Wrong vector sizes in push constants

[KoT3isGood]

Each uint and float are 4 bytes

layout(push_constant) uniform constants
{
   uint posX;
   uint posY;
   uint fontSize;
   uint textOffset;
   uint posZ;
   float r;
   float g;
   float b;
} PushConstants;

And so this push constant size is 32

Each vec3 is made from 3 floating points, so its size should be 12 bytes But when I replace r,g,b with vec3

layout(push_constant) uniform constants
{
   uint posX;
   uint posY;
   uint fontSize;
   uint textOffset;
   uint posZ;
   vec3 color;
} PushConstants;

Push constant size becomes 44 (according to Vulkan)

[arcady-lunarg]

This is becuase the vec3 is being aligned to a multiple of 16 bytes, which is the next higher power of 2 from its size. If you want to align the vec3 with the same alignment as a scalar float, you can use the GL_EXT_scalar_block_layout extension and declare your block with layout(push_constant, scalar) uniform constants, which will result in color being assigned an offset of 20.

[ravi688]

By default "Vulkan" GLSL uses std430 alignment rules for push constant buffers.