263     protected void bindBuffer(int vertexBuffer, int program, String attribute, int size, int type, int stride, int offset)
264     {
265         int            attributeLocation;
266 
267         attributeLocation = GLES20.glGetAttribLocation(program, attribute);
268 
269         // Binding an object makes it the target of subsequent manipulations.
270         GLES20.glBindBuffer(GLES20.GL_ARRAY_BUFFER, vertexBuffer);
271 
272         GLES20.glVertexAttribPointer(attributeLocation, size, type, false, stride, offset);
273 
274         GLES20.glEnableVertexAttribArray(attributeLocation);
275     }

Notes

We have come a long way by echoing the WebGL code in our OpenGL ES implimentation, but now we need to take a detour and talk about things that are different.

First, lookup the index of the attribute by name with glGetAttribLocation.

Enable the attribute for input by passing that index to glEnableVertexAttribArray.

We are working with multiple buffers so we bind the desired buffer.

glVertexAttribPointer describes exactly how to map the currently bound buffer to the attibute.

• We use the buffer most recently passed into glBindBuffer.
• We map the array to the attribute passed in as attribute.
• Size gives the number of elemements read from the buffer into the attribute. To fill in a vec3 attribute, such as position, 3 entries will be used.
• Each entry is a 32bit floating point number, GLES20.GL_FLOAT is usually passed in as the type.
• Entries are not normalized - the actual provided value is used.
• There are stride bytes start to start for successive values. For a vec3, it will be 4 bytes/float * 3 floats = 12 bytes.
• Start reading data at offset bytes, 0 for the position.