[gegl] warp: avoid processing input when the cached output is valid

[N/A <ell src gnome org>]

commit e8b674b2da891915b75f47d824a4d0ec28e1c462
Author: Ell <ell_se yahoo com>
Date:   Wed May 17 11:08:40 2017 -0400

    warp: avoid processing input when the cached output is valid
    
    When the previously processed stroke is valid, we pass the cached
    buffer directly as output, and don't need the input.  Make sure
    GEGL doesn't process the op's input for nothing.
    
    OTH, when the processed stroke is invalid, require the entire input,
    since the next call to process() is going to cache it.

 operations/common/warp.c |   27 +++++++++++++++++++++++----
 1 files changed, 23 insertions(+), 4 deletions(-)
---
diff --git a/operations/common/warp.c b/operations/common/warp.c
index ecb630c..ca39fb6 100644
--- a/operations/common/warp.c
+++ b/operations/common/warp.c
@@ -469,6 +469,24 @@ stamp (GeglProperties *o,
   priv->last_y = y;
 }
 
+static GeglRectangle
+get_required_for_output (GeglOperation       *operation,
+                         const gchar         *input_pad,
+                         const GeglRectangle *output_roi)
+{
+  GeglProperties *o    = GEGL_PROPERTIES (operation);
+  WarpPrivate    *priv = (WarpPrivate*) o->user_data;
+  GeglRectangle   rect = {0, 0, 0, 0};
+
+  /* we only need the input if the processed stroke is invalid, i.e., if
+   * there's work to do; otherwise, we just output the cached buffer directly.
+   */
+  if (! priv->processed_stroke_valid)
+    rect = *gegl_operation_source_get_bounding_box (operation, input_pad);
+
+  return rect;
+}
+
 static gboolean
 process (GeglOperation        *operation,
          GeglOperationContext *context,
@@ -629,10 +647,11 @@ gegl_op_class_init (GeglOpClass *klass)
   GObjectClass       *object_class    = G_OBJECT_CLASS (klass);
   GeglOperationClass *operation_class = GEGL_OPERATION_CLASS (klass);
 
-  object_class->finalize   = finalize;
-  operation_class->attach  = attach;
-  operation_class->prepare = prepare;
-  operation_class->process = process;
+  object_class->finalize                   = finalize;
+  operation_class->attach                  = attach;
+  operation_class->prepare                 = prepare;
+  operation_class->get_required_for_output = get_required_for_output;
+  operation_class->process                 = process;
   operation_class->no_cache = TRUE; /* we're effectively doing the caching
                                      * ourselves.
                                      */