Volumetric Rendering

with a AABBox

We define a customized solid similar to aabox, VAABox which perform ray marching along the primary ray and attenuation along the shadow ray for the rays passing through the aabox space. VAABox have similar characteristics as that of a AABox but also includes the functionality of computing density across its volume. Operations of ray-marching and computation of in-scattering rays is performmed by volume integrator defined for it. This way we are able to localize the effects generated by volume rendering (eg fog, fire, ..) rather than performing volume rendering for the whole object space. Other shapes like sphere, cones and any other quadrics with a definite volume can be used based on the requirements of the effects required.

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Performance Gains

Using OpenMP and BVH to turn your ray tracer into a monstor

We took utmost care to use as less memory as possible for the BVH node which only uses a float array of length 6 and three integers. The float array defines the 6 corners of the bounding box. We did not use the class BBox to save memory. We only store one index of the child node as we have defined the tree heirarchy such that the right node is always adjecent to the left node as we define the entire tree using std::unique_ptr. The decision to go left or right is based on the split axis. We have used OpemMP as much as possible to parallelize all for loops in BVH.

We also use OpenMP to parallelize our renderer.cpp. The performance gains were phenomenal after parallelizing the code. We used time functionality in linux to measure our run times and we saw an approximately 12x gain in performance. The parallelization is dynamic in renderer, meaning each pixel has a separate thread instead of a row of pixels getting a thread. There are still several places in the framework that can be parallelized but it requires a deeper understanding of memory management and OpenMP. We couldn't implement OpenMP in places where we use recursion but it will be interesting to check the final performance of the framework after optimization.

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Environment Map

Adding a tinge of horizon to make it romantic

Environment mappers are primarily used in rendering to make your scene look filled where there are no primitives present to avoid emptiness. We have defined the environment map to take the local texture coordinates of the image and project it on a flat surface. Our intention is to show a starry night in the backdrop but getting the resolution and mapping right proved to be a challenge. The image turned out to be a bit stretched in earlier iterations because our field of view and using higher resolution images improved the quality of background.

We also added a horizon effect with white color in the volume integrator. We achieve this by calulating the angle the ray makes with the Z-axis. We scale the angle appropriately and perform a weighted averaging of colors. Although it is not a perfect replica of raman scattering effect but it does the job of looking like a horizon. See above for a comparision between using horizon and not using horizon.

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Special Primitives

Smooth triangles for the win!

Using smooth triangles gave us a smoother surface compared to using non smooth triangles. It saved us using more number of primitives. This simple concept or peturbing the normal is highly useful in obtaining smooth surfaces. The above two images are taken from an earlier iteration of our scene. The topmost is with smooth triangle and the bottom one is without. Once can clearly tell the difference smooth triangles make.

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Textures and Materials

We have used several textures and materials in our scene to make it vibrant. We are aimiing to make all the textures and material in our scene get a wooden feel and outlook.

Floor

The floor uses perlin noise texture and fuzzy mirror material. Effects of perlin noise from the floor combine material and the simulated fog from volume rendering can be observed on the floor due to the fuzzy mirror material present on it.

Chess Board

Chess board is separated into three obj files : white squares, black squares, board edges. Material for white squares is a combination of flat material with appropriate imagetexture and mirror. Material for black squares and board edges is same, a combination of flat material and mirror. Mirror provides a smooth and glossy appearance and soft shadows of the pieces also enhance the appearance.

Chess pieces

Both white and black pieces have a material combination of cook torrance, phong, and mirror. In case of cook torrance material specular and diffuse texture are interchanged for white & black pieces. We tried using glass for white pieces particularly but found its appearance was highly dependent on the environment map. Also glass pieces placed in close proximity tend to lose the aesthetic value expected from the material.

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Lights

And then God said, let there be light

We have used two point lights in the scene near the white pieces.

Directional lights

Our scene lighting has the theme of sunrise and sunset designed in such a way that the colors emitted by the lights create a tinge of mystery. We have two directional lights on opposite sides of the chess board giving the scene a combined effect of sunrise and sunset. This is prominently visible on the black pieces on the left. The left side of the head has a whitish shine while the right side has a sunset coloured tinge.

Spotlight

We have added a spotlight shining on the queen of black pieces because there are several pieces in that area and we wanted to highlight the piece.

Area light

We have created an area light by sampling uniformly on a quad which is responsible for the soft shadows in the scene. We have also used a spherical area light by sampling uniformly on the surface of a sphere.

Volume Rendering lights

As the spotlights are used to illuminate the chess pieces so they had to be placed near them, this near proximity to the VAABox makes the intensity of the simulated fog quite high and they appaer to be white blobs. And as the distance in LightHit object for directional light is always FLT_MAX it never contributes to intnsity of the simulated fog. So we decided to use separate group of ligts for computation of in scattering in volume rendering.

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