I have a situation that is requiring me to use raw gl commands in the
drawImplementation of an osg::Drawable. I have a double buffer that is
not updated fully until draw time as opposed to update time and I am not
at liberty to change this. Currently in the drawImplementation, I get
the current buffer, then perform glVertex and glNormal commands on the
list of vertices in the buffer. This works just fine and there are no
problems other than it can slow down the scene do to the number of
verts. I was attempting to convert this to a glDrawElements call as a
quick improvement and saw a noticeable performance increase. Everything
is drawing just fine and I haven't found any slow downs or stability
issues, with one exception. If I enable osg::Stats, it crashes
immediately and I have no idea why. I was hoping someone might have some
insight for me. Here is the drawImplementation code:
{
//get the current active buffer
VertBuffer buffer = getCurBuffer();
//set up the client state
glPushClientAttrib(GL_CLIENT_VERTEX_ARRAY_BIT); //crashes immediately
without this
glEnableClientState(GL_VERTEX_ARRAY);
glEnableClientState(GL_NORMAL_ARRAY);
//set up arrays
glVertexPointer(3, GL_FLOAT, 0, (GLvoid*)pmCoords);
glNormalPointer(GL_FLOAT, 0, (GLvoid*)pmNormals);
//draw
if (buffer.vertexList.size() > 0)
{
glDrawElements(GL_TRIANGLES,
buffer.vertexList.size(), GL_UNSIGNED_INT, &(buffer.vertexList)[0]);
}
//disable client state
glDisableClientState(GL_VERTEX_ARRAY);
glDisableClientState(GL_NORMAL_ARRAY);
glPopClientAttrib();
}
In this, VertBuffer, is just a structure that holds a
std::vector<unsigned int> of the vertices to draw (vertexList), and some
other info that is not used during the draw. pmCoords and pmNormals are
lists of all available coordinates and their normals. The vertexList is
just a list of indices in these coordinates to draw at this time.
As I said, everything works fine if the draw is as follows instead:
glBegin(GL_TRIANGLES);
for (int ii = 0; ii < buffer.vertexList.size(); ii+= 3)
{
glNormal3fv(pmNormals[buffer.vertexList[ii]];
glVertex3fv(pmCoords[buffer.vertexList[ii]];
glNormal3fv(pmNormals[buffer.vertexList[ii+1]];
glVertex3fv(pmCoords[buffer.vertexList[ii+1]];
glNormal3fv(pmNormals[buffer.vertexList[ii+2]];
glVertex3fv(pmCoords[buffer.vertexList[ii+2]];
}
glEnd();
I've tried copying the data locally from the buffer and that did nothing
different. I even tried to create a small array locally that contained
the same data. If I only drew 1 triangle it was fine, but if I tried to
draw more, it would sometimes work and sometimes crash.
Karl Cary
SAIC
Software Developer
301-227-5656
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