Functions: Multi Function

This adds the `MultiFunction` type and some smallish utility types that it uses.
A `MultiFunction` encapsulates a function that is optimized for throughput by
always processing many elements at once.

This is an important part of the new particle system, because it allows us to
execute user generated node trees for many particles efficiently.

Reviewers: brecht

Differential Revision: https://developer.blender.org/D8030

1 files changed, 106 insertions, 0 deletions

diff --git a/source/blender/functions/FN_multi_function.hh b/source/blender/functions/FN_multi_function.hh
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+/*
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License
+ * as published by the Free Software Foundation; either version 2
+ * of the License, or (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software Foundation,
+ * Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
+ */
+
+#ifndef __FN_MULTI_FUNCTION_HH__
+#define __FN_MULTI_FUNCTION_HH__
+
+/** \file
+ * \ingroup fn
+ *
+ * A `MultiFunction` encapsulates a function that is optimized for throughput (instead of latency).
+ * The throughput is optimized by always processing many elements at once, instead of each element
+ * separately. This is ideal for functions that are evaluated often (e.g. for every particle).
+ *
+ * By processing a lot of data at once, individual functions become easier to optimize for humans
+ * and for the compiler. Furthermore, performance profiles become easier to understand and show
+ * better where bottlenecks are.
+ *
+ * Every multi-function has a name and an ordered list of parameters. Parameters are used for input
+ * and output. In fact, there are three kinds of parameters: inputs, outputs and mutable (which is
+ * combination of input and output).
+ *
+ * To call a multi-function, one has to provide three things:
+ * - `MFParams`: This references the input and output arrays that the function works with. The
+ *      arrays are not owned by MFParams.
+ * - `IndexMask`: An array of indices indicating which indices in the provided arrays should be
+ *      touched/processed.
+ * - `MFContext`: Further information for the called function.
+ *
+ * A new multi-function is generally implemented as follows:
+ * 1. Create a new subclass of MultiFunction.
+ * 2. Implement a constructor that initialized the signature of the function.
+ * 3. Override the `call` function.
+ */
+
+#include "FN_multi_function_context.hh"
+#include "FN_multi_function_params.hh"
+
+namespace blender {
+namespace fn {
+
+class MultiFunction {
+ private:
+  MFSignature m_signature;
+
+ public:
+  virtual ~MultiFunction()
+  {
+  }
+
+  virtual void call(IndexMask mask, MFParams params, MFContext context) const = 0;
+
+  IndexRange param_indices() const
+  {
+    return m_signature.param_types.index_range();
+  }
+
+  MFParamType param_type(uint param_index) const
+  {
+    return m_signature.param_types[param_index];
+  }
+
+  StringRefNull param_name(uint param_index) const
+  {
+    return m_signature.param_names[param_index];
+  }
+
+  StringRefNull name() const
+  {
+    return m_signature.function_name;
+  }
+
+  const MFSignature &signature() const
+  {
+    return m_signature;
+  }
+
+ protected:
+  MFSignatureBuilder get_builder(StringRef function_name)
+  {
+    m_signature.function_name = function_name;
+    return MFSignatureBuilder(m_signature);
+  }
+};
+
+inline MFParamsBuilder::MFParamsBuilder(const class MultiFunction &fn, uint min_array_size)
+    : MFParamsBuilder(fn.signature(), min_array_size)
+{
+}
+
+}  // namespace fn
+}  // namespace blender
+
+#endif /* __FN_MULTI_FUNCTION_HH__ */