# Tag Info

13

Radiosity does not account for specular reflections (i.e. it only handles diffuse reflections). Whitted's ray-tracing only considers glossy or diffuse reflection, possibly mirror-reflected. And finally, Kajiya's path-tracing is the most general one [2], handling any number of diffuse, glossy and specular reflections. So I think it depends on what you means ...

8

While it may not entirely clear from the formulation of the wikipedia article, the author raises an important issue: In contrast to many other approaches, Radiosity needs to perform its calculations for all existing patches, not only the visible ones. It is not the limitation to diffuse surfaces that increases the involved computations, but the fact that ...

4

Radiosity, by definition, handles only the diffuse component. You cannot 'limit' Radiosity to diffuse, because it already is handling just that diffuse component (remember - the diffuse lighting is just one (albeit popular) application of the energy distribution). So, you just misinterpreted the quote. Also, contrary to popular misconception, you do not ...

4

It's only more intense if $d\phi$ remains constant. However, for light source with constant luminance the flux is a function of $cos(\theta)$, i.e. depends on the light's angle of incidence with the surface and cancels out the term. Edit: I feel the need to clarify this a bit because you say that: thus light is somehow more "intense" It's not that the "...

4

Yes, you should set the lightmap texture as the render target and use UV-coordinates as vertex position coordinates in your shader to bake lighting into lightmaps. This way you'll write the baked lighting data of triangles into the correct lightmap texels that are used for rendering the triangles on the screen. The UV-map should be unique and no triangles ...

3

Radiosity is a way to calculate diffuse GI, i.e. every surface is assumed to be Lambertian surface without specular component. In the radiosity algorithm you split surfaces into small patches and calculate "form factor" between two patches, which defines how much energy is transferred from one patch to the other. The form factor between patches is ...

3

Your main idea is more or less correct. The cosine hidden in the projected area measure $dA^\perp = dA\cos(θ)$ compensates the weakening of irradiance due to incident angle (the Lambert's cosine law). This makes radiance independent from the incident angle. My guess is that the main motivation was to make it more practical to work with. The cosine in the ...

2

You need to convert luminous flux (lumens, $lm$) to luminance ($\frac{lm}{m^2sr}$) for the rendering equation. For that you need to know the physical properties of the light source. For example luminance $L$ of spherical light source of radius $r$ radiating over $4\pi$ solid angle and luminous flux $\phi$ has luminance: $$L = \frac{\phi}{4\pi^2r^2}$$ I think ...

2

How should I define the radiance, if I have a directional light, for example the sun? The radiance in physics has different definitions in different books. I will use the definition with irradiance and radiant flux here. Imagine photons having some energy $Q$. Your radiant flux $\Phi$ is the amount of energy $Q$ (and therefore the amount of photons) per ...

1

The lightmap representation used in Valve's stuff, like any finite-storage representation of the surfaces response to light, is only approximate, and the error in the approximation is higher or lower in different scenarios. Since it doesn't store the light in a direction tangent to the surface (where it would be exactly zero), you don't get an exact zero ...

1

Remember radiance corresponds to a particular direction. When the equation is considering directions quasi parallel to the surface normal, the differential flux (the numerator) will typically be a much greater quantity than for grazing angles. The numerator is not remaining constant.

1

In the end, what I gleaned from the Valve paper, and what I found in an existing light mapper implementation, led me to the following conclusion: When performing my final global illumination integration, instead of using a cosine-weighted hemisphere of samples, use a uniform hemisphere of samples. For each sample, project the sample's direction on each of ...

1

Take a look at Valve's paper on combining Radiosity and Normal Mapping. It had a lot of useful insights. If I'm not mistaken, it looks to me like you're trying to compute normal mapping using the energy value at the texel that is a result of Radiosity - e.g. it came from all directions through almost-endless bumping around the room across thousands of ...

1

The sentence says it: radiosity precomputes an "image" for all potential viewpoints at the same time, i.e. it doesn't focus on just the rays that hit a particular observer. Hence there are naturally many more rays to consider, as you are actually rendering a multitude of views simultaneously. Whether the surfaces are specular or diffuse isn't really ...

1

Gobal illumination, radiosity, etc is not a mutually exclusive set with using a fill light to adjust the feeling. Sometimes the artist can do wonders with a few well placed lights. So yes they are used, each game and situation is different. Perhaps they are just going for a unrealistic mood or the artist wants to tweak the result a bit.

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