Bitblt from directx application - c

Question

I got that code to get the pixel color from current mouse position.
It works well but the only problem is, I can't get it from an d3d application...
I tried it few times, but it only get only black color -
Red: 0
Green: 0
Blue: 0
Here's my code -
#include <stdio.h>
#include <stdlib.h>
#include <windows.h>
#include <d3d9.h>
HWND hWindow;
HDC hScreen;
HDC hdcMem;
HBITMAP hBitmap;
HGDIOBJ hOld;
int sX, sY, x, y;
BYTE* sData = 0;
POINT cursorPos;
int main()
{
int Red, Green, Blue;
hScreen = GetDC(hWindow);
sX = GetDeviceCaps(hScreen, HORZRES);
sY = GetDeviceCaps(hScreen, VERTRES);
hdcMem = CreateCompatibleDC (hScreen);
hBitmap = CreateCompatibleBitmap(hScreen, sX, sY);
BITMAPINFOHEADER bm = {0};
bm.biSize = sizeof(BITMAPINFOHEADER);
bm.biPlanes = 1;
bm.biBitCount = 32;
bm.biWidth = sX;
bm.biHeight = -sY;
bm.biCompression = BI_RGB;
bm.biSizeImage = 0; // 3 * sX * sY;
while (1) {
hOld = SelectObject(hdcMem, hBitmap);
BitBlt(hdcMem, 0, 0, sX, sY, hScreen, 0, 0, SRCCOPY);
SelectObject(hdcMem, hOld);
free(sData);
sData = (BYTE*)malloc(4 * sX * sY);
GetDIBits(hdcMem, hBitmap, 0, sY, sData, (BITMAPINFO*)&bm, DIB_RGB_COLORS);
GetCursorPos(&cursorPos);
x = cursorPos.x;
y = cursorPos.y;
Red = sData[4 * ( (y * sX) + x) +2];
Green = sData[4 * ( ( y * sX) + x) +1];
Blue = sData[4 * ( (y * sX) + x)];
printf("\nRed: %d\nGreen: %d\nBlue: %d\n", Red, Green, Blue);
Sleep(300);
}
}
Thanks!

Answer 1

Which kind of d3d application do you use? if the application use an Overlay surface, you can't get anything with code above. Overlay surface is widely used in Video players, it's totally different with normal surfaces in DirectX, the normal screen shot software can only catch data from primary surface, and Microsoft didn't provide any public interface to get data from Overlay surfaces, but some software can do this, the most common way is to hook DirectX, that's a different topic.
If your d3d application didn't use Overlay surface, you can use DiretX to get the data from screen, then get the pixel from the screen data you want.
Use CreateOffscreenPlainSurface to create an offscreen surface
Use GetFrontBufferData to get the data from screen
Lock the surface and read the pixel to get the color