learn-wgpu/docs/showcase/alignment/README.md

Memory Layout in GLSL

Alignments

The address of the position of an instance in memory has to a multiple of its alignment.

Normally alignment is the same as size. Exceptions are vec3, structs and arrays.

A vec3 is padded to be a vec4 which means it behaves as if it was a vec4 just that the last entry is not used.

{i,u,b}vec is shorthand for ivec, uvec, bvec so a vector of int or uint or bool. A vec is a vec of float.

type	Alignment in bytes	size in bytes
int, uint, float, bool	4	4
double	8	8
{i,u,b}vec2	8	8
dvec2	16	16
{i,u,b}vec3	16	12
{i,u,b}vec4	16	16
dvec3	32	24
dvec4	32	32
mat3 (like array of 3 vec3)	16	3*16
mat4 (like array of 4 vec4)	16	4*16

Reference section 7.6.2.2

In WGPU

To make uniform buffers portable they have to be std140 and not std430. Uniform structs have to be std140. Storage structs have to be std430.

Storage buffers for compute shaders can be std140 or std430.

std140 (since GLSL 1.4, OpenGL 3.1)

Array:

• determine the alignment of the member type and lets name it align_member
• the alignment of the array is maximum(align_member, 16)

Struct:

• determine the member with the largest alignment and lets name it max_member_align
• the alignment of the array is maximum(max_member_align, 16)

crates to make your struct compatible with std140

glsl_layout crevice

std430 (since GLSL 4.3, OpenGL 4.3)

more space efficient for structs and arrays

Array

• alignment is the alignment of the element type

Struct

• alignment is the alignment of the member with the largest alignment

crates to make yuor struct compatible with std430

glsl_layout issue crevice issue

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