Update stroke_to call to account for linear sRGB

Fixes the incorrect colors in issue #1069
Bumps libmypaint requirement to >= 1.6

lib/brush.hpp

@@ -69,6 +69,12 @@ class Brush {
       return mypaint_brush_stroke_to_2(c_brush, c_surface, x, y, pressure, xtilt, ytilt, dtime, viewzoom, viewrotation, barrel_rotation);
   }
 
+  bool stroke_to_linear (Surface * surface, float x, float y, float pressure, float xtilt, float ytilt, double dtime, float viewzoom, float viewrotation, float barrel_rotation)
+  {
+      MyPaintSurface2 *c_surface = surface->get_surface2_interface();
+      return mypaint_brush_stroke_to_2_linearsRGB(c_brush, c_surface, x, y, pressure, xtilt, ytilt, dtime, viewzoom, viewrotation, barrel_rotation);
+  }
+
   double get_total_stroke_painting_time()
   {
       return mypaint_brush_get_total_stroke_painting_time(c_brush);

lib/brush.py

@@ -638,6 +638,17 @@ def __init__(self, brushinfo):
         brushinfo.observers.append(self._update_from_brushinfo)
         self._update_from_brushinfo(ALL_SETTINGS)
 
+    def stroke_to(self, *args):
+        """ Delegates to mypaintlib with information about color space
+
+        Checks whether color transforms should be done in linear sRGB
+        so that HSV/HSL adjustments can be handled correctly.
+        """
+        if eotf() == 1.0:
+            return super(Brush, self).stroke_to(*args)
+        else:
+            return super(Brush, self).stroke_to_linear(*args)
+
     def _update_from_brushinfo(self, settings):
         """Updates changed low-level settings from the BrushInfo"""
 

lib/python_brush.hpp

@@ -56,4 +56,13 @@ class PythonBrush : public Brush {
     return res;
   }
 
+  bool stroke_to_linear (Surface * surface, float x, float y, float pressure, float xtilt, float ytilt, double dtime, float viewzoom, float viewrotation, float barrel_rotation)
+  {
+    bool res = Brush::stroke_to_linear (surface, x, y, pressure, xtilt, ytilt, dtime, viewzoom, viewrotation, barrel_rotation);
+    if (PyErr_Occurred()) {
+      res = false;
+    }
+    return res;
+  }
+
 };