help newbie draw pixels

[phaelax]

I'm trying to convert an existing program to use OGL because the native Java painting methods are just too slow. I have an array of pixel data updated constantly to draw animated fire.


I'm new to this whole OGL stuff.

I've got my pixel buffer and called GL11.glDrawPixels(). I see 1 line of pixels at the very top of the screen, the bottom of my image I'm assuming.  I'm trying to position it on the screen so I can see the whole thing, but whenever I call GL11.glRasterPos2i() I can't see any pixels, no matter what coordinates I use.

Also, how can I display text? I couldn't find a glDrawText() method.

[hvor]

I found similar problems when I switch myself from Java to openGL. How to write damn string on the screen? YOu will have to load a texture that is containing all the characters, and than you will be able to write something. GO to see NeHe tutorials how exactly to do it...

[Fool Running]

whenever I call GL11.glRasterPos2i() I can't see any pixels, no matter what coordinates I use

Could you post some code? This seems weird :lol:

[napier]

In OpenGL the Y axis is reversed, so 0,0 is in the lower left corner, not the upper left as in Java.  Maybe that is affecting your results.

Warning: glDrawPixels is slow.  OpenGL is not optimized for pixel operations like that.  You'll get better results rendering into a texture.  You could search in opengl forums for techniques like particle systems, fire and other special effects.

As for text, go to http://nehe.gamedev.net and look at the "2D Texture Font" tutorial #17.

I have a text demo using LWJGL here: http://potatoland.com/code/gl/lwjgl_demoText.zip

And source code here: http://potatoland.org/code/gl/GLApp.java
Look at buildFont() and glPrint()

[phaelax]

Well here's the whole code, mostly created from that german tutorial. (babel fish is nice)

thx for the other info.

import java.awt.Color;
import java.util.Random;
import java.util.Date;

import java.nio.ByteBuffer;

import org.lwjgl.opengl.Display;
import org.lwjgl.opengl.DisplayMode;
import org.lwjgl.LWJGLException;
import org.lwjgl.opengl.GL11;
import org.lwjgl.input.Keyboard;
import org.lwjgl.opengl.glu.GLU;
import org.lwjgl.opengl.OpenGLException;


public class JavaLWJGL2
{
    private DisplayMode displayMode = null;
    private String title;
    private int width = 320;
    private int height = 240;
    private byte[] fire = new byte[width*height*3];
    private ByteBuffer pixels;
    private int pos_y = 100;

    
    public JavaLWJGL2(String title)
    {
        this.title = title;
        randomizeFire();
        pixels = ByteBuffer.allocateDirect(width*height*3).put(fire);
        pixels.flip();
    }

    
    public void init()
    {
        initWindow();
        initKeyboard();
        initOpenGL();
        reSizeGLScene(displayMode.getWidth(), displayMode.getHeight());
        
        run();
    }
    
    private void initWindow()
    {
        try
        {
            displayMode = org.lwjgl.util.Display.getAvailableDisplayModes(
                                800,600,800,600,32,32,60,60)[0];
            Display.setDisplayMode(displayMode);
            Display.setFullscreen(false);
            Display.create();
            Display.setTitle(title);            
        }
        catch(LWJGLException e){System.out.println(e);}
    }
        


    private void initKeyboard()
    {
        try
        {
            if (!Keyboard.isCreated())
                Keyboard.create();
        }
        catch(LWJGLException e){System.out.println(e);}
    }


    private void initOpenGL()
    {
		GL11.glShadeModel(GL11.GL_SMOOTH);
		GL11.glClearColor(0.0f,0.0f,0.0f,0.0f);		
		GL11.glClearDepth(1.0f);					
		GL11.glEnable(GL11.GL_DEPTH_TEST);			
		GL11.glDepthFunc(GL11.GL_LEQUAL);
		GL11.glHint(GL11.GL_PERSPECTIVE_CORRECTION_HINT,GL11.GL_NICEST);
	}
	
	private void reSizeGLScene(int width, int height)
    {
		if (height == 0)
			height = 1;

        GL11.glViewport(0,0,width,height);                  // aktuellen viewport zurücksetzen
        GL11.glMatrixMode(GL11.GL_PROJECTION);              // Projection Matrix (PM) auswählen
        GL11.glLoadIdentity();                              // PM zurücksetzen
        GLU.gluPerspective(45.0f,(float)width/(float)height,0.1f,100.0f);   // 45Ã,° Perspektive
        GL11.glMatrixMode(GL11.GL_MODELVIEW);               // ModelView Matrix (MVM) auswählen
        GL11.glLoadIdentity();                              // MVM zurücksetzen
	}
	
	
	//make some random colored pixels
	private void randomizeFire()
	{
	    Random rand = new Random(new Date().getTime());
	    for(int i=0; i<fire.length;i++)
            fire[i] = (byte)rand.nextInt(256);
	}
	
	
	private void renderGLScene()
	{
	    randomizeFire();

	    GL11.glRasterPos2i(10,pos_y+10);
	    
	    GL11.glDrawPixels(width, height, GL11.GL_RGB, GL11.GL_UNSIGNED_BYTE, pixels);


	}
	   
	   
	private void cleanup()
	{
	    destroyWindow();
	    System.exit(0);
	}
	   
	private void destroyWindow()
	{
	    if (Display.isCreated())
	       Display.destroy();
	}
	
	private void checkKeyboardInput()
	{
	    if (Keyboard.isKeyDown(Keyboard.KEY_ESCAPE))
	       cleanup();
	    if (Keyboard.isKeyDown(Keyboard.KEY_DOWN))
	       pos_y -= 1;
	    if (Keyboard.isKeyDown(Keyboard.KEY_UP))
	       pos_y += 1;
	    
	}
	
	private void run()
	{
	    while(true)
	    {
	       if(Display.isCloseRequested())
	       {
	           cleanup();
	           break;
	       }
	       if(Display.isVisible() || Display.isDirty())
	       {
	           try
	           {
	               renderGLScene();
	               Display.update();
	           }
	           catch(OpenGLException e){System.out.println(e);}
	       }
	       checkKeyboardInput();
	   }
   }
	    
	    
    public static void main()
    {
        JavaLWJGL2 prog = new JavaLWJGL2("Java with Open GL");
        
        prog.init();
    }
}

[Fool Running]

GLU.gluPerspective(45.0f,(float)width/(float)height,0.1f,100.0f);   // 45Ã,° Perspektive

That is at least one possible problem (in reSizeGLScene). You are setting a perspective view that doesn't have the unit to pixels you want. You want to set a ortho view like this:

glOrtho(0, width, height, 0, -1, 1);

That will make 0, 0 the top left of the window. :lol: