title is kinda self explanatory. I'm sure i'm missing something obvious.
solved: just do this
You mean set [my rotation x V] to (my [left V])? (Dropdown in the set block \to my \to rotation x)?
Retracted
If you mean for individual costumes, no. For sprites, yes (see previous post).
no, my [center x V]
unfortunate.
I'm actually working on a simple way to add transparent pixels around a costume to give it, effectively, a rotation center.
setting the rotation center coordinates for a sprite actually stores it in its current costume, i.e. it really edits the costume.
you can?
you already can do that,
I was asking about
I thought that the set block worked on the sprite not the costume.
Sorry! I'm not familiar with that feature. There should be a way using rotation centers (because the two are correlated). I'll look into it more later.
..it rotates on its center. You are effectively setting the center of the costume with that block.
That block reports the center of the current costume, aka, ((my [left V]) + (([width V] of costume [[current] V]) / (2))
So the only way to set it, would be to increase the size of the costume.
im toying around with some of the blocks and I figured this out:
I'm not sure if that's what you're asking for but here you go 
what does this do? this looks like it should change rotation x/y, not center x/y. for me it did nothing though.
im assuming you are talking about moving the crosshair tool programmatically to the center of a sprite, right?
yeah
then the script i provided does work, check the costume editor! 
Sprites rotate on their center
Actually, the block my [center x V] returns where the center of the costume is on the stage, while my [rotation x V] returns where the center of the costume is on the SPRITE.
Here are the blocks I designed:
Note that this does not actually set the center x (I made an assumption about the use case):
To change this behaviour just remove the last subtraction block which includes the x/y position.
When I first read this I misunderstood it (knowing what I do now about the center x/y reporter). Clarification: Your script only sets the crosshair to the center of the sprite. I first read it as "moving the crosshair tool programmatically to change the center of a sprite". If this is how @sathvikrias interpreted it, then their reply:
makes sense. Note that this isn't your (@joecooldoo's) fault. I just read what I expected to see.
yeah, I don't get it. what does the block achieve?
Well, let me show you how it would work without the provision I made for the movement of the sprite.
Firstly, we have our costume:
Using a modified version of the block which works the way you want, this happens:
If we change the starting position of the sprite, however, there is no difference in where the sprite appears to be relative to the stage even as the costume changes:
Changing when we do our movements, however, results in a different outcome with the same costume:
This is because "my center x" is dependent upon the sprite's position as well as the costume's position relative to the sprite. If you are wanting to modify the costume's crosshair alone
then my version of the block is what you want. It will work no matter where the sprite is.
thanks. I didn't really understand the modification before.