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Light transformations

Started by GeneralQuery Oct 31, 2011 at 9:44 PM 3 replies 850+ views

Original Post

Oct 31, 2011 at 9:44 PM

When lighting in object space, I transform the world space light position into object space by multiplying by the object's inverse world matrix. However, I read that when lighting in view space, you should transform the world space light position by only the rotational part of the view matrix. Why is this?

Jason Z

325

Jason Z

Oct 31, 2011 at 9:55 PM

Where did you hear that? Unless there is a special context behind that statement, I don't think it makes any sense to leave out the translation component (or scaling for that matter) when you are moving a position from world space to object space...

MJP

Mod

2,105

MJP

Oct 31, 2011 at 11:28 PM

Typically the only time you want to ignore the translation component of a matrix is when applying it to a direction vector, such as a normal. For positions you usually apply the translation. For a light position transformed by a view matrix, you definitely want to apply the translation.

GeneralQuery

Author

GeneralQuery

Nov 1, 2011 at 12:12 AM

Ah yes, that makes perfect sense. I did wonder why that would be the case, in my head it did not fit with my understanding of transformations into different spaces. Thanks for clearing that up, guys.

Scoob Droolins

Nov 1, 2011 at 1:19 AM

If it's a directional light (like the sun), you could just do a rotate-only instead of a full translate/rotate. This would save you from having to renormalize the light vector.

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