feat(volumeMapper): add an interaction sample distance factor

Its purpose is to increase the sample distance when interacting to increase
the framerate without sacrifying XY sample distance / viewport resolution

Author: bruyeret

Sources/Rendering/Core/VolumeMapper/index.d.ts

@@ -72,10 +72,17 @@ export interface vtkVolumeMapper extends vtkAbstractMapper {
 	 * Get at what scale the quality is reduced when interacting for the first time with the volume
 	 * It should should be set before any call to render for this volume
 	 * The higher the scale is, the lower the quality of rendering is during interaction
-	 * @default 4
+	 * @default 16
 	 */
 	getInitialInteractionScale(): number;
 
+	/**
+	 * Get by how much the sample distance should be increased when interacting
+	 * This feature is only implemented in the OpenGL volume mapper
+	 * @default 4
+	 */
+	getInteractionSampleDistanceFactor(): number;
+
 	/**
 	 *
 	 */
@@ -202,6 +209,12 @@ export interface vtkVolumeMapper extends vtkAbstractMapper {
 	 */
 	setInitialInteractionScale(initialInteractionScale: number): boolean;
 
+	/**
+	 *
+	 * @param interactionSampleDistanceFactor
+	 */
+	setInteractionSampleDistanceFactor(interactionSampleDistanceFactor: number): boolean;
+
 	/**
 	 * Set the normal computation to be dependent on the transfer function.
 	 * By default, the mapper relies on the scalar gradient for computing normals at sample locations

Sources/Rendering/Core/VolumeMapper/index.js

@@ -147,7 +147,8 @@ const DEFAULT_VALUES = {
   imageSampleDistance: 1.0,
   maximumSamplesPerRay: 1000,
   autoAdjustSampleDistances: true,
-  initialInteractionScale: 100.0,
+  initialInteractionScale: 1.0,
+  interactionSampleDistanceFactor: 1.0,
   blendMode: BlendMode.COMPOSITE_BLEND,
   ipScalarRange: [-1000000.0, 1000000.0],
   filterMode: FilterMode.OFF, // ignored by WebGL so no behavior change
@@ -177,6 +178,7 @@ export function extend(publicAPI, model, initialValues = {}) {
     'maximumSamplesPerRay',
     'autoAdjustSampleDistances',
     'initialInteractionScale',
+    'interactionSampleDistanceFactor',
     'blendMode',
     'filterMode',
     'preferSizeOverAccuracy',

Sources/Rendering/OpenGL/VolumeMapper/index.js

@@ -179,7 +179,7 @@ function vtkOpenGLVolumeMapper(publicAPI, model) {
     );
 
     const maxSamples =
-      vec3.length(vsize) / model.renderable.getSampleDistance();
+      vec3.length(vsize) / publicAPI.getCurrentSampleDistance(ren);
 
     FSSource = vtkShaderProgram.substitute(
       FSSource,
@@ -468,7 +468,7 @@ function vtkOpenGLVolumeMapper(publicAPI, model) {
     );
 
     const maxSamples =
-      vec3.length(vsize) / model.renderable.getSampleDistance();
+      vec3.length(vsize) / publicAPI.getCurrentSampleDistance(ren);
 
     const state = {
       interpolationType: actor.getProperty().getInterpolationType(),
@@ -593,7 +593,10 @@ function vtkOpenGLVolumeMapper(publicAPI, model) {
     }
 
     program.setUniformi('texture1', model.scalarTexture.getTextureUnit());
-    program.setUniformf('sampleDistance', model.renderable.getSampleDistance());
+    program.setUniformf(
+      'sampleDistance',
+      publicAPI.getCurrentSampleDistance(ren)
+    );
 
     const volInfo = model.scalarTexture.getVolumeInfo();
     const ipScalarRange = model.renderable.getIpScalarRange();
@@ -739,7 +742,7 @@ function vtkOpenGLVolumeMapper(publicAPI, model) {
     );
 
     const maxSamples =
-      vec3.length(vsize) / model.renderable.getSampleDistance();
+      vec3.length(vsize) / publicAPI.getCurrentSampleDistance(ren);
     if (maxSamples > model.renderable.getMaximumSamplesPerRay()) {
       vtkWarningMacro(`The number of steps required ${Math.ceil(
         maxSamples
@@ -1133,6 +1136,16 @@ function vtkOpenGLVolumeMapper(publicAPI, model) {
     return [lowerLeftU, lowerLeftV];
   };
 
+  publicAPI.getCurrentSampleDistance = (ren) => {
+    const rwi = ren.getVTKWindow().getInteractor();
+    const baseSampleDistance = model.renderable.getSampleDistance();
+    if (rwi.isAnimating()) {
+      const factor = model.renderable.getInteractionSampleDistanceFactor();
+      return baseSampleDistance * factor;
+    }
+    return baseSampleDistance;
+  };
+
   publicAPI.renderPieceStart = (ren, actor) => {
     const rwi = ren.getVTKWindow().getInteractor();
 
@@ -1437,7 +1450,7 @@ function vtkOpenGLVolumeMapper(publicAPI, model) {
       for (let c = 0; c < numIComps; ++c) {
         const ofun = vprop.getScalarOpacity(c);
         const opacityFactor =
-          model.renderable.getSampleDistance() /
+          publicAPI.getCurrentSampleDistance(ren) /
           vprop.getScalarOpacityUnitDistance(c);
 
         const oRange = ofun.getRange();