QGLBuffer

fbucek

Hello, I have problem with QGLBuffer. I did not find any example so I do not know how exactly it works.

In this example I am drawing some tria elements, which is working correctly when QGLBuffer is NOT used.

When I use QGLBuffer, function glDrawElements causes application to crash.

It looks like array copied to buffer is different from source.

This is the fragment of code.

@
GLuint list = glGenLists(1);
glNewList(list, GL_COMPILE);

GLfloat faceColor[4];
faceColor[0] = qtGreen.redF();
faceColor[1] = qtGreen.greenF();
faceColor[2] = qtGreen.blueF();
faceColor[3] = qtGreen.alphaF();

m_vertexBuffer = new QGLBuffer(QGLBuffer::VertexBuffer);
m_vertexBuffer->create();

m_vertexBuffer->bind();
m_vertexBuffer->setUsagePattern(QGLBuffer::StaticDraw);
m_vertexBuffer->allocate(vertices.constData(), vertices.count());

glEnableClientState(GL_VERTEX_ARRAY);

glVertexPointer(3, GL_FLOAT, 0, 0); // THIS IS NOT WORKING - glDrawElements cause app to crash.
// glVertexPointer(3, GL_FLOAT, 0, vertices.constData()); // THIS IS WORKING PERFECTLY glDrawElements draws elements as intended.

glPushMatrix();
glMaterialfv(GL_FRONT, GL_AMBIENT_AND_DIFFUSE, faceColor);
glDrawElements(GL_TRIANGLES,m_count, GL_UNSIGNED_INT, m_index.constData()); // AFTER CALLING THIS FUNCTION APP CRASHES ( when i use QGLBuffer.
//checkGLError();
glDisableClientState(GL_VERTEX_ARRAY);
glPopMatrix();
glEndList();

return list;
@

Do you have any idea what can be wrong.

Thank you very much.

Typhlosion

Do not forget to release the GLBuffer when you don't need it anymore.
But I am having issues with this QGLBuffer too.
Any working example would be fine...

baysmith

Try changing
@
m_vertexBuffer->allocate(vertices.constData(), vertices.count());
@
to
@
m_vertexBuffer->allocate(vertices.constData(), vertices.count() * sizeof(GLfloat));
@

The second argument to "allocate":http://doc.qt.nokia.com/4.7/qglbuffer.html#allocate expects the number of bytes of space required, not the number of vertices.

nicolauz

i just stumbled of the same problem.
Have you found a solution?

nicolauz

never mind ... i used setAttributeArray instead of using setAttributeBuffer