GDI高速图像绘制

     虽然现在在图像图形上想提速，公认还是使用GPU了。但是如果机器没有一个好的显卡？你只是想写一个简单的.Net程序？GDI在其平台的易用性还是有很强的市场。只是一旦你需要使用GDI多次甚至大量的绘制图像时候，当你只是想简单的但是多次的复制图片的时候，使用Graphics.DrawImage()的性能绝对会崩溃。

    查了很久，Gameres几个哥们给了几个很好的建议，主要思路是直接对Bitmap位操纵，这样子还可以利用多线程（注意GDI是不能多线程调用的，至少我用TPL库就不成功）。

    下面用几个具体函数说明。

          第一个是从一个Source Bitmap的Rectangle sourceRect的地址的内容拷贝到 Dest Bitmap 的 Point destPos起点的地址。

         //Copy the data of sourceMap in sourceRect to destMap start from destPos
        //Currently the method only deals with the bitmap with format Format32bppArgb.
        public bool CopyBitMapWithLockBits(Bitmap sourceMap, ref Bitmap destMap, Rectangle sourceRect, Point destPos)
        {
            if (destPos.X + sourceRect.Width > destMap.Width ||
               destPos.Y + sourceRect.Height > destMap.Height)
                return false;

            //Key Step1 ：Use LockBits()  to lock the address of bitmap you want to write in.

             BitmapData sourceBitmapData = sourceMap.LockBits(new Rectangle(sourceRect.X, sourceRect.Y, sourceRect.Width, sourceRect.Height), ImageLockMode.ReadOnly, sourceMap.PixelFormat);
            BitmapData destBitmapData = destMap.LockBits(new Rectangle(destPos.X, destPos.Y, sourceRect.Width, sourceRect.Height), ImageLockMode.WriteOnly, sourceMap.PixelFormat);

 

            //Create the temp lock memory for transferring
            int ibytes = sourceRect.Width * 4 * sizeof(byte);
            byte[] rgbValues = new byte[ibytes];

 

            //Key Step2 : Copy the data from sourceMap to destMap . Notice you can't copy from a bitmap directly to another bitmap.You must use an intermediate adrress.
            for (int i = 0; i < sourceRect.Height; i++)
            {
                IntPtr sourceAddress = (IntPtr)sourceBitmapData.Scan0.ToInt64() + i * sourceBitmapData.Stride;
                IntPtr destAddress = (IntPtr)(destBitmapData.Scan0.ToInt64() + i * destBitmapData.Stride);
                Marshal.Copy(sourceAddress, rgbValues, 0, sourceRect.Width * 4);
                Marshal.Copy(rgbValues, 0,
                    destAddress, sourceRect.Width * 4);
            }

            //Key Step3 : Unlock the address

            sourceMap.UnlockBits(sourceBitmapData);
            destMap.UnlockBits(destBitmapData);

            return true;
        }

 

     第二个Demo是改写Graphics.FillRectangle()，直接自己对这片矩形地址填充ARGB的值。

        //Fill the bitmap in rect with color.This method is used to replace GDI.
        public void FillBitmap(ref Bitmap bitmap, Rectangle rect, Color color)
        {
            //=====Lock the whole region with the lockbits
            BitmapData bitmapData = bitmap.LockBits(new Rectangle(0, 0, bitmap.Width, bitmap.Height), ImageLockMode.WriteOnly, bitmap.PixelFormat);

            //get the number of lock memory
            int ibytes = rect.Width * rect.Height * 4 * sizeof(byte);

            //The address for intermediate computing and storing.

            byte[] rgbValues = new byte[ibytes];
            //initialize the first line
            for (int j = 0; j < rect.Width; j++)
            {
                rgbValues[4 * j + 0] = color.B;
                rgbValues[4 * j + 1] = color.G;
                rgbValues[4 * j + 2] = color.R;
                rgbValues[4 * j + 3] = color.A;
            }
            //initialize the rest lines of rgvValues with copy
            for (int i = 1; i < rect.Height; i++)
            {
                Buffer.BlockCopy(rgbValues, 0, rgbValues, i * rect.Width * 4, rect.Width * 4);
            }

            //copy the data from intermediate address to bitmap one line after another
            for (int i = 0; i < rect.Height; i++)
            {
                IntPtr destAddress = (IntPtr)(bitmapData.Scan0.ToInt64() + rect.Y * bitmapData.Stride + rect.X * 4 * sizeof(byte) + i * bitmapData.Stride);
                Marshal.Copy(rgbValues, i * rect.Width * 4,
                    destAddress, rect.Width * 4);
            }

            bitmap.UnlockBits(bitmapData);
        }

      因为我需要大量的调用DrawImage() 和FillRectangle()，经过这样一改写后，速度提升了200%有多。。