Moving, translating objects contained in vbo

Question

I'm having trouble understanding how to actually translate a single object contained in a vbo. So first I set up vao and vbo and bind and enter vertices of a cube...

    glGenVertexArrays(1, &_vertexArray1); //Bind to first VAO
    glBindVertexArray(_vertexArray1);
    glGenBuffers(1, &_vertexBufferCube1);
    glBindBuffer(GL_ARRAY_BUFFER, _vertexBufferCube1);
    glBufferData(GL_ARRAY_BUFFER, g_point_count * 3 * sizeof (float), &g_vp[0], GL_STATIC_DRAW);

glEnableVertexAttribArray(loc1);
glVertexAttribPointer(loc1, 3, GL_FLOAT, GL_FALSE, 0, NULL);
glEnableVertexAttribArray(loc2);
glVertexAttribPointer(loc2, 3, GL_FLOAT, GL_FALSE, 0, NULL);`

Then in my display function...

    // tell GL to only draw onto a pixel if the shape is closer to the viewer
glEnable (GL_DEPTH_TEST); // enable depth-testing
glDepthFunc (GL_LESS); // depth-testing interprets a smaller value as "closer"
glClearColor (0.5f, 0.5f, 0.5f, 1.0f);
glClear (GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
glUseProgram (shaderProgramID);


//Declare your uniform variables that will be used in your shader
int matrix_location = glGetUniformLocation (shaderProgramID, "model");
int view_mat_location = glGetUniformLocation (shaderProgramID, "view");
int proj_mat_location = glGetUniformLocation (shaderProgramID, "proj");

mat4 view = identity_mat4 ();
mat4 persp_proj = perspective(45.0, (float)width/(float)height, 0.1, 100.0);
mat4 model = identity_mat4 ();
view = translate (view, vec3 (0.0, 0.0, -5.0f));

glUniformMatrix4fv (proj_mat_location, 1, GL_FALSE, persp_proj.m);
glUniformMatrix4fv (view_mat_location, 1, GL_FALSE, view.m);
glUniformMatrix4fv (matrix_location, 1, GL_FALSE, model.m);


glBindVertexArray(_vertexArray1);
//model = translate (view, vec3 (0.0, -3.0F, 0.0));

glDrawArrays (GL_TRIANGLES, 0, g_point_count);
glBindVertexArray(0);

Now my issue is that I want to move the object in one vao independently of another. How should I be doing this? Should I just be translating the model matrix then unbind the vao and bind another one and translate the same model matrix again? After googling for a good while I think I should be using glPushMatrix and glTranslatef but what matrix do I push?

Essentially where is the matrix for my vao that needs to be translated in order to move the object in the vao?

score 1 · Accepted Answer · answered Dec 09 '13 at 12:44

Repeating what I answered you on Reddit:

Transformation matrices and VBOs don't interact. You can change either without having to do to anything with the other. Basic rule of thumb: If your model just moves around without deforming you modify the transformation (i.e. the modelview matrix). If your model deforms in a way that can be described by a handful of uniforms (skeletal animation) you change those. Only if the topology of your model changes or the deformation is outside of what your skeleton can do, you alter the data in the VBO.

Moving, translating objects contained in vbo

1 Answers1