OpenGL/SharpGL - Points only on -near surface of Ortho projection?
- by FTLPhysicsGuy
When you create points using three dimensions for each point and you use an Ortho projection to view the points, would there be a reason that only the points on the -near surface would appear? For example, if you use (the SharpGL method) gl.Ortho(0, width, height, 0, -10, 10), only the points at z=10 (because the near surface is at -10) actually show up.
I'm currently using SharpGL - but I'm hoping the issue I'm having isn't with that particular implementation/library.
EDIT: I'm adding the code below that demonstrates the issue. Note that this example requires SharpGL and is in fact a modification of a WPF sample project that comes with the current SharpGL source code (the original sample project is called TwoDSample).
The project requires a MainWindow.xaml and a MainWindow.xaml.cs. Here's the xaml:
<Window x:Class="TwoDSample.MainWindow"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
Title="MainWindow" Height="350" Width="525"
xmlns:my="clr-namespace:SharpGL.WPF;assembly=SharpGL.WPF">
<Grid>
<my:OpenGLControl Name="openGLControl1" OpenGLDraw="openGLControl1_OpenGLDraw" OpenGLInitialized="openGLControl1_OpenGLInitialized"
Resized="openGLControl1_Resized"/>
</Grid>
</Window>
Here is the code behind:
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Data;
using System.Windows.Documents;
using System.Windows.Input;
using System.Windows.Media;
using System.Windows.Media.Imaging;
using System.Windows.Navigation;
using System.Windows.Shapes;
using SharpGL.Enumerations;
namespace TwoDSample
{
/// <summary>
/// Interaction logic for MainWindow.xaml
/// </summary>
public partial class MainWindow : Window
{
public MainWindow()
{
InitializeComponent();
}
// NOTE: I use this to restrict the openGLControl1_OpenGLDraw method to
// drawing only once after m_drawCount is set to zero;
int m_drawCount = 0;
private void openGLControl1_OpenGLDraw(object sender, SharpGL.SceneGraph.OpenGLEventArgs args)
{
// NOTE: Only draw once after m_drawCount is set to zero
if (m_drawCount < 1)
{
// Get the OpenGL instance.
var gl = args.OpenGL;
gl.Color(1f, 0f, 0f);
gl.PointSize(2.0f);
// Draw 10000 random points.
gl.Begin(BeginMode.Points);
Random random = new Random();
for (int i = 0; i < 10000; i++)
{
double x = 10 + 400 * random.NextDouble();
double y = 10 + 400 * random.NextDouble();
double z = (double)random.Next(-10, 0);
// Color the point according to z value
gl.Color(0f, 0f, 1f); // default to blue
if (z == -10)
gl.Color(1f, 0f, 0f); // Red for z = -10
else if (z == -1)
gl.Color(0f, 1f, 0f); // Green for z = -1
gl.Vertex(x, y, z);
}
gl.End();
m_drawCount++;
}
}
private void openGLControl1_OpenGLInitialized(object sender, SharpGL.SceneGraph.OpenGLEventArgs args)
{
}
private void openGLControl1_Resized(object sender, SharpGL.SceneGraph.OpenGLEventArgs args)
{
// NOTE: force the draw routine to happen again when resize occurs
m_drawCount = 0;
// Get the OpenGL instance.
var gl = args.OpenGL;
// Create an orthographic projection.
gl.MatrixMode(MatrixMode.Projection);
gl.LoadIdentity();
// NOTE: Basically no matter what I do, the only points I see are those at
// the "near" surface (with z = -zNear)--in this case, I only see green points
gl.Ortho(0, openGLControl1.ActualWidth, openGLControl1.ActualHeight, 0, 1, 10);
// Back to the modelview.
gl.MatrixMode(MatrixMode.Modelview);
}
}
}
