glReadPixels返回比预期更多的数据

Question

我想使用JOGL保存我用openGL显示的视频。要做到这一点，我写我的帧到图片如下，然后，一旦我保存所有帧，我会使用ffmpeg。我知道这不是最好的方法，但我仍然没有太清楚如何加速tex2dimage和PBOs。在这方面的任何帮助将是非常有用的。

无论如何，我的问题是，如果我运行opengl类的作品，但如果我从另一个类调用这个类，然后我看到glReadPixels是trhowing我的错误。它总是返回更多的数据到缓冲区，比内存已分配给我的缓冲区“pixelsRGB”。有谁知道为什么？

作为一个例子：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：随着pleluron的答案，现在它的工作原理。良好的代码是：

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

与glPixelStore设置的GL_PACK_ALIGNMENT默认值是4。这意味着的pixelsRGB每一行应是4的倍数的地址开始，和你的缓冲区的宽度（1042 ）乘以像素（3）中的字节数不是4的倍数。添加一点填充使得下一行以4的倍数开始将使缓冲区的总字节大小大于您的预期。

要修复它，设置GL_PACK_ALIGNMENT 1。你也可以用GL_RGBA读取像素，并使用更大的缓冲区，因为数据是最有可能被同时存储在GPU和BufferedImage的方式。

编辑：BufferedImage没有一个方便的'setRGBA'，太糟糕了。