pyOpenGL VBOs with index

Question

I want to draw a Rectangle in pyOpenGL using VBOs with indices. I am using the glDrawRangeElements() function for that but I always get the same mistake in the line glDrawRangeElements:

WindowsError: exception: access violation reading 0x00000000

I tried a lot of things and was looking on the internet for the solution and was studying code examples all day so now I really do not know how to go on. It would be nice if someone here could help me.

This is should be the part of the code in which the error is created:

vertexPositions = [[-0.75, -0.75,  0.0],
                    [0.75, -0.75,  0.0],
                    [0.75,  0.75,  0.0],
                   [-0.75,  0.75,  0.0] ]
vertexIndices = [0, 1, 2,
                 1, 2, 3]
vertexComponents = 3

positionBufferObject = None
indexBufferObject = None

x = 0

def glGenVertexArray():
    vao_id = GL.GLuint(0)
    vertex_array_object.glGenVertexArrays(1, vao_id)
    return vao_id.value

def initialize_vertex_buffer():
    global positionBufferObject, indexBufferObject

    indexBufferObject = GL.glGenBuffers(1)
    GL.glBindBuffer(GL.GL_ELEMENT_ARRAY_BUFFER, indexBufferObject)

    array_type = (GL.GLushort * len(vertexIndices))
    GL.glBufferData(GL.GL_ELEMENT_ARRAY_BUFFER, len(vertexIndices) * 2, 
                         array_type(*vertexIndices), GL.GL_STATIC_DRAW)
    GL.glBindBuffer(GL.GL_ELEMENT_ARRAY_BUFFER, 0)

    positionBufferObject = GL.glGenBuffers(1)
    GL.glBindBuffer(GL.GL_ARRAY_BUFFER, positionBufferObject)

    array_type = (GL.GLfloat * len(vertexPositions))
    GL.glBufferData(GL.GL_ARRAY_BUFFER,
                    len(vertexPositions[0])*len(vertexPositions)*sizeOfFloat,
                    array_type(*vertexPositions), GL.GL_STATIC_DRAW
    )
    GL.glBindBuffer(GL.GL_ARRAY_BUFFER, 0)
    glBindVertexArray( glGenVertexArray() )


def init():
    initialize_vertex_buffer()


def display():
    global x
    GL.glClearColor(0.0, 0.0, 0.0, 0.0)
    GL.glClear(GL.GL_COLOR_BUFFER_BIT)

    GL.glMatrixMode(GL.GL_MODELVIEW)
    GL.glEnableClientState(GL.GL_VERTEX_ARRAY)
    GL.glEnableClientState(GL.GL_INDEX_ARRAY)
    GL.glLoadIdentity()
    GL.glTranslate(0, 0, -5)
    GL.glRotate(x, 0, 1, 0)

    GL.glBindVertexArray(glGenVertexArray())
    GL.glBindBuffer(GL.GL_ARRAY_BUFFER, positionBufferObject)
    GL.glBindBuffer(GL.GL_ELEMENT_ARRAY_BUFFER, indexBufferObject)
    GL.glEnableVertexAttribArray(0)

    GL.glDrawRangeElements(GL.GL_TRIANGLES,0, 4, 6, GL.GL_UNSIGNED_SHORT, c_void_p(0))

    #GL.glVertexAttribPointer(0, vertexComponents, GL.GL_FLOAT, False, 0, null)

    #GL.glDrawArrays(GL.GL_QUADS, 0, len(vertexPositions) / vertexComponents)

    GL.glDisableVertexAttribArray(0)
    GL.glDisableClientState(GL.GL_VERTEX_ARRAY)
    GL.glDisableClientState(GL.GL_INDEX_ARRAY)

    pygame.display.flip()

I have to admit that do not really have a clue of all these things yet, just trying to understand it because I need it for a project, so if there are any additional mistakes I have overlooked so far please tell my ;)

Thanks in advance

score 1 · Answer 1 · answered Jan 05 '12 at 04:49

1

Shouldn't your call:

GL.glBindVertexArray (glGenVertexArray())

be

GL.glBindVertexArray (GL.glGenVertexArray())

Also, you probably want to keep track of that vertex array so you can delete it later and free up the resources it uses.

answered Jan 05 '12 at 04:49

user1118321

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actually I defined my own function called glGenVertexArray() – jean-claude91 Jan 05 '12 at 08:47
Still, you don't want to create a new one each time in your `display` function. Just create it once in `init` and reuse it. – kloffy Jul 26 '16 at 06:19

pyOpenGL VBOs with index

1 Answers1