If you wish to take admission to the course of BE Computer Engineering, then you can apply through the lateral entry examination as you have completed your diploma in Mechanical engineering. The lateral entry examination, will directly provide you admission to the 2nd year of BE Computer Engineering.

Now if you wish take admission in the 1st year of the course, then you have to apply through the state level joint or the entrance required for your desired college but you need to have your 10+2 marks and based on the performance of the entrance you will be selected for the course. Thus there will be no involvement of the Diploma you have completed.

For more information regarding Lateral Entry examination consider the link below:

https://www.careers360.com/courses/b-tech-lateral-entry

For more information regarding Computer Science Engineering consider the link below:

https://www.careers360.com/courses/computer-science-engineering-course

I hope this helps. Goodnight!