OpenGL SSBO Instancing

Question

Binding a SSBO and accessing it via gl_InstanceID seems to work but im getting these really strange position artifacts and im not sure where they are coming from.

The way im generating the random positions is pretty standard and i also tested the positions with some debug lines. But they don't match when im adding them inside the vertex shader.

glm::fvec3 offset{ glm::sphericalRand(500.f) };

shader.vert

struct Transform
{
  vec3 position;
  vec3 rotation;
  vec3 scale;
  mat4 transform;
};

layout (std430, binding = 0) buffer TransformBuffer
{
  Transform transforms[];
};

layout (location = 0) in vec3 lPosition;

void main()
{
  gl_Position = uProjection * uView * vec4(lPosition + transforms[gl_InstanceID].position, 1.f);
}

code.cpp

struct Transform
{
  glm::fvec3 mPosition {};
  glm::fvec3 mRotation {};
  glm::fvec3 mScale    {};
  glm::fmat4 mTransform{};
};

glGenBuffers(1, &ssbo);
glBindBuffer(GL_SHADER_STORAGE_BUFFER, ssbo); 
glBufferData(GL_SHADER_STORAGE_BUFFER, 10000 * sizeof(Transform), pStorageData, GL_STATIC_DRAW);
glBindBufferBase(GL_SHADER_STORAGE_BUFFER, 0, ssbo);

glUseProgram(pid);
glBindVertexArray(vao);
glDrawElementsInstanced(GL_TRIANGLES, indices.size(), GL_UNSIGNED_INT, nullptr, 10000);

Answer 1

So it seems that the internal layout of opengl structs does not match the C/C++ layouts. I solved the problem by removing the opengl vector types and instead use raw arrays.

shader.vert

struct Transform
{
  float position[3];
  float rotation[3];
  float scale[3];
};