[Walter Soyka]

A screenshot of your entire UI will help us understand what you’re seeing.

Without that, here’s a guess. You may need to adjust the work area before you render:
https://helpx.adobe.com/after-effects/using/previewing.html#work_area

Walter Soyka
Designer & Mad Scientist at Keen Live [link]
Motion Graphics, Widescreen Events, Presentation Design, and Consulting
@keenlive   |   RenderBreak [blog]   |   Profile [LinkedIn]

[Walter Soyka]

[kevin tang] “Walter’s suggestion (math.round expression) worked well. Just out of curiosity, is there an advantage of using one over the other (mathround vs draft)? Are there any disadvantages to using math.round”

The expression will only work on a single property, and if you want to use other expressions too, you’ll have to figure out how to combine them.

If you use Draft mode, you have to modify your render settings — using the default “Best Settings” render settings template will override Draft mode on output.

[kevin tang] “Also, would there be any subpixel scaling issues, if I would like to scale a shape (let’s say a circle) with a constant stroke width of 1px?”

A circle with a 1px stroke will be tough — it will need antialiasing to look good.

For shape layers with specific linework, you want to manipulate the shape path/transforms themselves, prior to the stroke; if you manipulate the transform controls for the layer, the stroke will also be scaled.

Walter Soyka
Designer & Mad Scientist at Keen Live [link]
Motion Graphics, Widescreen Events, Presentation Design, and Consulting
@keenlive   |   RenderBreak [blog]   |   Profile [LinkedIn]

[Walter Soyka]

This should do the trick:

var maxWidth = thisComp.width - 100;
var maxHeight = thisComp.height - 200;
var myWidth = thisLayer.sourceRectAtTime(time).width;
var myHeight = thisLayer.sourceRectAtTime(time).height;

var resizeScale = Math.min(maxWidth/myWidth, maxHeight/myHeight, 1);
[resizeScale, resizeScale] * 100

Walter Soyka
Designer & Mad Scientist at Keen Live [link]
Motion Graphics, Widescreen Events, Presentation Design, and Consulting
@keenlive   |   RenderBreak [blog]   |   Profile [LinkedIn]

[Walter Soyka]

Hopefully this is a horizontal or vertical line!

You can defeat subpixel positioning by either setting the 1-pixel layer to draft mode (and adjusting your render settings accordingly in the render queue), or by applying an expression like this one to your position property that forces it to only yield whole values:

[Math.round(value[0]), Math.round(value[1])]

Walter Soyka
Designer & Mad Scientist at Keen Live [link]
Motion Graphics, Widescreen Events, Presentation Design, and Consulting
@keenlive   |   RenderBreak [blog]   |   Profile [LinkedIn]

[Walter Soyka]

For weird UI behavior, I suggest resetting preferences as a first troubleshooting step. Close After Effects, then hold Ctrl+Alt+Shift (Windows) or Cmd+Opt+Shift (macOS) while starting Ae.

Walter Soyka
Designer & Mad Scientist at Keen Live [link]
Motion Graphics, Widescreen Events, Presentation Design, and Consulting
@keenlive   |   RenderBreak [blog]   |   Profile [LinkedIn]

[Walter Soyka]

There is no way I know of to open a timeline in the same tab in Ae.

A couple of workarounds I could suggest:

1) Use a program like AutoHotkey (Windows) or Keyboard Maestro (macOS) to record a keyboard macro that opens the selected comp (Enter), moves back one tab in the timeline viewer (Alt+Shift+<), and closes the tab (Ctrl+W).

2) Learn to use the composition navigator, flowchart or mini-flowchart to navigate your project, and avoid opening comps you don’t want in the first place:
https://helpx.adobe.com/after-effects/using/precomposing-nesting-pre-rendering.html#opening_and_navigating_nested_compositions

Walter Soyka
Designer & Mad Scientist at Keen Live [link]
Motion Graphics, Widescreen Events, Presentation Design, and Consulting
@keenlive   |   RenderBreak [blog]   |   Profile [LinkedIn]

[Walter Soyka]

It’s tough to say without seeing the project file, though perhaps it’s a color management difference?

Walter Soyka
Designer & Mad Scientist at Keen Live [link]
Motion Graphics, Widescreen Events, Presentation Design, and Consulting
@keenlive   |   RenderBreak [blog]   |   Profile [LinkedIn]

[Walter Soyka]

If you can use the Drop Shadow layer style instead of the Drop Shadow effect, the shadow will not be affected by the layer’s orientation to its motion path.

Walter Soyka
Designer & Mad Scientist at Keen Live [link]
Motion Graphics, Widescreen Events, Presentation Design, and Consulting
@keenlive   |   RenderBreak [blog]   |   Profile [LinkedIn]

[Walter Soyka]

You want a particle system, like CC Particle World (included with Ae), or Trapcode Particular or Superliminal Stardust (third-party).

Walter Soyka
Designer & Mad Scientist at Keen Live [link]
Motion Graphics, Widescreen Events, Presentation Design, and Consulting
@keenlive   |   RenderBreak [blog]   |   Profile [LinkedIn]

[Walter Soyka]

David, I can help.

Walter Soyka
Designer & Mad Scientist at Keen Live [link]
Motion Graphics, Widescreen Events, Presentation Design, and Consulting
@keenlive   |   RenderBreak [blog]   |   Profile [LinkedIn]