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POUsing OpenTK (z-indexing)
 

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  1. POUsing OpenTK (z-indexing)
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    <p>I'm doing a cross between following some NeHe tutorials (translating it to OpenTK) and an OpenTK sample I found online to draw a triangle (for a simple initial setup):</p> <pre><code>using System; using System.Collections.Generic; using System.Linq; using System.Text; using System.Drawing; using System.Diagnostics; using System.IO; using OpenTK; using OpenTK.Graphics; using OpenTK.Graphics.OpenGL; using System.Windows.Forms; namespace GravSimBasic { class GLMain : GameWindow { int vbo; Vector3[,] vertices; float time = 0.01f; void CreateVertexBuffer() { vertices = new Vector3[2,3]; vertices[0,0] = new Vector3(-1f, -1f, (float)Math.Sin(time)); vertices[0, 1] = new Vector3(0.5f, -1f, (float)Math.Sin(time)); vertices[0, 2] = new Vector3(-0.25f, 1f, -(float)Math.Sin(time)); vertices[1, 0] = new Vector3(-0.5f, -1f, (float)Math.Cos(time)); vertices[1, 1] = new Vector3(1f, -1f, (float)Math.Cos(time)); vertices[1, 2] = new Vector3(0.25f, 1f, -(float)Math.Cos(time)); //MessageBox.Show("Length: " + vertices.Length.ToString()); GL.GenBuffers(1, out vbo); GL.BindBuffer(BufferTarget.ArrayBuffer, vbo); GL.BufferData&lt;Vector3&gt;(BufferTarget.ArrayBuffer, new IntPtr(vertices.Length * Vector3.SizeInBytes), vertices, BufferUsageHint.StaticDraw); } protected override void OnLoad(EventArgs e) { //set the window area GL.Viewport(0, 0, 400, 400); //background color GL.ClearColor(Color.Black); //set the view area GL.MatrixMode(MatrixMode.Projection); GL.LoadIdentity(); GL.Ortho(-2, 2, -2, 2, 2, -2); //now back to 'scene editing' mode GL.MatrixMode(MatrixMode.Modelview); GL.LoadIdentity(); //make things look nice GL.ShadeModel(ShadingModel.Smooth); //set up our z-rendering logic GL.ClearDepth(2.0000f); GL.Enable(EnableCap.DepthTest); GL.DepthFunc(DepthFunction.Lequal); //other improvements to quality GL.Hint(HintTarget.PerspectiveCorrectionHint, HintMode.Nicest); GL.Hint(HintTarget.LineSmoothHint, HintMode.Nicest); //initialize our scene data CreateVertexBuffer(); } protected override void OnRenderFrame(FrameEventArgs e) { time += 0.01f; vertices[0, 0].Z = (float)Math.Sin(time); vertices[0, 1].Z = (float)Math.Sin(time); vertices[0, 2].Z = -(float)Math.Sin(time); vertices[1, 0].Z = (float)Math.Cos(time); vertices[1, 1].Z = (float)Math.Cos(time); vertices[1, 2].Z = -(float)Math.Cos(time); GL.BufferData&lt;Vector3&gt;(BufferTarget.ArrayBuffer, new IntPtr(vertices.Length * Vector3.SizeInBytes), vertices, BufferUsageHint.StaticDraw); System.Threading.Thread.Sleep(10); GL.Clear(ClearBufferMask.ColorBufferBit); GL.EnableVertexAttribArray(0); GL.BindBuffer(BufferTarget.ArrayBuffer, vbo); GL.Color4(0.75f,0.0f,0.0f,0.25f); GL.VertexAttribPointer(0, 3, VertexAttribPointerType.Float, false, 0, 0); GL.DrawArrays(BeginMode.Triangles, 0, 3); GL.Color4(0.0f, 0.75f, 0.0f, 0.55f); GL.VertexAttribPointer(3, 3, VertexAttribPointerType.Float, false, 0, 0); GL.DrawArrays(BeginMode.Triangles, 3, 3); GL.DisableVertexAttribArray(0); SwapBuffers(); } } } </code></pre> <p>I suspect the issue is in lines 58-60, but I've changed the value in line 58 between -2.0, 0.00001, and 2.0, none changed the results. It could be the perspective setup a few lines earlier, though. I've tried almost all the functions available as a parameter for line 60 - Lequal seems to be the best option by what I would <em>expect</em>, and it does produce the closest result to what I want, but it isn't quite correct.</p> <p>Setup: There is a green and red triangle. They partially overlap on the x-y axis. The top z-axis of one is mapped by a -sin(time) function, and the bottom, a sin(time) function. The other uses cos() instead of sin, but is otherwise the same. The 'time' value changes each rendering.</p> <p>What I want/expect: Two overlapping triangles - one red, one green. As that rotate back and forth, the non-overlapping portion of each should always be visible, and the overlapping portions should only show the foremost triangle.</p> <p>What I get: (a) nothing (b) a display of both triangles, one on top of other. (c) A changing image of bits of one, both or none of the triangles - even if one or both are showing, the are bits of either triangle, that should be visible, that are missing (background).</p> <p>If I remove time, it shows a correct snapshot - the red triangle in front in the bottom half, and the green in front on the top.</p> <p>Can anyone help diagnose this?</p>
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