3D Preview for Windows Preview

The following images show screenshots of the 3D Preview (along with renderings of the same view) running on Windows XP. It will be included in the next release of Terragen for Windows. It's been part of Terragen for Macintosh for some time. The 3D Preview uses OpenGL and lets you move around the terrain in realtime, giving you a better appreciation for the shape of the terrain and making it easier to select interesting vantage points. It also helps give an impression of the atmosphere and clouds. It's particularly useful for helping to detect the "black horizon" problem when the sky cover size isn't large enough.

The 3D Preview is basically intended as a preview to help you position the camera, and as such it does not yet give a representation of the surface map or water, and the clouds and sky are not quite as they look when rendered. Nevertheless, the 3D Preview is very useful and makes a big difference to the way you use Terragen. We do intend to improve these other aspects of the 3D Preview as time allows.

You can interact with the 3D Preview using the keyboard and mouse. The keys, although not yet user configurable, should suit both right and left handed people and be quite familiar to those who've used first person type 3D games. There are options for normal, large and very small movements, which help with precision positioning. You can move in all the directions you would expect if you were walking over the terrain. The mouse can also be used to look around, and with a reasonably fast machine you can use the mouse to look around while moving ( mouselook ). The 3D Preview also updates when you move the camera in one of the 2D previews in the other windows, or when you change the camera settings in places like the Rendering Control window.

Even though the 3D Preview does benefit from a fast graphics card, it's highly scalable and is usable even on very slow machines without graphics cards. It's still usefully interactive on a 166 MHz machine without 3D acceleration. It is also designed to use as little memory as possible. It was deliberately designed this way to be useful to the widest number of people. You have a lot of control over its configuration. You can choose either high, medium or low quality defaults or you can configure the settings for each different terrain size. That way if you have a mid range computer you can set it up to use full detail for small terrains and low quality with no texturing on the largest terrains. The following two screenshots show the configuration dialogs for the 3D Preview. These screenshots are from Terragen Mac on OS X, but the Windows version will be very similar.

Here are the screenshots of the 3D Preview in action, along with renderings for comparison. Please note that the renderings are programmer art at its finest, I didn't have much time to tweak surface maps.

This is a shot of the crater of Mt. St. Helens. As you can see the surface texturing in the 3D Preview is quite basic, just a grass and rock texture blended according to slope. The main purpose of the texturing is simply to give you a better idea of the slope of the terrain. If you compare the screenshot with the rendered image the shadows are quite accurate, they're generated using the same method used during rendering.

The clouds are a little hard to see in this image. The clouds are the correct basic colour, but their appearance changes a good deal during rendering due to the lighting effects. The overall shape of the clouds is quite close though.

This image shows some water and the 3D Preview minimap. The minimap helps to give you an idea of where you are on the terrain, particularly useful if you can't see the 2D terrain/camera previews in other windows, or you've chosen to turn live updating of those off. The minimap can be toggled on and off. You can't yet click on it to position the camera, but that is being considered.

The clouds are a lighter colour in this image, and are easier to see. Although the clouds are low resolution you will notice they're very similar in shape to those in the rendered image.

This image shows another advantage of the 3D Preview. It can optionally change its aspect ratio to match that of the final rendered image. When using different aspect ratios it really helps to give you a better idea of your scene, as the render preview only uses a 4:3 aspect ratio.

This image also uses one of the Martian atmosphere files included with Terragen, just to show how things look with unusual sky colours. Again the colours of the clouds are quite different, due to lighting effects in the rendered image, but the shape is accurate.

---

16:9 aspect ratio, with wide angle zoom

This image shows another scene with a 16:9 aspect ratio, but this time the zoom is set to a very wide angle (very low zoom setting).

This is a bit of a rundown on the technology, such as it is, behind the 3D Preview for those who are interested. The 3D Preview uses OpenGL, primarily because it's cross platform. The terrain is a progressively refined split only ROAM, with distance based progressive level of detail. Although ROAM is quite out of fashion for terrain engines these days, with preference going to techniques which can take better advantage of the ability of newer graphics card to deal with large batches of vertices, ROAM is very well suited in this case for a couple of reasons. It is quite efficient with memory. Everything is based off the heightfield already stored in memory, and only a relatively small amount of memory ( not counting textures and the lightmap ) is needed for a pool of nodes for the ROAM. Most other techniques would require duplication of the terrain data in some form, which increases memory use. Although this is less of an issue on newer machines, it's important for older ones. Many techniques also rely on vertex data being stored in VRAM for good performance, and if you have a graphics card with very little VRAM or no graphics card at all, then you're out of luck. Another benefit of ROAM is that it's very scalable and it's easy to dynamically adjust the number of triangles being rendered. This helps to maintain a good level of interactivity with a useful level of detail even on very slow machines without 3D acceleration.

The ROAM is continuously refined until the target number of triangles rendered per frame is met. The terrain is divided into a number of patches which are frustum culled. Patches which are below water and never visible are not used. As mentioned above, progressive level of detail based on distance is utilised. These techniques help to ensure that the maximum number of triangles per frame are available for detail where it matters, closer to the camera. The 3D Preview is very good at maintaining correct silhouettes of distant terrain even on the largest terrains, helping to give you an accurate impression of your scene.

17/Sep/2004, Jo Meder