CODEWITHSUNDEEP
openglgraphics
McLovin
McLovin

Reputation: 3417

BRDFs in real time graphics

I'm reading a book called Real Time Rendering (3rd edition) and the author expresses the BRDF function for non-area light sources:

img

I don't understand.

  1. What's the difference between irradiance and radiance? English isn't my first language and dictionaries fail me.

  2. "... is the irradiance of a light source measured in a plane perpendicular to the light direction vector l " can someone explain this? How can the light quantity be measured in a plane?

  3. I followed basic OpenGL books and tutorials and I never worked with these kind of stuff. Radiance and irradiance were never introduced in the Shaders. Is this concept really needed?

Upvotes: 1

Views: 188

Answers (1)

MuertoExcobito
MuertoExcobito

Reputation: 10039

  1. Irradiance is power onto a surface, per unit area. Radiance is the amount of power, per unit area, at a given solid angle. If you think about them in terms of the units they are measured in (W/m^2 and W/(st*m^2) from Wikipedia), it becomes easier to understand.

  2. It's not 'light quantity', it's power. It's essentially how much power the light is delivering to the plane, if the ray of light hits it directly.

  3. None of this is required at all to write a shader. BRDFs are lighting models, used to try and mimic physical properties of materials. Obviously, they are greatly simplified from how materials in the real world work. Otherwise, a shader program wouldn't have enough time to actually calculate them. A shader can be as simple as outputting a constant color - it doesn't necessarily need to do anything related to the physical world.

Upvotes: 1

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