I decided to give a third spin of Joe Stegman's dynamic image generation code. This time, it's many times faster (about 10x) than the original implementation and the png is generated in-place (no recoding necessary).

I used some hacky optimizations :) For example, replacing the big CRC loop with a constant (0), definitely improves speed a lot! :)

There are no more intermediate memory streams or buffers: whenever SetPixel() is called, the value is written directly into PNG. Also all the header and size information is created just once. That also helped performance quite a bit.

With the new code my raindrops sample runs 20% faster (90% of the time used in calculating the drops): www.nokola.com/raindrops

Download the source code containing the new PngEncoder class here: www.nokola.com/sources/water.zip

Here's how to use the new image generator class:

PngEncoder surface = new PngEncoder(640, 480); // image dimension

surface.SetPixelSlow(40, 30, 200, 135, 32, 255); // set pixel at (40,30) with color RGBA=(200,135,32,255)

           

// draw a white horizontal line fast

int rowStart = surface.GetRowStart(30);

for (int i = 0; i < 10; i++) {

// SetPixelAtRowStart() is good for blitting/copying existing images onto this one

surface.SetPixelAtRowStart(i + 40, rowStart, 255, 255, 255, 255);

}

 

// display the image

BitmapImage img = new BitmapImage();

img.SetSource(surface.GetImageStream());

imgWater.Source = img; // this is just a normal Silverlight Image

 

And, here's the GetImageStream() function for comparison with the previous implementation:

public Stream GetImageStream()

{

MemoryStream ms = new MemoryStream();

ms.Write(_buffer, 0, _buffer.Length);

ms.Seek(0, SeekOrigin.Begin);

return ms;

}

Compare this to the previous function, that had numerous for()-s, encoding logic, etc :)

hoho! I'm very happy for doing this!

Edit: here's the source code for the SetPixelXX functions - to prove they are actually not slow :)

public void SetPixelSlow(int col, int row, byte red, byte green, byte blue, byte alpha)

{

int start = _rowLength * row + col * 4 + 1;

      int blockNum = start / _blockSize;

      start += ((blockNum + 1) * 5);

      start += _dataStart;

 

      _buffer[start] = red;

      _buffer[start + 1] = green;

      _buffer[start + 2] = blue;

      _buffer[start + 3] = alpha;

}

 

public void SetPixelAtRowStart(int col, int rowStart, byte red, byte green, byte blue, byte alpha)

{

int start = rowStart + (col << 2);

 

      _buffer[start] = red;

      _buffer[start + 1] = green;

      _buffer[start + 2] = blue;

      _buffer[start + 3] = alpha;

}

 

public int GetRowStart(int row)

{

int start = _rowLength * row + 1;

      int blockNum = start / _blockSize;

      start += ((blockNum + 1) * 5);

      start += _dataStart;

      return start;

}