Fix #101263: Vector pass wrongly saved in File Output

The vector pass and potentially other vectors that store 4 values are
stored wrongly, in particular, the last channel is ignored. To fix this
we identify if a vector pass is 4D and store the information in the
result meta data, then use this information to either save a 3D or a 4D
pass in the File Output node.

This is a partial fix for the GPU compositor only. The complete fix for
the CPU compositor will be submitted separately as it is not
straightforward and will likely require a refactor.

Pull Request: https://projects.blender.org/blender/blender/pulls/124522

source/blender/compositor/realtime_compositor/COM_context.hh

@@ -91,7 +91,7 @@ class Context {
                                         const char *pass_name) = 0;
 
   /* Get the name of the view currently being rendered. */
-  virtual StringRef get_view_name() = 0;
+  virtual StringRef get_view_name() const = 0;
 
   /* Get the precision of the intermediate results of the compositor. */
   virtual ResultPrecision get_precision() const = 0;

source/blender/compositor/realtime_compositor/COM_meta_data.hh

@@ -28,6 +28,10 @@ struct CryptomatteMetaData {
 struct MetaData {
   /* The result stores non color data, which is not to be color-managed. */
   bool is_non_color_data = false;
+  /* The result stores a 4D vector as opposed to a 3D vector. This is the case for things like
+   * velocity passes, and we need to mark them as 4D in order to write them to file correctly. This
+   * field can be ignored for results that are not of type Vector. */
+  bool is_4d_vector = false;
   /* Stores Cryptomatte meta data. This will only be initialized for results that represent
    * Cryptomatte information. See the CryptomatteMetaData structure for more information. */
   CryptomatteMetaData cryptomatte;

source/blender/draw/engines/compositor/compositor_engine.cc

@@ -156,7 +156,7 @@ class Context : public realtime_compositor::Context {
     }
   }
 
-  StringRef get_view_name() override
+  StringRef get_view_name() const override
   {
     const SceneRenderView *view = static_cast<SceneRenderView *>(
         BLI_findlink(&get_render_data().views, DRW_context_state_get()->v3d->multiview_eye));

source/blender/nodes/composite/nodes/node_composite_file_output.cc

@@ -641,7 +641,12 @@ class FileOutputOperation : public NodeOperation {
         }
         break;
       case ResultType::Vector:
-        file_output.add_pass(pass_name, view_name, "XYZ", float4_to_float3_image(size, buffer));
+        if (result.meta_data.is_4d_vector) {
+          file_output.add_pass(pass_name, view_name, "XYZW", buffer);
+        }
+        else {
+          file_output.add_pass(pass_name, view_name, "XYZ", float4_to_float3_image(size, buffer));
+        }
         break;
       case ResultType::Float:
         file_output.add_pass(pass_name, view_name, "V", buffer);

source/blender/render/intern/compositor.cc

@@ -327,7 +327,7 @@ class Context : public realtime_compositor::Context {
     return input_texture;
   }
 
-  StringRef get_view_name() override
+  StringRef get_view_name() const override
   {
     return input_data_.view_name;
   }
@@ -429,6 +429,23 @@ class Context : public realtime_compositor::Context {
         },
         false);
 
+    RenderLayer *render_layer = RE_GetRenderLayer(render_result, view_layer->name);
+    if (!render_layer) {
+      RE_ReleaseResult(render);
+      return;
+    }
+
+    RenderPass *render_pass = RE_pass_find_by_name(
+        render_layer, pass_name, this->get_view_name().data());
+    if (!render_pass) {
+      RE_ReleaseResult(render);
+      return;
+    }
+
+    if (StringRef(render_pass->chan_id) == "XYZW") {
+      meta_data.is_4d_vector = true;
+    }
+
     RE_ReleaseResult(render);
   }