Cody Bennett CodyJasonBennett

3-Byte Tangent Frame Encoding (Doom Eternal 2020)

This method stores a full TBN frame using just 3 bytes per vertex (plus a bitfield), instead of the traditional 28 bytes (normal: vec3, tangent: vec4). It leverages octahedral encoding for normals and a rotation angle for tangent reconstruction.

Motivation

Storing both glm::vec3 normal and glm::vec4 tangent is costly. Since the bitangent can be reconstructed via a cross product, we only need:

A unit normal (encoded in 2 bytes)
An angle to rotate a base tangent around the normal (1 byte)

In PIX, Select Target Process => Launch Win32 and set the following 2 entries according to where Canary / Chrome is installed:

Path to executable: "C:\Users\alexis\AppData\Local\Google\Chrome SxS\Application\chrome.exe"
Working directory: "C:\Users\alexis\AppData\Local\Google\Chrome SxS\Application"
Command line arguments: --disable-gpu-sandbox --disable-direct-composition
- You can add those arguments if you want to be able to see the disassembled shader code: --enable-dawn-features=emit_hlsl_debug_symbols,disable_symbol_renaming
Launch Suspended unchecked, Launch for GPU capture and Force D3D11On12 checked

Then click on "Launch".

Important: you should close all your Canary / Chrome windows/processes before clicking on the "Launch" button!

cam.setPosition( cam.getPosition()+(targetPos-cam.getPosition())*0.01 );
cam.lookAt(targetPos);

Trigonometry

const float PI = 3.1415926535897932384626433832795;
const float PI_2 = 1.57079632679489661923;
const float PI_4 = 0.785398163397448309616;

float PHI = (1.0+sqrtf(5.0))/2.0;

	// each pixel is assigned 4 random u32 values per frame
	@group(0) @binding(1)
	var<storage, read> rnd_state: array<u32>;

	// the current state within this pixel
	var<private> local_rnd_state:vec4u;

	fn random_u32(state:ptr<private,vec4u>) -> u32 {
	var st:vec4u = *state;
	/* Algorithm "xor128" from p. 5 of Marsaglia, "Xorshift RNGs" */

	import time

	import math
	import torch

	import taichi as ti
	import taichi.math as tm

	import tinytex as ttex
	from tinycio import fsio

	// Copyright (c) 2023 Tomasz Stachowiak
	//
	// This contribution is dual licensed under EITHER OF
	//
	// Apache License, Version 2.0, (http://www.apache.org/licenses/LICENSE-2.0)
	// MIT license (http://opensource.org/licenses/MIT)
	//
	// at your option.

	#include "/inc/frame_constants.hlsl"

	/** Using a faux sphere in screen space, determine the arc transform to orbit
	* the camera around a target position. A continuous orientation will
	* be provided for further calls.
	*/
	function arcBallTransform(
	scrSize, // Screen size, vec2
	scrPos0, // Starting mouse position, vec2
	scrPos1, // Ending Mouse Positiong, vec2
	rotOrientation, // Current arc orientation, quaternion
	targetPos, // Position to orbit around

	<html>
	<head>
	<style>
	body {
	margin: 0;
	padding: 10px;
	color: #ffffff;
	background: #222222;
	font-family: sans-serif;
	font-size: 7px;