feat(Mapper): Always use textures for cell data coloring

The rendering result is the same at almost no cost
But you can change the color map without reuploading the whole VBO when it has the same range

Author: bruyeret

Examples/Applications/GeometryViewer/index.js

@@ -270,6 +270,8 @@ function createPipeline(fileName, fileContents) {
 
   const lookupTable = vtkColorTransferFunction.newInstance();
   const source = vtpReader.getOutputData(0);
+  // interpolateScalarsBeforeMapping is only used when displaying point data
+  // This setting is not relevant for cell data
   const mapper = vtkMapper.newInstance({
     interpolateScalarsBeforeMapping: true,
     useLookupTableScalarRange: true,

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

@@ -14,6 +14,7 @@ interface IPrimitiveCount {
 
 interface IAbstractScalars {
   cellFlag: boolean;
+  scalars: Nullable<vtkDataArray>;
 }
 
 interface ICoincidentTopology {
@@ -55,9 +56,13 @@ export interface vtkMapper extends vtkAbstractMapper3D {
    * When rendering multiblock datasets, if any 2 blocks provide different
    * lookup tables for the scalars, then also we cannot use textures. This case
    * can be handled if required.
-   * @param input
+   * @param scalars
+   * @param cellFlag True when the scalars are per cell instead of per point
    */
-  canUseTextureMapForColoring(input: any): boolean;
+  canUseTextureMapForColoring(
+    scalars: vtkDataArray,
+    cellFlag: boolean
+  ): boolean;
 
   /**
    * Call to force a rebuild of color result arrays on next MapScalars.

Sources/Rendering/Core/Mapper/index.js

@@ -165,7 +165,7 @@ function vtkMapper(publicAPI, model) {
     // Decide between texture color or vertex color.
     // Cell data always uses vertex color.
     // Only point data can use both texture and vertex coloring.
-    if (publicAPI.canUseTextureMapForColoring(input)) {
+    if (publicAPI.canUseTextureMapForColoring(scalars, cellFlag)) {
       publicAPI.mapScalarsToTexture(scalars, alpha);
     } else {
       model.colorCoordinates = null;
@@ -413,7 +413,11 @@ function vtkMapper(publicAPI, model) {
     return true;
   };
 
-  publicAPI.canUseTextureMapForColoring = (input) => {
+  publicAPI.canUseTextureMapForColoring = (scalars, cellFlag) => {
+    if (cellFlag) {
+      return true; // cell data always use textures.
+    }
+
     if (!model.interpolateScalarsBeforeMapping) {
       return false; // user doesn't want us to use texture maps at all.
     }
@@ -423,15 +427,6 @@ function vtkMapper(publicAPI, model) {
       return false;
     }
 
-    const gasResult = publicAPI.getAbstractScalars(
-      input,
-      model.scalarMode,
-      model.arrayAccessMode,
-      model.arrayId,
-      model.colorByArrayName
-    );
-    const scalars = gasResult.scalars;
-
     if (!scalars) {
       // no scalars on this dataset, we don't care if texture is used at all.
       return false;

Sources/Rendering/OpenGL/PolyDataMapper/index.js

@@ -198,7 +198,8 @@ function vtkOpenGLPolyDataMapper(publicAPI, model) {
       ).result;
     } else {
       if (
-        model.renderable.getInterpolateScalarsBeforeMapping() &&
+        (model.renderable.getAreScalarsMappedFromCells() ||
+          model.renderable.getInterpolateScalarsBeforeMapping()) &&
         model.renderable.getColorCoordinates() &&
         !model.drawingEdges
       ) {