Disc gizmo performance drop

[vlazed]

Compared to arrow gizmos, disc gizmo drawing causes an 80% FPS drop (from 300 to 60 FPS). This was tested on the 64-bit branch with vanilla ragdolls and seems to be introduced with the December 2025 patch

I will hold this thread up to comment+update it with more details

[vlazed]

Disc drawing functions internally uses DrawQuad to form a disc. Each disc is made up of 32 points, and there are 3 discs, which total 96 points. In addition, there are multiple functions called to orient/project the points to the screen.

DrawQuad by itself also calls some functions to set the position and texture coordinates at each point. These may be cpu instructions

This amount of effort on the cpu may be causing the performance drops.

Penol told me rotations discs were always costly with performance. I speculate the December updates may have amplified the cost, so this may a path to read into

[vlazed]

On the other hand, I noticed that the disc drawing could be simplified by moving the disc drawing on the shader side completely: instead of drawing 32 points, I can draw 4 points (a single quad) and make the disc entirely on a pixel shader, following some intuitions by RNDX to reduce aliasing. Maybe this could help with performance

Not sure about moving all gizmo drawing entirely on the shader side. Since disc gizmos are relatively easier to draw, it might be better to compare the performance before making that decision entirely

[vlazed]

My above comment assumes "Full drawn discs" is checked. If this isn't the case, there would need to be a method to only draw parts of the disc that are close to us.

One method I have in mind uses a depth render target to make transparent the farthest parts of the disc. This depth would have to be relative to the disc itself, so for instance the disc does not become invisible when the player is too faraway

I'm also thinking of somehow interpolating pixel values from one vertex to the other using a vertex shader, where the interpolation function uses eye position. I'm unsure if this requires the quad to be subdivided or if I need to choose the degree (quadratic, cubic, bezier) which interpolation take place