使用类似于 Inspect 的 GDI+(或 GDI)在屏幕上绘图

我正在尝试使用 GDI+ 在屏幕上(整个屏幕，在所有其他窗口的顶部)进行绘制.
我已将 NULL 传递给 GetDC 以将 HDC 传送到屏幕，然后使用它创建一个 Graphics 对象，并使用 DrawRectangle 在屏幕上绘制矩形.
一切正常......除了......矩形的内部不会更新.

I'm trying to draw on the screen (the whole screen, on top of every other window) using GDI+.
I've passed NULL to GetDC to get a HDC to the screen, and then used that to create a Graphics object, and used DrawRectangle to draw rectangles on the screen.
Everything works..except...the inside of the rectangle won't update.

就像我在命令提示符上绘制它并移动命令提示符一样，矩形的内部仍然是黑色的.我希望看到矩形下面是什么.

Like if I draw it over a command prompt, and move the command prompt, the inside of the rectangle remains black. I expect to see whats under the rectangle.

这是进行绘图的代码..

Here's the code that's doing the drawing..

Pen BluePen(Color(255, 0, 255, 0), 2);
Graphics graphics(screenDC);
graphics.DrawRectangle(&BluePen, myRect);

很简单，那么我需要做些什么才能在屏幕显示时更新矩形的内部?或者让它真正透明.

Pretty simple, so is there something I have to do to get the inside of the rectangle to update when the screen does? Or to get it truely transparent.

================= 编辑 ==================

好吧，我已经放弃了，并认为这是不可能的，直到……我意识到 Windows SDK 附带的 Inspect 工具可以完美地做到这一点.

Well I had given up on this, and assumed it wasn't possible, until...I realized the Inspect tool that comes with the Windows SDK does this perfectly.

我想重新创建类似于高亮矩形的东西，如果我选择一个窗口(例如 Firefox)，然后将 Inspect 置于焦点上，我可以自由地移动它并完美更新所有内容.甚至没有任何闪烁.

I would like to recreate something similar to the highlight rectangle, and if I select a window (such as Firefox) and then bring Inspect into focus I can move it around freely with everything being updated perfectly. There's not even any flickering.

那么……有人知道 Inspect 是如何做到这一点的吗?

So...does anyone know how Inspect manages to do this?

在 GDI 而不是 GDI+ 中的答案也很好...

Also answers in GDI instead of GDI+ are fine...