Here's a little breakdown and implementation details of the real-time painted world in my last demo - JG.
Here's the video:
The "painted" effect wasn't planned. Originally I only had an idea to render a natural scenery of a certain kind, and I wasn't ready to spend a whole lot of time on it. It became clear to me, a "realistic" approach won't work, resulting in either very mediocre visuals (due to engine limitations and the complexity of real-time vegetation modeling), or a whole year of trying to catch up with Crysis. So it wasn't the way.
What I really wanted is to preserve the atmosphere, the feeling, avoiding ruining it with technical limitations.
So I have to render something very complex without killing myself and players' computers, what do I do? Intuition said: "bake everything". I recalled seeing outdoor 3D scans: even with bad geometry (or even as point clouds), they still looked quite convincing, thanks to right colors being in right places, with all nice and filtered real-life lighting already integrated into everything. Unfortunately, the time of year was absolutely the opposite of desired, so I wasn't able to try my mad photogrammetry skills.
But what if we "scan" a realistic offline 3D scene? Vue surfaced in my memory as something that movie/exterior visualization folks use to produce nice renderings of nature. I had no idea what to expect from it, but I tried.
I took a sample scene, rendered it from several viewpoints and put those into Agisoft Photoscan to reconstruct some approximate geometry with baked lighting. And... alas, no luck. Complex vegetation structure and anti-aliasing weren't the best traits for shape reconstruction.
Then it hit me. What does Agisoft do? It generates depth maps, then a point cloud out of multiple depths. But I can render a depth map right in Vue, so why do I need to reconstruct?
Being familiar with deferred rendering and depth->position conversion, I was able to create a point cloud out of Vue renderings. Not quite easily, though: Vue's depth appeared to have some non-conventional encoding. Luckily, I finally found an answer to it.
And from this:
With some MaxScript magic, we get this:
Which is a solid single textured mesh.
Hard part is over, now I only needed to repeat the process until I get a relatively hole-free scene. Finally it's time to have some fun with shaders :)
Each projected pixel acts as a camera-facing quad, textured with one of those stroke textures:
Almost. There was a bug in my atlas reading code, so some quads only had a fraction of stroke on them. However, it actually looked better, than the intended version, so I left the bug. It's now a feature :)
Quads size obviously depends on depth, becoming larger with distance. It was quite important to not mix together small and large quads, so I had to carefully choose viewpoints.
Test scene looked promising, so I started to work on the one I wanted:
I made the house, fence and terrain from scratch. Plants were taken from various existing packs. Then I assembled the final composition out of this stuff. I lost count on the amount of renderings I had to do to cover all playable area:
Some had to be photoshopped a little to get rid of dark spots and to add more colors:
At first, I had troubles with getting the lighting right, so I had a lot of these black spots to fix, then I actually managed to tune it better. Final scene is actually a mix of different approaches, because I didn't have the time to re-render everything with different settings, and because it actually looked less monotonous.
Some early screenshots:
At this moment I also had stroke direction set up properly, what was pretty important, as uniform strokes had very unnatural look. At first, I tried to generate stroke direction procedurally (similar to how you generate normal map from a height map), but it wasn't sufficient. It was obvious to me how some strokes must lay, for example, I really wanted vertical strokes for the grass and fence strokes following the shape of the fence. Not being able to direct it with purely procedural approach, I simply decided to manually paint stroke direction in additional textures. Final version uses manual direction near the camera and procedural for distant quads. Here're some examples of direction maps:
To be honest, painting vectors with colors in Photoshop wasn't the most exciting thing to do, but still, it was the quickest way I could think of.
The difference was quite obvious. Here's uniform direction on the left, changed on the right:
And this is it. The point cloud nature of the scene also allowed me to have some fun in the ending part, making quads behave like a surreal particle system. All motion was done in vertex shader.
I hope it was somewhat interesting to read, at least I'll not forget the technique myself :)
Recently I was asked how to fill inevitable holes between quads. The way I did here is simple - I just used very rough underlying geometry: