Updates to skip transformation calculation when slice normal of the viewport api is in negative x direction

src/VTKViewport/vtkInteractorStyleMPRSlice.js

@@ -9,9 +9,11 @@ import vtkMouseRangeManipulator from 'vtk.js/Sources/Interaction/Manipulators/Mo
 import vtkCoordinate from 'vtk.js/Sources/Rendering/Core/Coordinate';
 import Constants from 'vtk.js/Sources/Rendering/Core/InteractorStyle/Constants';
 import ViewportData from './ViewportData';
+import { helpers } from '../helpers/index';
 import EVENTS from '../events';
 
 const { States } = Constants;
+const { isAntiParallel } = helpers;
 
 // ----------------------------------------------------------------------------
 // Global methods
@@ -362,13 +364,19 @@ function vtkInteractorStyleMPRSlice(publicAPI, model) {
     const sliceNormal = publicAPI.getSliceNormal();
 
     // Get rotation matrix from normal to +X (since bounds is aligned to XYZ)
-    const transform = vtkMatrixBuilder
-      .buildFromDegree()
-      .identity()
-      .rotateFromDirections(sliceNormal, [1, 0, 0]);
-
+    // Special handling if sliceNormal is [-1,0,0] as rotateFromDirections returns zero matrix.
     const fp = camera.getFocalPoint();
-    transform.apply(fp);
+    if (isAntiParallel(sliceNormal, [1, 0, 0])) {
+      fp[0] = fp[0] * -1;
+    } else {
+      const transform = vtkMatrixBuilder
+        .buildFromDegree()
+        .identity()
+        .rotateFromDirections(sliceNormal, [1, 0, 0]);
+
+      transform.apply(fp);
+    }
+
     return fp[0];
   };
 
@@ -534,12 +542,17 @@ function vtkInteractorStyleMPRSlice(publicAPI, model) {
       const points = boundsToCorners(bounds);
 
       // Get rotation matrix from normal to +X (since bounds is aligned to XYZ)
-      const transform = vtkMatrixBuilder
-        .buildFromDegree()
-        .identity()
-        .rotateFromDirections(sliceNormal, [1, 0, 0]);
-
-      points.forEach(pt => transform.apply(pt));
+      // Special handling if sliceNormal is [-1,0,0] as rotateFromDirections returns zero matrix.
+      if (isAntiParallel(sliceNormal, [1, 0, 0])) {
+        points.forEach(pt => (pt[0] = pt[0] * -1));
+      } else {
+        const transform = vtkMatrixBuilder
+          .buildFromDegree()
+          .identity()
+          .rotateFromDirections(sliceNormal, [1, 0, 0]);
+
+        points.forEach(pt => transform.apply(pt));
+      }
 
       // range is now maximum X distance
       let minX = Infinity;

src/VTKViewport/vtkSVGCrosshairsWidget.js

@@ -1,6 +1,9 @@
 import macro from 'vtk.js/Sources/macro';
 import vtkMatrixBuilder from 'vtk.js/Sources/Common/Core/MatrixBuilder';
 import vtkCoordinate from 'vtk.js/Sources/Rendering/Core/Coordinate';
+import { helpers } from '../helpers/index';
+
+const { isAntiParallel } = helpers;
 
 let instanceId = 1;
 
@@ -158,13 +161,20 @@ function vtkSVGCrosshairsWidget(publicAPI, model) {
 
       const istyle = renderWindow.getInteractor().getInteractorStyle();
       const sliceNormal = istyle.getSliceNormal();
-      const transform = vtkMatrixBuilder
-        .buildFromDegree()
-        .identity()
-        .rotateFromDirections(sliceNormal, [1, 0, 0]);
 
       const mutatedWorldPos = worldPos.slice();
-      transform.apply(mutatedWorldPos);
+
+      // Special handling if sliceNormal is [-1,0,0] as rotateFromDirections returns zero matrix.
+      if (isAntiParallel(sliceNormal, [1, 0, 0])) {
+        mutatedWorldPos[0] = mutatedWorldPos[0] * -1;
+      } else {
+        const transform = vtkMatrixBuilder
+          .buildFromDegree()
+          .identity()
+          .rotateFromDirections(sliceNormal, [1, 0, 0]);
+        transform.apply(mutatedWorldPos);
+      }
+
       const slice = mutatedWorldPos[0];
 
       istyle.setSlice(slice);

src/VTKViewport/vtkSVGRotatableCrosshairsWidget.js

@@ -4,6 +4,9 @@ import vtkCoordinate from 'vtk.js/Sources/Rendering/Core/Coordinate';
 import liangBarksyClip from '../helpers/liangBarksyClip';
 import { vec2, vec3 } from 'gl-matrix';
 import { projectVector2D } from 'vtk.js/Sources/Common/Core/Math';
+import { helpers } from '../helpers/index';
+
+const { isAntiParallel } = helpers;
 
 let instanceId = 1;
 
@@ -441,13 +444,20 @@ function vtkSVGRotatableCrosshairsWidget(publicAPI, model) {
 
       const istyle = renderWindow.getInteractor().getInteractorStyle();
       const sliceNormal = istyle.getSliceNormal();
-      const transform = vtkMatrixBuilder
-        .buildFromDegree()
-        .identity()
-        .rotateFromDirections(sliceNormal, [1, 0, 0]);
 
       const mutatedWorldPos = worldPos.slice();
-      transform.apply(mutatedWorldPos);
+
+      // Special handling if sliceNormal is [-1,0,0] as rotateFromDirections returns zero matrix.
+      if (isAntiParallel(sliceNormal, [1, 0, 0])) {
+        mutatedWorldPos[0] = mutatedWorldPos[0] * -1;
+      } else {
+        const transform = vtkMatrixBuilder
+          .buildFromDegree()
+          .identity()
+          .rotateFromDirections(sliceNormal, [1, 0, 0]);
+        transform.apply(mutatedWorldPos);
+      }
+
       const slice = mutatedWorldPos[0];
 
       istyle.setSlice(slice);

src/helpers/index.js

@@ -3,6 +3,7 @@ import formatDA from './formatDA';
 import formatTM from './formatTM';
 import formatNumberPrecision from './formatNumberPrecision';
 import isValidNumber from './isValidNumber';
+import isAntiParallel from './isAntiParallel';
 import uuidv4 from './uuidv4.js';
 
 const helpers = {
@@ -11,6 +12,7 @@ const helpers = {
   formatTM,
   formatNumberPrecision,
   isValidNumber,
+  isAntiParallel,
 };
 
 export { helpers, uuidv4 };

src/helpers/isAntiParallel.js

@@ -0,0 +1,7 @@
+import { vec3 } from 'gl-matrix';
+
+export default function isAntiParallel(originalVector, referenceVector) {
+  vec3.normalize(originalVector, originalVector);
+  vec3.normalize(referenceVector, referenceVector);
+  return vec3.dot(originalVector, referenceVector) === -1;
+}