ssbo in my particles system is not updated - glsl

Question

I work on particles system and I want to use SSBO to make update of velocity and position on my particles with compute shader. But I see for each update-call the compute use same values of positions but compute update position because in draw-call particles are moved.
Load particles into SSBOs
// Load Positions
glGenBuffers(1, &m_SSBOpos);
glBindBuffer(GL_SHADER_STORAGE_BUFFER, m_SSBOpos);
// Allocation de la mémoire vidéo
glBufferData(GL_SHADER_STORAGE_BUFFER, pb.size() * 4 * sizeof(float), NULL, GL_STATIC_DRAW);
GLint bufMask = GL_MAP_WRITE_BIT | GL_MAP_INVALIDATE_BUFFER_BIT; // the invalidate makes a big difference when re-writing
float *points = (float *) glMapBufferRange(GL_SHADER_STORAGE_BUFFER, 0, pb.size() * 4 * sizeof(float), bufMask);
for (int i = 0; i < pb.size(); i++)
{
points[i * 4] = pb.at(i).m_Position.x;
points[i * 4 + 1] = pb.at(i).m_Position.y;
points[i * 4 + 2] = pb.at(i).m_Position.z;
points[i * 4 + 3] = 0;
}
glUnmapBuffer(GL_SHADER_STORAGE_BUFFER);
// Load vélocité
glGenBuffers(1, &m_SSBOvel);
glBindBuffer(GL_SHADER_STORAGE_BUFFER, m_SSBOvel);
// Allocation de la mémoire vidéo
glBufferData(GL_SHADER_STORAGE_BUFFER, pb.size() * 4 * sizeof(float), NULL, GL_STATIC_DRAW);
float *vels = (float *)glMapBufferRange(GL_SHADER_STORAGE_BUFFER, 0, pb.size() * 4 * sizeof(float), bufMask);
for (int i = 0; i < pb.size(); i++)
{
vels[i * 4] = pb.at(i).m_Velocity.x;
vels[i * 4 + 1] = pb.at(i).m_Velocity.y;
vels[i * 4 + 2] = pb.at(i).m_Velocity.z;
vels[i * 4 + 3] = 0;
}
glUnmapBuffer(GL_SHADER_STORAGE_BUFFER);
Update
glBindBufferBase(GL_SHADER_STORAGE_BUFFER, 4, shaderUtil.getSSBOpos());
glBindBufferBase(GL_SHADER_STORAGE_BUFFER, 5, shaderUtil.getSSBOvel());
// UPDATE DES PARTICULES
shaderUtil.UseCompute();
glUniform1i(shaderUtil.getDT(), fDeltaTime);
glDispatchCompute(NUM_PARTICLES / WORK_GROUP_SIZE, 1, 1);
glMemoryBarrier(GL_SHADER_STORAGE_BARRIER_BIT);
shaderUtil.DeleteCompute();
Draw
shaderUtil.Use();
glUniformMatrix4fv(glGetUniformLocation(shaderUtil.getProgramID(), "projection"), 1, GL_FALSE, glm::value_ptr(projection));
glUniformMatrix4fv(glGetUniformLocation(shaderUtil.getProgramID(), "modelview"), 1, GL_FALSE, glm::value_ptr(View * Model));
glPointSize(10);
// Rendu
glBindBuffer(GL_ARRAY_BUFFER, shaderUtil.getSSBOpos());
glVertexPointer(4, GL_FLOAT, 0, (void *)0);
glEnableClientState(GL_VERTEX_ARRAY);
glDrawArrays(GL_POINTS, 0, NUM_PARTICLES);
glDisableClientState(GL_VERTEX_ARRAY);
glBindBuffer(GL_ARRAY_BUFFER, 0);
shaderUtil.Delete();
Comput shader
#version 430 compatibility
#extension GL_ARB_compute_shader : enable
#extension GL_ARB_shader_storage_buffer_object : enable
layout(std140, binding = 4) buffer Pos
{
vec4 Positions[]; // array of structures
};
layout(std140, binding = 5) buffer Vel
{
vec4 Velocities[]; // array of structures
};
uniform float dt;
layout(local_size_x = 128, local_size_y = 1, local_size_z = 1) in;
void main()
{
uint numParticule = gl_GlobalInvocationID.x;
vec4 v = Velocities[numParticule];
vec4 p = Positions[numParticule];
vec4 tmp = vec4(0, -9.81, 0,0) + v * (0.001 / (7. / 1000.));
v += tmp ;
Velocities[numParticule] = v;
p += v ;
Positions[numParticule] = p;
}
Do you know why it's happened ?