Speedup classical kuwahara filter using summed area table

Conflicts:
	source/blender/compositor/nodes/COM_KuwaharaNode.cc
	source/blender/compositor/operations/COM_KuwaharaClassicOperation.cc
	source/blender/compositor/operations/COM_KuwaharaClassicOperation.h

@@ -0,0 +207,4 @@
+  ASSERT_EQ(sum[0], 4);
+}
+
+TEST_F(SummedTableAreaSumTest, RightLine)

@@ -32,0 +58,4 @@
+         * Note: best results are achieved using this optimization as well as the running error
+         * compensation in SummedAreaTableOperation.
+         */
+        CalculateMeanOperation *mean = new CalculateMeanOperation();

@@ -172,0 +223,4 @@
+
+          int xx = x + dx;
+          int yy = y + dy;
+          if (xx >= 0 && yy >= 0 && xx < image->get_width() && yy < image->get_height()) {

@@ -0,0 +123,4 @@
+  /* Track floating point error. See below. */
+  float4 running_compensation = {0.0f, 0.0f, 0.0f, 0.0f};
+
+  for (BuffersIterator<float> it = result->iterate_with({}, *rect); !it.is_end(); ++it) {

@@ -8631,2 +8631,4 @@
       "Controls how directional the filter is. 0 means the filter is completely omnidirectional "
       "while 2 means it is maximally directed along the edges of the image");
+
+  prop = RNA_def_property(srna, "fast", PROP_BOOLEAN, PROP_NONE);

@@ -8633,0 +8634,4 @@
+  prop = RNA_def_property(srna, "fast", PROP_BOOLEAN, PROP_NONE);
+  RNA_def_property_boolean_sdna(prop, nullptr, "fast", 1);
+  RNA_def_property_ui_text(
+      prop, "Fast", "Use faster computation. Might produce artefacts for large images.");

@@ -32,0 +35,4 @@
+        kuwahara_classic->set_use_sat(false);
+      }
+      else {
+        SummedAreaTableOperation *sat = new SummedAreaTableOperation();

@@ -0,0 +64,4 @@
+  MemoryBuffer *image = inputs[0];
+
+  /* First pass: copy values from input to output and square values if necessary. */
+  threading::parallel_for(IndexRange(area.ymin, area.ymax), 1, [&](const IndexRange range_y) {

@@ -0,0 +102,4 @@
+  threading::parallel_for(IndexRange(area.ymin, area.ymax), 1, [&](const IndexRange range_y) {
+    for (int64_t y = *range_y.begin(); y < *range_y.end(); y++) {
+      /* Track floating point error. See below. */
+      float4 running_compensation = {0.0f, 0.0f, 0.0f, 0.0f};

@@ -0,0 +130,4 @@
+  area.ymin = 1;
+  area.ymax = 3;
+  float4 sum = summed_area_table_sum(sat_.get(), area);
+  ASSERT_EQ(sum[0], 9);

@@ -7,11 +7,13 @@
 
 #include "COM_KuwaharaNode.h"
 
+#include "COM_CalculateMeanOperation.h"

@@ -0,0 +13,4 @@
+SummedAreaTableOperation::SummedAreaTableOperation()
+{
+  this->add_input_socket(DataType::Color);
+  this->add_input_socket(DataType::Value);

@@ -0,0 +79,4 @@
+  threading::parallel_for(IndexRange(area.xmin, area.xmax), 1, [&](const IndexRange range_x) {
+    for (const int x : range_x) {
+      for (const int y : IndexRange(area.ymin, area.ymax)) {
+        float4 color;

@@ -0,0 +101,4 @@
+      for (const int x : IndexRange(area->xmin, area->xmax)) {
+
+        float4 color;
+        image_reader_->read_sampled(&color.x, x, y, sampler);

@@ -0,0 +113,4 @@
+    for (const int x : range_x) {
+      for (const int y : IndexRange(area->ymin, area->ymax)) {
+        float4 color;
+        output->read_elem_checked(x, y - 1, &color.x);

@@ -0,0 +163,4 @@
+
+  float4 a, b, c, d, addend, substrahend;
+  buffer->read_sampled(
+      &a.x, corrected_upper_bound[0], corrected_upper_bound[1], PixelSampler::Nearest);

@@ -0,0 +9,4 @@
+namespace blender::compositor {
+
+/**
+ * \brief base class of CalculateMean, implementing the simple CalculateMean