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# for http://blender.stackexchange.com/questions/61699/how-to-draw-geometry-in-3d-view-window-with-bgl

import bpy
import bgl
import blf

def draw_line_3d(color, start, end, width=1):
    bgl.glLineWidth(width)
    bgl.glColor4f(*color)
    bgl.glBegin(bgl.GL_LINES)
    bgl.glVertex3f(*start)
    bgl.glVertex3f(*end)

def draw_typo_2d(color, text):
    font_id = 0  # XXX, need to find out how best to get this.
    # draw some text
    bgl.glColor4f(*color)
    blf.position(font_id, 20, 70, 0)
    blf.size(font_id, 20, 72)
    blf.draw(font_id, text)


def draw_callback_3d(self, context):
    bgl.glEnable(bgl.GL_BLEND)
      
    # object locations
    cube_loc = bpy.data.objects['Cube'].location
    lamp_loc = bpy.data.objects['Lamp'].location
    camera_loc = bpy.data.objects['Camera'].location

    # green line   
    draw_line_3d((0.0, 1.0, 0.0, 0.7), camera_loc, cube_loc)
    
    # red line
    draw_line_3d((1.0, 0.0, 0.0, 0.7), cube_loc, lamp_loc)
    
    # blue line
    draw_line_3d((0.0, 0.0, 1.0, 0.7), lamp_loc, camera_loc, 2)
    
    bgl.glEnd()
    # restore opengl defaults
    bgl.glLineWidth(1)
    bgl.glDisable(bgl.GL_BLEND)
    bgl.glColor4f(0.0, 0.0, 0.0, 1.0)

def draw_callback_2d(self, context):
    
    bgl.glEnable(bgl.GL_BLEND)

    # draw text
    draw_typo_2d((1.0, 1.0, 1.0, 1), "Hello Word ")

    bgl.glEnd()
    # restore opengl defaults
    bgl.glLineWidth(1)
    bgl.glDisable(bgl.GL_BLEND)
    bgl.glEnable(bgl.GL_DEPTH_TEST)
    bgl.glColor4f(0.0, 0.0, 0.0, 1.0)


class ModalDrawOperator(bpy.types.Operator):
    bl_idname = "view3d.modal_operator"
    bl_label = "Simple Modal View3D Operator"

    def modal(self, context, event):
        context.area.tag_redraw()

        if event.type in {'RIGHTMOUSE', 'ESC'}:
            bpy.types.SpaceView3D.draw_handler_remove(self._handle_3d, 'WINDOW')
            bpy.types.SpaceView3D.draw_handler_remove(self._handle_2d, 'WINDOW')
            return {'CANCELLED'}

        return {'PASS_THROUGH'}
        #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_3d = bpy.types.SpaceView3D.draw_handler_add(draw_callback_3d, args, 'WINDOW', 'POST_VIEW')
            self._handle_2d = bpy.types.SpaceView3D.draw_handler_add(draw_callback_2d, args, 'WINDOW', 'POST_PIXEL')

            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()