[Ohrrpgce] Slice rotation and zoom

James Paige Bob at hamsterrepublic.com
Sat Feb 23 11:31:38 PST 2019

That is all very interesting!

> Right now, rotating around a custom offset and specialising
> SliceX/YAnchor() to compensate for that offset + rotation angle seems
> preferable. Funny, I almost got rid of those functions a couple weeks
> ago because they seemed unneeded.

I think I agree with your conclusions here, although some of this is over
my head, and I don't understand all the issues 100%

James Paige

On Fri, Feb 22, 2019 at 5:51 PM Ralph Versteegen <teeemcee at gmail.com> wrote:

> I've added a rotozoomer and slice rotate/zoom options, though there
> are various things that need to be addressed before I expose it to
> users. And those are mostly to do with slice positioning. This email
> is about that, and not anything interesting.
> It's natural that changing the size of a sprite slice should stretch
> its sprite to match its width and height, just like lines, rects and
> ellipses.
> The hidden "scaled" sprite slice setting (a bool), only available in
> 32-bit color mode, already acts like this. (I'll be getting rid of
> this now-redundant setting).
> Sprite slices could still have zoom/zoom x/zoom y properties, but they
> could just provide an alternative way to set the size of the slice.
> (But sub-pixel zoom is a nice thing to have, so I'll probably still
> store the zoom separately. I need to modify the rotozoomer to support
> this.)
> We will need a backcompat bit to enable zooming, because you can
> already change the width and height of a sprite by setting it to fill,
> but it does nothing. (Even though "set slice width/height" is
> disallowed, Fill Parent is a loophole)
> That's all fine, but rotation is a problem. As they rotate, the size
> of the axis-aligned bounding box changes. But if you want to set both
> the sprite size and rotation, the slice width and height should be the
> non-rotated size, not the bounding box size.
> But if bounding box is used for positioning/alignment, it would mean
> their position can't be calculated like other slices.
> And how should child slices of the sprite be positioned, how should
> the Fill Parent setting for both the sprite and its children work,
> "Cover Children", "slice at pixel", and whatever else I've forgotten?
> In a perfect world, perhaps all children of a rotated sprites would be
> rotated too, like an OpenGL transformation matrix stack... but we
> wouldn't really expect child slices of a stretched sprite to be
> stretched in the same way. I think that if we ever implemented
> whole-slice-tree zooming/rotating, they should actually be completely
> separate slice properties, not sprite properties. Still, even if the
> child slices aren't rotated, maybe the alignment points on the rotated
> parent should be rotated too, for convenience when positioning? Oh,
> but then child X and Y offsets would also have to be rotated for
> consistency. How about we assume that in future we would add separate
> settings to rotate and stretch a slice tree, so anything we add now
> should be orthogonal to that instead of overlapping: we shouldn't add
> transformation of child positions now, because there's a better way to
> do it later.
> Still, that leaves the problem that the bounding box size is not equal
> to the "specified size" set in the slice editor/by scripts.
> If rotated sprites always rotated around their center and we treated
> the bounding box size as being equal to the specified size, even
> though the drawn sprite might extend far outside it, then all the
> problems can go away. "slice at pixel" could always be given special
> cases for rotated sprites, ellipses, and lines anyway.
> But you should be able to customise the point around which a sprite is
> rotated, otherwise correctly positioning a sprite rotated around a
> corner (eg a swung weapon) would require complicated calculations by
> the user.
> At a minimum sprites should rotate around their anchor point, but even
> that's not flexible enough - for a weapon swung in an arc the point
> should actually be outside the sprite. You could add blank space to
> the sprite, though.
> Again, if the bounding box size and position didn't change at all
> there would be no problem, except the sprite is likely to be
> completely outside its bounding box! That seems a tad ridiculous. If
> the box size didn't change but the position did that seems reasonable
> enough, and only the calculation of the anchor point would need to be
> specialised. Allowing the size to change requires replacing most
> occurrences of sl->Width and sl->Height in the code!
> Another example: a ball rolling along the top of a surface. You might
> want its anchor point to be the bottom of the slice, but to rotate
> around the center.
> Right now, rotating around a custom offset and specialising
> SliceX/YAnchor() to compensate for that offset + rotation angle seems
> preferable. Funny, I almost got rid of those functions a couple weeks
> ago because they seemed unneeded.
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