How to implement Ballot() with DX11


Today I will talk about a quick (slow) hack for getting some platform specific code working crossplatform. This is really about correctness, and not speed - I mean, otherwise the shader code wouldn't run on windows anyway. This hack won't be necessary once we can switch over to DXC - Microsoft's new shader compiler with shader model 6.0, but for now, that's out of reach.

In order to explain what the function Ballot() actually does, I need to first take a little diversion to explain GPU hardware.

GPU SIMDs The way a (modern, discrete) GPU works is that it executes instructions WAVE_SIZE (64 on AMD and 32 on Nvidia) at a time, all in lockstep. An easy way to think about it is that a set of WAVE_SIZE threads all share one instruction pointer. A group of WAVE_SIZE threads all located on a single SIMD is called a wave (or warp, using NV terminology). The cool thing about this is that threads that are within the same wave can share data between each other. Here's a …

Rotating a vector using integer math


Today's galaxy brain idea is to use integer math to do arbitrary rotation about a point.
Why? I can already hear you saying "We have very nice floating point units that are good at this already!" and I say, No thanks to the floating point unit. They're all well and good, but converting between floats and ints is slow on the GPU, wasting a whole instruction and especially so when you want to do index calculations. Also consider that on newer versions of GCN, we have packed ops, but no packed float/int conversions. Also, also consider that GCN doesn't have scalar floating point ops, and if you want to do float math in a scalar context, you'll be issuing vector instructions with SGPR sources! If you are maxed out on VALU and want to offload some calculations to SALU, then you're only making your problem worse if you need to do floating point ops.
 Think about the index rotation case: read in some integer index data, maybe a thread ID.convert to floatd…

How to do nothing in HDR


Today's post is about how to do nothing in HDR. That's just a clickbait way of saying I want to transform an SDR/SRGB gamma encoded (hereafter referred to as just SDR) image such that it appears like an SDR image after PQ encoding. The buffer you'll retreive from an SDR swapchain on windows is precisely that: an SDR/SRGB gamma encoded texture. Essentially, I want to press the button that turns on HDR and see nothing happen.

This is useful because maybe you want to toggle or lerp between SDR/HDR, so that you can compare the two. In the HDR Injector, I need to do this because once I've created the HDR swapchain, windows doesn't want to go back to the SDR swapchain for some reason. Also, I need to be able to sample parts of the SDR backbuffer to determine which parts had UI on them, or if color grading/tonemapping/post-processing occurred.

Why is this even a problem? As I mentioned in my previous posts, HDR images are encoded in a different way than SDR images. I…

How to render to HDR displays on Windows 10


If you missed it, yesterday I wrote an artisanal blogue poaste about a tool I am working on called the HDR injector. Today, I will write about how to present an HDR image in Windows. Some of this will be a summary of the talk by Evan Hart at GDC 2018.

There are three steps, which I don't think are explained anywhere, except maybe within these ultra-rare DX12 samples that I had to catch midair from a hot tweet.
Set your swapchain effect to DXGI_SWAP_EFFECT_FLIP_DISCARD. Emphasis on FLIP. The GDC talk above seems to think this isn't 100% required, but I couldn't get any HDR working without it.Set your swapchain buffer format to an HDR compatible backbuffer format. The ones that work for me are: DXGI_FORMAT_R16G16B16A16_FLOAT and  DXGI_FORMAT_R10G10B10A2_UNORM, though I expect other formats might work. I haven't tested all of them.Depending on which format you picked in (2) you need to select the correct color space. If you  selected RGBA1010102, then you want to pick…

HDR Injector

Hi, friends.
It's been about 3 years since my last blog post. A few things have happened in the mean time. I currently live in the SF bay (deep under the sea, biding my time) and work for Sony, doing PS4 graphics support. Cool. I'm not really going to talk about that today - just a quick catch up for those of you playing along at home.
I will talk about a little project I've been working on in my free time.  HDR basics Fast forward. We currently live in the year 2018: a time of incredible power. The planet glows with unnatural energies and we're able to channel these Occult Phenomena directly into our eyes via Highe Dynamick Range televison and monitor devices.
The advantage of these devices is twofold:
Enhanced brightness - things can be brighter, and show a more realistic range of brights/darksWide color - you can show a wider range of colors. This is hard to describe if you haven't already seen it. It's astounding how good it can look. Personally, I am ext…

Global Game Jam: Friendship is Tragic

Greetings bros, antibros, and those not on the bro-spectrum.
I did that global game jam thing!

Check it out: Aww yeah.
I did this game jam at Gamenest in SF, which is totally not even a little bit close to where I live in LA. It's only an 8 hour bus ride. That's fine for a weekend trip, right? Totes.

This is the best game jam I've done so far. Probably because it was the least ambitious, and therefore the most polished. Also, I suspect you won't be able to figure out how to play the game because there is no explanation, rules, or instructions! Fantastic!

Infinity Ward? Yeah, it's a pretty sweet job. I'm doing my best not to lose my indie cred, but it's hard. In my secret activision-owned-indie-free-time, I'm working on some sick ghost video game stuff. Did someone say PIXEL ART? NO? too bad.

Rocks and floating platforms. Of course.

Super Hairpiece, Infinity Ward.

Hey bros and anti-bros, I've got some news. This might be the last post for a while. Or at least the last post that is video games related. More on that later, but first!
Super Hairpiece I made this game along with some friends at the PurpleMonkey Gamejam some time last month.

The game is about throwing a toupee on to a procedurally generated bald spot on a guys head. You should try it out. Here are the links: 64 bits 32 bits
It's also got a nifty screenshot mode so you can take hair-larious (im so sorry) pictures of your styled dude.

Woooo super hairpiece! What else?
That job thing I got a job at Infinity Ward, the guys who make some Calls of Duty (or is it Call of Duties?) making their video game programs work! That means I'm actually posting this right now from an apartment in Woodland Hills, CA. Yeah, I moved to the west coast. Sorry boston dudes! We had fun though, there's no way I could have gotten to where I am today without the filthybrutal Boston indie games sce…