[Blender] How to handle mouse and keyboard events in Blender scripts

If you are making a Blender plugin, you will want to handle events from the mouse and keyboard and provide more interactive features. The function to change the size of an object just by moving the mouse when pressing the S key in Object mode is just an example of handling an event from the mouse, and the operation feeling is good.

So this time, I will show you how to handle mouse and keyboard events in Blender script with samples.

sample

Again, the sample is shown first. This sample allows you to scale the object according to the mouse position. We have dealt with the following events so that you can understand the pattern of input events in Blender.

• When you move the mouse
• When the mouse is clicked
• When you press a key on the keyboard

Source code

mouse_keyboard_event_test.py

import bpy

bl_info = {
    "name" : "Mouse/Keyboard event test",
    "author" : "Nutti",
    "version" : (0,1),
    "blender" : (2, 7, 0),
    "location" : "UV > Mouse/Keyboard event test",
    "description" : "Mouse/Keyboard event test.",
    "warning" : "",
    "wiki_url" : "",
    "tracker_url" : "",
    "category" : "UV"
}

running = False     #True if event acquisition is in progress

class MouseKeyboardEventTest(bpy.types.Operator):
    """Mouse/Keyboard event test."""
    
    bl_idname = "uv.mouse_keyboard_event_test"
    bl_label = "Mouse/Keyboard event test"
    bl_description = "Mouse/Keyboard event test"
    bl_options = {'REGISTER', 'UNDO'}
    
    obj_scale = 1.0     #Object magnification
    orig_x = 0.0        #X coordinate when the button is pressed
    orig_scale = []     #Object magnification when the button is pressed

    def modal(self, context, event):
        global running
    
        #Exit if not working
        if running is False:
            return {'PASS_THROUGH'}
        
        #Apply magnification to objects
        active_obj = bpy.context.active_object
        active_obj.scale[0] = self.orig_scale[0] * self.obj_scale
        active_obj.scale[1] = self.orig_scale[1] * self.obj_scale
        active_obj.scale[2] = self.orig_scale[2] * self.obj_scale
        
        #############################################
        #mouse/Processing to handle keyboard events
        #############################################
        
        #Mouse movement-Set the magnification of the object based on the X coordinate of the mouse
        if event.type == 'MOUSEMOVE':
            factor = 1.0 / 100.0
            self.obj_scale = 1.0 + (event.mouse_x - self.orig_x) * factor
            return {'RUNNING_MODAL'}
        #When you press the spacebar-Return the magnification when the button is pressed
        elif event.type == 'SPACE':
            if event.value == 'PRESS':
                self.orig_x = event.mouse_x
                return {'RUNNING_MODAL'}
        #When right click is pressed-Confirm the changed enlargement ratio and end the operation
        if event.type == 'RIGHTMOUSE':
            if event.value == 'PRESS':
                running = False
                return {'FINISHED'}
        
        return {'RUNNING_MODAL'}
    
    def invoke(self, context, event):
        global running
        
        if context.area.type == 'VIEW_3D':
            #Accept each event if the button is pressed while it is not running
            if running is False:
                running = True
                #Initial state setting
                self.obj_scale = 1.0
                self.orig_x = event.mouse_x
                active_obj = bpy.context.active_object
                self.orig_scale = [
                    active_obj.scale[0],
                    active_obj.scale[1],
                    active_obj.scale[2]
                ]
                #modal handler settings
                context.window_manager.modal_handler_add(self)
                return {'RUNNING_MODAL'}
        return {'CANCELLED'}
        
# 'N'Place a button in the menu that appears on the right side of VIEW 3D when you press a key
class OBJECT_PT_MKET(bpy.types.Panel):
    bl_label = "Mouse/Keyboard Event Test"
    bl_space_type = "VIEW_3D"
    bl_region_type = "UI"
    
    def draw(self, context):
        sc = context.scene
        layout = self.layout
        #Button placement
        layout.operator(MouseKeyboardEventTest.bl_idname, text="Start", icon="PLAY")


def register():
    bpy.utils.register_module(__name__)


def unregister():
    bpy.utils.unregister_module(__name__)


if __name__ == "__main__":
    register()

How to use

Follow the steps below to install the script. Blender Wiki

If you click the "Start" button in "Mouse / Keyboard Event Test" of the menu displayed on the right side when you press the'N'key in View 3D, the following operations will be accepted.

Sample explanation

The basic explanation of the Blender script is introduced in the following article, so here we will focus on the explanation of the newly added elements. [\ Blender ] How to make a Blender plugin

Button registration

Add a button to the menu on the right that appears when you press the'N'key in View 3D. Button registration is beyond the scope of this article, so think of it like this for now.

# 'N'Place a button in the menu that appears on the right side of VIEW 3D when you press a key
class OBJECT_PT_MKET(bpy.types.Panel):
    bl_label = "Mouse/Keyboard Event Test"
    bl_space_type = "VIEW_3D"
    bl_region_type = "UI"
    
    def draw(self, context):
        #Button placement
        # ...

invoke method

** A method that is called when the class is called **. In this sample, it is called when the button is clicked.

    def invoke(self, context, event):
        global running
        
        if context.area.type == 'VIEW_3D':
            #Accept each event if the button is pressed while it is not running
            if running is False:
                running = True

                #Initial state setting
                # ....

                #modal handler settings
                context.window_manager.modal_handler_add(self)
                return {'RUNNING_MODAL'}
        return {'CANCELLED'}

We have specified a handler (an object with a modal method) in the context.window_manager.modal_handler_add function to accept mouse events after clicking the button. Here, specify self because the class has both ʻinvoke and modal` methods at the same time. In addition, various initial state settings are also made.

If you set a handler here, the modal method will continue to be called ** after **, so we have prepared a running variable to eliminate operations on the object even if an event occurs at the time of stop.

modal method

If you register a handler with the context.window_manager.modal_handler_add function in the ʻinvoke` method, it will be called ** when an event occurs from the mouse or keyboard **.

    def modal(self, context, event):
        global running

        #Exit if not working
        if running is False:
            return {'PASS_THROUGH'}

        # ....
        
        #Mouse movement-Set the magnification of the object based on the X coordinate of the mouse
        if event.type == 'MOUSEMOVE':
            factor = 1.0 / 100.0
            self.obj_scale = 1.0 + (event.mouse_x - self.orig_x) * factor
            return {'RUNNING_MODAL'}
        #When you press the spacebar-Return the magnification when the button is pressed
        elif event.type == 'SPACE':
            if event.value == 'PRESS':
                self.orig_x = event.mouse_x
                return {'RUNNING_MODAL'}
        #When right click is pressed-Confirm the changed enlargement ratio and end the operation
        if event.type == 'RIGHTMOUSE':
            if event.value == 'PRESS':
                running = False
                return {'FINISHED'}
        
        return {'RUNNING_MODAL'}

The modal method handles each event as follows.

At the end

I introduced how to handle events from the mouse and keyboard in Blender scripts. By knowing keyboard and mouse events, I think that ** more things can be achieved with scripts **, so why not try using it?

Reference information

• Operator(bpy_struct)