How to create and use VBOs in OpenGL ES 2

Question

I am looking for help with understanding VBOs. I have done a ton of research and have found tutorials on the subject, but they are still vague to me. I have a few questions:

Where should a VBO be created, and how should I create one?

I am currently using the code right below to initialize my vertex and index buffers:

    vertices = new float[]
            {
                    p[0].x, p[0].y, 0.0f,
                    p[1].x, p[1].y, 0.0f,
                    p[2].x, p[2].y, 0.0f,
                    p[3].x, p[3].y, 0.0f,
            };

    // The order of vertex rendering for a quad
    indices = new short[] {0, 1, 2, 0, 2, 3};

    ByteBuffer bb = ByteBuffer.allocateDirect(vertices.length * 4);
    bb.order(ByteOrder.nativeOrder());
    vertexBuffer = bb.asFloatBuffer();
    vertexBuffer.put(vertices);
    vertexBuffer.position(0);

    ByteBuffer dlb = ByteBuffer.allocateDirect(indices.length * 2);
    dlb.order(ByteOrder.nativeOrder());
    drawListBuffer = dlb.asShortBuffer();
    drawListBuffer.put(indices);
    drawListBuffer.position(0);

If I am correct, this is not creating a VBO. So, if I wanted to make a VBO, would the code to create a VBO go right after the code listed above? If so, how would it be created?

Also, how is a VBO rendered and drawn to screen?

Is it rendered and drawn the same way as just using vertex and index arrays? If not, what is the process? Currently, I render and draw my objects as shown in the code below:

    GLES20.glUseProgram(GraphicTools.sp_SolidColor);

    mPositionHandle =
            GLES20.glGetAttribLocation(GraphicTools.sp_SolidColor, "vPosition");

    GLES20.glEnableVertexAttribArray(mPositionHandle);

    GLES20.glVertexAttribPointer(mPositionHandle, 3,
            GLES20.GL_FLOAT, false,
            0, vertexBuffer);

    mtrxHandle = GLES20.glGetUniformLocation(GraphicTools.sp_SolidColor,
            "uMVPMatrix");

    GLES20.glUniformMatrix4fv(mtrxHandle, 1, false, m, 0);

    GLES20.glDrawElements(GLES20.GL_TRIANGLES, indices.length,
            GLES20.GL_UNSIGNED_SHORT, drawListBuffer);

    GLES20.glDisableVertexAttribArray(mPositionHandle);

If you have any questions, let me know. Thanks in advance.

Answer 1

A Vertex Buffer Object is a buffer where vertex array data can be stored. The data are uploaded one time to the graphics memory (GPU) and can be used repeatedly to draw a mesh.

First you have to create 2 buffer objects, one for the vertices and one for the indices:

int buffers[] = new int[2];
GLES20.glGenBuffers(2, buffers, 0);
int vbo = buffers[0];
int ibo = buffers[1];

Then you have to bind the buffer and to transfer the data

GLES20.glBindBuffer(GLES20.GL_ARRAY_BUFFER, vbo);
GLES20.glBufferData(
    GLES20.GL_ARRAY_BUFFER,
    vertexBuffer.capacity() * 4, // 4 = bytes per float
    vertexBuffer,
    GLES20.GL_STATIC_DRAW);
GLES20.glBindBuffer(GLES20.GL_ARRAY_BUFFER, 0);

GLES20.glBindBuffer(GLES20.GL_ELEMENT_ARRAY_BUFFER, ibo);
GLES20.glBufferData(
    GLES20.GL_ELEMENT_ARRAY_BUFFER,
    drawListBuffer.capacity() * 2, // 2 = bytes per short
    drawListBuffer,
    GLES20.GL_STATIC_DRAW);
GLES20.glBindBuffer(GLES20.GL_ELEMENT_ARRAY_BUFFER, 0);

If you want to draw the mesh, then you have to define the array of generic vertex attribute data and you have to bind the index buffer, but you don't have to transfer any data to the GPU:

GLES20.glBindBuffer(GLES20.GL_ARRAY_BUFFER, vbo);
GLES20.glVertexAttribPointer(
        mPositionHandle, 3,
        GLES20.GL_FLOAT, false,
        0, 0);                        // <----- 0, because "vbo" is bound
GLES20.glEnableVertexAttribArray(mPositionHandle);

GLES20.glBindBuffer(GLES20.GL_ELEMENT_ARRAY_BUFFER, ibo);
GLES20.glDrawElements(
    GLES20.GL_TRIANGLES, indices.length,
    GLES20.GL_UNSIGNED_SHORT, 0);     // <----- 0, because "ibo" is bound

GLES20.glDisableVertexAttribArray(mPositionHandle);
GLES20.glBindBuffer(GLES20.GL_ARRAY_BUFFER, 0);
GLES20.glBindBuffer(GLES20.GL_ELEMENT_ARRAY_BUFFER, 0);

See also An Introduction to Vertex Buffer Objects (VBOs)