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[Paco]

After successfully loading textures, meshes, and setting up the transformation pipeline, the next step was obviously lights. I set a GU_DIFFUSE_AND_SPECULAR Point Light right next to my typical tessellated cube.

Global ambient seems to be used always.
Diffuse seems to work fine. The contribution from diffuse gets added to the ambient light based on distance.

Specular, however, is all over the place. I get streaks of specular light across my cube's faces, and the worst part: rotating the camera CHANGES the specular highlights, but moving the camera doesn't. That should never happen, since specular light is based on vertex normal, vector from vertex to light, and vector from camera position to vertex. Position should affect but orientation shouldn't, but I'm seeing the opposite.

The interesting bit is that specular highlights only seem to show when I'm roughly looking towards -Z. This made me think of D3D's obscure D3DRS_LOCALVIEWER flag, which does away with any Camera position and uses a (0,0,1) Halfway vector, but I never really played with that one.

I played around with the scaling of the world matrix (and the model's size) but no changes - that's a good sign, but I have ran out of ideas. In any case, specular does not get added on top of the texture, rather added to the diffuse and later modulated with the texture (i.e. the rasterizer doesn't get a separate specular interpolant), so it may be wiser to forget about it altogether, but I don't like unfinished business.

Any guru that can shed some (heh) light on this topic?

A somewhat unrelated curiosity: where do vertex normals come from if they aren't included in the vertex format? They seem to be (1, 0, 0) but I'm not 100% sure (tried with normal-less sprites).
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Paco

[Paco]

[holger]

try reg 0x5f, bits [9..8], light type.

[jsgf]

[jsgf]

[ector]

I can confirm that the specular is "LOCAL_VIEWER". I ran the lights sample on the real psp and the specular reflections in the ground really looks like local_viewer. I then implemented lighting in my experimental PSP emulator, using the local viewer approach, and arrived at an essentially identical image.
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http://www.dtek.chalmers.se/~tronic/PSPTexTool.zip Free texture converter for PSP with source. More to come.

[Paco]

Ok so the LOCAL VIEWER thing seems confirmed. My highlights currently seem to appear at the sides of the object, but never at the front, exactly the typical issue people comment on before they discover the switch and turn it on (it defaults to off in OpenGL, I think).

Now the remaining question is... Is localviewer compatible with a coordinate system in which the Z goes positive into the scene (your typical left-handed csys)? I am afraid it isn't, since the specular model uses a fixed vector for view-space vertex-to-eye (essentially -vertex, with vertex.z being positive in a left-handed system), and this fixed vector seems to be (0,0,1).

http://www.ibiblio.org/pub/packages/development/graphics/mesa/patches_to_1.2.3/src/light.c

shows how the source for Mesa doesn't even try to guess what kind of coordinate system is being used, and puts a (0,0,1) straight there. This is also suggested in the actual documentation for OpenGL (which is typically right-handed) and, interestingly, for Direct3D, which promotes left-handedness.

Time to go back and change all the maths for the system before it's too late. :(

Edit: yup, changed my projection matrix, vertex culling order and Z-buffer setup and the specular highlights come out correct now.
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Paco

[Paco]