N64 3-Point Texture Filtering in mupen64plus-libretro

The Nintendo 64 console used a lot of weird hardware that contributed to its distinct look. For example, N64s used bilinear filtering when scaling some textures, similar to how modern GPUs handle texture resizing, but instead of using 4 sampling points like modern hardware, the N64 only used 3 (current texel, upper-left and bottom-right). This caused textures to have a distinctive, hexagonal "rupee" shape:

Image taken by TrekkiesUnite118 on the Sega-16 forums; see the texture pattern on the wall.

When emulating an N64, if you use modern 4-sample bilinear filtering, those textures don't render properly, which can lead to ugly artifacts, like the jagged texture under these stairs in Kakariko Village:

Way back in 2010, there was a discussion on the devmaster forums about reproducing this 3-point sampling in software with some great screenshots and code samples. Then, a couple of years later, ArthurCarvalho posted an HLSL shader that performed the same function on the Emutalk forums.

Skip to 2014 and my friend aliaspider, author of the awesome GTU shader and the guy responsible for porting RetroArch to the PSP (among many other things), ported this HLSL code to GLSL and plopped it into the rendering code for the libretro fork of mupen64plus, where it is applied on a per-texture basis. This clears up many of the texture artifacts typical of N64 emulation and provides that familiar, pointy-textured look:

To my knowledge, no other N64 emulators have implemented this texture filtering option at the time of this writing. Update (9/15/2015): looks like gonetz has added it to his crowdfunded gliden64 plugin.

CRT-Royale and 3dfx Shaders

Two fairly new shaders have popped up that are worth mentioning: TroggleMonkey's CRT-Royale and leilei's 3dfx. They're both available in Cg format in libretro's common-shaders github repo, though CRT-Royale utilizes some advanced features that aren't available in RetroArch v1.0.0.2 (the most recent release at the time of this writing).

CRT-Royale is particularly exciting for me because TroggleMonkey managed to overcome some issues with shadow-mask emulation that I thought were totally intractable at current common resolutions (i.e., 1080p). The result is some really great phosphor emulation at reasonable scale factors, along with all of the bells and whistles users have come to expect from CRT shaders, including "halation"/glow, bob-deinterlacing support and curvature, along with a ton of options that are unique to this shader.

I'm not going to cover many of them here because it would take forever to get screenshots and there's not much point when TroggleMonkey has included a very informative README with the code, along with support for RetroArch's new runtime parameter support (so you can see the effect of your changes in real-time). However, I thought the shadow mask stuff was super-cool and deserved some closeups. Here's a shot of the shader with default settings (as always, click to embiggen):

First, we'll look at my favorite effect, the in-line shadow mask (called slot-mask in the code):

This is the same configuration I was shooting for with my PhosphorLUT shader, and you can see that the configuration of the phosphors has that familiar vertical, staggered orientation:

Next, we have the very similar aperture grille:

 

The main difference between this and the in-line slot mask is that it doesn't have the slight staggering (only really visible in the closeups and at super-huge resolutions). In closeup of the LUT, you can see that it just removes the crossbars between triads:

Last, we have the dot-triad shadow mask (called "shadow-mask-EDP" in the code), which was common on CRT computer monitors:

 As you can see, it looks very similar to the high-res shots I took of my Compaq CRT monitor (from my emulation/TV post). And here's the dot-triad blown up:

The other shader I wanted to show is leilei's 3dfx shader, which tries to mimic the effects of a 3dfx GPU, known for some distinctive dithering among other things. In addition to obvious applications like RetroArch's Quake core, Nintendo's N64 also used a GPU that was very similar to a 3dfx, which makes it appropriate for RA's Mupen64plus core. When run at low-ish internal resolutions and paired with RetroArch's per-texture 3-point filtering, you can get a pretty good approximation of what N64s looked like.

Here are some shots of the shader at 320x240 and 640x480 (i.e., native and double res, respectively):

Native res:

Double internal res:

 As you can see, the doubled res looks significantly sharper, but the scanlines are thinner and less pronounced (and twice as many of them) relative to the native res. I also like native res because it makes HUD/menu items look a little less "pasted-on":
Native res:

Doubled internal res:

Repairing/Replacing N64 Analog Stick

I recently purchased a small CRT TV and have been hooking my old consoles up to it, and I noticed the analog stick on my N64 controller was in pretty rough shape. The deadzone was gigantic and it was affecting my performance in some games, so I decided to look into repairing or replacing it with a new stick.

I settled on this replacement stick, available for $11 from Amazon at the time of this writing.

The replacement process is very easy and takes only a few minutes, with no special tools required other than a small philips-head screwdriver, though a flathead screwdriver and some needlenose pliers will make the job easier.

To start, just flip over the controller and remove the 7 large screws on the back, then remove the 2 small screws next to the memory card / rumble slot (they're easy to miss/forget):

You should then be able to lift the back panel off, which should reveal something like this:

The circuit board and rubber membrane for the Z-button are held down with little plastic clips on the sides of the analog stick assembly, so unclip the board and set the rubber membrane somewhere safe.

The R and L buttons are just sitting in their homes, held in by a tiny plastic peg-in-hole system, so you may wish to remove them at this time, as well, just to get them out of your way:

Next, remove the 4 small screws that hold the analog stick assembly in place (in my case, 3 silver screws on the sides and and bottom, and 1 black screw in the middle) and lift the assembly out. It will still be connected to the PCB by a connector, which you should be able to slide out (pictured below):

Mine was very stubborn and required holding the connector housing in place with my fingers while prying with a flathead screwdriver, alternately loosening the sides until it popped out.

Once it's out, you just do the steps in reverse. The connector assembly was the biggest hassle and required some squeezing with my needlenose pliers before it would snap into place. The wires on the connector are pretty small, so make sure you don't accidentally damage them while squeezing, and don't rip the connector housing off of the PCB!

I had an additional screw left over (the middle black one from the analog stick assembly; it's actually part of the OEM stick assembly), but I just stuck it into the hole they left in the new analog stick, even though it doesn't thread into anything.

And here's the finished product:

This stick is more like a Gamecube or Xbox 360 analog stick than the OEM N64 sticks, and as such feels much sturdier. The movement is also largely frictionless, unlike the OEM sticks, which makes it superior for games like Mario Party that really wear out the OEMs (and your palms). On the other hand, the sensitivity is really high and it's difficult to do precise aiming on games like Goldeneye and Perfect Dark, as the reticle tends to jump around a bit when you try to zero in on a small target (like a head...). For this reason, I will likely keep at least 1 controller with the OEM-style stick around for that sort of thing.