Tracking HDC from injected process - c++

Question

I'm facing quite a dilemma. I've injected my DLL into other process as well as hooked few
WinAPI calls from there, ExtTextOutW#GDI32, DrawTextExW#GDI32 and AlphaBlend#Msimg32 to be specific. Now, the problem is that when the other application writes something with those two GDI32 functions, i don't know the exact location where it comes up. This is because the DC which contains the text gets processed with AlphaBlend, which also eventually puts it to the window's DC.
So, how can I track certain HDC? In pseudo code, here's how the other application draws
text to the screen:
HDC h = DrawTextW("STRING")
Do something with h. The "STRING" gets new HDC, say h2.
Pass h2 to AlphaBlend, which draws it to the screen.
Like I said, I loose track with the original h as the string gets new DC before AlphaBlend.
Any idea, how I can make a connection from h > h2 with certain string in it?
I don't know if I was able to explain the problem properly, please ask if you've got any questions...

Answer 1

static BOOL (WINAPI *AlphaBlend_t)(
HDC hdcDest,
int nXOriginDest,
int nYOriginDest,
int nWidthDest,
int nHeightDest,
HDC hdcSrc,
int nXOriginSrc,
int nYOriginSrc,
int nWidthSrc,
int nHeightSrc,
BLENDFUNCTION blendFunction
) = AlphaBlend;
BOOL MyAlphaBlend(
HDC hdcDest,
int nXOriginDest,
int nYOriginDest,
int nWidthDest,
int nHeightDest,
HDC hdcSrc,
int nXOriginSrc,
int nYOriginSrc,
int nWidthSrc,
int nHeightSrc,
BLENDFUNCTION blendFunction
)
{
// modify hdcDest to hdcDest2
return AlphaBlend_t(hdcDest2, ...);
}
That should do the trick. Put in any code to modify the HDC in the latter function.