Optimizing 3D Assets
In Qt Quick 3D, you can import 3D models and scenes that are created using 3D modeling tools. To see the supported file formats, see the Balsam tool documentation.
3D Content Overview
In this section, you will find an overview of creating and exporting 3D assets to use in Qt Quick 3D. For more detailed information, see the section for the specific 3D modeling tool that you are using.
Geometry
- Use Triangles Qt Quick 3D only supports geometry exported as triangles. Many 3D modeling tools provide an option to triangulate meshes during export, while you must do it manually before the export with some tools.
If models are not triangulated on export, they will be triangulated on import which may lead to less than optimal results. If models are exported using primitives that can not be triangulated, then those primitives will be
ignored on import.
- Handling Pivot Points Each DCC (Digital Content Creation) tool handles pivot points differently. In Qt Quick 3D, there is only one pivot per object and it is used as the origin for position, scale, and rotation
operations. In your DCC tool, feel free to adjust the position of a 3D model's pivot as needed. However, extreme edits to pivots in 3D modeling tools can cause problems upon import, especially if animated. This difference is
often manifested as a difference in the position or orientation of an object. As an artist, you can prevent these kinds of problems by only making simple edits to your pivot points. Keep your pivot points to the default
(world) alignment, don't scale them, and make sure that if you have multiple pivots (Maya) that they are all at the same location in space.
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Transformation As you would expect you can import full 3D transform information including position, rotation, scale, and pivot. Qt Quick 3D can handle right-handed coordinate systems, Y-up and quaternion based
rotation. The principal limitation in this area is pivot points. As discussed above, only simple edits to pivot points are supported.
Most DCC tools allow artists to freeze transformations, and we highly recommend performing this operation before importing mesh data into Qt Quick 3D. This operation ensures that the imported mesh has clean
transformation data and no arbitrary transformation values, which can be confusing or an impediment to your work.
Note: After freezing transforms, you may have to reposition the pivot point in some DCC tools.
Animations
Animations are supported on imported attribute. Position, rotation, scale, and pivot can all be animated. An example of our advanced support for animations would be a hierarchy of items, rotated simultaneously on an
arbitrary axis.
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Time-based Animations By default, in many 3D modeling tools, when you are creating keyframes you are associating them with certain frame numbers. This is great in the film industry where frame rates are constant, but
this technique necessarily has problems in applications where the frame rate may not be rock solid. Our solution to this problem is to express the locations of keyframes in time values instead of frame numbers. That way, if
you say "this logo animation plays for 3 seconds", we can guarantee that it plays for 3 seconds. If you express it in frames, "this logo animation plays for 180 frames", it may play for 3 seconds if you're
getting 60 fps, but if you drop to 30 fps the animation is going to go much slower.
Luckily, accounting for this is relatively simple. Many 3D modeling tools default to a setting of 24 frames per second, so your keyframes are translated at that ratio. If you want a keyframe at one second, put it on
frame 24. Two seconds? Frame 48, and so on. Usually, configurable frame rates are offered, and the frame rate setting should be respected upon import. It's also worthwhile to note that for example Maya, starts at frame one
by default. If you have a keyframe at frame one, the time for that keyframe is 1/24 or 0.041 seconds. It may be a good idea to go into your Maya animation settings and start your animations at frame 0, or 0/24 = 0
seconds.
- Different Animation Systems 3D modeling tools offer highly complex and specialized animation systems. We recommend using Qt Quick 3D's animation capabilities whenever practical. This helps in keeping the mesh
information clean on import.
- Baking Animations You must bake all animations before exporting.
Materials
For materials, material slot IDs and UV layouts are imported.
- Textures Images applied to different material IDs are imported. We recommend using
.png or compressed image formats.
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Using Powers of Two Texture Map Pixel Dimensions As is the case with most real-time graphics, texture maps run optimally when their pixel dimensions are set to powers of two. See image dimensions for more detailed information on images.
Lights and Cameras
Lights and cameras can be imported.
- Lights For light, directional, point, and spot lights with position, rotation, light color, and the attenuation factors properties will be imported.
- Cameras Perspective and orthographic cameras can be imported. Position, and rotation properties are imported, as well as start and end clipping. For perspective cameras, field of view is also imported.
Other
- Axis Conversion Qt Quick 3D uses a Y-up coordinate system, ensure that
Up Axis is set to Y.
- Hierarchy Qt Quick 3D supports importing hierarchical information. Hierarchies of arbitrary depth are supported, including grouped nodes. Hierarchical transforms are applied as expected.
