glReadPixels返回比預期更多的數據

Question

我想使用JOGL保存我用openGL顯示的視頻。要做到這一點，我寫我的幀到圖片如下，然後，一旦我保存所有幀，我會使用ffmpeg。我知道這不是最好的方法，但我仍然沒有太清楚如何加速tex2dimage和PBOs。在這方面的任何幫助將是非常有用的。

無論如何，我的問題是，如果我運行opengl類的作品，但如果我從另一個類調用這個類，然後我看到glReadPixels是trhowing我的錯誤。它總是返回更多的數據到緩衝區，比內存已分配給我的緩衝區「pixelsRGB」。有誰知道爲什麼？

作爲一個例子：width = 1042;高度= 998。分配= 3.119.748 glPixels返回= 3.121.742

public void display(GLAutoDrawable drawable) { 
     //Draw things..... 

     //bla bla bla 
     t++; //This is a time variable for the animation (it says to me the frame). 

     //Save frame   
     int width = drawable.getSurfaceWidth(); 
     int height = drawable.getSurfaceHeight(); 
     ByteBuffer pixelsRGB = Buffers.newDirectByteBuffer(width * height * 3); 
     gl.glReadPixels(0, 0, width,height, gl.GL_RGB, gl.GL_UNSIGNED_BYTE, pixelsRGB); 
     BufferedImage bufferedImage = new BufferedImage(width, height, BufferedImage.TYPE_INT_ARGB); 

     int[] pixels = new int[width * height]; 

     int firstByte = width * height * 3; 
     int sourceIndex; 
     int targetIndex = 0; 
     int rowBytesNumber = width * 3; 

     for (int row = 0; row < height; row++) { 
      firstByte -= rowBytesNumber; 
      sourceIndex = firstByte; 
      for (int col = 0; col < width; col++) { 
       int iR = pixelsRGB.get(sourceIndex++); 
       int iG = pixelsRGB.get(sourceIndex++); 
       int iB = pixelsRGB.get(sourceIndex++); 

       pixels[targetIndex++] = 0xFF000000 
        | ((iR & 0x000000FF) << 16) 
        | ((iG & 0x000000FF) << 8) 
        | (iB & 0x000000FF); 
      } 

     } 

     bufferedImage.setRGB(0, 0, width, height, pixels, 0, width); 


     File a = new File(t+".png"); 
     ImageIO.write(bufferedImage, "PNG", a); 
} 

注：隨着pleluron的答案，現在它的工作原理。良好的代碼是：

public void display(GLAutoDrawable drawable) { 
     //Draw things..... 

     //bla bla bla 
     t++; //This is a time variable for the animation (it says to me the frame). 

     //Save frame   
     int width = drawable.getSurfaceWidth(); 
     int height = drawable.getSurfaceHeight(); 
     ByteBuffer pixelsRGB = Buffers.newDirectByteBuffer(width * height * 4); 
     gl.glReadPixels(0, 0, width,height, gl.GL_RGBA, gl.GL_UNSIGNED_BYTE, pixelsRGB); 
     BufferedImage bufferedImage = new BufferedImage(width, height, BufferedImage.TYPE_INT_ARGB); 

     int[] pixels = new int[width * height]; 

     int firstByte = width * height * 4; 
     int sourceIndex; 
     int targetIndex = 0; 
     int rowBytesNumber = width * 4; 

     for (int row = 0; row < height; row++) { 
      firstByte -= rowBytesNumber; 
      sourceIndex = firstByte; 
      for (int col = 0; col < width; col++) { 
       int iR = pixelsRGB.get(sourceIndex++); 
       int iG = pixelsRGB.get(sourceIndex++); 
       int iB = pixelsRGB.get(sourceIndex++); 

       sourceIndex++; 

       pixels[targetIndex++] = 0xFF000000 
        | ((iR & 0x000000FF) << 16) 
        | ((iG & 0x000000FF) << 8) 
        | (iB & 0x000000FF); 
      } 

     } 

     bufferedImage.setRGB(0, 0, width, height, pixels, 0, width); 


     File a = new File(t+".png"); 
     ImageIO.write(bufferedImage, "PNG", a); 
} 

Answer 1

與glPixelStore設置的GL_PACK_ALIGNMENT默認值是4。這意味着的pixelsRGB每一行應是4的倍數的地址開始，和你的緩衝區的寬度（1042 ）乘以像素（3）中的字節數不是4的倍數。添加一點填充使得下一行以4的倍數開始將使緩衝區的總字節大小大於您的預期。

要修復它，設置GL_PACK_ALIGNMENT 1。你也可以用GL_RGBA讀取像素，並使用更大的緩衝區，因爲數據是最有可能被同時存儲在GPU和BufferedImage的方式。

編輯：BufferedImage沒有一個方便的'setRGBA'，太糟糕了。