Concatenating transforms to scale positions but not objects

[Mark Raynsford]

On 2019-08-06T19:11:42 +0100
Mark Raynsford <org.openjdk at io7m.com> wrote:

> Hello!
> 
> I realize the subject is somewhat convoluted. I'm putting together
> something that bears a passing resemblance to a DAW such as Ardour:

Given the tumbleweeds and sounds of crickets, I'm guessing that I
expressed my question rather poorly.

Here's what I'm trying to do: I'm trying to set up a pane with a
transform such that I can place objects inside that pane using
positions that don't correspond to JavaFX "scene pixels". For example,
1024 units in my coordinate system might correspond to 1 "scene pixel"
(is there a better name for the units that JavaFX uses?). However: The
objects that are *inside* the objects that I add to the pane want to
work in "scene pixels" (for example; Labels seem to want to work in
pixel positions when rendering text).

Here's a GitHub gist that gives a short example of this:

https://gist.github.com/io7m/20b071e11da2dcd96896a43fad6df644

I create one container group (actually a Pane) that adds a transform
such that 1 unit == 32 pixels. I add objects to this container. Each
object I add has an *external* pane with a size and position specified
in units, and an *internal* pane that solely exists to invert the scale
of the transform of the *external* pane. Inside this *internal* pane, I
can add Labels and so on and these all render correctly.

I set up bindings between the transforms so that I can effectively
scale and pan the scene by adjusting the transform on the group
container. However: Something about this setup seems to be confusing
something inside JavaFX; the results I'm seeing onscreen don't seem to
match what JavaFX believes the bounds of various objects are. This
causes visual issues when I try to do things like set borders on
objects, and also seems to confuse ScenicView.

Here's a shot with the container group selected (looks correct):

https://ataxia.io7m.com/2019/08/10/view0.png

Here's a shot with the *external* pane of the bottom object selected:

https://ataxia.io7m.com/2019/08/10/view1.png

Note that, although the object actually renders onscreen as the right
size (one of the pale grey boxes), ScenicView seems to believe that the
object's bounds are 1x1: They *are* 1x1, but they're 1x1 when expressed
in my custom coordinate system, not in JavaFX "scene pixels".

Here's a shot with the *internal* pane of the bottom object selected:

https://ataxia.io7m.com/2019/08/10/view2.png

This looks correct in the sense that the bounds encompass the label and
nothing else.

Am I doing something wrong here? I can't tell if I'm basically abusing
transforms or not.

-- 
Mark Raynsford | http://www.io7m.com