Qt3DOpenVDBRenderer

Visualize OpenVDB Grids (Level Sets) in Qt3D

Adds Qt3D GeometryRenderer-Components for OpenVDB Grids. Moreover a Qml-OpenVDB vdb-reader exists. The compiled library can be used by a program, that does not need openvdb-headers.

Features

• fast, parallelized surface generation
• surface is rendered as dense pointcloud
• three methods for surface generation, varying in speed and quality
• normal generation
• surfel shader

Qml Types

• QOpenVDBGrid: Wraps openvdb::GridBase
• QOpenVDBGridReader: Reads the first grid of a vdb file.
• QOpenVDBGridGeometry: Can be used as Qt3DRender::QGeometry to render a LevelSet/FloatGrid using Qt3DRender::GeometryRenderer

You can choose a OpenVDBGridPointSurfaceGeometry::generationMethod

• OpenVDBGridPointSurfaceGeometry.MarchingCubesCenter for optimal adaption to the real surface
• OpenVDBGridPointSurfaceGeometry.VoxelCenter for fast surface generation with a voxel-like look
• OpenVDBGridPointSurfaceGeometry.Surrounding for debugging purposes. This needs a bit more work for coloring inside and outside voxels
• future: In addition to OpenVDBGridPointSurfaceGeometry, there might be OpenVDBGridMeshSurfaceGeometry introduced

Usage

Register Qml-Types:

qmlRegisterType<QOpenVDBGridReader>("openvdb", 1, 0, "OpenVDBReader");
qmlRegisterType<QOpenVDBGrid>("openvdb", 1, 0, "OpenVDBGrid");
qmlRegisterType<QOpenVDBGridPointSurfaceGeometry>("openvdb", 1, 0, "OpenVDBGridPointSurfaceGeometry");

Read OpenVDB Grid in Qml:

OpenVDBReader {
    id: ovdbReader
    filename: "data/bunny.vdb"
}

At the moment OpenVDB Grids are rendered as dense pointclouds. This seems to be the fastest/nices way of visualizing OpenVDB Levelset, since this is the method Houdini uses. Make sure your Entity and Framegraph is configured correctly to render points.

GeometryRenderer {
    id: bunnyRendererMarchingCubes
    geometry: OpenVDBGridPointSurfaceGeometry {
        grid: ovdbReader.grid
        generationMethod: OpenVDBGridPointSurfaceGeometry.MarchingCubesCenter
    }
    primitiveType: GeometryRenderer.Points
}

The layer is needed to identify points in the framegraph:

FrameGraph {
  (...)
    LayerFilter {
        layers: pointLayer
        StateSet {
            renderStates: [
                PointSize { specification: PointSize.Programmable },
                DepthTest { func: DepthTest.Less },
                DepthMask { mask: true }
            ]
        }
    }
  (...)
}

Instead of PerVertexColorMaterial, a custom shader can be used to enable programmable per vertex point size. Choose a Pointsize near the size of a voxel to simulate a surface. Example comes with two shaders.

property Material materialPoint: Material {
    effect: Effect {
        techniques: Technique {
            renderPasses: RenderPass {
                shaderProgram: ShaderProgram {
                    vertexShaderCode: loadSource("qrc:/shader/pointcloud.vert")
                    fragmentShaderCode: loadSource("qrc:/shader/pointcloud.frag")
                }
            }
        }
    }
    parameters: Parameter { name: "pointSize"; value: 0.1 }
}