How can I make a 2d gpu polygon and text follow the cursor?

Question

The code:

import bpy, bmesh
import bgl
import blf
import gpu
from gpu_extras.batch import batch_for_shader

vertices = (
    (60, 425), (310, 425),
    (60, 580), (310, 580))

indices = (
    (0, 1, 2), (2, 1, 3))

shader = gpu.shader.from_builtin('2D_UNIFORM_COLOR')
batch = batch_for_shader(shader, 'TRIS', {"pos": vertices}, indices=indices)
    
def draw_bevel(self, context):

    #box
    shader.bind()
    shader.uniform_float("color", (0.3, 0.3, 0.3, 0.8))
    batch.draw(shader)

    #text
    font_id = 0  
    x_offset = 0
    y_offset = 0
    active = context.active_object
    bevelWV = active.modifiers["Bevel"].width
    bevelWV = round(bevelWV, 4)
    bevelSG = active.modifiers["Bevel"].segments
    bevelSG = round(bevelSG, 4)
    
    blf.color(font_id, 0, 0.292, 1, 0.7)
    blf.position(font_id, 78, 510, 0)
    blf.size(font_id, 27, 176)
    blf.draw(font_id, "BEVEL" )
    
    blf.color(font_id, 0, 1, 0.232, 0.7)
    blf.position(font_id, 83, 480, 0)
    blf.size(font_id, 27, 81)
    blf.draw(font_id, "WIDTH" )
    
    blf.color(font_id, 0, 1, 0.232, 0.7)
    blf.position(font_id, 83, 450, 0)
    blf.size(font_id, 27, 81)
    blf.draw(font_id, "SEGS" )
    
    blf.color(font_id, 1, 1, 1, 0.7)
    blf.position(font_id, 195, 480, 0)
    blf.size(font_id, 27, 81)
    blf.draw(font_id, str(bevelWV))
    
    blf.color(font_id, 1, 1, 1, 0.7)
    blf.position(font_id, 195, 450, 0)
    blf.size(font_id, 27, 81)
    blf.draw(font_id, str(bevelSG))


class BevelSetModal(bpy.types.Operator):
    """Move an object with the mouse, example"""
    bl_idname = "bevel.set_operator"
    bl_label = "Bevel Set modal"

    first_mouse_x = IntProperty()
    first_value = FloatProperty()

    @classmethod
    def poll(cls, context):
        mod_types = set()
        for o in context.selected_objects:
            for m in o.modifiers:
                mod_types.add(m.type)
        return 'BEVEL' in mod_types and context.object.type == 'MESH'


    def modal(self, context, event):
        context.area.tag_redraw()
        if event.type == 'MOUSEMOVE':
            self.mouse_path.append((event.mouse_region_x, event.mouse_region_x))
            delta = self.first_mouse_x - event.mouse_x
            bpy.context.object.modifiers["Bevel"].width = self.first_value + delta * -0.001
            
        elif event.type == 'MOUSEMOVE'+'P':
            self.mouse_path.append((event.mouse_region_x, event.mouse_region_x))
            delta = self.first_mouse_x - event.mouse_x
            bpy.context.object.modifiers["Bevel"].profile = self.first_value + delta * -0.001    
          
        elif event.type == 'V' and event.value=='PRESS':    
            bpy.context.object.modifiers["Bevel"].use_only_vertices = True
      
        elif event.type == "WHEELUPMOUSE":
            bpy.context.object.modifiers["Bevel"].segments += 1
        
        elif event.type == "WHEELDOWNMOUSE":
            bpy.context.object.modifiers["Bevel"].segments -= 1  

        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')
            bpy.context.object.modifiers["Bevel"].width = self.first_value
            return {'CANCELLED'}

        return {'RUNNING_MODAL'}

    def invoke(self, context, event):
        
        if context.area.type == 'VIEW_3D':         
            args = (self, context)            
            self._handle = bpy.types.SpaceView3D.draw_handler_add(draw_bevel, args, 'WINDOW', 'POST_PIXEL')
            self.mouse_path = []
            
        
        if context.object:
            self.first_mouse_x = event.mouse_x
            self.first_value = bpy.context.object.modifiers["Bevel"].width
            context.window_manager.modal_handler_add(self) 

            return {'RUNNING_MODAL'}
        else:
            self.report({'WARNING'}, "No active object, could not finish")
            return {'CANCELLED'}

Basically what this does is draw a 2d polygon box using the new gpu module in 2.8 and some blf text which displays the bevel modifier data, in a modal operator (if there is a bevel modifier present on the mesh object).

---

As you can see the coordinates of the box and the blf text are both hardcoded. My goal is make the elements get aligned to the right side of the cursor and move along with it. I absolutely have no idea on how to even approach this.

---

I tried adding the solution provided by @brockmann but this is what happens:

The box is just moving diagonally instead of following the mouse x,y. The example script works fine on its own but the mouse coordinates seem to be confliciting with the modal operator mouse maps.

Answer 1

Record the cursor path using Event.mouse_region_* and offset the vertices of the rectangle based on x and y coords of the cursor. Following code is based on operator_modal_draw.py template:

import bpy
import bgl
import blf
import gpu
from gpu_extras.batch import batch_for_shader

        
def draw_callback_px(self, context):
    x, y = self.mouse_path[-1]
    
    vertices = (
        (x, y-50), (x+70, y-50),
        (x, y), (x+70, y))

    indices = (
        (0, 1, 2), (2, 1, 3))

    bgl.glEnable(bgl.GL_BLEND)
    bgl.glEnable(bgl.GL_LINE_SMOOTH)
    shader = gpu.shader.from_builtin('2D_UNIFORM_COLOR')
    batch = batch_for_shader(shader, 'TRIS', {"pos": vertices}, indices=indices)
    bgl.glEnable(bgl.GL_BLEND)
    bgl.glLineWidth(1) # Set the line width
    shader.bind()
    shader.uniform_float("color", (0.2, 0.7, 0.2, 0.5))
    batch.draw(shader)

    font_id = 0  # XXX, need to find out how best to get this.

    # draw some text
    font_offset = 10
    blf.position(font_id, x+font_offset, y-font_offset*2, 0)
    blf.size(font_id, 20, 72)
    blf.draw(font_id, "Hello")
    
    # restore opengl defaults
    bgl.glLineWidth(1)
    bgl.glDisable(bgl.GL_BLEND)


class ModalDrawOperator(bpy.types.Operator):
    """Draw a line with the mouse"""
    bl_idname = "view3d.modal_operator"
    bl_label = "Simple Modal View3D Operator"
    
    @classmethod
    def poll(cls, context):
        return context.active_object is not None 
    
    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':
            # the arguments we pass the the callback
            args = (self, context)
            # Add the region OpenGL drawing callback
            # draw in view space with 'POST_VIEW' and 'PRE_VIEW'
            self._handle = bpy.types.SpaceView3D.draw_handler_add(draw_callback_px, args, '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()

---

To control the bevel modifier interactively I'd suggest store a reference to the bevel modifier in your invoke() method. This way you can access all the modifier properties from all other methods as well as adding a bevel modifier in case there is no modifier added to the object already.

import bpy
import bgl
import blf
import gpu
from gpu_extras.batch import batch_for_shader

        
def draw_callback_px(self, context):
    x, y = self.mouse_path[-1]
    
    vertices = (
        (x, y-50), (x+100, y-50),
        (x, y), (x+100, y))

    indices = (
        (0, 1, 2), (2, 1, 3))

    bgl.glEnable(bgl.GL_BLEND)
    bgl.glEnable(bgl.GL_LINE_SMOOTH)
    shader = gpu.shader.from_builtin('2D_UNIFORM_COLOR')
    batch = batch_for_shader(shader, 'TRIS', {"pos": vertices}, indices=indices)
    bgl.glEnable(bgl.GL_BLEND)
    bgl.glLineWidth(1) # Set the line width
    shader.bind()
    shader.uniform_float("color", (0.2, 0.7, 0.2, 0.5))
    batch.draw(shader)

    font_id = 0  # XXX, need to find out how best to get this.

    # draw some text
    font_offset = 10
    blf.position(font_id, x+font_offset, y-font_offset*2, 0)
    blf.size(font_id, 20, 72)
    blf.draw(font_id, "{:.2f}".format(self.bevel_mod.width))
    
    # restore opengl defaults
    bgl.glLineWidth(1)
    bgl.glDisable(bgl.GL_BLEND)


class ModalDrawOperator(bpy.types.Operator):
    """Draw a line with the mouse"""
    bl_idname = "view3d.modal_operator"
    bl_label = "Simple Modal View3D Operator"
    
    def bevel_modifier(self, context):
        obj = context.active_object
        mods = [m for m in obj.modifiers if m.type == 'BEVEL']
        return mods[0] if mods else obj.modifiers.new("Interactive Bevel", 'BEVEL')
    
    @classmethod
    def poll(cls, context):
        return context.active_object is not None 
    
    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))
            self.bevel_mod.width = event.mouse_region_x * .001

        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':
            # the arguments we pass the the callback
            args = (self, context)
            # Add the region OpenGL drawing callback
            # draw in view space with 'POST_VIEW' and 'PRE_VIEW'
            self._handle = bpy.types.SpaceView3D.draw_handler_add(draw_callback_px, args, 'WINDOW', 'POST_PIXEL')

            self.mouse_path = []
            
            # Bevel Modifier
            self.bevel_mod = self.bevel_modifier(context)
            self.bevel_offset = self.bevel_mod.width

            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()