Colors in OpenGL VBOs? - opengl

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?

Answer 1

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().