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PODrawing multiple objects from one Vertex Buffer Object in OpenGL/OpenTK
 

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  1. PODrawing multiple objects from one Vertex Buffer Object in OpenGL/OpenTK
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    <p>I am trying to experimenting drawing method using VBO in OpenGL. Many people normally use 1 vbo to store one object data array. I was trying to do something quite opposite which is storing multiple object data into 1 vbo then drawing it. There is story behind why i want to do this. I want to group many of objects as a single object sometime. However my code doesn't do the justice. Following is my pseudo code:</p> <pre><code>//Data int[] _vBO = new int[1]; //vertex buffer objects _triangleVertices = new float[] { 0.0f, 1.0f, 0.0f, -1.0f, -1.0f, 0.0f, 1.0f, -1.0f, 0.0f, //first triangle lineloop, positions in the middle of the screen. 3.0f, 1.0f, 0.0f, 2.0f, -1.0f, 0.0f, 4.0f, -1.0f, 0.0f, //second triangle lineloop, positions on the left side of the first triangle. -3.0f, 1.0f, 0.0f, -4.0f, -1.0f, 0.0f, -2.0f, -1.0f, 0.0f }; //third triangle lineloop, positions on the right side of the first triangle. //Setting Up void init() { GL.GenBuffers(1, _vBO); GL.BindBuffer(BufferTarget.ArrayBuffer, _vBO[0]); GL.BufferData(BufferTarget.ArrayBuffer, new IntPtr(sizeof(float) * _triangleVertices.Length), _triangleVertices, BufferUsageHint.StaticDraw); GL.VertexPointer(3, VertexPointerType.Float, 0, 0); GL.EnableClientState(Array.VertexArray); } //Drawing void display() { GL.Clear(ClearBufferMask.ColorBufferBit); GL.Clear(ClearBufferMask.DepthBufferBit); //setting up camera and projection. float[] eyes = { 0.0f, 0.0f, -10.0f }; float[] target = { 0.0f, 0.0f, 0.0f }; Matrix4 projection = Matrix4.CreatePerspectiveFieldOfView(0.785398163f, 4.0f / 3.0f, 0.1f, 100f); //45 degree = 0.785398163 rads Matrix4 view = Matrix4.LookAt(eyes[0], eyes[1], eyes[2], target[0], target[1], target[2], 0, 1, 0); Matrix4 model = Matrix4.Identity; Matrix4 MV = view * model; GL.MatrixMode(MatrixMode.Projection); GL.LoadIdentity(); GL.LoadMatrix(ref projection); GL.MatrixMode(MatrixMode.Modelview); GL.LoadIdentity(); GL.LoadMatrix(ref MV); GL.Viewport(0, 0, glControlWindow.Width, glControlWindow.Height); GL.Enable(EnableCap.DepthTest); //Enable correct Z Drawings GL.DepthFunc(DepthFunction.Less); //Enable correct Z Drawings GL.MatrixMode(MatrixMode.Modelview); //Draw drawTriangleLineLoops(); //Finally... GraphicsContext.CurrentContext.VSync = true; //Caps frame rate as to not over run GPU glControlWindow.SwapBuffers(); //Takes from the 'GL' and puts into control } void drawTriangleLineLoops() { GL.BindBuffer(BufferTarget.ArrayBuffer, _vBO[0]); GL.VertexPointer(3, VertexPointerType.Float, 0, 0); GL.EnableClientState(ArrayCap.VertexArray); GL.DrawArrays(BeginMode.LineLoop, 0, 3); //drawing first triangle lineloop, first vertex starts at index 0. GL.DrawArrays(BeginMode.LineLoop, 9, 3); //drawing second triangle lineloop, first vertex starts at index 9. GL.DrawArrays(BeginMode.LineLoop, 18, 3); //drawing third triangle lineloop, first vertex starts at index 18. GL.DisableClientState(ArrayCap.VertexArray); } </code></pre> <p>I expect 3 different triangles to be drawn, but only one was drawn. I don't know what went wrong.</p> <p><img src="https://dl.dropboxusercontent.com/u/13010803/TriangleLineLoops.jpg" alt="Line Loop Error"></p>
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    1. USstoney78us
    1. USstoney78us
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      1. PODrawing multiple objects from one Vertex Buffer Object in OpenGL/OpenTK
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      1. VTUpMod
    1. COUnrelated, but why on earth are you using double-precision floating-point vertex attributes? You will not gain anything by doing this, most hardware (pre-D3D11/OpenGL 4) is not even capable of using double-precision FP for vertex attributes - the driver winds up converting it to single-precision. You're basically wasting client memory and increasing driver overhead by using this.
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      1. PODrawing multiple objects from one Vertex Buffer Object in OpenGL/OpenTK
      1. USAndon M. Coleman
    2. CO@AndonM.Coleman Interesting, I would expect proffesional-grade GPUs such as Quadro to be able to handle this.
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      1. PODrawing multiple objects from one Vertex Buffer Object in OpenGL/OpenTK
      1. USBartek Banachewicz
    3. COThanks for ur comment. The vertex data that i read in is in double. I didn't want to convert it to float at this point, but you are right double-precision floating-point is inefficient.
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      1. PODrawing multiple objects from one Vertex Buffer Object in OpenGL/OpenTK
      1. USstoney78us
 

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