C++ Getting RGB from hBitmap
The issue is that your screen is actually 32bits deep not 24. The code below will give you the result you need:
/* Globals */
int ScreenX = 0;
int ScreenY = 0;
BYTE* ScreenData = 0;
void ScreenCap()
{
HDC hScreen = GetDC(NULL);
ScreenX = GetDeviceCaps(hScreen, HORZRES);
ScreenY = GetDeviceCaps(hScreen, VERTRES);
HDC hdcMem = CreateCompatibleDC(hScreen);
HBITMAP hBitmap = CreateCompatibleBitmap(hScreen, ScreenX, ScreenY);
HGDIOBJ hOld = SelectObject(hdcMem, hBitmap);
BitBlt(hdcMem, 0, 0, ScreenX, ScreenY, hScreen, 0, 0, SRCCOPY);
SelectObject(hdcMem, hOld);
BITMAPINFOHEADER bmi = {0};
bmi.biSize = sizeof(BITMAPINFOHEADER);
bmi.biPlanes = 1;
bmi.biBitCount = 32;
bmi.biWidth = ScreenX;
bmi.biHeight = -ScreenY;
bmi.biCompression = BI_RGB;
bmi.biSizeImage = 0;// 3 * ScreenX * ScreenY;
if(ScreenData)
free(ScreenData);
ScreenData = (BYTE*)malloc(4 * ScreenX * ScreenY);
GetDIBits(hdcMem, hBitmap, 0, ScreenY, ScreenData, (BITMAPINFO*)&bmi, DIB_RGB_COLORS);
ReleaseDC(GetDesktopWindow(),hScreen);
DeleteDC(hdcMem);
DeleteObject(hBitmap);
}
inline int PosB(int x, int y)
{
return ScreenData[4*((y*ScreenX)+x)];
}
inline int PosG(int x, int y)
{
return ScreenData[4*((y*ScreenX)+x)+1];
}
inline int PosR(int x, int y)
{
return ScreenData[4*((y*ScreenX)+x)+2];
}
bool ButtonPress(int Key)
{
bool button_pressed = false;
while(GetAsyncKeyState(Key))
button_pressed = true;
return button_pressed;
}
int main()
{
while (true)
{
if (ButtonPress(VK_SPACE))
{
// Print out current cursor position
POINT p;
GetCursorPos(&p);
printf("X:%d Y:%d \n",p.x,p.y);
// Print out RGB value at that position
std::cout << "Bitmap: r: " << PosR(p.x, p.y) << " g: " << PosG(p.x, p.y) << " b: " << PosB(p.x, p.y) << "\n";
} else if (ButtonPress(VK_ESCAPE))
{
printf("Quit\n");
break;
} else if (ButtonPress(VK_SHIFT))
{
ScreenCap();
printf("Captured\n");
}
}
system("PAUSE");
return 0;
}