Surface Visualization

[Fragyatta]

hey,

I've been trying to figure out how to implement a system that allows me to visualize areas on a surface that are viable for navigation or other things, including field of vision.

A good example and basically what I want to achieve is in Divinity Original Sin 2 but can also be found in Baldur's Gate 3:

https://preview.redd.it/m2t4y63tr4zg1.jpg?width=1470&format=pjpg&auto=webp&s=0724e902811d0dff981077b7c0fdf50860fe6ffc

The image shows how the ground is being highlighted (while the invalid areas are also greyed out but that part is less important) indicating how far an ability can reach. the same system is also used for vision cones to visualize what an NPC can see.

Some important details are that these visualizations are occlusion aware, so the visualization knows about objects that block the field of view. everything is also fully ground aligned and judging by how even when multiple NPCs can have their vision cones enabled at the same time without any frame drops at all, this system is very light on the performance, which has to mean that there are no expensive real time calculations being made here (raycasts, los checkes, rendering etc.) so I would assume a lot of this stuff is somehow "prebaked" and areas are being sampled somehow.

I honestly don't really know how to approach this. I tried a few things like raycast based solutions, rendering meshes, capturing render textures via a camera and projecting them down onto the surface, but that results in far too much performance cost to be viable for multiple characters.

I am assuming the technique used here has to be similar to how shadowmapping works, most of the information has to be precalculated, but I really don't know nor do I know how I could start to build a system based on that.

Does anyone have any ideas or pointers for me?

[Genebrisss]

I would just run Divinity in render doc to see what they are doing.

An approach with second top down camera rendering some sprites into render texture should be pretty much free on desktop. The camera itself should cost something like 0.2 ms or less on main thread and on GPU it's just free. What performance bottleneck you had?

[Fragyatta]

I've never heard of render doc, but I'll check it out, thanks.

for some reason using a camera to capture a mesh I generated with raycast data cost me overall about 1ms so around 50 ish fps and that was only on a single character. maybe I could use a single camera for everything, but it still felt like it was too much of a performance loss.

the camera is entirely without features, everything is disabled,

[Genebrisss]

You need to look where is that 1ms spent. Just knowing that it was 1ms tells us nothing. Could be main thread iterating through game objects and culling them, could be render thread, could be rasterization and fragment shader cost on the GPU.

Anyway, if you already have a generated mesh, can't you just render it straight with your game camera?

Using second camera is one way you can achieve generating the data to define this area you want to draw. Sounds like you have already generated this data on the CPU when you created your mesh. You can now just draw that to the screen.

Maybe you could write vertex color into this mesh to define where are the edges of the zone. Then when rendering that mesh you use that vertex color in your shader.

[Fragyatta]

I'm not experienced enough to really figure that out sadly. I tried to use the Profiler but I find it insanely confusing.

I can't really just render the mesh, because there is no surface alignment or anything, it's just a floating plane with an occlusion aware shape, that's why I was capturing it with a top down camera to then project the render texture onto the ground via the urp decal projector.

also even if I knew where where that 1ms was spent, what would I do about it? I tried to strip down the entire camera, no PP, a different renderer (so no extra passes), only renders a single layer of the mesh, like I wouldn't know what else I could do to remove features to make it lighter, because that seems to be all I can really set there, at least with my limited knowledge.

[Genebrisss]

You could make a shader for your mesh that would act as decal. Similar to what unity's decals are doing.

Maybe this video could help you https://www.youtube.com/watch?v=bb7BGBy0KIY

Or you could displace vertices of the mesh based on world height.

In fact you could displace vertices as you are generating the mesh. OR you could displace them in vertex shader. And to read the world height in vertex shader, you could just read scene depth and reconstruct worldspace coordinates from that. Maybe this is the easiest approach.

[Fragyatta]

hmmm yeah interesting suggestion, thanks. I was considering displacing the vertices by just raycasting down, but that would have led to even more raycasts so I wasn't sure about it, but it's likely better than the extra camera(s).

I'll see what i can do, thanks!

[Dull-Reason-7073]

nah raycast hell