volplay

volplay is a library for creating, manipulating and interacting with volumetric data. Focus of this library is clean, reference code. All computations carried out on CPU with minimal focus on parallelism.

Creating and Manipulating Signed Distance Fields

A signed distance field in volplay is represented by a hierarchy of volplay::SDFNode. Leaf nodes represent primitives such as spheres, boxes and planes. Intermediate nodes encapsulate functions on other nodes such as intersection, union, difference, repetition and transformation.

To start creating a signed distance field use volplay::make().

#include <volplay/volplay.h>

namespace vp = volplay;

vp::SDFNodePtr u = vp::make()
    .join()
        .sphere().radius(0.5)
        .transform().translate(vp::Vector(5, 0, 0))
            .sphere().radius(0.2)
        .end()
    .end();

Here the join() member method creates a new volplay::SDFUnion. Its children are an volplay::SDFSphere node with radius 0.5 and a transformed volplay::SDFSphere with radius 0.2. The complete graph is shown below. The domain specific language chosen comes quite close to a natural language one would prefer to create hierarchies.

Ray-tracing Signed Distance Fields

The namespace volplay::rendering provides methods to directly visualize the signed distance field by ray-tracing it. Besides the signed distance field itself, rendering can make use of material properties of individual nodes. The ray-tracing pipeline is implemented in volplay::rendering::Renderer and involves the following other entities:

• A scene volplay::SDFNode to be rendered. Each node can be attributed with materials volplay::rendering::Material
• A camera volplay::rendering::Camera defining the viewpoint and lens parameters.
• A set of lights volplay::rendering::Lights.
• A set of image generators volplay::rendering::ImageGenerator encapsulating the types of images to be generated.

The example example_raytracer.cpp demonstrates rendering of two spheres resting on a plane. When executed the following set of images is generated. From left to right: Blinn-Phong shaded image with shadows and materials applied, depth image of scene and heat image of scene showing hotspots of raytracing.

Surface Reconstruction from Signed Distance Fields

The namespace volplay::surface provides methods to explicitly generate a polygonal mesh from an iso-surface in a signed distance field. Currently an implementation of Dual Contouring volplay::surface::DualContouring is available. Results can be exported in .OFF format. Here is an example

#include <volplay/volplay.h>

namespace vp = volplay;
namespace vps = volplay::surface;

vp::SDFNodePtr scene = vp::make()
    .difference()
        .join()
            .sphere().radius(1)
            .transform().translate(vp::Vector(0.8f, 0.8f, 0.8f))
                .sphere().radius(1)
            .end()
        .end()
        .plane().normal(vp::Vector::UnitZ())
    .end();

vps::DualContouring dc;
dc.setLowerBounds(vp::Vector(-2,-2,-2));
dc.setUpperBounds(vp::Vector(2,2,2));
dc.setResolution(vp::Vector::Constant(vp::S(0.05)));
vps::IndexedSurface surface = dc.compute(scene);

vps::OFFExport off; 
off.exportSurface("surface.off", surface);

This produces the surface below. One of the big benefits of Dual Contouring is that it naturally preserves sharp features.

References

http://aka-san.halcy.de/distance_fields_prefinal.pdf http://www.iquilezles.org/www/articles/distfunctions/distfunctions.htm http://www.ronaldperry.org/SIG2006Course_FriskenPerryDistFields.pdf http://cg.ibds.kit.edu/downloads/IntModelingSDF.pdf http://iquilezles.org/www/material/nvscene2008/rwwtt.pdf http://elib.uni-stuttgart.de/opus/volltexte/2010/5229/pdf/DIP_2970.pdf http://csokavar.hu/raytrace/imm6392.pdf http://9bitscience.blogspot.co.at/2013/07/raymarching-distance-fields_14.html http://www.arcsynthesis.org/gltut/Illumination/Tut12%20Monitors%20and%20Gamma.html http://www.cambridgeincolour.com/tutorials/gamma-correction.htm