Colors in OpenGL VBOs?

Question

I'm trying to add colors to my object that using a single struct and single VBO in OpenGL. To do this, I have a Vertex struct that I created that looks like this:

typedef struct {
    float x;
    float y;
    float z;
    float r;
    float g;
    float b;
    float a;
} Vertex;

I already know that I'm setting all of the coordinates and colors correctly to get what I want, because I ran a test iterating over each object I have stored in my list and drawing out the points and setting the colors using glVertex3f and glColor4f (this was significantly slower than what I'm looking for). But when I try to draw it using VBOs I just get a huge mess of colored triangles going everywhere.

The part of my rendering loop that draws the VBO looks like this:

glBindBuffer(GL_ARRAY_BUFFER, vbo);
glEnableClientState(GL_VERTEX_ARRAY);
glVertexPointer(3, GL_FLOAT, 0, NULL);
glEnableClientState(GL_COLOR_ARRAY);
glColorPointer(4, GL_FLOAT, offsetof(Vertex, r), NULL);
glDrawArrays(GL_TRIANGLES, 0, vertex_amount);
glBindBuffer(GL_ARRAY_BUFFER, 0);

What am I doing wrong?

genpfault genpfault · Accepted Answer · 2016-10-20T22:43:19

glVertexPointer(3, GL_FLOAT, 0, NULL);
                             ^

The position values in an array of Vertexs are not tightly packed so you can't use 0 for stride. Use sizeof( Vertex ).

glColorPointer(4, GL_FLOAT, offsetof(Vertex, r), NULL);
                            ^^^^^^^^^^^^^^^^^^^

I'm...not sure what you're going for here. Perhaps you thought the 3rd parameter of glVertexPointer()/glColorPointer() was pointer instead of stride? Move your offsetof() to the final parameter, pointer.

All together:

glVertexPointer(3, GL_FLOAT, sizeof( Vertex ), offsetof(Vertex, x) );
glColorPointer(4, GL_FLOAT, sizeof( Vertex ), offsetof(Vertex, r) );

You may have to cast the pointer parameter values to void* depending on how you've implemented offsetof().

Colors in OpenGL VBOs?

1 Answers