The template python “operator_modal_draw.py”, we can see that the variable “draw_callback_px” is referenced globally.
However if we reference-it locally, the function would look like this:
import bpy
import bgl
import blf
class ModalDrawOperator(bpy.types.Operator):
"""Draw a line with the mouse"""
bl_idname = "view3d.modal_operator"
bl_label = "Simple Modal View3D Operator"
def draw_callback_px(self, context):
print("mouse points", len(self.mouse_path))
font_id = 0 # XXX, need to find out how best to get this.
# draw some text
blf.position(font_id, 15, 30, 0)
blf.size(font_id, 20, 72)
blf.draw(font_id, "Hello Word " + str(len(self.mouse_path)))
# 50% alpha, 2 pixel width line
bgl.glEnable(bgl.GL_BLEND)
bgl.glColor4f(0.0, 0.0, 0.0, 0.5)
bgl.glLineWidth(2)
bgl.glBegin(bgl.GL_LINE_STRIP)
for x, y in self.mouse_path:
bgl.glVertex2i(x, y)
bgl.glEnd()
# restore opengl defaults
bgl.glLineWidth(1)
bgl.glDisable(bgl.GL_BLEND)
bgl.glColor4f(0.0, 0.0, 0.0, 1.0)
def modal(self, context, event):
context.area.tag_redraw()
if event.type == 'MOUSEMOVE':
self.mouse_path.append((event.mouse_region_x, event.mouse_region_y))
elif event.type == 'LEFTMOUSE':
bpy.types.SpaceView3D.draw_handler_remove(self._handle, 'WINDOW')
return {'FINISHED'}
elif event.type in {'RIGHTMOUSE', 'ESC'}:
bpy.types.SpaceView3D.draw_handler_remove(self._handle, 'WINDOW')
return {'CANCELLED'}
return {'RUNNING_MODAL'}
def invoke(self, context, event):
if context.area.type == 'VIEW_3D':
# Add the region OpenGL drawing callback
# draw in view space with 'POST_VIEW' and 'PRE_VIEW'
self._handle = bpy.types.SpaceView3D.draw_handler_add(self.draw_callback_px, (context,), 'WINDOW', 'POST_PIXEL')
self.mouse_path = []
context.window_manager.modal_handler_add(self)
return {'RUNNING_MODAL'}
else:
self.report({'WARNING'}, "View3D not found, cannot run operator")
return {'CANCELLED'}
def register():
bpy.utils.register_class(ModalDrawOperator)
def unregister():
bpy.utils.unregister_class(ModalDrawOperator)
if __name__ == "__main__":
register()
The amount of local variables is less than the amount of global variables. This is advantageous for loops. But there are other things into consideration.
Then, this solution is better or worse for performance?