Improve viewport rotation gizmo drawing

[passivestar]

• More accurate text placement, using Vector2 to avoid loss of precision
• Don't draw lines under the circles
• Enable antialiasing
• Use slightly smaller font size so letters don't get too close to the edge
• Limit text alpha to avoid pitch black
• Use brighter axis color on hover instead of pure white
• Use remap for alpha calculation so that foreground axes stay opaque longer
• Slightly reduce minimum possible alpha for better depth separation
• Thicker lines

Before	After

[passivestar]

Added a little bit of space below the gizmo too:

Before	After

[fire]

Is it difficult for you to make a side by side video? It might help the nontechnical to provide comments.

[Calinou]

Tested locally, it works as expected. Code looks good to me.

Great work!

Preview with Inter as the editor font:

gizmo_new.mp4

200% editor scale with the default font:

gizmo_new_2x.mp4

The only issue I can notice is that with certain custom fonts (as shown above), the X/Y/Z labels can be slightly off-center. I'm not sure if much can be done about this. (For reference, this issue was already present before your PR.)

[passivestar]

Is it difficult for you to make a side by side video? It might help the nontechnical to provide comments

If you mean to show the alpha behavior - it's very subtle and I'm not sure a lot of people would necessarily notice the difference in motion. The reason I did that alpha change is for cleaner ortho views, I wanted the perpendicular axes in ortho views to stay opaque. Before, if you look at the ortho picture on top you can notice that while Z is opaque, X and Y are half transparent, and with this PR axes only start getting transparent once they get past the 0 dot product point

The only issue I can notice is that with certain custom fonts (as shown above), the X/Y/Z labels can be slightly off-center. I'm not sure if much can be done about this. (For reference, this issue was already present before your PR.)

I noticed that too while testing at lower res (doesn't seem to be a problem at high dpi). I'm thinking it might be a problem with either imprecise char size calculation or how chars are rasterized or smth like that but I haven't dug that deep into the engine, only did what I could in the gizmo code

To give an example this is how "Y" is rasterized. As you can see it matches with the opaque pixels but on the left there are some transparent pixels that when viewed from the distance may make the char look unaligned. This is 200%, may get worse at 100%. I'm not sure if there's anything I can do about this. Whether it'll be perfectly centered or 1px to the left/right seems to be a matter of chance :D

[akien-mga]

The only issue I can notice is that with certain custom fonts (as shown above), the X/Y/Z labels can be slightly off-center. I'm not sure if much can be done about this. (For reference, this issue was already present before your PR.)

I noticed that too while testing at lower res (doesn't seem to be a problem at high dpi). I'm thinking it might be a problem with either imprecise char size calculation or how chars are rasterized or smth like that but I haven't dug that deep into the engine, only did what I could in the gizmo code

One option could be to replace the manual draw labels in editor font with a custom SVG for X, Y, Z well centered in the circle. There might still be issues depending on the scale used in the editor for scaling up/down the SVG, but at least we can ensure it's using the same font and metrics won't mess it up.

Alternatively, we could draw these labels with the default editor font regardless of custom fonts defined by the user.

[akien-mga]

Looks good to me. This is pretty low risk so should be fine to include in 4.3 despite the feature freeze.

[akien-mga]

Thanks!