Core/Actor';
+import vtkFullScreenRenderWindow  from 'vtk.js/Sources/Rendering/Misc/FullScreenRenderWindow';
+import vtkImageMarchingSquares    from 'vtk.js/Sources/Filters/General/ImageMarchingSquares';
+import vtkOutlineFilter           from 'vtk.js/Sources/Filters/General/OutlineFilter';
+import vtkMapper                  from 'vtk.js/Sources/Rendering/Core/Mapper';
+import vtkSampleFunction          from 'vtk.js/Sources/Imaging/Hybrid/SampleFunction';
+import vtkSphere                  from 'vtk.js/Sources/Common/DataModel/Sphere';
+// import vtkPlane                   from 'vtk.js/Sources/Common/DataModel/Plane';
+import vtkImplicitBoolean         from 'vtk.js/Sources/Common/DataModel/ImplicitBoolean';
+
+import controlPanel from './controller.html';
+
+const { Operation } = vtkImplicitBoolean;
+
+// ----------------------------------------------------------------------------
+// Standard rendering code setup
+// ----------------------------------------------------------------------------
+
+const fullScreenRenderer = vtkFullScreenRenderWindow.newInstance();
+const renderer = fullScreenRenderer.getRenderer();
+const renderWindow = fullScreenRenderer.getRenderWindow();
+
+// ----------------------------------------------------------------------------
+// Example code
+// ----------------------------------------------------------------------------
+const actor = vtkActor.newInstance();
+renderer.addActor(actor);
+
+const mapper = vtkMapper.newInstance();
+actor.setMapper(mapper);
+
+// Build pipeline
+const sphere = vtkSphere.newInstance({ center: [-2.5, 0.0, 0.0], radius: 0.5 });
+const sphere2 = vtkSphere.newInstance({ center: [2.5, 0.0, 0.0], radius: 0.5 });
+// const plane = vtkPlane.newInstance({ origin: [0, 0, 0], normal: [0, 1, 0] });
+const impBool = vtkImplicitBoolean.newInstance({ operation: Operation.UNION, functions: [sphere, sphere2] });
+const sample = vtkSampleFunction.newInstance({ implicitFunction: impBool, sampleDimensions: [5, 3, 3], modelBounds: [-5.0, 5.0, -1.0, 1.0, -1.0, 1.0] });
+
+// Isocontour
+const mSquares = vtkImageMarchingSquares.newInstance({ slice: 1 });
+
+// Connect the pipeline proper
+mSquares.setInputConnection(sample.getOutputPort());
+mapper.setInputConnection(mSquares.getOutputPort());
+
+// Update the pipeline to obtain metadata (range) about scalars
+sample.update();
+const cValues = [];
+const [min, max] = sample.getOutputData().getPointData().getScalars().getRange();
+for (let i = 0; i < 20; ++i) {
+  cValues[i] = min + ((i / 19) * (max - min));
+}
+mSquares.setContourValues(cValues);
+
+// Create an outline
+const outline = vtkOutlineFilter.newInstance();
+outline.setInputConnection(sample.getOutputPort());
+const outlineMapper = vtkMapper.newInstance();
+outlineMapper.setInputConnection(outline.getOutputPort());
+const outlineActor = vtkActor.newInstance();
+outlineActor.setMapper(outlineMapper);
+renderer.addActor(outlineActor);
+
+// ----------------------------------------------------------------------------
+// UI control handling
+// ----------------------------------------------------------------------------
+fullScreenRenderer.addController(controlPanel);
+
+// Define the volume resolution
+document.querySelector('.volumeResolution').addEventListener('input', (e) => {
+  const value = Number(e.target.value);
+  sample.setSampleDimensions(value, value, value);
+  mSquares.setSlice((value / 2.0));
+  renderWindow.render();
+});
+
+// Define the sphere radius
+document.querySelector('.sphereRadius').addEventListener('input', (e) => {
+  const value = Number(e.target.value);
+  sphere.setRadius(value);
+  sphere2.setRadius(value);
+  sample.modified();
+  renderWindow.render();
+});
+
+// Indicate whether to merge conincident points or not
+document.querySelector('.mergePoints').addEventListener('change', (e) => {
+  mSquares.setMergePoints(!!e.target.checked);
+  renderWindow.render();
+});
+
+
+// -----------------------------------------------------------
+const cam = renderer.getActiveCamera();
+cam.setFocalPoint(0, 0, 0);
+cam.setPosition(0, 0, 1);
+renderer.resetCamera();
+renderWindow.render();
+
+// -----------------------------------------------------------
+// Make some variables global so that you can inspect and
+// modify objects in your browser's developer console:
+// -----------------------------------------------------------
+
+global.source = sample;
+global.filter = mSquares;
+global.mapper = mapper;
+global.actor = actor;