Blender operator to shoot a ray into the scene and draw a 3D cube on the closest face

face_raycast.py

import bpy
from bpy_extras import view3d_utils
import gpu
from gpu_extras.batch import batch_for_shader
from mathutils import Vector

def draw(shade, bat):
    shade.bind()
    shade.uniform_float("color", (1, 0, 0, 0.25))
    bat.draw(shade)
    
def remove(handler):
    bpy.types.SpaceView3D.draw_handler_remove(handler, 'WINDOW')
    for area in bpy.context.window.screen.areas:
        if area.type == 'VIEW_3D':
           area.tag_redraw()
    
indices = (
    (0, 1, 3), (0, 2, 3), (4, 5, 7), (4, 6, 7),
    (0, 4, 5), (0, 1, 5), (2, 0, 4), (2, 6, 4),
    (1, 3, 7), (1, 5, 7), (3, 2, 6), (3, 6, 7))

def main(context, event, cor):
    """Run this function on left mouse, execute the ray cast"""
    # get the context arguments
    scene = context.scene
    region = context.region
    rv3d = context.region_data
    coord = event.mouse_region_x, event.mouse_region_y

    # get the ray from the viewport and mouse
    view_vector = view3d_utils.region_2d_to_vector_3d(region, rv3d, coord)
    ray_origin = view3d_utils.region_2d_to_origin_3d(region, rv3d, coord)

    ray_target = ray_origin + view_vector

    isHit, loc, normal, index, hit_obj, matrix = scene.ray_cast(context.evaluated_depsgraph_get(), ray_origin, view_vector)

    if isHit:
        return hit_obj, index, matrix
        
    return None, 0, None


class ViewOperatorRayCast(bpy.types.Operator):
    """Modal object selection with a ray cast"""
    bl_idname = "view3d.modal_operator_raycast"
    bl_label = "RayCast View Operator"
    
    
    def __init__(self):
        self.prev_obj = None
        self.prev_index = 0
        self.shader = None
        self.batch = None
        self.draw_handler = None
                  
    def modal(self, context, event):
        if event.type in {'MIDDLEMOUSE', 'WHEELUPMOUSE', 'WHEELDOWNMOUSE'}:
            # allow navigation
            return {'PASS_THROUGH'}
        elif event.type == 'MOUSEMOVE':
            coords = [
                Vector((-0.05, -0.05, -0.05)), Vector((+0.05, -0.05, -0.05)),
                Vector((-0.05, +0.05, -0.05)), Vector((+0.05, +0.05, -0.05)),
                Vector((-0.05, -0.05, +0.05)), Vector((+0.05, -0.05, +0.05)),
                Vector((-0.05, +0.05, +0.05)), Vector((+0.05, +0.05, +0.05))]

            hit_obj, index, matrix = main(context, event, coords)
            
            if hit_obj is not None and (self.prev_obj != hit_obj or self.prev_index != index):
                face_world_loc = matrix @ (hit_obj.data.polygons[index].center)
                coords = [face_world_loc + c for c in coords]

                self.shader = gpu.shader.from_builtin('3D_UNIFORM_COLOR')
                self.batch = batch_for_shader(self.shader, 'TRIS', {"pos": coords}, indices=indices)
                if self.draw_handler is not None:
                    remove(self.draw_handler)
                self.draw_handler = bpy.types.SpaceView3D.draw_handler_add(draw, (self.shader, self.batch), 'WINDOW', 'POST_VIEW')
                for area in bpy.context.window.screen.areas:
                    if area.type == 'VIEW_3D':
                        area.tag_redraw()
            
                self.prev_obj = hit_obj
                self.prev_index = index

            return {'RUNNING_MODAL'}
        elif event.type in {'RIGHTMOUSE', 'ESC'}:
            if self.draw_handler is not None:
                remove(self.draw_handler)
            return {'CANCELLED'}

        return {'RUNNING_MODAL'}

    def invoke(self, context, event):
        if context.space_data.type == 'VIEW_3D':
            context.window_manager.modal_handler_add(self)
            return {'RUNNING_MODAL'}
        else:
            self.report({'WARNING'}, "Active space must be a View3d")
            return {'CANCELLED'}


def menu_func(self, context):
    self.layout.operator(ViewOperatorRayCast.bl_idname, text="Raycast View Modal Operator")


# Register and add to the "view" menu (required to also use F3 search "Raycast View Modal Operator" for quick access).
def register():
    bpy.utils.register_class(ViewOperatorRayCast)
    bpy.types.VIEW3D_MT_view.append(menu_func)


def unregister():
    bpy.utils.unregister_class(ViewOperatorRayCast)
    bpy.types.VIEW3D_MT_view.remove(menu_func)


if __name__ == "__main__":
    register()