fix a FG crasher when we have more than 32 passes (#2911)

The FrameGraph cannot store pointers internally because all objects
are stored in vectors. Unfortunately we were storing the writer of
resources as a pointer. 

This is fixed by storing an index instead.

filament/src/PostProcessManager.cpp

@@ -258,7 +258,7 @@ FrameGraphId<FrameGraphTexture> PostProcessManager::structure(FrameGraph& fg,
     // generate depth pass at the requested resolution
     auto& structurePass = fg.addPass<StructurePassData>("Structure Pass",
             [&](FrameGraph::Builder& builder, auto& data) {
-                data.depth = builder.createTexture("Depth Buffer", {
+                data.depth = builder.createTexture("Structure Buffer", {
                         .width = width, .height = height,
                         .levels = uint8_t(levelCount),
                         .format = TextureFormat::DEPTH24 });

filament/src/fg/FrameGraph.cpp

@@ -148,13 +148,14 @@ void FrameGraph::moveResourceBase(FrameGraphHandle fromHandle, FrameGraphHandle
 
     // The pass that is writing to "fromHandle" no longer does (and might be culled)
     // (note: there can only be a single pass that can be a writer)
-    PassNode* const pass = from.writer;
-    if (pass) {
+    if (from.writerIndex.isValid()) {
+        PassNode* const pass = &mPassNodes[from.writerIndex.index];
+        assert(pass);
         auto pos = std::find_if(pass->writes.begin(), pass->writes.end(),
                 [fromHandle](auto handle) { return handle == fromHandle; });
         assert(pos != pass->writes.end());
         pass->writes.erase(pos);
-        from.writer = to.writer;
+        from.writerIndex = to.writerIndex;
     }
 
     // The 'to' node becomes the 'from' node and therefore inherits passes that are reading
@@ -284,12 +285,11 @@ FrameGraph& FrameGraph::compile() noexcept {
             resourceNodes[resource.index]->readerCount++;
         }
 
-#ifndef NDEBUG
+        // set the writers
         for (FrameGraphHandle resource : pass.writes) {
             assert(resource.isValid());
-            assert(resourceNodes[resource.index]->writer == &pass);
+            resourceNodes[resource.index]->writer = &pass;
         }
-#endif
     }
 
     /*

filament/src/fg/FrameGraphHandle.h

@@ -30,6 +30,7 @@ namespace filament {
 
 namespace fg {
 struct PassNode;
+struct ResourceNode;
 class RenderTargetResourceEntry;
 } // namespace fg
 
@@ -69,6 +70,7 @@ class FrameGraphHandle {
     friend class FrameGraph;
     friend class FrameGraphPassResources;
     friend struct fg::PassNode;
+    friend struct fg::ResourceNode;
     friend class fg::RenderTargetResourceEntry;
 
     // private ctor -- this cannot be constructed by users

filament/src/fg/fg/PassNode.cpp

@@ -113,8 +113,8 @@ FrameGraphHandle PassNode::write(FrameGraph& fg, const FrameGraphHandle& handle)
 
     // record the write
     auto& newNode = fg.getResourceNodeUnchecked(r);
-    assert(!newNode.writer);
-    newNode.writer = this;     // needed by move resources
+    assert(!newNode.writerIndex.isValid());
+    newNode.writerIndex = r; // needed by move resources
 
     writes.push_back(r);
     return r;

filament/src/fg/fg/ResourceNode.h

@@ -34,6 +34,8 @@ struct ResourceNode { // 24
     ResourceNode(ResourceNode&&) noexcept = default;
     ResourceNode& operator=(ResourceNode const&) = delete;
 
+    FrameGraphHandle writerIndex;   // only needed by moveResource
+
     // updated during compile()
     ResourceEntryBase* resource;    // actual (aliased) resource data
     PassNode* writer = nullptr;     // writer to this node