Model does not blend with ground color when opacity is less than 100%.

[malortie]

Context

When 'Show Ground' is enabled and when the opacity of the model is less than 100%, the region occupied by the model appears to blend with the background color instead of blending with the ground color.

Tested with

Software: Half-Life Asset Manager
Version: 1.0.0
OS: Microsoft Windows 10 Home

Steps to reproduce

1. Launch Half-Life Asset Manager
2. Load a model e.g. scientist.mdl
3. In 'Model Display', check 'Show Ground'
4. Rotate the camera in a way the model covers a significant portion of the ground
5. Set 'Opacity' to a low value e.g. 10%

Expected behavior: The rendered model color should blend with the ground color. Actual behavior: The rendered model color blends with the background color.

[SamVanheer]

It's probably happening because the ground is drawn after the model. I'll need to double check the order that everything is drawn in.

[SamVanheer]

This will need a fair amount of refactoring to turn every object in the scene into its own distinct thing that can be depth sorted for proper rendering.

[SamVanheer]

I've mostly eliminated this problem but it still happens when the camera is at certain angles. I suppose it can be eliminated at least in this case by checking which quad vertex is furthest from the camera and using that for depth sorting.

[SamVanheer]

Using the furthest vertex breaks transparency when viewed from under the ground.

[SamVanheer]

I've looked into this and it's more complicated to fix than i hoped for. The solution to this problem is to use an order-independent transparency implementation but that's an advanced technique that requires relatively new hardware and graphics API functionality.

See https://learnopengl.com/Guest-Articles/2020/OIT/Introduction and the second page found linked in the sidebar which notes:

The only caveat is we need to write our code in OpenGL ^4.0 to be able to use blending to multiple render targets (e.g. utilizing glBlendFunci).

I've tried switching to additive blending but that breaks the opacity setting and causes affected meshes to render with a glow like additive in-game does.

The system requirements would be raised too high to be acceptable right now so i can't fully fix this problem.

I did fix a bug that caused the render order to change depending on camera angles, so it behaves like it used to in HLMV.

[malortie]

Given this isn't critical, I'll close the issue.

This can always be revisited later if there's ever a need for it.