jogamp - Multiple VAO and VBO with JOGL

jogamp › jogl

Multiple VAO and VBO with JOGL

Posted by Chen norris on Apr 19, 2018; 5:48pm
URL: https://forum.jogamp.org/Multiple-VAO-and-VBO-with-JOGL-tp4038824.html

Hello everyone,

This is my very first post in here about JOGL so sorry in advance if I missed a step before posting in here.
The problem I'm facing deals with VAO/VBO comprehension. As an example, I'd like to render a square in very specific (and not optimized) way : I would like to render two triangles with two different VAOs. The structure of my code looks like this :

INIT :

creation of two VAOs (one for each triangle),
creation of three VBOs (position, color and index). As far as I understood, the number of VBOs to create doesn't rely on the number of VAOs that's why I don't need to create six VBOs but only as many VBOs as I have attributes (a VBO for the position, a VBO for the color and a VBO for the index, shared between all VAOs),
binding of the first VAO, then buffering the first triangle's attributes (3 positions, 3 colors and 3 indices),
binding of the second VAO, then buffering the second triangle's attributes (3 positions, 3 colors and 3 indices).

RENDERING :

binding of the first VAO, call to glDrawElement method, and unbinding the first VAO,
binding of the second VAO, call to glDrawElement method, and unbinding the second VAO.

My code for the init part is then the following :

    // creation of two VAOs

    int[] tempVertexArrayObject = new int[2];

    gl3.glGenVertexArrays(2, tempVertexArrayObject, 0);

    vaoId1 = tempVertexArrayObject[0];

    vaoId2 = tempVertexArrayObject[1];

    // creation of three VBOs

    IntBuffer idArray = GLBuffers.newDirectIntBuffer(3);

    gl3.glGenBuffers(3, idArray);

    positionBufferId = idArray.get(0);

    colorBufferId = idArray.get(1);

    indexBufferId = idArray.get(2);

    // binding and buffering the first VAO

    gl3.glBindVertexArray(vaoId1);

    // buffering positions

    gl3.glBindBuffer(GL.GL_ARRAY_BUFFER, positionBufferId);

    gl3.glBufferData(GL.GL_ARRAY_BUFFER, positionBuffer.capacity() * Buffers.SIZEOF_FLOAT, positionBuffer, GL.GL_STATIC_DRAW);

    gl3.glEnableVertexAttribArray(positionHandler);

    gl3.glVertexAttribPointer(positionHandler, 3, GL.GL_FLOAT, false, 0, 0);

    gl3.glBindBuffer(GL.GL_ARRAY_BUFFER, 0);

    // buffering colors

    gl3.glBindBuffer(GL.GL_ARRAY_BUFFER, colorBufferId);

    gl3.glBufferData(GL.GL_ARRAY_BUFFER, colorBuffer.capacity() * Buffers.SIZEOF_FLOAT, colorBuffer, GL.GL_STATIC_DRAW);

    gl3.glEnableVertexAttribArray(colorHandler);

    gl3.glVertexAttribPointer(colorHandler, 4, GL.GL_FLOAT, false, 0, 0);

    gl3.glBindBuffer(GL.GL_ARRAY_BUFFER, 0);

    // buffering indices

    gl3.glBindBuffer(GL.GL_ELEMENT_ARRAY_BUFFER, indexBufferId);

    gl3.glBufferData(GL.GL_ELEMENT_ARRAY_BUFFER, indexBuffer.capacity() * Buffers.SIZEOF_INT, indexBuffer, GL.GL_STATIC_DRAW);

    // binding and buffering the second VAO + buffering positions + ...

    // same as before, but gl.glBindVertexArray(vaoId2) instead of gl.glBindVertexArray(vaoId1), and with other buffers

    // that contain data for the other triangle

My code for the rendering part is the following :

    // Drawing the first triangle

    gl3.glBindVertexArray(vaoId1);

    gl3.glDrawElements(GL3.GL_TRIANGLES, 3, GL3.GL_UNSIGNED_INT, 0);

    gl3.glBindVertexArray(0);

    // Drawing the second triangle

    gl3.glBindVertexArray(vaoId2);

    gl3.glDrawElements(GL3.GL_TRIANGLES, 3, GL3.GL_UNSIGNED_INT, 0);

    gl3.glBindVertexArray(0);

Of course, I didn't put the part where I clear my background, I enable depth test, ...
My problem is that only the second triangle is drawn, as if buffering data when VAO #2 is binded buffers data for VAO #1. Another strange behavior I can see is that when I only call the Drawing the first triangle instructions, I can see my second triangle.

Any advice on something I misunderstood or on something I may do wrong ?

Thanks in advance for your help.