Pydrivers: Ipo Drivers controlled by Python expressions

wiki with info: http://mediawiki.blender.org/index.php/BlenderDev/PyDrivers

(there are two sample .blends in the patch tracker entry, last link in
the wiki page)

Notes:

In usiblender.c I just made Python exit before the main library gets
freed. I found a situation with pydrivers where py's gc tried to del
objects on exit and their ID's were not valid anymore (so sigsegv).

Ton needs to check the depsgraph part.

For now pydrivers can reference their own object, something normal
ipodrivers can't. This seems to work fine and is quite useful, but if
tests prove the restriction is necessary, we just need to uncomment a
piece of code in EXPP_interface.c, marked with "XXX".

Thanks Ton for the ipodrivers code and adding the hooks for the py part
and Martin for the "Button Python Evaluation" patch from which I started
this one.

Anyone interested, please check the wiki, the .blends (they have
README's) and tell me about any issue.

source/blender/python/BPY_interface.c

@@ -43,6 +43,7 @@
 #include "BKE_library.h"
 #include "BKE_object.h"		/* during_scriptlink() */
 #include "BKE_text.h"
+#include "DNA_curve_types.h" /* for struct IpoDriver */
 #include "DNA_screen_types.h"
 #include "DNA_userdef_types.h"	/* for U.pythondir */
 #include "MEM_guardedalloc.h"
@@ -73,6 +74,9 @@
  */
 //#include "api2_2x/Registry.h"
 
+/* for pydrivers (ipo drivers defined by one-line Python expressions) */
+PyObject *bpy_pydriver_Dict = NULL;
+
 /*Declares the modules and their initialization functions
 *These are TOP-LEVEL modules e.g. import `module` - there is no
 *support for packages here e.g. import `package.module` */
@@ -175,6 +179,11 @@ void BPY_end_python( void )
 		bpy_registryDict = NULL;
 	}
 
+	if( bpy_pydriver_Dict ) {
+		Py_DECREF( bpy_pydriver_Dict );
+		bpy_pydriver_Dict = NULL;
+	}
+
 	Py_Finalize(  );
 
 	BPyMenu_RemoveAllEntries(  );	/* freeing bpymenu mem */
@@ -919,6 +928,187 @@ void BPY_clear_script( Script * script )
 	unlink_script( script );
 }
 
+/* PyDrivers */
+
+/* PyDrivers are Ipo Drivers governed by expressions written in Python.
+ * Expressions here are one-liners that evaluate to a float value. */
+
+/* For faster execution we keep a special dictionary for pydrivers, with
+ * the needed modules and aliases. */
+static int bpy_pydriver_create_dict(void)
+{
+	PyObject *d, *mod;
+
+	if (bpy_pydriver_Dict) return -1;
+
+	d = PyDict_New();
+	if (!d) return -1;
+
+	bpy_pydriver_Dict = d;
+
+	/* import some modules: builtins, Blender, math, Blender.noise */
+
+	PyDict_SetItemString(d, "__builtins__", PyEval_GetBuiltins());
+
+	mod = PyImport_ImportModule("Blender");
+	if (mod) {
+		PyDict_SetItemString(d, "Blender", mod);
+		PyDict_SetItemString(d, "b", mod);
+		Py_DECREF(mod);
+	}
+
+	mod = PyImport_ImportModule("math");
+	if (mod) {
+		PyDict_SetItemString(d, "math", mod);
+		PyDict_SetItemString(d, "m", mod);
+		Py_DECREF(mod);
+	}
+
+	mod = PyImport_ImportModule("Blender.Noise");
+	if (mod) {
+		PyDict_SetItemString(d, "noise", mod);
+		PyDict_SetItemString(d, "n", mod);
+		Py_DECREF(mod);
+	}
+
+	/* If there's a Blender text called pydrivers.py, import it.
+	 * Users can add their own functions to this module. */
+	mod = importText("pydrivers"); /* can also use PyImport_Import() */
+	if (mod) {
+		PyDict_SetItemString(d, "pydrivers", mod);
+		PyDict_SetItemString(d, "p", mod);
+		Py_DECREF(mod);
+	}
+	else
+		PyErr_Clear();
+
+	/* short aliases for some Get() functions: */
+
+	/* ob(obname) == Blender.Object.Get(obname) */
+	mod = PyImport_ImportModule("Blender.Object");
+	if (mod) {
+		PyObject *fcn = PyObject_GetAttrString(mod, "Get");
+		Py_DECREF(mod);
+		if (fcn)
+			PyDict_SetItemString(d, "ob", fcn);
+	}
+
+	/* me(meshname) == Blender.Mesh.Get(meshname) */
+	mod = PyImport_ImportModule("Blender.Mesh");
+	if (mod) {
+		PyObject *fcn = PyObject_GetAttrString(mod, "Get");
+		Py_DECREF(mod);
+		if (fcn)
+			PyDict_SetItemString(d, "me", fcn);
+	}
+
+	/* ma(matname) == Blender.Material.Get(matname) */
+	mod = PyImport_ImportModule("Blender.Material");
+	if (mod) {
+		PyObject *fcn = PyObject_GetAttrString(mod, "Get");
+		Py_DECREF(mod);
+		if (fcn)
+			PyDict_SetItemString(d, "ma", fcn);
+	}
+
+	return 0;
+}
+
+/* error return function for BPY_eval_pydriver */
+static float pydriver_error(IpoDriver *driver) {
+
+	if (bpy_pydriver_oblist)
+		bpy_pydriver_freeList();
+
+	if (bpy_pydriver_Dict) { /* free the global dict used by pydrivers */
+		Py_DECREF(bpy_pydriver_Dict);
+		bpy_pydriver_Dict = NULL;
+	}
+
+	driver->flag |= IPO_DRIVER_FLAG_INVALID; /* py expression failed */
+
+	fprintf(stderr, "\nError in Ipo Driver: Object %s\nThis is the failed Python expression:\n'%s'\n\n", driver->ob->id.name+2, driver->name);
+
+	PyErr_Print();
+
+	return 0.0f;
+}
+
+/* for depsgraph.c, runs py expr once to collect all refs. made
+ * to objects (self refs. to the object that owns the py driver
+ * are not allowed). */
+struct Object **BPY_pydriver_get_objects(IpoDriver *driver)
+{
+	/*if (!driver || !driver->ob || driver->name[0] == '\0')
+		return NULL;*/
+
+	/*PyErr_Clear();*/
+
+	/* clear the flag that marks invalid python expressions */
+	driver->flag &= ~IPO_DRIVER_FLAG_INVALID;
+
+	/* tell we're running a pydriver, so Get() functions know they need
+	 * to add the requested obj to our list */
+	bpy_pydriver_running(1);
+
+	/* append driver owner object as the 1st ob in the list;
+	 * we put it there to make sure it is not itself referenced in
+	 * its pydriver expression */
+	bpy_pydriver_appendToList(driver->ob);
+
+	/* this will append any other ob referenced in expr (driver->name)
+	 * or set the driver's error flag if driver's py expression fails */
+	BPY_pydriver_eval(driver);
+
+	bpy_pydriver_running(0); /* ok, we're done */
+
+	return bpy_pydriver_obArrayFromList(); /* NULL if eval failed */
+}
+
+/* This evals py driver expressions, 'expr' is a Python expression that
+ * should evaluate to a float number, which is returned. */
+float BPY_pydriver_eval(IpoDriver *driver)
+{
+	char *expr = NULL;
+	PyObject *retval, *floatval;
+	float result = 0.0f; /* default return */
+
+	if (!driver) return result;
+
+	expr = driver->name; /* the py expression to be evaluated */
+	if (!expr || expr[0]=='\0') return result;
+
+	if (!bpy_pydriver_Dict) {
+		if (bpy_pydriver_create_dict() != 0) {
+			fprintf(stderr, "Pydriver error: couldn't create Python dictionary");
+			return result;
+		}
+	}
+
+	retval = PyRun_String(expr, Py_eval_input, bpy_pydriver_Dict,
+		bpy_pydriver_Dict);
+
+	if (retval == NULL) {
+		return pydriver_error(driver);
+	}
+	else {
+		floatval = PyNumber_Float(retval);
+		Py_DECREF(retval);
+	}
+
+	if (floatval == NULL) 
+		return pydriver_error(driver);
+	else {
+		result = (float)PyFloat_AsDouble(floatval);
+		Py_DECREF(floatval);
+	}
+
+	/* all fine, make sure the "invalid expression" flag is cleared */
+	driver->flag &= ~IPO_DRIVER_FLAG_INVALID;
+
+	return result;
+}
+
 /*****************************************************************************/
 /* ScriptLinks                                                        */
 /*****************************************************************************/