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objarni's picture

GL.WriteBuffer missing

Posted Wednesday, 28 May, 2008 - 09:17 by objarni in

Where is the equivalent to the c API glWriteBuffer()?

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Inertia's picture

Re: GL.WriteBuffer missing

Posted Wednesday, 28 May, 2008 - 15:25 by Inertia

glDrawBuffer might be what you're looking for?

the Fiddler's picture

Re: GL.WriteBuffer missing

Posted Wednesday, 28 May, 2008 - 17:17 by the Fiddler

I can't find mention of that function anywhere in the specs or the manual, or even the mesa3d headers.

A quick google search returns about 7 results - are you sure such a function exists?

objarni's picture

Re: GL.WriteBuffer missing

Posted Wednesday, 28 May, 2008 - 22:14 by objarni

Ahh! DrawBuffer is the one, thank you!

robpson's picture

Re: GL.WriteBuffer missing

Posted Friday, 30 May, 2008 - 07:05 by robpson

DrawBuffer seems not to work. Shouldnt this sample show the same output if the doublebuffer flag is toggled??:

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Text;
using System.Windows.Forms;
using OpenTK.Graphics;
 
namespace WindowsFormsApplication1
{
  public partial class Form1 : Form
  {
 
    bool doublebuffer = true; // try toggling this!
 
    public Form1()
    {
      InitializeComponent();
      GL.Viewport(0, 0, glControl1.Width, glControl1.Height);
 
      //map coordinates to pixels:
      GL.MatrixMode(MatrixMode.Projection);
      GL.LoadIdentity();
      GL.Ortho(0.0, glControl1.Width, 0.0, glControl1.Height, -1, 1);
 
      GL.ClearColor(Color.Coral);
    }
 
    private void glControl1_Paint(object sender, PaintEventArgs e)
    {
 
      if (!doublebuffer)
        GL.DrawBuffer(DrawBufferMode.Front);
 
      GL.MatrixMode(MatrixMode.Modelview);
      GL.LoadIdentity();
 
      GL.Clear(ClearBufferMask.ColorBufferBit | ClearBufferMask.DepthBufferBit);
 
      GL.Begin(BeginMode.Polygon);
      GL.Color3(1.0, 0.0, 0.0);
      GL.Vertex2(100, 100);
      GL.Color3(0.0, 1.0, 0.0);
      GL.Vertex2(200, 100);
      GL.Color3(0.0, 0.0, 1.0);
      GL.Vertex2(100, 200);
      GL.End();
 
      if (doublebuffer)
        glControl1.SwapBuffers();
    }
 
  }
}
the Fiddler's picture

Re: GL.WriteBuffer missing

Posted Friday, 30 May, 2008 - 08:14 by the Fiddler

I think you are missing a GL.Flush() call:

if (doublebuffer)
    glControl1.SwapBuffers();
else
    GL.Flush();

Also, the GLControl is creating a doublebuffered context - I don't know if this complicates things. Also, single buffering is the devil - I'd avoid subjecting my users to its ugliness. :-)

Inertia's picture

Re: GL.WriteBuffer missing

Posted Friday, 30 May, 2008 - 14:15 by Inertia

GL.DrawBuffer does work, you should check whether there are any GL.Errors and verify what buffer is set with GL.GetInteger( GetPName.DrawBuffer, etc.

Edit: Thanks for pointing at the DrawBuffer function, there's another inconsistency :P

Why do GL.DrawBuffer and GL.DrawBuffers use different enums? They're essentially the same, but DrawBuffers accepts an array of buffers.

I've also missed a couple of tokens when revisiting the enum, it should also contain the ColorAttachment0-15 tokens. If you bind a FBO it will automatically be set to ColorAttachment0 instead of the backbuffer.

Some code might be more clear:

DrawBuffersEnum[] bufs = new DrawBuffersEnum[2] { (DrawBuffersEnum) FramebufferAttachment.ColorAttachment0Ext, (DrawBuffersEnum) FramebufferAttachment.ColorAttachment1Ext };
 
GL.DrawBuffers( bufs.Length, bufs );
 
GL.GetInteger( GetPName.DrawBuffer0, out temp ); // temp==ColorAttachment0, addressed with gl_FragData[0]
GL.GetInteger( GetPName.DrawBuffer1, out temp ); // temp==ColorAttachment1, addressed with gl_FragData[1]

Edit Again: Could it be that the front buffer is protected in some way in double buffered contexts?