fix: Fix hardware selector high pass

Moving the call to `processPixelBuffers()` at the end of rendering as the processing of the raw
pixel buffers needs all the passes to be completed.
Moving the call to `updateMaximumPointCellIds()` as it needs a selector that is not always set when
the VBO is recomputed.

Author: bruyeret

Sources/Rendering/Core/Mapper/index.js

@@ -740,11 +740,11 @@ function vtkMapper(publicAPI, model) {
         let inValue = 0;
         inValue += rawHighData[pos];
         inValue *= 256;
-        inValue += rawLowData[pos];
+        inValue += rawLowData[pos + 2];
         inValue *= 256;
         inValue += rawLowData[pos + 1];
         inValue *= 256;
-        inValue += rawLowData[pos + 2];
+        inValue += rawLowData[pos];
 
         const outValue = idMap[inValue];
         const highData = selector.getPixelBuffer(PassTypes.ID_HIGH24);

Sources/Rendering/OpenGL/HardwareSelector/index.d.ts

@@ -331,6 +331,23 @@ export function extend(
   initialValues?: IOpenGLHardwareSelectorInitialValues
 ): void;
 
+/**
+ * The WebGL implementation of the hardware selector renders the id of the VBO
+ * vertices (gl_VertexID) with an offset to a RGBA texture.
+ * Only the RGB channels of the RGBA texture are used. This means that a single
+ * render can only draw 24 bits of information. To reach 32 bits, the hardware
+ * selector renders a second pass which only writes in the R channel of the
+ * texture.
+ *
+ * Note:
+ * - With Webgl 2, it is now possible to render directly to a R32 texture and
+ * even render to multiple render targets.
+ * - The raw pixel buffers fetched from WebGL are processed in the core mapper
+ * (see `processSelectorPixelBuffers`) instead of the PolydataMapper.
+ * - The processing of the raw pixel buffers does not output an UInt32Array as
+ * we could expect, but one or two textures with the same layout as the RGBA
+ * textures as input.
+ */
 export const vtkOpenGLHardwareSelector: {
   newInstance: typeof newInstance;
   extend: typeof extend;

Sources/Rendering/OpenGL/HardwareSelector/index.js

@@ -482,6 +482,7 @@ function vtkOpenGLHardwareSelector(publicAPI, model) {
     const rpasses = model._openGLRenderWindow.getRenderPasses();
 
     publicAPI.beginSelection();
+    const pixelBufferSavedPasses = [];
     for (
       model.currentPass = PassTypes.MIN_KNOWN_PASS;
       model.currentPass <= PassTypes.MAX_KNOWN_PASS;
@@ -503,9 +504,17 @@ function vtkOpenGLHardwareSelector(publicAPI, model) {
         publicAPI.postCapturePass(model.currentPass);
 
         publicAPI.savePixelBuffer(model.currentPass);
-        publicAPI.processPixelBuffers();
+        pixelBufferSavedPasses.push(model.currentPass);
       }
     }
+
+    // Process pixel buffers
+    pixelBufferSavedPasses.forEach((pass) => {
+      model.currentPass = pass;
+      publicAPI.processPixelBuffers();
+    });
+    model.currentPass = PassTypes.MAX_KNOWN_PASS;
+
     publicAPI.endSelection();
 
     // restore original background
@@ -860,9 +869,9 @@ function vtkOpenGLHardwareSelector(publicAPI, model) {
 
   //----------------------------------------------------------------------------
 
-  publicAPI.attach = (w, r) => {
-    model._openGLRenderWindow = w;
-    model._renderer = r;
+  publicAPI.attach = (openGLRenderWindow, renderer) => {
+    model._openGLRenderWindow = openGLRenderWindow;
+    model._renderer = renderer;
   };
 
   // override

Sources/Rendering/OpenGL/PolyDataMapper/index.js

@@ -955,7 +955,7 @@ function vtkOpenGLPolyDataMapper(publicAPI, model) {
         FSSource = vtkShaderProgram.substitute(
           FSSource,
           '//VTK::Picking::Impl',
-          '  gl_FragData[0] = vec4(float(idx)/255.0, 0.0, 0.0, 1.0);'
+          '  gl_FragData[0] = vec4(float((idx/16777216)%256)/255.0, 0.0, 0.0, 1.0);'
         ).result;
         break;
       default:
@@ -1761,6 +1761,8 @@ function vtkOpenGLPolyDataMapper(publicAPI, model) {
     if (publicAPI.getNeedToRebuildBufferObjects(ren, actor)) {
       publicAPI.buildBufferObjects(ren, actor);
     }
+    // Always call this function as the selector can change
+    publicAPI.updateMaximumPointCellIds();
   };
 
   publicAPI.getNeedToRebuildBufferObjects = (ren, actor) => {
@@ -1948,7 +1950,6 @@ function vtkOpenGLPolyDataMapper(publicAPI, model) {
         model.renderable.setSelectionWebGLIdsToVTKIds(
           model.selectionWebGLIdsToVTKIds
         );
-        publicAPI.updateMaximumPointCellIds();
       }
 
       model.VBOBuildString = toString;