SHEnvironmentMap - Revision history

Patapom at 12:36, 12 January 2011

2011-01-12T12:36:37Z

2011-01-12T12:33:52Z

2011-01-11T13:21:32Z

2011-01-11T13:10:23Z

2011-01-11T13:09:38Z

2011-01-04T12:40:12Z

2011-01-04T02:38:30Z

2011-01-04T02:34:51Z

2011-01-04T02:34:20Z

2011-01-04T02:33:32Z

← Older revision		Revision as of 12:36, 12 January 2011
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−	~~Interestingly enough, we~~ can move dynamic objects in the scene and they will be correctly occluded and receive color bleeding from their environment :	+	We can then move dynamic objects in the scene and they will be correctly occluded and receive color bleeding from their environment (unfortunately, the reverse is not true : colored objects won't bleed on the environment) (in this picture, only ambient and indirect lighting is shown and the indirect lighting has been boosted by a factor 3 to emphasize the color bleeding effect) :
	[[File:SHEnvMapExageratedIndirect.png]]		[[File:SHEnvMapExageratedIndirect.png]]

−	~~(In this picture, only ambient and indirect lighting is shown and the indirect lighting has been boosted by a factor 3 to emphasize the color bleeding effect)~~

@@ Line 135: / Line 135: @@
 This part is really simple.
-We render a screen quad and for every pixel :
+We render a screen quad and for every pixel in <u>screen space</u> :
 * Retrieve the world position and normal from the geometry buffers provided by our deferred renderer
-* Use the world position to retrieve the 9 SH coefficients from the SH Env Map calculated earlier
+* Use the world position to sample the 9 SH coefficients from the SH Env Map calculated earlier
 * Estimate the irradiance in the normal direction using the SH coefficients

@@ Line 113: / Line 113: @@
+  }
-Which can be viewed like this :
+See how the W and XYZ component are intertwined ? Each of them are multiplied together using the SH triple product. A good implementation can be found in [http://research.microsoft.com/en-us/um/people/johnsny/papers/shtriple_fixed.pdf Snyder's Paper] that needs "only" 120 multiplications and 74 additions (twice that as we're doing 2 products).
-[[File:SHEnvMapCompositing.png|800px]]
+That may seem a lot but don't forget we're only doing this on vertices of a very sparse environment mesh. The results are later interpolated by the card and each pixel is written "as is" (no further processing is needed in the pixel shader).
-See how the W and XYZ component are intertwined ? Each of them are multiplied together using the SH triple product. A good implementation can be found in [http://research.microsoft.com/en-us/um/people/johnsny/papers/shtriple_fixed.pdf Snyder's Paper] that needs "only" 120 multiplications and 74 additions (twice that as we're doing 2 products).
+Basically, the process can be viewed like this :
-That may seem a lot but don't forget we're only doing this on vertices of a very sparse environment mesh. The results are later interpolated by the card and each pixel is written "as is" (no further processing is needed in the pixel shader).
+[[File:SHEnvMapCompositing.png|800px]]
@@ Line 176: / Line 176: @@
 [[File:SHEnvMapFinalRendering.png]]

@@ Line 115: / Line 115: @@
 Which can be viewed like this :
-[[File:SHEnvMapCompositing.png]]
+[[File:SHEnvMapCompositing.png|800px]]
 See how the W and XYZ component are intertwined ? Each of them are multiplied together using the SH triple product. A good implementation can be found in [http://research.microsoft.com/en-us/um/people/johnsny/papers/shtriple_fixed.pdf Snyder's Paper] that needs "only" 120 multiplications and 74 additions (twice that as we're doing 2 products).

@@ Line 112: / Line 112: @@
     return Result;
+  }
 See how the W and XYZ component are intertwined ? Each of them are multiplied together using the SH triple product. A good implementation can be found in [http://research.microsoft.com/en-us/um/people/johnsny/papers/shtriple_fixed.pdf Snyder's Paper] that needs "only" 120 multiplications and 74 additions (twice that as we're doing 2 products).

← Older revision		Revision as of 12:40, 4 January 2011
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−	No matter what you choose though, you'll need at most 7 targets/3D slices since you're writing 93=27 SH components that can be packed in 74=28 ~~RGBA textures~~.	+	No matter what you choose though, you'll need at most 7 targets/3D slices since you're writing 93=27 SH components that can be packed in 7 RGBA textures (as there is room for 74=28 coefficients).

@@ Line 59: / Line 59: @@
 === SH Environment Map ===
-My first idea was to render the environment mesh into a texture viewed from above and let the graphic card interpolate the SH nodes by itself as it is, after all, its speciality.
+My first idea was to render the environment mesh into a texture viewed from above and let the graphic card interpolate the SH nodes by itself (and it's quite good at it I heard).
 I decided to create a vertex format that took a 3D position, 9 SH coefficients and triangulate my SH environment nodes into a mesh that I would "somehow" render in a texture. I needed to render the pixels the camera can see, so the only portion of the SH environment mesh I needed was some quad that bounded the 2D projection of the camera frustum, as seen in the figure below.

← Older revision		Revision as of 02:34, 4 January 2011
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	[[File:SHEnvNetwork.png]]		[[File:SHEnvNetwork.png]]

−	The game map seen from above with the network of SH environment nodes.	+	''The game map seen from above with the network of SH environment nodes''.

← Older revision		Revision as of 02:34, 4 January 2011
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	[[File:SHEnvNetwork.png]]		[[File:SHEnvNetwork.png]]
−	The game map seen from above with the SH environment nodes ~~network~~.	+
		+	The game map seen from above with the network of SH environment nodes.

@@ Line 15: / Line 15: @@
 == Let's put some ambience ==
-That's when I decided to re-use my old "ambient SH" trick I wrote a few years ago. The idea was to pre-compute some SH for the environment at different places in the game map, and to evaluate the irradiance for each object depending on its position in the network, as shown in the figure below.
+That's when I decided to re-use my old "ambient SH" trick I wrote a few years ago. The idea was to pre-compute some SH for the environment at different places in 2D in the game map, and to evaluate the irradiance for each object depending on its position in the network, as shown in the figure below.
 [[File:SHEnvNetwork.png]]
 The algorithm was something like :