30 votes
Accepted

Progressive Path Tracing with Explicit Light Sampling

There are multiple areas in path tracing that can be importance sampled. In addition, each of those areas can also use Multiple Importance Sampling, first proposed in Veach and Guibas's 1995 paper. To ...
RichieSams's user avatar
  • 3,782
20 votes
Accepted

Cause of shadow acne

Image 1: A bad case of shadow acne. (Synthetic and a bit exaggerated) Shadow acne is caused by the discrete nature of the shadow map. A shadow map is composed of samples, a surface is continuous. ...
joojaa's user avatar
  • 8,437
20 votes
Accepted

Difference between BVH and Octree/K-d trees

Well I researched quite a lot after that and this paper helped a lot. "Space Subdivision algorithms" by Macdonald 1988. So just summing what I understood. Some of them are obvious reasons but after ...
gallickgunner's user avatar
16 votes
Accepted

Raytracing: why are the spheres in the image below appear stretched?

Shapes appearing stretched in the periphery is a consequence of perspective projection. The wider the field of view (FOV) is, the stronger the stretching effect gets. To demonstrate the effect I ...
Julien Guertault's user avatar
15 votes

Rendering equation - why unsolvable directly?

I'm sadly not able to add a comment to the answer above (not enough reputation), so I will do it like this. I'd like to point out that what Dragonseel describes is simply an integral equation (...
Vanbus's user avatar
  • 304
15 votes

Path tracing the Cook-Torrance BRDF

I am posting this for anyone wondering about the confusion between the terms $\frac{1}{\pi}$ and $\frac{1}{4}$. The term $\frac{1}{\pi}$ is an error from the original Cook-Torrance reference. In ...
Samu's user avatar
  • 546
14 votes

How is Anti Aliasing Implemented in Ray Tracing?

Raxvan is completely right that "traditional" anti aliasing techniques will work in raytracing, including those that use information such as depth to do antialiasing. You could even do temporal anti ...
Alan Wolfe's user avatar
  • 7,801
13 votes
Accepted

What's the current state-of-the-art algorithm for ray-tracing height-fields?

For the current state-of-the-art, look for this paper: "Maximum Mipmaps for Fast, Accurate, and Scalable Dynamic Height Field Rendering", Tevs et al. 2008 The basic idea is to skip a lot of space by ...
Rama's user avatar
  • 146
13 votes

Rendering equation - why unsolvable directly?

The rendering equation is as follows: Now, the integral is over the sphere around the point $x$. You integrate over some attenuated light, incoming from every direction. But how much light comes in? ...
Dragonseel's user avatar
  • 1,810
13 votes
Accepted

How is Anti Aliasing Implemented in Ray Tracing?

I think it's safe to say that there are two different ways of doing AA in raytracing: 1: if you have the final image and the depth image it is possible to apply almost all existing techniques that ...
Raxvan's user avatar
  • 253
13 votes
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A recent approach for subsurface scattering

As mentioned in the comments, I would highly suggest starting with Full Volumetric Scattering. This is two fold: Since you are doing path tracing, adding volumetrics isn't super difficult. Fully ...
RichieSams's user avatar
  • 3,782
12 votes
Accepted

Anti-aliasing / Filtering in Ray Tracing

There is a great paper from 2006 on this topic, Filter Importance Sampling. They propose your method 2, study the properties, and come out generally in favor of it. They claim that this method gives ...
Nathan Reed's user avatar
12 votes
Accepted

Path tracing the Cook-Torrance BRDF

According to this paper, the $\frac{1}{\pi}$ in your $f_r$ should be $\frac{1}{4}$: $$ f_r = \frac{DFG}{4(n\cdot w_i)(n \cdot w_o)}, $$ so you would end up with $$ \frac{\pi}{2}L_i(p,w_k)\left(\frac{...
wolle's user avatar
  • 302
12 votes
Accepted

Mirror Reflections: Ray Tracing or Rasterisation?

There are a couple of special cases where mirror-like reflections can be rendered efficiently using rasterization techniques, and these are commonly used in games, although they don't work for the ...
Nathan Reed's user avatar
12 votes
Accepted

Does cosine weighted hemisphere sampling still require NdotL when calculating contribution for indirect light?

You always need to multiply by the cosine term indeed (that's part of the rendering equation). Though when you do indirect diffuse using ray-tracing and thus monte-carol integration (which is the most ...
user18490's user avatar
  • 656
12 votes
Accepted

How am I able to perform perspective projection without a near plane?

The near and far planes of a viewing frustum aren't needed for simple 3D→2D projection. What the near and far planes actually do, in a typical rasterizer setup, is define the range of values for the ...
Nathan Reed's user avatar
11 votes
Accepted

What effects does path tracing capture that recursive ray tracing does not?

Generally speaking, path tracing removes a number of assumptions that ray tracing makes. Ray tracing usually assumes that there is no indirect lighting (or that indirect lighting can be approximated ...
John Calsbeek's user avatar
11 votes
Accepted

Non Real Time Raytracing

Path tracing is the standard technique in non-realtime photorealistic rendering, and you should look specifically into bidirectional path tracing to get effects like caustics, which you can't really ...
JarkkoL's user avatar
  • 3,636
10 votes

How to raytrace Bezier surfaces?

is it a total pipe dream to hope to solve the Ray/Bezier-surface intersection algebraically Yes, it's a pipe dream. A bicubic Bezier patch is an algebraic surface of degree 18. To intersect a ray ...
bubba's user avatar
  • 348
10 votes

Cause of shadow acne

As an addition to the answer of joojaa: Using a bias to offset the shadow function does indeed solve the problem with shadow acne, but it can introduce an additional problem: Peter Panning As you see ...
Dragonseel's user avatar
  • 1,810
9 votes

Why does the 1/r² term appear with point sources?

The concept of a point source is an approximation. Physically, light sources are extended objects and emit light from every point on their surface; but when you're far enough away (i.e. the distance ...
Nathan Reed's user avatar
9 votes
Accepted

Ray casting in fan configuration produces point cloud with curvature, how to eliminate curvature?

The direction vectors start at +15 degrees on the YZ plane, and continue in increments of -2 degrees down to -15. There's your problem—by generating the rays that way, you're doing something more ...
Nathan Reed's user avatar
9 votes
Accepted

Area Lights in Path Tracing

I'm going to provide the simple/naive/brute force answer to this question, which does work, and gives accurate results. There are better answers however, which make the rendering converge faster with ...
Alan Wolfe's user avatar
  • 7,801
8 votes
Accepted

Should ideal specular multiply light colour with material colour?

What "ideal" means in this context is that there is no divergence in the direction of light reflection vectors (i.e. no roughness) but that they are all considered to be perfect reflections from an ...
JarkkoL's user avatar
  • 3,636
8 votes
Accepted

Ray Tracing Shadows: The Shadow Line Artifact

The shadow terminator problem (as it's also known) is still something of an open problem in ray-tracing. As you say, disabling self-shadowing is not a very good workaround, because non-convex meshes ...
Dan Hulme's user avatar
  • 6,810
8 votes
Accepted

Subsurface Scattering Without Rays?

There are lots of ways to fake SSS with greater or lesser fidelity. A few recent-ish methods: Screen-space blurring of object lighting (described in detail here) Using “interior” ambient-occlusion ...
Noah Witherspoon's user avatar
8 votes
Accepted

Can a glass plate act like a lens?

The box.obj file has no vertex normals, and by default Mitsuba will generate smooth normals for OBJ files that don't specify their own normals. This creates the ...
Nathan Reed's user avatar
8 votes

Grainy image in my simple ray tracer

It's likely due to shadow rays. When the light source is exactly on the plane of the wall, a shadow ray traced to it may or may not be found to intersect the wall before it reaches the light. The ...
Nathan Reed's user avatar
8 votes
Accepted

Should direct illumination and path tracers render the same scene equally bright?

The results that you are getting, are not correct. More specifically, your direct illumination ray tracer is not correct. When limiting a path tracer's bounces to only allow for any direct ...
bram0101's user avatar
  • 1,605

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