bytes are 1 bit offset [Resolved]
Posted Thursday, 30 April, 2009 - 08:47 by Anonymous| Project: | The Open Toolkit library |
| Version: | 0.9.7 |
| Component: | Code |
| Category: | support request |
| Priority: | minor |
| Assigned: | Typhon |
| Status: | closed |
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Disclaimer: I'm new to OpenGL/TK, so this could very well be my own fault.
I made a VBO ( a 64x64 square grid ), and in order to do picking, I'm using the vertex colors to determine which grid square I've clicked on. Note: I'm using LINQ for clarity of the concept -- I'm aware of the performance implications.
public void GeneratePickVBO() { var vertices = faces // get a list of [face, faceIndex, vertex] // each faceindex shows up 4 times, once per vertex in that face .SelectMany( (face, i) => face.vertices.Select(v => new { vertex = v, index = i })) // convert to list of [vertex] .Select(v => { return new PickVertex() { RGBA = (uint)v.index, Position = v.vertex.Position };}) .ToArray(); GL.BindBuffer(BufferTarget.ArrayBuffer, vboPickID[0]); GL.BufferData(BufferTarget.ArrayBuffer, (IntPtr)(vertices.Length * Marshal.SizeOf(typeof(PickVertex))), vertices, BufferUsageHint.DynamicDraw); pickReady = true; }
where pickVertex is shown below (Marshal.SizeOf(typeof(PickVertex)) returns 16, as expected)
[StructLayout(LayoutKind.Sequential)] struct PickVertex { public UInt32 RGBA; public Vector3 Position; }
and the rendering code is
GL.Enable(EnableCap.VertexArray); GL.Enable(EnableCap.ColorArray); GL.BindBuffer(BufferTarget.ArrayBuffer, mesh.vboPickID[0]); GL.InterleavedArrays(InterleavedArrayFormat.C4ubV3f, 0, IntPtr.Zero); GL.DrawArrays(BeginMode.Quads, 0, mesh.faces.Count * 4); byte[] pixels = new byte[10]; GL.ReadPixels<byte>(MapZone.X, MapZone.Y, 1, 1, PixelFormat.Rgb, PixelType.Byte, pixels); Message.Post("foo", "RenderPick: [{0:X}] [{1:X}] [{2:X}] [{3:x}]", pixels[0], pixels[1], pixels[2], pixels[3]);
So the following image is produced:
Anyways, the problem is that every 2 adjacent squares has the same red-byte (so the progression is 00,00,01,01,02,02) etc. ditto for when the green byte comes into play. the first two are 00, the second couple are 01, etc.
I checked and I can partially fix the problem with the change, which skips the lowest-order bit of the red component. I'd have to shift a hole in the lowest order-bit of the green and blue as well in order to accomplish a more complete solution:
RGBA = (uint)v.index*2U,
Thoughts?
Comments
#1
Sorry, wasn't logged in. Anyways, I just opened the screenshot and took samples of the pixels, and they are correctly drawn. So the error comes when I'm ReadPixeling them back out.
Ooops I figured it out. I'm reading them out as PixelFormat.Byte instead of PixelFormat.UnsignedByte. dumb mistake.
#2
#3