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  A problem for Java NIO FileChannel.map(....) don't work..why?  (Read 698 times)
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Offline wdl7770016

Senior Newbie





« Posted 2012-08-07 13:00:51 »

it's my code :
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import java.io.File;
import java.io.FileInputStream;
import java.io.IOException;
import java.nio.ByteBuffer;
import java.nio.channels.FileChannel;
import java.nio.channels.FileChannel.MapMode;

import org.lwjgl.LWJGLException;
import org.lwjgl.opengl.Display;
import org.lwjgl.opengl.DisplayMode;
import org.lwjgl.opengl.GL11;
import org.lwjgl.opengl.GL14;

public class GameMain2 {
   private ByteBuffer byteBuffer;
   /**
    *
    * @param args
    */

   public static void main(String[] args) {
      new GameMain2().launch();
   }

   public void launch() {
      try {
         Display.setDisplayMode(new DisplayMode(800, 600));
         Display.setTitle("YourGame");
         Display.create();
         this.initGL();
      }
      catch (LWJGLException e) {
         e.getStackTrace();
      }

      while (!Display.isCloseRequested()) {
         this.render();
         Display.update();
         Display.sync(60);
      }
      Display.destroy();
   }

   private void initGL() {
      GL11.glClearColor(0, 0, 0, 0);
     
      GL11.glOrtho(0, 800, 0, 600, -1, 1);

      //GL11.glEnable(GL11.GL_TEXTURE_2D);
     
      try {
         File f = new File("src/img/logo.png");
         FileInputStream fileIn = new FileInputStream(f);
         FileChannel fc = fileIn.getChannel();
         this.byteBuffer = fc.map(MapMode.READ_ONLY, 0, fc.size());
         //fileIn.close();
        System.out.println(this.byteBuffer.position());
      }
      catch (IOException e) {
         e.getStackTrace();
      }
   }
   
   private void render() {
      GL11.glClear(GL11.GL_COLOR_BUFFER_BIT);
      //GL11.glColor3f(0, 1, 1);
     GL14.glWindowPos2d(20, 20);
      //GL11.glBitmap(142, 142, 0, 0, 0, 0, this.byteBuffer);
     GL11.glDrawPixels(142, 142, GL11.GL_RGB, GL11.GL_BYTE, this.byteBuffer);
   }
}


Q1:the System.out.println(this.byteBuffer.position()); is still return 0,which means that no byte map into byteBuffer..
Q2:when I use FileChannel.read() to read byte to byteBuffer it's ok,but when I render use glDrawPixels it always return :
Number of remaining buffer elements is 4332, must be at least 60492. Because at most 60492 elements can be returned, a buffer with at least 60492 elements is required, regardless of actual returned element count
I don't know what It means...
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« Reply #1 - Posted 2012-08-07 15:14:05 »

Q1:the System.out.println(this.byteBuffer.position()); is still return 0,which means that no byte map into byteBuffer..
the .position() of the buffer is no indication of whether any data was loaded. When reading bytes from a mapped bytebuffer, the data is automatically loaded from disk - .position() is there for whatever you want to use it for. The data is there.

Q2:when I use FileChannel.read() to read byte to byteBuffer it's ok,but when I render use glDrawPixels it always return :
Number of remaining buffer elements is 4332, must be at least 60492. Because at most 60492 elements can be returned, a buffer with at least 60492 elements is required, regardless of actual returned element count
I don't know what It means...
You are trying to feed PNG encoded data into a method that expects pixels.



On a sidenote.... how long are you going to try to make glDrawPixels(..) work? It's the absolute slowest way to render an image. Try to read up on textures instead.

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Offline wdl7770016

Senior Newbie





« Reply #2 - Posted 2012-08-07 15:24:49 »

Quote
the .position() of the buffer is no indication of whether any data was loaded. When reading bytes from a mapped bytebuffer, the data is automatically loaded from disk - .position() is there for whatever you want to use it for. The data is there.
sorry I had make a big mistake Tongue

Quote
You are trying to feed PNG encoded data into a method that expects pixels.
so I can't direct use the png file because it had not decode right?

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