Cannot get the correct name stack in OpenTK
I am referring to LWJGL tutorial here (https://www.youtube.com/watch?v=V9e7A4konHo) for the picking. The source code for this tutorial can be found here (https://docs.google.com/document/d/1MEcdkcCCM-BKmuL2Rg5SR-_RG6cCH7Ek9_hU7xXlW4Y/pub).
Basically what I want to do here is to translate this Java code into C# code using OpenTK. In this code, there are 2 objects (rectangles) being rendered to screen. Then I want to get the correct name stack when I click on the object. However, when I run my code, I only get the same name of 1, even though I click on other object. Also, when I click on the object, the screen get zoom in, which is not I want.
I am not sure what is wrong in my code. What I suspect the wrong part is the GluPickMatrix function. Here is my code:
using System;
using OpenTK;
using OpenTK.Graphics.OpenGL;
using OpenTK.Input;
namespace OpenTkSelectTry
{
public class Game2D
{
GameWindow window;
private int BUFSIZE = 512;
public Game2D(GameWindow wd)
{
this.window = wd;
start();
}
public void start()
{
window.Load += loaded;
window.Resize += resize;
window.MouseDown += select;
window.RenderFrame += renderFrame;
window.Run(1.0 / 60.0);
}
public void loaded(object o,EventArgs e)
{
GL.ClearColor(0.0f,0.0f,0.0f,0.0f);
}
public void renderFrame(object o,EventArgs e)
{
GL.LoadIdentity();
GL.Clear(ClearBufferMask.ColorBufferBit | ClearBufferMask.DepthBufferBit);
GL.Begin(BeginMode.Quads);
GL.Color3(1.0, 1.0, 0.0);
GL.Vertex3(-5.0,-5.0,-80.0);
GL.Vertex3(5.0, -5.0, -80.0);
GL.Vertex3(5.0, 5.0, -80.0);
GL.Vertex3(-5.0, 5.0, -80.0);
GL.Color3(1.0, 0.0, 0.0);
GL.Vertex3(-10.0, -10.0, -80.0);
GL.Vertex3(0.0, -10.0, -80.0);
GL.Vertex3(0.0, 0.0, -80.0);
GL.Vertex3(-10.0, 0.0, -80.0);
GL.End();
window.SwapBuffers();
}
public void resize(object o,EventArgs e)
{
GL.Viewport(0, 0, window.Width, window.Height);
GL.MatrixMode(MatrixMode.Projection);
GL.LoadIdentity();
GL.Ortho(-50.0, 50.0, -50.0, 50.0, -100.0, 100.0);
GL.MatrixMode(MatrixMode.Modelview);
GL.Enable(EnableCap.DepthTest);
}
public void select(object o, MouseEventArgs e)
{
var buffer = new int[BUFSIZE];
var viewPort = new int[4];
int hits;
GL.GetInteger(GetPName.Viewport, viewPort);
GL.SelectBuffer(BUFSIZE, buffer);
GL.RenderMode(RenderingMode.Select);
GL.InitNames();
GL.PushName(0);
GL.MatrixMode(MatrixMode.Projection);
GL.PushMatrix();
GL.LoadIdentity();
GluPickMatrix(e.Mouse.X, viewPort[3] - e.Mouse.Y, 5.0, 5.0, viewPort);
GL.Ortho(-50.0, 50.0, -50.0, 50.0, -100.0, 100.0);
GL.MatrixMode(MatrixMode.Modelview);
GL.LoadIdentity();
GL.LoadName(1);
GL.Begin(BeginMode.Quads);
GL.Color3(1.0, 1.0, 0.0);
GL.Vertex3(-5.0, -5.0, -80.0);
GL.Vertex3(5.0, -5.0, -80.0);
GL.Vertex3(5.0, 5.0, -80.0);
GL.Vertex3(-5.0, 5.0, -80.0);
GL.LoadName(2);
GL.Color3(1.0, 0.0, 0.0);
GL.Vertex3(-10.0, -10.0, -80.0);
GL.Vertex3(0.0, -10.0, -80.0);
GL.Vertex3(0.0, 0.0, -80.0);
GL.Vertex3(-10.0, 0.0, -80.0);
GL.End();
GL.PopMatrix();
GL.Flush();
hits = GL.RenderMode(RenderingMode.Render);
Console.WriteLine("hit: {0}", hits);
if (hits>0)
{
int choose = buffer[3];
int depth = buffer[1];
for (int i=0;i<hits;i++)
{
if (buffer[i * 4 + 1] < depth)
{
choose = buffer[i * 4 + 3];
depth = buffer[i * 4 + 1];
}
}
Console.WriteLine("choosen: {0}", choose);
}
}
private void GluPickMatrix(double x, double y, double deltax, double deltay, int[] viewport)
{
if (deltax <= 0 || deltay <= 0)
{
return;
}
GL.Translate((viewport[2] - 2 * (x - viewport[0])) / deltax, (viewport[3] - 2 * (y - viewport[1])) / deltay, 0);
GL.Scale(viewport[2] / deltax, viewport[3] / deltay, 1.0);
}
}
}
The main function:
using System;
using OpenTK;
namespace OpenTkSelectTry
{
class Program
{
static void Main(string[] args)
{
var window = new GameWindow(500, 500);
var gm = new Game2D(window);
Console.WriteLine();
Console.WriteLine();
Console.WriteLine("Press enter to finish...");
Console.ReadLine();
}
}
}
Here is the 2 objects rendered in the screen initially:
After I click on the object, the screen zoom in (not what I want), and the name stack is not correct (always 1).
the screen zoom in (not what I want),
This is because you've changed the matrix mode in the select method. Choose the MatrixMode.Projection, before GL.PopMatrix():
and the name stack is not correct (always 1).
It is not allowed to call GL.LoadName within a GL.Begin/GL.End sequence. This causes an invalide operation error (GL.GetError). You need to draw 2 separate quads.
public void select(object o, MouseEventArgs e)
{
// [...]
GL.MatrixMode(MatrixMode.Projection);
GL.PushMatrix();
GL.LoadIdentity();
GluPickMatrix(e.Mouse.X, viewPort[3] - e.Mouse.Y, 5.0, 5.0, viewPort);
GL.Ortho(-50.0, 50.0, -50.0, 50.0, -100.0, 100.0);
GL.MatrixMode(MatrixMode.Modelview);
GL.LoadIdentity();
GL.LoadName(1);
GL.Begin(BeginMode.Quads);
GL.Color3(1.0, 1.0, 0.0);
GL.Vertex3(-5.0, -5.0, -80.0);
GL.Vertex3(5.0, -5.0, -80.0);
GL.Vertex3(5.0, 5.0, -80.0);
GL.Vertex3(-5.0, 5.0, -80.0);
GL.End();
GL.LoadName(2);
GL.Begin(BeginMode.Quads);
GL.Color3(1.0, 0.0, 0.0);
GL.Vertex3(-10.0, -10.0, -80.0);
GL.Vertex3(0.0, -10.0, -80.0);
GL.Vertex3(0.0, 0.0, -80.0);
GL.Vertex3(-10.0, 0.0, -80.0);
GL.End();
GL.MatrixMode(MatrixMode.Projection);
GL.PopMatrix();
GL.MatrixMode(MatrixMode.Modelview);
// [...]
}
The original example uses Perspective projection instead of Orthographic projection. Use Matrix4.CreatePerspectiveFieldOfView to specify a perspective projection matrix. Use GL.MultMatrix to multiply the current matrix by the projection matrix:
GL.Ortho(-50.0, 50.0, -50.0, 50.0, -100.0, 100.0);
Matrix4 perspective = Matrix4.CreatePerspectiveFieldOfView(
40f * (float)Math.PI / 180f, 500f / 500f, 0.001f, 400f);
GL.MultMatrix(ref perspective);