gi3dviewer

README

GoGi 3D Viewer

This viewer allows you to open and view 3D objects, using the supported object file formats.

Currently, this is just:

• .obj -- Wavefront .obj file format -- widely supported. The Blender app exports quads which work well. For other apps, it is a good idea to export triangles or quads -- e.g., SketchUp has an option to export triangles and that should be selected.

Installation

The usual Go install procedure will work -- see Install for details.

Camera Navigation

The default camera navigation controls allow you to move around the scene. To get the keyboard versions to work, you need to set the focus on the 3D scene, which can be done by clicking into it or tabbing or using the arrow keys as usual in GoGi. These are the different modes of movement:

• Orbit moves the camera around in a sphere, with it always pointing at the same Target location (the origin by default).

• Pan moves the camera and the target together along the horizontal / vertical direction defined by the current viewing plane (the plane of the screen).

• AxisPan moves the camera and the target along the world horizontal / vertical (X, Y) axes.

• TargetPan moves the target in world horizontal / vertical / depth (X, Y, Z) axes, and tells the camera to LookAt that new target location.

Here are the default bindings (you can see the gi3d.Scene NavEvents method in gi3d/scene.go for how it works -- set the NoNav flag to true to disable it and you can write a different mapping by either making a new version of the Scene type or wrapping the Scene in a custom outer type that handles all the keyboard mappings.

• Mouse or keyboard arrows with no modifiers does Orbit rotation
• Shift+Mouse / Shift+Arrow = Pan
• Ctrl+Mouse / Alt+Arrow = AxisPan
• Alt+Mouse / Ctrl+Arrow = TargetPan
• + / - = Zoom in / out along current view axis.
• Alt++ / Alt+- = TargetPan along depth Z axis
• Space = reset to the Defaults initial camera location (+10 in Z, Up is +Y, and looking at origin)

Inspect and Edit the Scene

Use the standard GoGi Ctrl+Alt+I shortcut to invoke the GoGi Editor and you can click on the scene and other elements of the scenegraph and edit / inspect them. Toolbar actions have been enabled on everything to call useful methods, so you can pretty much configure the entire scene dynamically on the fly.

Scenegraph Structure

• Scene is the root node of the 3D scenegraph.

  • Camera is a field on the Scene that has all the current camera settings. By default the camera does a naturalistic Perspective projection, but you can enable Orthographic by ticking the Ortho button -- you will generally need to reduce the Far plane value to be able to see anything -- the Ortho projection shows you the entire scene within those two planes, and it scales accordingly to be able to fit everything.

  • Lights contain the lighting parameters for the scene -- if you don't have any lights, everything will be dark!

    • Ambient lights contribute generic lighting to every surface uniformly -- usually have this at a low level to represent scattered light that has bounced around everywhere.
    • Dir ectional lights represent a distant light-source like the sun, with effectively parallel rays -- the position of the light determines its direction by pointing back from there to the origin -- think of it as the location of the sun. Only the normal direction value is used so the magnitude of the values doesn't matter.
    • Point lights have a specific position and radiate light uniformly in all directions from that point, with both a linear and quadratic decay term.
    • Spot lights are the most sophisticated lights, with both a position and direction, and an angular cutoff so light only spreads out in a cone, with appropriate decay factors.

  • Meshes are the library of Mesh shapes that can be used in the scene. These provide the triangle-based surfaces used to define shapes. The shape.go code provides the basic geometric primitives such as Box, Sphere, Cylinder, etc, and you can load mesh shapes from standard .obj files as exported by almost all 3D rendering programs. You can also write code to generate your own custom / dynamic shapes, as we do with the NetView in the emergent neural network simulation system.

  • Textures are the library of Texture files that define more complex colored surfaces for objects. These can be loaded from standard image files.

  • Solids are the Children of the Scene, and actually determine the content of the 3D scene. Each Solid has a Mesh field with the name of the mesh that defines its shape, and a Mat field that determines its material properties (Color, Texture, etc). In addition, each Solid has its own Pose field that determines its position, scale and orientation within the scene. Because each Solid is a ki.Ki tree node, it can contain other scene elements as its Children -- they will inherit the Pose settings of the parent (and so-on up the tree -- all poses are cumulative) but not automatically any material settings. You can call CopyMatToChildren if you want to apply the current materials to the children nodes. And use Style parameters to set these according to node name or Class name.

  • Groups can be used to apply Pose settings to a set of Children that are all grouped together (e.g., a multi-part complex object can be moved together etc by putting a set of Solids into a Group)