I have a function in my custom Bitmap class called CaptureScreen() which bit-blits the screen to a compatible HBITMAP, then calls GetDIBits() to store the pixel data in a buffer. There are two calls to GetDIBits(), the first getting the BITMAPINFO structure filled up, and the second getting the actual pixel data. The problem is that the first call to GetDIBits() fails, and GetLastError() returns 6, ERROR_INVALID_HANDLE. I cannot figure out why. Here is the code:
CaptureScreen():
int Bitmap::CaptureScreen(RECT rect) {
Release();//Release the last information just in case
if(rect.right==-1)rect.right=GetSystemMetrics(SM_CXSCREEN)-1;//set defaults
if(rect.bottom==-1)rect.bottom=GetSystemMetrics(SM_CYSCREEN)-1;
HDC scrDC=CreateDC("DISPLAY\0",0,0,0);
HDC comDC=CreateCompatibleDC(scrDC);
if(!scrDC || !comDC)return 1;
HBITMAP hbmp=CreateCompatibleBitmap(scrDC,rect.right-rect.left+1,
rect.bottom-rect.top+1);
if(!hbmp) {
DeleteDC(comDC);
DeleteDC(scrDC);
return 1;
}
if(!SelectObject(comDC,hbmp)) {
DeleteObject(hbmp);
DeleteDC(comDC);
DeleteDC(scrDC);
return 1;
}
if(!BitBlt(comDC,0,0,rect.right-rect.left+1,rect.bottom-rect.top+1,scrDC,rect.left,
rect.right,SRCCOPY)) {
DeleteObject(hbmp);
DeleteDC(comDC);
DeleteDC(scrDC);
return 1;
}
BITMAPINFO bi;
bi.bmiHeader.biSize=sizeof(BITMAPINFOHEADER);
if(!GetDIBits(comDC,hbmp,0,0,0,&bi,DIB_RGB_COLORS)) {//returns 0
MessageBoxNum(GetLastError());
//displays 6, aka ERROR_INVALID_HANDLE. I cannot figure out which parameter is bad.
DeleteObject(hbmp);
DeleteDC(comDC);
DeleteDC(scrDC);
return 1;
}
infoHeader=bi.bmiHeader;
pixel=new PIXEL[infoHeader.biSizeImage/sizeof(PIXEL)];
if(!GetDIBits(comDC,hbmp,0,infoHeader.biHeight,pixel,&bi,DIB_RGB_COLORS)) {
DeleteObject(hbmp);
DeleteDC(comDC);
DeleteDC(scrDC);
return 1;
}
DeleteObject(hbmp);
DeleteDC(comDC);
DeleteDC(scrDC);
return 0;
}
Bitmap Class:
struct PIXEL {
BYTE b,g,r;
};
class Bitmap {
//...some functions
protected:
BITMAPINFOHEADER infoHeader;
PIXEL* pixel;
};
So it seems to be creating DCs and bit blitting okay. I think there is something wrong with my call to GetDIBits or my BITMAPINFO declaration, but I'm not sure. I tried using scrDC in the GetDIBits call (as opposed to comDC), but it doesn't work either (I also tried calling SelectObject(comDC,0)... doesn't work). Am I missing something obvious?
Edit- Just for ease of reading, here's the CaptureScreen() function without error handling code:
//CREATE OBJECTS
HDC scrDC=CreateDC("DISPLAY\0",0,0,0);//create DC for screen
HDC comDC=CreateCompatibleDC(scrDC);//create DC for bitmap
HBITMAP hbmp=CreateCompatibleBitmap(scrDC,rect.right-rect.left+1,
rect.bottom-rect.top+1);//create bitmap
SelectObject(comDC,hbmp);
//BIT BLIT
BitBlt(comDC,0,0,rect.right-rect.left+1,rect.bottom-rect.top+1,scrDC,rect.left,rect.right,SRCCOPY);
//^^copy screen to bitmap
//GET DEVICE INDEPENDENT BITS
BITMAPINFO bi;
bi.bmiHeader.biSize=sizeof(BITMAPINFOHEADER);//give its own size
GetDIBits(comDC,hbmp,0,0,0,&bi,DIB_RGB_COLORS);//fill bi with info
//this^^^ is the function that fails
infoHeader=bi.bmiHeader;//copy the info header
pixel=new PIXEL[infoHeader.biSizeImage/sizeof(PIXEL)];//allocate space
GetDIBits(comDC,hbmp,0,infoHeader.biHeight,pixel,&bi,DIB_RGB_COLORS);
//get pixel data
//delete created objects
DeleteObject(hbmp);
DeleteDC(comDC);
DeleteDC(scrDC);
return 0;
