Shaders wont bind to the uniform block

Question

I'm having an issue with interface block binding.

Example shader:

const char* vertexShader =      
        "#version 330 core\n"
        "uniform globalMatrices"
        "{"
        "   mat4 vPMatrix;"
        "};"
        "layout(location = 0) in vec2 vPosition;"
        "layout(location = 1) in vec4 vColor;"
        "out vec4 color;"
        "void main()"
        "{"
        "   color = vColor;"
        "   gl_Position = vPMatrix * vec4(vPosition, 1.0, 1.0);"
        "}"

After creating the shader program i call functions:

    //this is done once per shader
    void BindShaderToMatrixBlock(unsigned int program)
    {
        GLuint globalUniformBlockIndex = glGetUniformBlockIndex(program, "globalMatrices");
        glUniformBlockBinding(program, globalUniformBlockIndex, 0);
    }
    //this is done once 
    void BindUniformBlockMatrix()
    {
        glGenBuffers(1, &uniformBlockMatrix);
        glBindBuffer(GL_UNIFORM_BUFFER, uniformBlockMatrix);
        glBufferData(GL_UNIFORM_BUFFER, sizeof(glm::mat4), NULL, GL_DYNAMIC_DRAW);
        glBindBuffer(GL_UNIFORM_BUFFER, 0);
        glBindBufferRange(GL_UNIFORM_BUFFER, 0, uniformBlockMatrix, 0, sizeof(glm::mat4));
    }

And this is how i update the matrix:

inline void SetVPMatrix(const void* data)
{
    glBindBuffer(GL_UNIFORM_BUFFER, uniformBlockMatrix);
    glBufferSubData(GL_UNIFORM_BUFFER, 0, sizeof(glm::mat4), data);
}

I tried to debug as much as i could and confirmed that the data gets delivered to the uniform block but for some reason the matrix in the shader stays unchanged.

Answer 1

I did several changes to the code and something of the following fixed my problem:

• changed the order so that all the block binding was done before initializing the uniform buffer
• added "layout (std140)" to the uniform block in the vertex shader
• i made sure that i unbound everything after binding and executing series of commands

thanks wondra for the link, it helped.