Graphics Reference
In-Depth Information
token are used to create buffer objects that will store indices of a primitive.
Other buffer object types in OpenGL ES 3.0 are described elsewhere in this
book: uniform buffers (Chapter 4), transform feedback buffers (Chapter 8),
pixel unpack buffers (Chapter 9), pixel pack buffers (Chapter 11), and
copy buffers (the
Copying Buffer Objects
section later in this chapter).
For now, we will focus on the buffer objects used for specifying vertex
attributes and element arrays.
Note:
To get best performance, we recommend that OpenGL ES 3.0
applications use vertex buffer objects for vertex attribute data and
element indices.
Before we can render using buffer objects, we need to allocate the
buffer objects and upload the vertex data and element indices into
appropriate buffer objects. This is demonstrated by the sample code in
Example 6-4.
Example 6-4
Creating and Binding Vertex Buffer Objects
void initVertexBufferObjects(vertex_t *vertexBuffer,
GLushort *indices,
GLuint numVertices,
GLuint numlndices,
GLuint *vboIds)
{
glGenBuffers(2, vboIds);
glBindBuffer(GL_ARRAY_BUFFER, vboIds[0]);
glBufferData(GL_ARRAY_BUFFER, numVertices *
sizeof(vertex_t), vertexBuffer,
GL_STATIC_DRAW);
// bind buffer object for element indices
glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, vboIds[1]);
glBufferData(GL_ELEMENT_ARRAY_BUFFER,
numIndices * sizeof(GLushort),
indices, GL_STATIC_DRAW);
}
The code in Example 6-4 creates two buffer objects: a buffer object to store
the actual vertex attribute data, and a buffer object to store the element
indices that make up the primitive. In this example, the
glGenBuffers
command is called to get two unused buffer object names in
vboIds
.
The unused buffer object names returned in
vboIds
are then used to
create an array buffer object and an element array buffer object. The array
