Introduce pixelpipe zoom knocking

Currently we use dt_dev_pixelpipe_set_shutdown() to stop a running pixelpipe asap, this is
used for changing the nodes involved in the pipe (history changes) or when toggling between
darkroom HQ mode on/off as examples, we do this for UI responsiveness.

Being in darkroom mode **while** the dt_dev_pixelpipe_process() is still running, a UI move of the
the displayed part of the main canvas or zooming-in/out results in a new control job which is
currently processed *after the complete* dt_dev_pixelpipe_process().

This commit adds an early-exit & restart pipe mechanism for a faster UI response, avoiding up to
one pixelpipe run with a good chance of finding valid pixelpipe cache data.

1. A new shutdown mode DT_DEV_PIXELPIPE_STOP_ZOOM has been added to dt_dev_pixelpipe_stopper_t.
   It is
   a) checked, reported and handled in dt_dev_process_image_job()
   b) tested in dt_dev_pixelpipe_process() via _module_pipe_stop() making sure the pipe
      possibly exits with TRUE state and a shutdown mode.
   In all cases we ensure pixelpipe cache integrity via _module_pipe_stop().

2. How is this shutdown mode induced?
   If we zoom in/out or reposition the main canvas we set shutdown to DT_DEV_PIXELPIPE_STOP_ZOOM
   in dt_dev_zoom_move() enforcing the pipe restart.

Author: jenshannoschwalm

src/develop/develop.c

@@ -3268,7 +3268,11 @@ void dt_dev_zoom_move(dt_dev_viewport_t *port,
   port->pipe->changed |= DT_DEV_PIPE_ZOOMED;
 
   if(port->widget)
+  {
+    if(port->pipe->processing)
+      dt_dev_pixelpipe_set_shutdown(port->pipe, DT_DEV_PIXELPIPE_STOP_ZOOM);
     dt_control_queue_redraw_widget(port->widget);
+  }
   if(port == &dev->full)
     dt_control_navigation_redraw();
 }

src/develop/pixelpipe_hb.c

@@ -49,7 +49,8 @@
 
 static inline gboolean _pipe_has_shutdown(dt_dev_pixelpipe_t *pipe)
 {
-  return dt_atomic_get_int(&pipe->shutdown) != DT_DEV_PIXELPIPE_STOP_NO;
+  const dt_dev_pixelpipe_stopper_t stopper = dt_atomic_get_int(&pipe->shutdown);
+  return stopper != DT_DEV_PIXELPIPE_STOP_NO && stopper != DT_DEV_PIXELPIPE_STOP_ZOOM;
 }
 
 // benchmarking and pfm dumps should happen for these pipes if there is no shutdown request
@@ -108,6 +109,7 @@ const char *dt_dev_pixelpipe_shutdown_to_str(const dt_dev_pixelpipe_stopper_t st
   case DT_DEV_PIXELPIPE_STOP_NO:    return "DT_DEV_PIXELPIPE_STOP_NO";
   case DT_DEV_PIXELPIPE_STOP_NODES: return "DT_DEV_PIXELPIPE_STOP_NODES";
   case DT_DEV_PIXELPIPE_STOP_HQ:    return "DT_DEV_PIXELPIPE_STOP_HQ";
+  case DT_DEV_PIXELPIPE_STOP_ZOOM:  return "DT_DEV_PIXELPIPE_STOP_ZOOM";
   case DT_DEV_PIXELPIPE_STOP_LAST:  return "DT_DEV_PIXELPIPE_STOP_LAST";
   default:                          return "DT_DEV_PIXELPIPE_STOP_MODULE";
   }
@@ -1323,8 +1325,11 @@ static inline gboolean _module_pipe_stop(dt_dev_pixelpipe_t *pipe,
   }
 #endif
 
-  // stopper reflects the iop_order of the stopping mode so we must invalidate output cachelines.
-  dt_dev_pixelpipe_cache_invalidate_iop(pipe, stopper, "module pipe stop: ");
+  if(stopper == DT_DEV_PIXELPIPE_STOP_ZOOM)
+    dt_dev_pixelpipe_cache_invalidate_iop(pipe, module->iop_order, "zoomed pipe stop: ");
+  else
+    // stopper reflects the iop_order of the stopping mode so we must invalidate output cachelines.
+    dt_dev_pixelpipe_cache_invalidate_iop(pipe, stopper, "module pipe stop: ");
 
   return TRUE;
 }

src/develop/pixelpipe_hb.h

@@ -127,6 +127,9 @@ typedef enum dt_dev_pixelpipe_status_t
     Used to switch between darkroom HQ modes.
     Requires a restart of the pipe but pixelpipe cache can stay.
 
+    DT_DEV_PIXELPIPE_STOP_ZOOM
+    As we stopped inside a module the output cacheline must be invalidated.
+
     DT_DEV_PIXELPIPE_STOP_LAST
     If the shutdown value is >= DT_DEV_PIXELPIPE_STOP_LAST it is understood as the iop_order
     of a module. Any module can use dt_dev_pixelpipe_set_shutdown() to it's iop_order at runtime,
@@ -140,6 +143,7 @@ typedef enum dt_dev_pixelpipe_stopper_t
   DT_DEV_PIXELPIPE_STOP_NO = 0,
   DT_DEV_PIXELPIPE_STOP_NODES,
   DT_DEV_PIXELPIPE_STOP_HQ,
+  DT_DEV_PIXELPIPE_STOP_ZOOM,
   DT_DEV_PIXELPIPE_STOP_LAST,
 } dt_dev_pixelpipe_stopper_t;