Per-pixel alpha blend function math [Resolved]

[agent]

finally... i just got home from work... here's the source code to the dll

jsgfx.cpp

#include <windows.h>

// The Representation of a 32 bit color table entry
#pragma pack(push)
#pragma pack(1)
typedef struct ssBGR {
  unsigned char b;
  unsigned char g;
  unsigned char r;
  unsigned char pad;
} sBGR;

typedef sBGR *pBGR;
#pragma pack(pop)

//prototypes
void __stdcall SoftBlt(HDC hdcDest, int nLeft, int nTop, int nWidth, int nHeight, HDC hdcSrc, HDC hdcSrcMask);
pBGR MyGetDibBits(HDC hdc, HBITMAP hBmp, int nWidth, int nHeight);
int MySetDibBits(HDC hdc, HBITMAP hBmp, int nWidth, int nHeight, pBGR buf);
sBGR Pixelate(sBGR dest,sBGR source,BYTE Alpha);

void __stdcall SoftBlt(HDC hdcDest, int nLeft, int nTop, int nWidth, int nHeight, HDC hdcSrc, HDC hdcSrcMask)
{	
	//STEP 1 - 3
	HDC hdcTMPDest = CreateCompatibleDC(hdcDest);
	HBITMAP hbTMPDest = CreateCompatibleBitmap(hdcDest, nWidth, nHeight);
	SelectObject(hdcTMPDest, hbTMPDest);
	BitBlt(hdcTMPDest, 0, 0, nWidth, nHeight, hdcDest, nLeft, nTop, SRCCOPY);

	pBGR dibDest = MyGetDibBits(hdcTMPDest, (HBITMAP) GetCurrentObject(hdcTMPDest, OBJ_BITMAP), nWidth, nHeight);
	pBGR dibSource = MyGetDibBits(hdcSrc, (HBITMAP) GetCurrentObject(hdcSrc, OBJ_BITMAP), nWidth, nHeight);
	pBGR dibMask = MyGetDibBits(hdcSrcMask, (HBITMAP) GetCurrentObject(hdcSrcMask, OBJ_BITMAP), nWidth, nHeight);
	
	//STEP 4
	for (int y = 0; y < nHeight; ++y)
	{
	  for (int x = 0; x < nWidth; ++x)
	  {
		sBGR bgrDest = dibDest[y * nWidth + x];
		sBGR bgrSource = dibSource[y * nWidth + x];
		sBGR bgrMask = dibMask[y * nWidth + x];

		unsigned char mask = ((bgrMask.b + bgrMask.g + bgrMask.r) / 3);
//Blend function

		//bgrDest.r = 255;
		//bgrDest.g = 0;
		//bgrDest.b = 0;


		bgrDest = Pixelate(bgrDest, bgrSource, mask);

		//bgrDest.r = 255 - bgrDest.r; 
		//bgrDest.g = 255 - bgrDest.g;
		//bgrDest.b = 255 - bgrDest.b;

		dibDest[y * nWidth + x] = bgrDest;
	  }
	}

	//STEP 5

	HDC hdcTmp = CreateCompatibleDC(hdcDest);
	HBITMAP hbTmp = CreateCompatibleBitmap(hdcDest, nWidth, nHeight);
	SelectObject(hdcTmp, hbTmp);
	
	//STEP 6
	MySetDibBits(hdcTmp, hbTmp, nWidth, nHeight, dibDest);

	//STEP 7
	BitBlt(hdcDest, nLeft, nTop, nWidth, nHeight, hdcTmp, 0, 0, SRCCOPY);

	//Step 8
	DeleteObject(hbTMPDest);
	DeleteObject(hbTmp);
	
	DeleteDC(hdcTMPDest);
	DeleteDC(hdcTmp);

	free(dibDest);
	free(dibSource);
	free(dibMask);
}


sBGR Pixelate(sBGR dest,sBGR source,BYTE Alpha)
{

  float FinalRed,FinalGreen,FinalBlue;

  FinalRed  = (Alpha/255.0f*(float)source.r) + ((1.0f-Alpha/255.0f)*(float)dest.r);
  FinalGreen= (Alpha/255.0f*(float)source.g) + ((1.0f-Alpha/255.0f)*(float)dest.g);
  FinalBlue = (Alpha/255.0f*(float)source.b) + ((1.0f-Alpha/255.0f)*(float)dest.b);
  
  int nFinalRed,nFinalGreen,nFinalBlue;
  
  if(FinalRed>=FinalGreen && FinalRed>=FinalBlue)
  {
    if(FinalRed>255.0f)
    {
      nFinalRed=255;
      nFinalGreen=(int)(FinalGreen/FinalRed*255.0f);
      nFinalBlue =(int)(FinalBlue/FinalRed*255.0f);
    }
    else
    {
      nFinalRed  =(int)(FinalRed);
      nFinalGreen=(int)(FinalGreen);
      nFinalBlue =(int)(FinalBlue);
    }
  }
  else if(FinalGreen>=FinalRed && FinalGreen>=FinalBlue)
  {
    if(FinalGreen>255.0f)
    {
      nFinalRed  =(int)(FinalRed/FinalGreen*255.0f);
      nFinalGreen=255;
      nFinalBlue =(int)(FinalBlue/FinalGreen*255.0f);
    }
    else
    {
      nFinalRed  =(int)(FinalRed);
      nFinalGreen=(int)(FinalGreen);
      nFinalBlue =(int)(FinalBlue);
    }
  }
  else if(FinalBlue>=FinalRed && FinalBlue>=FinalGreen)
  {
    if(FinalBlue>255.0f)
    {
      nFinalRed  =(int)(FinalRed/FinalBlue*255.0f);
      nFinalGreen=(int)(FinalGreen/FinalBlue*255.0f);
      nFinalBlue=255;
    }
    else
    {
      nFinalRed  =(int)(FinalRed);
      nFinalGreen=(int)(FinalGreen);
      nFinalBlue =(int)(FinalBlue);
    }
  }
  sBGR tempBGR;
  tempBGR.r=nFinalRed;
  tempBGR.g=nFinalGreen;
  tempBGR.b=nFinalBlue;
  return tempBGR;
}




pBGR MyGetDibBits(HDC hdc, HBITMAP hBmp, int nWidth, int nHeight)
{
  BITMAPINFO bi;
  BOOL bRes;
  pBGR buf;

  bi.bmiHeader.biSize = sizeof(bi.bmiHeader);
  bi.bmiHeader.biWidth = nWidth;
  bi.bmiHeader.biHeight = - nHeight;
  bi.bmiHeader.biPlanes = 1;
  bi.bmiHeader.biBitCount = 32;
  bi.bmiHeader.biCompression = BI_RGB;
  bi.bmiHeader.biSizeImage = nWidth * 4 * nHeight;
  bi.bmiHeader.biClrUsed = 0;
  bi.bmiHeader.biClrImportant = 0;

//  buf = new sBGR[nWidth * nHeight];
  buf = (pBGR) malloc(nWidth * 4 * nHeight);

  bRes = GetDIBits(hdc, hBmp, 0, nHeight, buf, &bi, DIB_RGB_COLORS);
  if (!bRes) {
//    delete [] buf;
    free(buf);
    buf = 0;
  }
  return buf;
}

int MySetDibBits(HDC hdc, HBITMAP hBmp, int nWidth, int nHeight, pBGR buf)
{
  BITMAPINFO bi;

  bi.bmiHeader.biSize = sizeof(bi.bmiHeader);
  bi.bmiHeader.biWidth = nWidth ;
  bi.bmiHeader.biHeight = - nHeight ;
  bi.bmiHeader.biPlanes = 1;
  bi.bmiHeader.biBitCount = 32;
  bi.bmiHeader.biCompression = BI_RGB;
  bi.bmiHeader.biSizeImage = nWidth * 4 * nHeight;
  bi.bmiHeader.biClrUsed = 0;
  bi.bmiHeader.biClrImportant = 0;

  return ( SetDIBits(hdc , hBmp ,0, nHeight ,buf,&bi,DIB_RGB_COLORS) );

}

jsgfx.def

LIBRARY "jsgfx.dll"

EXPORTS
SoftBlt

VB Declare (you'll need to change the path for the Lib keyword as appropriate)

Private Declare Function SoftBlt Lib "H:\Microsoft Visual Studio\MyProjects\jsgfx\Debug\jsgfx.dll" (ByVal hdcDest As Long, ByVal nLeft As Long, ByVal nTop As Long, ByVal nWidth As Long, ByVal nHeight As Long, ByVal hdcSrc As Long, ByVal hdcSrcMask As Long ) As Long

if you use a control's hdc, the control's AutoRedraw property will need to be set to true, and you'll need to call the update method for the destination control after calling SoftBlit

the function does not currently produce a properly Alpha Blended image. Only SoftBlit is exported.


UPDATE!!!
I fixed the above code. Now it does work as advertised. See also http://www.vbforums.com/showthread.php?postid=1488575 for more information.