Fix #119973: Flip node produces artifacts

The Flip node produces artifacts if not connected directly to an input.
This due to a wrong calculation of depending area of interest, which is
a regressed introduced in 70a8a9e.

This is fixed by reverting the removal of the area of interest
calculation method in the aforementioned commit.

Pull Request: https://projects.blender.org/blender/blender/pulls/120149

source/blender/compositor/operations/COM_FlipOperation.cc

@@ -34,6 +34,34 @@ void FlipOperation::execute_pixel_sampled(float output[4], float x, float y, Pix
   input_operation_->read_sampled(output, nx, ny, sampler);
 }
 
+bool FlipOperation::determine_depending_area_of_interest(rcti *input,
+                                                         ReadBufferOperation *read_operation,
+                                                         rcti *output)
+{
+  rcti new_input;
+
+  if (flip_x_) {
+    const int w = int(this->get_width()) - 1;
+    new_input.xmax = (w - input->xmin) + 1;
+    new_input.xmin = (w - input->xmax) - 1;
+  }
+  else {
+    new_input.xmin = input->xmin;
+    new_input.xmax = input->xmax;
+  }
+  if (flip_y_) {
+    const int h = int(this->get_height()) - 1;
+    new_input.ymax = (h - input->ymin) + 1;
+    new_input.ymin = (h - input->ymax) - 1;
+  }
+  else {
+    new_input.ymin = input->ymin;
+    new_input.ymax = input->ymax;
+  }
+
+  return NodeOperation::determine_depending_area_of_interest(&new_input, read_operation, output);
+}
+
 void FlipOperation::update_memory_buffer_partial(MemoryBuffer *output,
                                                  const rcti &area,
                                                  Span<MemoryBuffer *> inputs)

source/blender/compositor/operations/COM_FlipOperation.h

@@ -16,6 +16,9 @@ class FlipOperation : public MultiThreadedOperation {
 
  public:
   FlipOperation();
+  bool determine_depending_area_of_interest(rcti *input,
+                                            ReadBufferOperation *read_operation,
+                                            rcti *output) override;
   void execute_pixel_sampled(float output[4], float x, float y, PixelSampler sampler) override;
 
   void init_execution() override;