Cycles: add cycles.merge_images operator for combing EXR renders.

This is only available through the API, mainly intended for render farms to
combine rendered multilayer EXR Files with different samples. The images are
currently expected to have the exact same render layers and passes, just with
different samples.

Variance passes are still simply a weighted average, ideally these should be
merged more intelligently.

Differential Revision: https://developer.blender.org/D4554

intern/cycles/blender/blender_python.cpp

@@ -23,6 +23,7 @@
 #include "blender/blender_session.h"
 
 #include "render/denoising.h"
+#include "render/merge.h"
 
 #include "util/util_debug.h"
 #include "util/util_foreach.h"
@@ -638,9 +639,8 @@ static PyObject *opencl_compile_func(PyObject * /*self*/, PyObject *args)
 }
 #endif
 
-static bool denoise_parse_filepaths(PyObject *pyfilepaths, vector<string>& filepaths)
+static bool image_parse_filepaths(PyObject *pyfilepaths, vector<string>& filepaths)
 {
-
 	if(PyUnicode_Check(pyfilepaths)) {
 		const char *filepath = PyUnicode_AsUTF8(pyfilepaths);
 		filepaths.push_back(filepath);
@@ -709,12 +709,12 @@ static PyObject *denoise_func(PyObject * /*self*/, PyObject *args, PyObject *key
 	/* Parse file paths list. */
 	vector<string> input, output;
 
-	if(!denoise_parse_filepaths(pyinput, input)) {
+	if(!image_parse_filepaths(pyinput, input)) {
 		return NULL;
 	}
 
 	if(pyoutput) {
-		if(!denoise_parse_filepaths(pyoutput, output)) {
+		if(!image_parse_filepaths(pyoutput, output)) {
 			return NULL;
 		}
 	}
@@ -753,6 +753,42 @@ static PyObject *denoise_func(PyObject * /*self*/, PyObject *args, PyObject *key
 	Py_RETURN_NONE;
 }
 
+static PyObject *merge_func(PyObject * /*self*/, PyObject *args, PyObject *keywords)
+{
+	static const char *keyword_list[] = {"input", "output", NULL};
+	PyObject *pyinput, *pyoutput = NULL;
+
+	if (!PyArg_ParseTupleAndKeywords(args, keywords, "OO", (char**)keyword_list, &pyinput, &pyoutput)) {
+		return NULL;
+	}
+
+	/* Parse input list. */
+	vector<string> input;
+	if(!image_parse_filepaths(pyinput, input)) {
+		return NULL;
+	}
+
+	/* Parse output string. */
+	if(!PyUnicode_Check(pyoutput)) {
+		PyErr_SetString(PyExc_ValueError, "Output must be a string.");
+		return NULL;
+	}
+	string output = PyUnicode_AsUTF8(pyoutput);
+
+	/* Merge. */
+	ImageMerger merger;
+	merger.input = input;
+	merger.output = output;
+
+	if(!merger.run()) {
+		PyErr_SetString(PyExc_ValueError, merger.error.c_str());
+		return NULL;
+	}
+
+	Py_RETURN_NONE;
+}
+
+
 static PyObject *debug_flags_update_func(PyObject * /*self*/, PyObject *args)
 {
 	PyObject *pyscene;
@@ -916,6 +952,7 @@ static PyMethodDef methods[] = {
 
 	/* Standalone denoising */
 	{"denoise", (PyCFunction)denoise_func, METH_VARARGS|METH_KEYWORDS, ""},
+	{"merge", (PyCFunction)merge_func, METH_VARARGS|METH_KEYWORDS, ""},
 
 	/* Debugging routines */
 	{"debug_flags_update", debug_flags_update_func, METH_VARARGS, ""},