VBO problem with triangle strip

Newbie & Debugging Questions
#1

Hi all,

I have a problem using a VBO in combination with a triangle strip. The program crashes when I use a larger geometry (128x128 points) and with a smaller geometry (32x32) the program runs but I see a lot of extra triangles.

The programs executes perfectly when I disable VBO’s (see code in green bold).

I think the problem is in the way I define the ELEMENT_ARRAY_BUFFER, but nothing seems to help.

Using a vbo for the geometry and the non vbo version for the glDrawElements results in a guaranteed crash :slight_smile:

Any help is appreciated ???

public void draw(ViewPoint vp, GL gl, GLU glu, DrawingMode mode) {
final boolean VBOSupported = gl.isFunctionAvailable(“glGenBuffersARB”) &&
gl.isFunctionAvailable(“glBindBufferARB”) &&
gl.isFunctionAvailable(“glBufferDataARB”) &&
gl.isFunctionAvailable(“glDeleteBuffersARB”);

    TerrainTriangleStrip strip =refinement.refineTerrain(vp);
    
    if (VBOSupported){
        if ( !vboCreated){
            terrainData.rewind();
            int[] id = new int[2];
            gl.glGenBuffersARB(2,id,0);
            
            vboID = id[0];
            indicesID = id[1];
            gl.glBindBufferARB(GL.GL_ARRAY_BUFFER_ARB,vboID);
            System.out.println(glu.gluErrorString(gl.glGetError()));
            gl.glBufferDataARB(GL.GL_ARRAY_BUFFER_ARB,
                    terrainData.limit(),terrainData,GL.GL_STATIC_DRAW_ARB);
            System.out.println(glu.gluErrorString(gl.glGetError()));
            vboCreated = true;
            System.out.println("VBO created");
        }
        gl.glBindBufferARB(GL.GL_ARRAY_BUFFER_ARB,vboID);
        gl.glInterleavedArrays(GL.GL_N3F_V3F,0,0);
        [b]gl.glBindBufferARB(GL.GL_ELEMENT_ARRAY_BUFFER_ARB,indicesID);
        gl.glBufferDataARB(GL.GL_ELEMENT_ARRAY_BUFFER_ARB,
                strip.getSize()*Integer.SIZE,strip.getStrip(),GL.GL_STATIC_DRAW_ARB);
        gl.glDrawElements(GL.GL_TRIANGLE_STRIP,strip.getSize(),GL.GL_UNSIGNED_INT,0);[/b]
    }
    
    [b]if ( ! VBOSupported){
        strip.getStrip().rewind();
        terrainData.rewind();
        gl.glPolygonMode(GL.GL_FRONT_AND_BACK, GL.GL_LINE);
        gl.glInterleavedArrays(GL.GL_N3F_V3F,0,terrainData);
        gl.glDrawElements(GL.GL_TRIANGLE_STRIP,strip.getSize(),GL.GL_UNSIGNED_INT,strip.getStrip());
    }[/b]
}
#2

I’m one step closer to the solution of my problem. I specified a STATIC DRAW buffer but this crashes with a lot of geometric data. When I specify a STREAM DRAW vbo buffer my application doesn’t crash anymore, BUT

I get a lot of extra triangles in my application. A lot of vertices seem to connect back to index 0, which is really strange to say the least.
(say attached screenshot)

Without vbo’s the same triangle strip is rendered correctly.

Anybody have any idea what could be the cause ? ???

#3

I really gave it some time, but LWJGL is quite a bit different from JOGL in this case.

Anyway, suppose you passed all the right arguments, the only difference I see is that you don’t rewind your strip in your VBO code.

#4

Thanks Riven, but I found my mistake (good thing this is the clueless newbie section)

I didn’t specify the correct size for my buffers.
I used the limit() function to get the size for the vbo buffer , but offcourse it has to be terrainData.limit()*4 (float size),same goes for the triangle strip buffer.

#5

Ah, right, LWJGL does that all for you, as it respects the position/limit of the Buffer. You also wouldn’t need to pass GL_UNSIGNED_INT if you passed an IntBuffer. JOGL seems a tiny bit more lowlevel on this one.