shafik

What is the Strict Aliasing Rule and Why do we care?

(OR Type Punning, Undefined Behavior and Alignment, Oh My!)

What is strict aliasing? First we will describe what is aliasing and then we can learn what being strict about it means.

In C and C++ aliasing has to do with what expression types we are allowed to access stored values through. In both C and C++ the standard specifies which expression types are allowed to alias which types. The compiler and optimizer are allowed to assume we follow the aliasing rules strictly, hence the term strict aliasing rule. If we attempt to access a value using a type not allowed it is classified as undefined behavior(UB). Once we have undefined behavior all bets are off, the results of our program are no longer reliable.

Unfortunately with strict aliasing violations, we will often obtain the results we expect, leaving the possibility the a future version of a compiler with a new optimization will break code we th

sebbbi

// NOTE: Must bind 8x single mip RWTexture views, because HLSL doesn't have .mips member for RWTexture2D. (SRVs only have .mips member)
// NOTE: globallycoherent attribute is needed. Without it writes aren't guaranteed to be seen by other groups
globallycoherent RWTexture2D<float> MipTextures[8];
RWTexture2D<uint> Counters[8];
groupshared uint CounterReturnLDS;

[numthreads(16, 16, 1)]
void GenerateMipPyramid(uint3 Tid : SV_DispatchThreadID, uint3 Group : SV_GroupId, uint Gix : SV_GroupIndex)
{
	[unroll]

Erkaman

/*
The MIT License (MIT)

Copyright (c) 2018 Eric Arnebäck

Permission is hereby granted, free of charge, to any person obtaining a copy
of this software and associated documentation files (the "Software"), to deal
in the Software without restriction, including without limitation the rights
to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
copies of the Software, and to permit persons to whom the Software is

pixelsnafu

Volumetric Clouds Resources List

1. A. Schneider, "Real-Time Volumetric Cloudscapes," in GPU Pro 7: Advanced Rendering Techniques, 2016, pp. 97-127. (Follow up presentations here, and here.)

2. S. Hillaire, "Physically Based Sky, Atmosphere and Cloud Rendering in Frostbite" in Physically Based Shading in Theory and Practice course, SIGGRAPH 2016. [video] [course notes] [scatter integral shadertoy]

3. [R. Högfeldt, "Convincing Cloud Rendering – An Implementation of Real-Time Dynamic Volumetric Clouds in Frostbite"](https://odr.chalmers.se/hand

yknishidate

import math
import random
import matplotlib.pyplot as plt


class UniformDistribution:
    def __init__(self, a: float, b: float) -> None:
        self.a = a
        self.b = b

jdupuy

// Helper function: sample the visible hemisphere from a spherical cap
vec3 SampleVndf_Hemisphere(vec2 u, vec3 wi)
{
	// sample a spherical cap in (-wi.z, 1]
	float phi = 2.0f * M_PI * u.x;
	float z = fma((1.0f - u.y), (1.0f + wi.z), -wi.z);
	float sinTheta = sqrt(clamp(1.0f - z * z, 0.0f, 1.0f));
	float x = sinTheta * cos(phi);
	float y = sinTheta * sin(phi);
	vec3 c = vec3(x, y, z);