Proper way to use indexed VBO

Question

I am working on a simple 3D Engine. I currently have a working setup with multiple VAO's which I can switch between during the render loop, but they all are not using index buffers.

I'm now trying to add a new VAO composed of 4 VBO's: vert position, color, normal and indices.

Everything compiles and runs but the drawing calls to the second VAO (with indexed vertices) do not render. I'm sure there is a problem with my setup somewhere, so I've added this code which includes all the VAO and VBO generations, calls, and uses. Does anything in this code seem wrong, and is this the correct way to set it all up?

VAO1 has 3 buffers: position, color, normals

VAO2 has 3 buffers: position, color, normals and vertex indices

//Initalize vaos and vbos
GLuint vao1, vbo1[3];
GLuint vao2, vbo2[4];

//Generate Vertex arrays:
glGenVertexArrays(1, &vao1);
glGenVertexArrays(1, &vao2);

//Generate Buffers:
glGenBuffers(3, vbo1);
glGenBuffers(4, vbo2);

//Initalize Bufferdata vectors:
vector<GLfloat> VertPosBuffer1Vector;
vector<GLfloat> VertNormalBuffer1Vector;
vector<GLfloat> VertColorBuffer1Vector;

vector<GLfloat> VertPosBuffer2Vector;
vector<GLfloat> VertNormalBuffer2Vector;
vector<GLfloat> VertColorBuffer2Vector;
vector<GLuint> VertIndexBuffer2Vector;

//Fill Buffers:
//(not included but all vectors are filled with data)

//VAO 1
glBindVertexArray(vao1);

//Vertex position buffer:
glBindBuffer(GL_ARRAY_BUFFER, vbo1[0]);
glBufferData(GL_ARRAY_BUFFER, sizeof(GLfloat)*VertPosBuffer1Vector.size(), &VertPosBuffer1Vector[0], GL_STATIC_DRAW);
glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, 0, (void*)0);
glEnableVertexAttribArray(0);

//Vertex color buffer:
glBindBuffer(GL_ARRAY_BUFFER, vbo1[1]);
glBufferData(GL_ARRAY_BUFFER, sizeof(GLfloat)*VertColorBuffer1Vector.size(), &VertColorBuffer1Vector[0], GL_STATIC_DRAW);
glVertexAttribPointer(1, 3, GL_FLOAT, GL_FALSE, 0, (void*)0);
glEnableVertexAttribArray(1);

//Vertex normal buffer:
glBindBuffer(GL_ARRAY_BUFFER, vbo1[2]);
glBufferData(GL_ARRAY_BUFFER, sizeof(GLfloat)*VertNormalBuffer1Vector.size(), &VertNormalBuffer1Vector[0], GL_STATIC_DRAW);
glVertexAttribPointer(2, 3, GL_FLOAT, GL_FALSE, 0, (void*)0);
glEnableVertexAttribArray(2);

//VAO 2
glBindVertexArray(vao2);

//Vertex position buffer:
glBindBuffer(GL_ARRAY_BUFFER, vbo2[0]);
glBufferData(GL_ARRAY_BUFFER, sizeof(GLfloat)*VertPosBuffer2Vector.size(), &VertPosBuffer2Vector[0], GL_STATIC_DRAW);
glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, 0, (void*)0);
glEnableVertexAttribArray(0);   

//Vertex color buffer:
glBindBuffer(GL_ARRAY_BUFFER, vbo2[1]);
glBufferData(GL_ARRAY_BUFFER, sizeof(GLfloat)*VertColorBuffer2Vector.size(), &VertColorBuffer2Vector[0], GL_STATIC_DRAW);
glVertexAttribPointer(1, 3, GL_FLOAT, GL_FALSE, 0, (void*)0);
glEnableVertexAttribArray(1);   

//Vertex normal buffer:
glBindBuffer(GL_ARRAY_BUFFER, vbo2[2]);
glBufferData(GL_ARRAY_BUFFER, sizeof(GLfloat)*VertNormalBuffer2Vector.size(), &VertNormalBuffer2Vector[0], GL_STATIC_DRAW);
glVertexAttribPointer(2, 3, GL_FLOAT, GL_FALSE, 0, (void*)0);
glEnableVertexAttribArray(2);

//Vertex index buffer:
glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, vbo2[3]);
glBufferData(GL_ELEMENT_ARRAY_BUFFER, sizeof(GLuint)*VertIndexBuffer2Vector.size(), &VertIndexBuffer2Vector[0], GL_STATIC_DRAW);
glVertexAttribPointer(3, 3, GL_FLOAT, GL_FALSE, 0, (void*)0);
glEnableVertexAttribArray(3);

//unbind vao
glBindVertexArray(0);
//bind first vao
glBindVertexArray(vao1);

and

//RENDERLOOP

//render objects from vao1 using:
glDrawArrays(GL_TRIANGLES, start, size);

//switch vao
glBindVertexArray(0); 
glBindVertexArray(vao2);

//render objects from vao2 using:
glDrawElements(
   GL_TRIANGLES,        
   start,           
   GL_UNSIGNED_INT, 
   (void*)0         
);

I have checked that the data in my buffers are correct.

Is it correct that the shader doesn't take in any information of indices? The shader will be the same as if I didn't use an index buffer?

Thank you

bofjas bofjas · Accepted Answer · 2016-05-22T11:55:52

The indices are not a vertex attribute. So what you need to do is remove these two lines:

glVertexAttribPointer(3, 3, GL_FLOAT, GL_FALSE, 0, (void*)0);
glEnableVertexAttribArray(3);

I also noticed that you are using the variable "start" as the count argument for glDrawElements. I don't know the values of start and size, but I assume you should use "size" as the second argument in glDrawElements.

Proper way to use indexed VBO

1 Answers