Tuesday, November 15, 2016

Tiled Terrain Update and Screenshots

The past few weeks I haven't been working on 3DWorld as much as usual, partly because I'm preparing to move to a new house and have been distracted with other things. The work I've been doing with 3DWorld is mostly related to minor improvements to visuals and optimizations for generating and rendering large outdoor scenes. I've made many small improvements to tiled terrain mode. Each individual change has only a minor impact on the scene, but together they do improve visual quality considerably. I'll discuss some of these changes and show new screenshots in this blog post.

Terrain Normal Maps

I've modified the terrain texturing system in 3DWorld to support separate detail normal maps for each terrain texture layer (sand, dirt, grass, rock, and snow). I found suitable normal map textures online for all layers except for grass, for which I couldn't find a texture that I liked. The grass texture layer is drawn with a fine field of triangle grass blades, which cover up the mesh so that the normal map isn't visible anyway. This adds many more texture lookups inside the terrain fragment shader, but my GeForce GTX 1070 shows almost no change in frame rate. I'm sure this feature hurts frame rates on older/slower/cheaper cards though.

Here are some screenshots of steep normal mapped hills showing all of the texture layers. I have disabled trees and water so that the terrain is fully visible. Grass and plants are left enabled.

A different normal map is assigned to each of the five ground texture layers that make up this steep hillside.

Terrain normal maps viewed from a different angle.

Normal maps applied to rocky mountains, viewed from above from a distance. The terrain appears to have very high detail.

These new normal maps add a good deal of complexity and realism to the scene with little cost. They make the mesh appear to be highly detailed, almost for free.

Leafy Plants

After reviewing several other terrain generation and rendering systems written by other people, I decided that 3DWorld's terrain needs more detailed ground cover. The area on the ground under the trees was too bare, even with all of the grass. I had this as a todo list item for maybe a year before I finally got around to adding another plant type. Here they are. I call them "leafy plants".

View of a grassy beach with some new procedurally generated leafy plants.

There are four different types of leafy plants that appear at different elevations, including one type that is underwater. They're created by applying tree leaf textures to spherical sections that are scaled to an ellipsoid shape. This gives the leaves a smooth curve, rather than having them be boring flat polygons. However, they are also more expensive to create and draw than other types of plants that use single polygons (quads) for leaves. I had to use a sparse distribution of leafy plants to keep performance under control. These new plants seem to blend in well with the other plants, grass, and flowers. They're just one more component to the 3DWorld ground cover, meant to fill the gaps between the trees.

Improved Pine Tree Branch Randomization

I made another pass at procedural generation of pine tree branch sizes, positions, and orientations. This new approach uses more random numbers to produce a less symmetric branch coverage, which removes some of the repeating patterns found in my previous pine tree forests. Each branch is rotated a small random amount around the vertical (z) axis of the tree, and shifted a random distance up or down in z as well. This makes the trees look more natural and realistic, especially when shadows are enabled. Keep in mind that every tree in this scene is unique. Instancing is only used to save memory when there are more than ~100K trees.

Pine tree forest on the mountain, with high detail shadows and more randomized tree branch placement.

Note that in this screenshot, and the images from the following sections, I've increased the high resolution shadow map distance. This improves shadow map quality, at the expense of increased GPU memory usage and slightly longer tile generation time. My current GPU has 8GB of memory, so spending a few hundred MB on improved shadows seems like a good decision. The shadow map smoothly transitions to a lower resolution baked mesh shadow at about half the max view distance. It's possible to push the shadow maps out to the full view distance, at the loss of a smooth frame rate.

Large Numbers of Trees

I decided to test the limits of how many trees I could get onscreen at once. I optimized some of the tree placement and pine tree leaf/branch generation code so that it scaled better to many trees. At this point the number of trees is probably limited by the time taken to send the vertex data from the CPU to the GPU. I'm not sure how to profile this, or optimize it further.

Here is a scene showing pine trees on a terrain with tall mountains that extends into the distance.

Tall mountains covered with pine trees. The terrain height has been scaled and zoomed out to produce sharp peaks.

This is a scene showing tens of thousands of deciduous trees drawn using 50 unique generated tree models. 3DWorld can create hundreds of unique tree models with an 8GB graphics card. However, this increases initial scene load time, and I prefer to keep loading under a few seconds. [Update: I can see duplicate trees in this screenshot, so I increased the number of unique trees to 100 and tweaked the type randomization code to remove them.]

Distant, foggy mountains with trees.

Here I have decreased tree size and increased tree density in the config text file. The active area of the scene contains 4-5M pine trees, and around 1M trees are visible in these next two screenshots. This scene renders at a consistent 78 FPS, mostly independent of which way the camera is facing.

Maximum tree density: Pine trees cover every dry patch of land. This scene contains at least 1M trees and renders at 78 FPS. The white spot on the distance is a patch of bare snow that is too steep for trees.

A million pine trees near sunset. Note the complex cloud lighting and the dark tree shadows.

Fall Leaves

Yes, it's that time of year again. The trees outside my house are turning bright colors (mostly red) and covering the sidewalk with leaves. Once again I'm showing off screenshots of colorful fall trees in 3DWorld. I have tree leaf color parameters tied into the editing UI this time, which allows me to change colors interactively using the arrow keys on the keyboard. Here are two screenshots showing fall deciduous trees in a variety of colors.

Trees with colorful fall leaves spread across the rocky ground.

More fall leaves with grass, flowers, and plants.

I'll continue to work on trees in tiled terrain mode. Maybe I can add winter trees that have no leaves and are covered with snow in time for Christmas. Of course, we don't get snow here in San Jose, CA.