Texture warping

[Noxious Ninja]

Well, I just got into PSX emulation, and I must say, ePSXe looks much nicer than a real PSX.

But I have one problem. Whenever a texture is viewed from an angle, it usually gets skewed. When it is viewed head-on, it is fine. Is it just me, or the emu? I've got a Voodoo Banshee and Lewpy's Glide plugin 1.35. I've tried other plugins as well, and it seems to do it on all of them.

[fivefeet8]

Post a screenshot and lets see what your talking about..

Originally posted by The Khan Artist
Well, I just got into PSX emulation, and I must say, ePSXe looks much nicer than a real PSX.

But I have one problem. Whenever a texture is viewed from an angle, it usually gets skewed. When it is viewed head-on, it is fine. Is it just me, or the emu? I've got a Voodoo Banshee and Lewpy's Glide plugin 1.35. I've tried other plugins as well, and it seems to do it on all of them.

a real psx does it as well...psx doesnt have perspective correction. The reason you notice that better on pc is because the screen is much clearer/sharper.

[Shadow Lady]

Originally posted by Samor


a real psx does it as well...psx doesnt have perspective correction. The reason you notice that better on pc is because the screen is much clearer/sharper.

and that is why some people prefer to play the emu in a TV whit their export card ^^

[Noxious Ninja]

Here's it straight:

[Noxious Ninja]

And skewed:

[Noxious Ninja]

So that would be entirely the fault of the GFX plugin, right?

Since HLE is all about making things look better, I think this should be 'fixed'. I for one wouldn't complain.

And I don't have a real PSX, I'm more of a Nintendo guy. I just rent games to play.

[Kane]

It's like samor says, the playstation doesn't have perspective correction, and because of the way ePSXe is programmed, it can't add that feature. The only way to do it is High Level emulation, and that is, as far as I am aware, even more complex than the current method, and you would end up with lower overall compatibility - like Ultra HLE, some games would work 100% most will have glitches which make it unplayable

[Noxious Ninja]

So perspective correction is/would be the task of the main emulator?

I thought ePSXe was a high-level emulator... or is it just the hardware gfx plugins which are high-level?

[Kane]

I think ifit were HLE like most n64 emus, it would need an ini file or something to tell it how to use each game...

I'm not sure, but I remember Pete Burnet, or it may have been Lewpy, talking about this. They said it would be rather fun to get in to HLE. I'm gonna sound like I'm losing my memory here, but I think they were talking about whether or notT&L could be put into the plugins

As I understand it, HLE is like wrapping (Glide wrappers, sort of thing)

[liquid]

HLE is High Level Emulation, which has nothing to do with the graphics or sounds. It has to do with the accuracy of the emulation of a particular CPU. Basically if an instruction can be executed on the host computer's CPU, then there is no need to emulate that instruction, thereby optimizing the speed of the emulation. however, accuracy is sacraficed since the instruction was never actually emulated. This is what you call High Level Emulation.

Originally posted by The Khan Artist
So perspective correction is/would be the task of the main emulator?

I thought ePSXe was a high-level emulator... or is it just the hardware gfx plugins which are high-level?

from what I gathered from all the technical talk, perspective correction would only be possible if you could somehow change something in the game itself....and no emulator does that. The filters and extra's you see are all kind of add-ons. The actual game cant be altered and that would be required for perspective correction.

[Kane]

Surely though, if you had an HLE PSX emu, the emu would just send the equivilent of 'draw a texture on this polygon' to the graphics plugin, and the plugin could do what it liked with it

[Noxious Ninja]

To quote Lewpy's plugin:
"A 'DMA Chain' is the standard method of how the PSX CPU transfers primitives to the GPU. It is a long linked list of primitives, to be drawn in order."

So the CPU sends the 3D commands to the GPU. The plugin converts them to, in this case, Glide3 commands, and feigns the proper responses to the rest of the system, a perfect example of HLE. But how do the textures get drawn? That's what I wanna know. Maybe I should go read some tech docs...

Edit: just noticed Lod Kane's post. That's exactly what I'm trying to say.

[Kane]

You may find this educational, I got it from som PSX tech docs

Primitives.
A basic figure which the GPU can draw is called a primitive, and it can draw the following:

· Polygon
The GPU can draw 3 point and 4 point polygons. Each point of the polygon specifies a point in the frame buffer. The polygon can be also be gourad shaded. The correct order of vertices for 4 point polygons is as follows

1 2

3 4

A 4 point polygon is processed internally as two 3 point polygons. also note when drawing a polygon the GPU will not draw the right most and bottom edge. So a (0,0)-(32,32) rectangle will actually be drawn as (0,0)-(31,31). Make sure adjoining polygons have the same coordinates if you want them to touch each other!.

· Polygon with texture
A primitive of this type is the same as above, except that a texture is applied. Each vertex of the polygon maps to a point on a texture page in the frame buffer. The polygon can be gourad shaded.
Because a 4 point polygon is processed internally as two 3 point polygons, texture mapping is also done independently for both halves. This has some annoying consequences.

This is where it is

[Pete Bernert]

To do perspective correction, ATI's True Form, real hardware T&L and other fancy stuff the plugin would need the depth info (z-coord) of the polygon points. But all depth infos are calculated internally by the game (usually using GTE commands), and the gpu knows nothing about em.

If psx games would use a standard library for doing the 3d calculations, it would be possible to hook in the libraries, and do some HLE like the current N64 emus are doing it, but most psx games are accessing the psx hardware directly to get more speed, therefore that's not possible, too (and, to be honest: such library HLE for bypassing the real hardware emulation is an hack, nothing more, nothing less... speed will be better that way, sure, but many compatibility issues will show up).

Well, a psx emu team could analyze exactly how a certain game is calculating the coords, and extract the extra informations... but be aware that this would only work with exactly THIS game, the next one would be totally different.

[Kane]

Basically you would end up with a bleemcast effect: 1 Game 1 Emu. Ok.

[Cyberman]

HLE is a hack.
If you noticed Ultra HLE has a large INI file for settings for individual games.
For the PSX you would need a different setup for each game OR you would have to scan the code loaded in during dynamic REC for GTE opcodes etc. In otherwords it would be a real pain.

I suppose setting up an algorythm system for each game could work. However it would require people to experiment with each PSX game out there.

The N64 is much easier to look for these things since it's media is just a ROM image. The PSX is an interesting mix of audio videa and executable code on a disk that's 720 Megs in size.. I think this is one of the big pitfalls.

Deadalus takes about 30 seconds to find the HLE opcodes for a simple game (mario64). Imagine how long it would take when loading a new executable on the PSX? Consider that FF7 has a different program to run the battles as it does to explore the world.. etc. You have a huge performance hit each time

Cyb

[Noxious Ninja]

Originally posted by Lord Kane
Basically you would end up with a bleemcast effect: 1 Game 1 Emu. Ok.

Maybe after ePSXe is otherwise perfect... or when I learn C++ & PSX emulation tech stuff.

[Noxious Ninja]

Oh, I also tried with VGS, and yeah, it does occur, but, like Samor said, it's just not as noticeably because of the lower res.

Oh, well. I'm still sticking to ePSXe, because it's much faster for me then VGS.