A problem for Java NIO FileChannel.map(....) don't work..why?

[wdl7770016]

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...

[Riven]

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.

[wdl7770016]

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

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?