Difference calculation based on partial position

An apparatus for processing video data comprising a processor and a non-transitory memory with instructions thereon, wherein the instructions upon execution by the processor, cause the processor to:

• determine whether to enable a first tool, for a conversion between a current block and a bitstream based on a rule, wherein the rule indicates that the first tool and a second tool are not both used by the current block;
• and
• perform, based on the determining, a conversion between the current block and the bitstream;
• wherein one of the first tool and the second tool is a decoder side motion vector derivation tool to derive a refinement of motion information related to the current block, and
• the other of the first tool and the second tool comprises:
• a merge mode with motion vector differences which comprises motion vector expression comprising a first parameter representing a motion vector difference and a second parameter indicating a base candidate, wherein the first parameter comprises a motion magnitude and a motion direction,
• wherein the decoder side motion vector derivation tool is disabled upon a determination that the current block is coded with the merge mode with motion vector differences.

A non-transitory computer-readable storage medium storing instructions that cause a processor to:

• determine whether to enable a first tool, for a conversion between a current block and a bitstream based on a rule, wherein the rule indicates that the first tool and a second tool are not both used by the current block;
• and
• perform, based on the determining, a conversion between the current block and the bitstream;
• wherein one of the first tool and the second tool is a decoder side motion vector derivation tool to derive a refinement of motion information related to the current block, and
• the other of the first tool and the second tool comprises:
• a merge mode with motion vector differences which comprises motion vector expression comprising a first parameter representing a motion vector difference and a second parameter indicating a base candidate, wherein the first parameter comprises a motion magnitude and a motion direction,
• wherein the decoder side motion vector derivation tool is disabled upon a determination that the current block is coded with the merge mode with motion vector differences.

A non-transitory computer-readable recording medium storing a bitstream which is generated by a method performed by a video processing apparatus, wherein the method comprises:

• determining whether to enable a first tool, for a conversion between a current block and a bitstream based on a rule, wherein the rule indicates that the first tool and a second tool are not both used by the current block;
• and
• generating the bitstream from the current block based on the determining;
• wherein one of the first tool and the second tool is a decoder side motion vector derivation tool to derive a refinement of motion information related to the current block, and
• the other of the first tool and the second tool comprises:
• a merge mode with motion vector differences which comprises motion vector expression comprising a first parameter representing a motion vector difference and a second parameter indicating a base candidate, wherein the first parameter comprises a motion magnitude and a motion direction,
• wherein the decoder side motion vector derivation tool is disabled upon a determination that the current block is coded with the merge mode with motion vector differences.