I have seen (on emulator at least) that when launching an HMMV command, if you are reaching for the right edge of the screen, the value of the NX parameter does not need to be exact. For example, if you want to make a rectangle (200,100)-(255,150), you can use the value 255 for NX (instead of 255-200=55), the fill will be done correctly.
My question is : does it affect the VDP speed of executing that command ?
If I had to hazard a guess I would say it does not affect the speed. Otherwise I would expect the VRAM to be affected.
But if you would want to know for sure then you’d need to do a test. Wait for vsync, change the background colour to red, execute the copy (tall enough so that it takes about half a frame), wait for it to complete, change the background colour to black. Then try with a wider NX and see if the background colour position changes.
