yuriks's picture

VBO problems: nothing gets drawn

Hey. I'm having some issues using VBOs. This is the code I have right now:

        public void Draw(Point position)
            int[] vertexData = {
                                                     position.X, position.Y,
                                                     position.X + Image.Width, position.Y,
                                                     position.X, position.Y + Image.Height,
                                                     position.X + Image.Width, position.Y + Image.Height
            uint glVertexBuffer;
            GL.GenBuffers(1, out glVertexBuffer);
            GL.BindBuffer(BufferTarget.ArrayBuffer, glVertexBuffer);
            GL.BufferData(BufferTarget.ArrayBuffer, (IntPtr)(vertexData.Length * sizeof(int)), vertexData, BufferUsageHint.StreamDraw);
            int size; // This is 32, like it should be so I assumed the buffer got uploaded correctly.
            GL.GetBufferParameter(BufferTarget.ArrayBuffer, BufferParameterName.BufferMapped, out size);
            GL.BindBuffer(BufferTarget.ArrayBuffer, glVertexBuffer);
            GL.VertexPointer(2, VertexPointerType.Int, 0, 0);
            //GL.BindTexture(TextureTarget.Texture2D, glTexture);
            GL.Color3(1.0f, 1.0f, 1.0f);
            GL.BindBuffer(BufferTarget.ArrayBuffer, glVertexBuffer);
            GL.DrawArrays(BeginMode.TriangleStrip, 0, vertexData.Length);
            GL.BindBuffer(BufferTarget.ArrayBuffer, 0);
            GL.DeleteBuffers(1, ref glVertexBuffer);
            GL.TexCoord2(0, 0);
            GL.Vertex2(position.X, position.Y);
            GL.TexCoord2(1, 0);
            GL.Vertex2(position.X + Image.Width, position.Y);
            GL.TexCoord2(0, 1);
            GL.Vertex2(position.X, position.Y + Image.Height);
            GL.TexCoord2(1, 1);
            GL.Vertex2(position.X + Image.Width, position.Y + Image.Height);

I call SwapBuffer later on in another function. The commented out immediate mode section is what I want to replace, and that works fine, but using VBOs, nothing get's drawn. I've checked using GL.GetError after every function call and no errors are reported. Anyone got a clue on what I'm doing wrong?


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the Fiddler's picture

Actually, this has been tried before: Tao 1.3 universally replaced void* with array types (float[], float[,], float[,,], byte[], byte[,], ...), IIRC ~20 overloads for each void* (bloated), when only five or six were valid at any time (incorrect). And what if you actually needed a float[][]? (inflexible)

Sometimes the simplest solution is the best one.

What we could do is detect 0 and replace it with IntPtr.Zero (adding overhead). Or we could document that you should use IntPtr.Zero instead of 0.

Right now, I'm leaning towards the latter - but I'm always open to ideas.

Just to clarify this, the following ideas are impossible:

  1. We cannot detect the correct overloads automatically (no such info in the specs).
  2. We cannot add the correct overloads by hand (too many, too error prone).
objarni's picture

I can see the (practical) problem of "X number of overloads", yes. So I rest my case :)