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mrowle1
18th June 1999, 01:08
Ok, I guess I'll have to explain each of these claims..

1) Multiple Light Sources - G400
The only reason that EMBM can handle multiple light sources is because it
uses the environment map (which represents a render of the whole scene
including all light sources). It is equivalent to saying lets take a
picture of the whole scene with the lights around and then map it to a
texture. Naturally you'll have the light sources on the final texture.
DOT3 is not using environment mapping but just the regular per-pixel bump
mapping, so it won't calculate all the lights but just one. IF you include
an environment map, then you will have the multiple light sources on your
texture.

2) Polychromatic Light Color - G400
Again, the bump map is created by the environment map (which is in color) so
the bump map will be in color. Again, the P3 can use a blend of the bump
map ( monochrome ) and the environment map to achieve polychromatic light
color. Keep in mind that the G400 is blending 3 textures whereas the P3 is
only blending 2 since it isn't using an environment map.

3) Light FallOff Control - G400
I'm not sure what they mean by this.

4) Per Pixel Luminance control - G400
I think they are trying to say that the P3 doesn't use specular highlights
for the bump. This is false since specular highlights can be calculated per
pixel once the interpolated normal has been calculated.

5) Distortion - G400
Agreed.

6) How about moving light sources? Since the G400 can't build the
environment map on the fly, moving a light source in front of the bump
mapped texture will yield no changing specular highlight. This is an
important issue since most games use dynamic lights. This is a big fall
back of using environment maps.

I'm not trying to say that EMBM is not a good feature at all. It is. But
programming with the original DOT3 bump mapping has allowed me to really
understand what is going on underneath the hood.


--Marlin

R0M
18th June 1999, 03:05
1) Agreed but with an environment map it will also need an additional pass.

2) With Environment-mapping it requires 3 textures also: Bump-Map (as you stated), Base Map and Environment Map.

6) The Environmemt map can be built on the fly, that's how the moving lightsource in the <a href='ftp://ftp.matrox.com/pub/mga/devrel/powerrender.zip'>Power Render</A> demo works.

Regards,

------------------
"The opinions or comments expressed by me do not necessary reflect those of Matrox Graphics Inc."


[This message has been edited by R0M (edited 06-18-99).]

Arron
18th June 1999, 07:55
To anyone who is joining this in the middle, Marlin and I have thrown a couple of emails at each other trying to get this one sorted.

The basic premise is, which is better, Dot3 or EMBM? The 1. to 6. comes from the matrox site http://www.matrox.com/g400/feat_story/may99/bump_charts.htm

OK, on with the story/discussion (Ant, please chuck anybody who flames out of here, if you would be so kind).

1. Dot3 only supports a single light source and monchromatic at that. Traditional Dot3 takes an average of multiple light sources and turns them into a single light source. As for the G400 side of the tale, EMBM does not have to use an environment map from the screen, it can use a light map just like Dot3 does if you want it to.

2. The above means that in Dot3 you cannot have polychromatic light sources. The EMBM bumps will show different coloured shadows for different coloured lights from different directions.

3. Light fall off - you don't know what that means? Oh well, that makes two of us http://forums.gagames.com/forums/smile.gif

4. Now come on, luminance has nothing to do with specular lighting. I must admit though, I have no idea how they do it without a gloss map. Also, it is one of the few areas where I have serious reservations about the G400 and the EMBM technique.

5. Good, we both agree http://forums.gagames.com/forums/smile.gif

6. No, see R0M's answer. EMBM has to be able to build the environment map on the fly or the whole process would fall over. The Power Render demo is the living proof of this.

The ball is in your court http://forums.gagames.com/forums/wink.gif
Arron.

PS. Excuse the typpuing, just bought the cheapeset keyboerad I've ever ownerd.



[This message has been edited by Arron (edited 06-18-99).]

Arron
18th June 1999, 08:02
PPS. I'm pretty sure that Dot3 couldn't do this:
http://www.matrox.com/g400/press_room/artwork/media/images/expend1_on.jpg

Mind you, I have been out of the games business for a while, so forgive me if I'm wrong.

mrowle1
18th June 1999, 10:23
Arron,

1. Dot3 only supports a single light source and monchromatic at that. Traditional Dot3 takes an average of multiple light sources and turns them into a single light source. As for the G400 side of the tale, EMBM does not have to use an environment map from the screen, it can use a light map just like Dot3 does if you want it to.

True, but then you lose the environment mapped details.

2. The above means that in Dot3 you cannot have polychromatic light sources. The EMBM bumps will show different coloured shadows for different coloured lights from different directions.

Ok. So then what happens when the P3 implements EMBM?

3. Light fall off - you don't know what that means? Oh well, that makes two of us

Hehehe.

4. Now come on, luminance has nothing to do with specular lighting. I must admit though, I have no idea how they do it without a gloss map. Also, it is one of the few areas where I have serious reservations about the G400 and the EMBM technique.

The topic of luminance is sketchy at best. I am under the impression that the luminance of the texture deals with the overall brightness of the pixel.


6. No, see R0M's answer. EMBM has to be able to build the environment map on the fly or the whole process would fall over. The Power Render demo is the living proof of this.

Very well, that may explain the slowdown AND the 3rd pass. 1 to rerender the scene and store a EM in frame buffer memory, and the other pass to blend the created EM with the bump texture and a third pass to blend that to the base texture.


The ball is in your court now. http://forums.gagames.com/forums/smile.gif


--Marlin



------------------
************************************************** ********************
Marlin Rowley
Graphics and Visualization Research Programmer
Deparment of Computer Science
University of Maryland, Baltimore County
Email:mrowle1@gl.umbc.edu
ICQ:8921514
************************************************** ********************

LightHeaded
18th June 1999, 10:57
Gentlemen,

What you are discussing is way over my head, but I think I can help you on two small items:

Light Fall-Off-
Comes in 3 popular flavors....Inverse Square Law, Linear and None.

Inverse Square Law (the real thing)
Real light diminishes as an inverse function of the square of the distance. Assuming a surface that is normal to the source, the formula for illuminance (foot-candles or lux) is:

Footcandles= Intensity [candela] divided by distance [feet] squared.

or

Lux= Intensity [candela] divided by distance [meters] squared.

This is known as the Inverse Square Law. If the distance is doubled, the illuminance is quartered. A candela is the intesity of light in a given direction, irrespective of direction or distance. It can be determined by a formula which looks at the total lumen package of the source, analyzes the distribution pattern, and then derives the intensity relative to a steradian.

If the surface is not normal to the source, then the formula must be adapted to cosine correct for distance and angle. This is known as the Cosine-Cubed Law.

Linear Fall-Off

This is not how light really works, but is popular in some rendering applications where the real thing doesn't look spiffy enough. This is exactly what it says....the illuminance decreases linear to the distance.

None

Pretty obvious. 20 inches or 20 miles away...same illuminance on the surface. Sometimes called an "infinite" light.

Luminance and Specularity-
Not really related to each other, with the possible exception that direct ray luminance without diffusion is capable of producing highly specular reflections on "shiny" surfaces.

Also, a key point remember about light is that a "beam" of light" is not uniform in intensity across it's width. A classic "spot" light in many rendering programs has two benchmark angles....the BEAM angle where intensity drops to 50% of maximum and FIELD angle where intensity drops to 10% of maximum. This relationship is not linear as a usual rule....that is, the 50% diameter is not halfway out (much less) and the 10% diameter is even less farther out from the 50% diameter.

Finally, different colored lighting from multiple sources and directions not only should produce shadows of their complement but also interference blends at overlaps. If the surface is specular, then the lighting behaves much differently in terms of color than if it is diffuse.

I don't know if this is even remotely helpful to your discussion....I just thought I would throw it out. Butt in...shoot off mouth...then I leave.

Cheers to you !



------------------
Paul Luntsford, LC
PLA Designs, Inc. Theatre and Lighting Consultants
NT4, AOpenAX6BC, P3-500, 100MHzFSB,256MB SDRAM(PC100),MillG200AGP/16MB SGRAM





[This message has been edited by LightHeaded (edited 06-18-99).]

Arron
19th June 1999, 03:12
Blimey, I think we just entered the Twilight Zone! Warning! Propeller-Heads only! http://forums.gagames.com/forums/smile.gif

Anyway, back to the numbers...

1. True, you would lose the environment map, but that just puts you back where Dot3 is.

2. 3D Labs have stated that they have stopped all work on EMBM for Permedia3. We may never have a proper answer http://forums.gagames.com/forums/frown.gif

3. Thanks for the details on Light Drop Off, Paul. For those of a less technical nature, it means the further away a light is, the less it reflects from a surface. Glad we sorted that one out (see Lightheaded's full answer in the previous post for a full explanation), bottle-caps of valour all round http://forums.gagames.com/forums/smile.gif

4. Luminance in 3D graphics is just whether a surface is shiny or matt. I still don't understand how Matrox have implemented this on a per pixel basis without a Gloss Map (a bitmap that has a value for the 'glossiness' of each pixel/texel). So far, all of the demos I have seen look far too glossy which is why I have reservations about EMBM. Mind you, in Dot3 everything is the same glossiness, unless you have a gloss map which would mean another texture to process.
===========
Phew! Time to pause for breath! By the way, I'm definitely interested in seeing the Permedia3, but have a horrible feeling that it's going to be a bit of a disappointment. Some of the performance figures on the 3D Labs site just don't add up and they haven't published any worthwhile benchmark figures, only obscure ones. Then there are other details like the fact that Permedia3 takes two clock cycles for trilinear filtering. I hope my fears are not well founded.

Anyway, let the verbal tennis continue http://forums.gagames.com/forums/smile.gif

Arron.

PS. Does anyone have a definitive answer as to whether the graphic in the link that I posted above would be possible in Dot3?

CraziFuzzy
19th June 1999, 06:55
ok... luminance is NOT how shiny a surface is, but how much a surface shines.... dang that sounds stupid... let me eplain. Lumanance is how much light a surface gives off. while specularity, or glossiness, is how mych a surface reflects light... A glow in the dark poster, has luminance, while a well waxed floor has glossiness..

mrowle1
21st June 1999, 15:00
Arron,

I am probably going to buy the Permedia3. Benchmarks are not my main concern. The two benefits that the P3 have over the G400 are significant enough for me that I must choose the P3. Granted, the G400 will be the king as far as fillrate and raw bandwidth are concerned, but I'm not really looking for a card that can do 30fps at 1280x1024 (although that is quite nice).

So what advantages does a programmer see that will lead him to purchase the P3 over the famous G400?

1) OpenGL ICD STABLE NT drivers! 3dlabs has proven to make awesome drivers and I simply can't pass up that for running my 3d applications like Maya and Lightwave.

2) Virtual Texturing. Believe it or not, this will become extremely important in future games and software. Why? The ability to do volume rendering. Without doing some kind of virtual texturing or compression, 32MB of RAM is just not enough to hold 3d volume data.

Lastly, two issues that may need to be addressed. P3 may take 2 passes for trilinear filtering because its texturing pipeline can't do the filtering in one pass. The pipeline is definitely designed to do bump-mapping in one pass (regarding the specs). And the other thing is luminance is the brightness of the object itself (without calculating any light sources). I just looked it up in my text. http://forums.gagames.com/forums/smile.gif

I'll let you know if the P3 is worthy of gaming though. I suspect it definitely won't be in the same category as the G400 in speed, but I think that the P3 has the best features of any 3d chipset.


--Marlin

------------------
************************************************** ********************
Marlin Rowley
Graphics and Visualization Research Programmer
Deparment of Computer Science
University of Maryland, Baltimore County
Email:mrowle1@gl.umbc.edu
ICQ:8921514
************************************************** ********************

Franck
21st June 1999, 18:07
I'll have both of them in my case for a while... Eh eh... http://forums.gagames.com/forums/wink.gif

I suspect mrowle1's expectations shall reveal true. The Permedia3 will certainly find its place in my graphic station at work, while the G400Max will give me hours of pleasure at home... (Though the dual-head feature could be quite nice here, cause two graphic cards in Win98... pfff!!!)

Nice, this Dot3/Embm topic! You guys enlighten me further I would have expected!

watahiro
21st June 1999, 21:03
Check this out.....

http://www.pvr-net.com/ubb/NonCGI/Forum3/HTML/000027.html