Confused about the sense of GDI at all [closed] - c++

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I was starting to learn Windows programing few years ago, and I always used only "native" environment for my needs. I mean, I write code only using Winapi, not DirectX\Draw\2D\etc for graphics, not any external libraries for music or something else, just only Winapi. I'm working on the next evolution step of my graphical render due last time. Previouly algorithms were good, they redraws only parts of windows that should to be redraw, and it works for not fullscreened windows. But when I worked with full-screen cases, I've got very small fps.
So, few monthes ago, I've understood, that I can make a brand new algorithm: instead of make draws in WM_PAINT, every time recreate dc'c, bitmaps, I can run a parallel thread, where in eternal loop goes redrawing, dc'c and bitmaps creates only one time + I even can don't use Gdi or Gdi+ functions such as Rectangle, Graphics::FillRect, but write my own faster functions. So I did it. And what I've got:
62 fps, 1920\1080 with no any graphical load
why?
It's just this code
void render()
{
COLORREF *matrix;
matrix = re->GetMatrix();
while (1)
{
Sleep(1000 / 120);
re->Render();
//below goes fps counter, that counts in another thread
while (!mu.try_lock())
{
}
frames++;
mu.unlock();
}
}
re->Render function
inline void Card::Render()
{
//SetDIBits(hdcc, bm, 0, bi.bmiHeader.biHeight, matrix, &bi, DIB_RGB_COLORS);
//StretchBlt(hdc, 0, 0, width, height, hdcc, 0, 0, width, height, SRCCOPY);
//method above with Stretch or just BitBlt is awfull at all
SetDIBitsToDevice(hdc, 0, 0, width, height, 0, 0, 0, bi.bmiHeader.biHeight, matrix, &bi, DIB_RGB_COLORS);//hdc is a surface dc, not memory
}
So if I understanding well, it is the maximum, that can be taken from Gdi. If I right, the question is - what is the sense of Gdi? Computer games were developed on Direct 2D then DirectX\OpenGL, user interfaces, before NT 8 were not window less, and(or) used DirectDraw. I'm confused, is it really to write good software render do not using any library, just by yourself?

Answer 1

Part of the problem is here:
Sleep(1000 / 120);
comes out to 8 ms (after integer division). But Sleep is not a very precise timing mechanism. It will sleep for at least the amount of time specified. And, with the default clock tick rate, it will sleep for at least 15.6 ms on most configurations. A frame duration of 15.6 ms is very close to 62 frames per second, so that's probably the root problem.
Beyond that, you will have problems with GDI because the graphics operations are largely performed in system memory which then has to be transferred to graphics memory. At higher resolutions, it can be difficult to do this at a high frame rate, depending on the hardware in use.

Answer 2

I’m not sure I understand your question but here’s my best guess.
I can run a parallel thread
Not a good idea for GDI. WinAPI can go multithreading, but it’s tricky to use correctly, see this article: https://msdn.microsoft.com/en-us/library/ms810439.aspx
62 fps, 1920\1080 with no any graphical load. why?
GDI wasn’t designed for the high-FPS use case you want from that. It was designed to redraw stuff when something changed. It was designed before modern GPUs.
On modern hardware, the way to get high FPS and/or low latency rendering is by using GPU-centric technologies. In C++, that’s Direct3D and Direct2D.
is it really to write good software render do not using any library
Sure it’s possible. Just not the way you’re trying to do it with SetDIBitsToDevice.
On modern hardware + OS, your API calls (regardless on what the API is) will become commands sent to 3D GPU. That’s why newer GPU-centric APIs like D3D and D2D often deliver better performance.
If you want to implement a software render that’s fine, just keep in mind you have to upload the result to a GPU texture. On modern Windows, WinAPI does just that under the hood.
Legacy Windows (i.e. anything before Vista) didn’t rely on GPU for that. But games didn’t use GDI either, they used DirectX 9, DirectDraw, etc…