OpenGL Buffer to Attribute

Question

I'm trying to get some float values to my vertex shader on a per vertex basis - the float value will define the size of gl_PointSize for rendering

Here is my shader:

attribute float vSpacial;

void main(void)
{
   gl_FrontColor = gl_Color;
   gl_Position = gl_ModelViewProjectionMatrix * gl_Vertex;
   gl_PointSize = vSpacial;
}

Here is how I set up the buffers for the verts, colours, and "spacial" point size information:

GLint spacial = glGetAttribLocation(program, "vSpacial");
float spacialData[] = {11.0f, 50.0f, 100.0f};

GLuint VBO;
glGenBuffers(1, &VBO);
glBindBuffer(GL_ARRAY_BUFFER, VBO);
glBufferData(GL_ARRAY_BUFFER, sizeof(positions), &positions, GL_STATIC_DRAW);
glBindBuffer(GL_ARRAY_BUFFER, 0);

GLuint CBO;
glGenBuffers(1, &CBO);
glBindBuffer(GL_ARRAY_BUFFER, CBO);
glBufferData(GL_ARRAY_BUFFER, sizeof(colors), &colors, GL_STATIC_DRAW);
glBindBuffer(GL_ARRAY_BUFFER, 0);

GLuint SPO;
glGenBuffers(1, &SPO);
glBindBuffer(GL_ARRAY_BUFFER, SPO);
glBufferData(GL_ARRAY_BUFFER, sizeof(spacial), &spacial, GL_STATIC_DRAW);
glBindBuffer(GL_ARRAY_BUFFER, 0);

and here is how I'm rendering:

        // Set up projection
        glMatrixMode(GL_PROJECTION);
        glLoadIdentity();
        gluPerspective(45, 1024.0/768.0, 1, 1000);
        // Set up camera view
        glMatrixMode(GL_MODELVIEW);
        glLoadIdentity();
        gluLookAt(0,0,-5,
                  0,0,0,
                  0,1,0);

        glClearColor( 0.0f, 0.0f, 0.0f, 0.0f );
        glClear( GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);

        // ---
        glUseProgram(program);

        glPushMatrix();
        glRotatef( theta, 0.0f, 0.0f, 1.0f );

        glEnableClientState(GL_VERTEX_ARRAY);
        glEnableClientState(GL_COLOR_ARRAY);
        glEnable(GL_PROGRAM_POINT_SIZE);


        glBindBuffer(GL_ARRAY_BUFFER, VBO);
        glVertexPointer(3, GL_FLOAT, 0, BUFFER_OFFSET(0));
        glBindBuffer(GL_ARRAY_BUFFER, CBO);
        glColorPointer(3, GL_FLOAT, 0, BUFFER_OFFSET(0));

        glBindBuffer(GL_ARRAY_BUFFER, SPO);
        glEnableVertexAttribArray(spacial);
        glVertexAttribPointer(spacial, 1, GL_FLOAT, GL_FALSE, 0, BUFFER_OFFSET(0));

        glDrawArrays(GL_POINTS, 0, 3);

        glDisableVertexAttribArray(spacial);

        glDisable(GL_PROGRAM_POINT_SIZE);
        glDisableClientState(GL_COLOR_ARRAY);
        glDisableClientState(GL_VERTEX_ARRAY);

        glBindBuffer(GL_ARRAY_BUFFER, 0);

        glPopMatrix();

        // ---

        glFlush();
        SwapBuffers( hDC );

        theta += 1.0f;

Currently I see nothing rendering - If I comment out the line glBindBuffer(GL_ARRAY_BUFFER, SPO); I will see one point being rendered by itself (not using the spacial value I pass in).

jProg2015 jProg2015 · Accepted Answer · 2014-01-21T15:09:09

Ironically Immediately noticed the problem with this::

I should be using spacialData not spacial in the BufferData call.

MORAL OF THE STORY: Name variables well and don't program tired (without coffee).

OpenGL Buffer to Attribute

1 Answers