CODEWITHSUNDEEP
openglparameters
proggamer12
proggamer12

Reputation: 302

What does the last parameter of glVertexAttribPointer mean?

I began learning OpenGL, but I don't understand what the last parameter in glVertexAttribPointer means.

Upvotes: 0

Views: 509

Answers (1)

GraphicsMuncher
GraphicsMuncher

Reputation: 4641

It's a pointer offset into the array you're using. However, it's a byte count that you have to cast to a pointer, which isn't exactly intuitive.

If you're using interleaved attributes, it's the number of bytes from the beginning to the first instance of that attribute.

Example:

VVVNNNTTVVVNNTT

Where Vertex position data, N is the normal vector, and T is the texture corodinate.

The offset for V is 0 (it's at the beginning)

The offset for N is (GLvoid*) (3*sizeof(vertex data type))

The offset for T is (GLvoid*) (3*sizeof(vertex data type) + 3*sizeof(normal data type) )

Furthermore, if you have successive attributes, it would be the starting point for each attribute as well.

Example:

VVVV...VVVNNN...NNNTT...TT

The offset for V is 0 (it's at the beginning)

The offset for N is (GLvoid*) (3*sizeof(vertex data type)*number_of_vertices)

The offset for T is (GLvoid*) (3*sizeof(vertex data type)*number_of_vertices + 3*sizeof(normal data type)*number_of_normals)

Upvotes: 4

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