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# DirectX drawing in other thread

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4 replies to this topic

### #1Milla.M  Members

Posted 02 July 2012 - 01:06 AM

Hi
I have some directx code that I want to run in second thread.
I read the following http://www.codermind...-Direct3D9.html which says that is ok to use directx device from other thread as long as you are not using concurrently from many threads, and I am not doing that. And that you have to call CreateDevice and CreateWindow from the same thread , and some others functions like TestCooperativeLevel, Reset etc

And I am doing the following :

1) create window and directx device in main thread

2) start second thread and do the rendering and updating there , basically :

update
BeginScene
Draw
EndScene
Present

3) Also I care to call TestCooperativeLevel, Reset, pDevice->Release and pDirect3D->Release() from the main thread.

Problem :
The code is working when I test it in debug mode. But it doesn't in relase mode i.e it seems that the rendering threads draws all fine, but my main thread seems blocked and doesn't process messages, or maybe sometimes process them very slow. If just comment the call to Present , everything is fine ( of course it doesnot draw on screen ) i.e the main thread is responsive and second thread is running too. Sooo, is there some problem when calling Present from other thread, if the window and device is created in main thread ? As I read the following http://msdn.microsof...4(v=vs.85).aspx such restriction has only on CreateDevice,TestCooperativeLevel and Release.

### #2Tordin  Members

Posted 02 July 2012 - 06:22 AM

Could you post some code on how you do this?

I have had similar errors, and had to solve it with a sleep(1);

And if i remember correct, you should not render on a secondthread, you should render on your main thread, but do all the updating and setup all data to
just be scheduald for drawing, so that the main thread do as litle as possible when the drawing´s begins.

but if you switch to dx11, you get a even more efficent way for multithreading and dx support. (Worth a tought)
"There will be major features. none to be thought of yet"

### #3Milla.M  Members

Posted 02 July 2012 - 08:07 AM

Hi
I can send minimum ( doesn't compile code). I should mention that the code uses wild magic 5 library for rendering, and I am using Qt , to start the second thread. The second thread starts its own message loop , so it can receive the update message . I don't know if you familiar wit qt signal/slots mechanism but this should be irrelevant here.
void Initialize( HWND parentHWND)
{
// DirectX uses a projection matrix for depth in [0,1].
Wm5::Camera::SetDefaultDepthType(Wm5::Camera::PM_DEPTH_ZERO_TO_ONE);

// === Create the window for rendering. ===
// Register the window class.
static wchar_t sWindowClass[] = L"My Window";
WNDCLASS wc;
wc.style		 = CS_HREDRAW | CS_VREDRAW | CS_OWNDC;
wc.lpfnWndProc   = MyEventHandler;
wc.cbClsExtra	= 0;
wc.cbWndExtra	= 0;
wc.hInstance	 = 0;
wc.hIcon		 = 0;
wc.hCursor	   =0;
wc.hbrBackground = (HBRUSH)GetStockObject(WHITE_BRUSH);
wc.lpszClassName = sWindowClass;
RegisterClass(&wc);

DWORD dwStyle;
dwStyle = WS_CHILDWINDOW;

// resize it, to fit its parent
RECT rect;
::GetWindowRect(parentHWND, &rect);
int width = rect.right - rect.left;
int height = rect.bottom - rect.top;

static wchar_t sWindowName[] = L"MyWindow";
// Create the application window.
HWND handle = CreateWindow(sWindowClass,
sWindowName,
dwStyle,
0,//xPos
0,//yPos
width,
height,
parentHWND,
0,
0,
0);

// Create the device for rendering.
mRenderInput.mWindowHandle = handle;
mRenderInput.mDriver = Direct3DCreate9(D3D_SDK_VERSION);
assertion(mRenderInput.mDriver != 0, "Failed to create Direct3D9\n");
mRenderer = new0 Wm5::Renderer(mRenderInput, width, height,
mColorFormat, mDepthStencilFormat, mNumMultisamples);

// Display the window.
ShowWindow(handle, SW_SHOW);
UpdateWindow(handle);

}
class MyRunner: public QObject
{

public slots :
void update()
{

mSceneGraph->Update();
mCuller.ComputeVisibleSet(mSceneGraph->GetRoot());

if (mRenderer->PreDraw()) // PreDraw just calls BeginScene
{
mRenderer->ClearBuffers();
mRenderer->Draw(mCuller.GetVisibleSet());
mRenderer->PostDraw(); // PostDraw just calls EndScene
mRenderer->DisplayColorBuffer(); // DisplayColorBuffer just calls Present
}

emit(SignalUpdate()); // this post message to the second thread message loop so it can basically start the update cycle anew

}
};
{
void run()
{
this->exec(); // this starts message loop
}
};
HWND mainAppHwnd = GetMainHwnd();
Initialize(mainAppHwnd);
MyRunner* runner = new MyRunner;


"And if i remember correct, you should not render on a secondthread, you should render on your main thread, but do all the updating and setup all data to
just be scheduald for drawing, so that the main thread do as litle as possible when the drawing´s begins."

I don't uderstand this.
Does this mean that in my case that I should call the updating of the scenegraph, and drawing functions on second thread, but only call Present on main thread ?

By the way what problem did you solve with Sleep(1) ?

Also I can't switch to DirectX11

Edited by Milla.M, 02 July 2012 - 08:13 AM.

### #4Tordin  Members

Posted 02 July 2012 - 08:59 AM

"And if i remember correct, you should not render on a secondthread, you should render on your main thread, but do all the updating and setup all data to

just be scheduald for drawing, so that the main thread do as litle as possible when the drawing´s begins."

I don't uderstand this.

Does this mean that in my case that I should call the updating of the scenegraph, and drawing functions on second thread, but only call Present on main thread ?

by this i mean, have your scenegraph updated at the secondary thread(s).

i belive it has something to do with dx9 isént built around multithreading.

"

By the way what problem did you solve with Sleep(1) ?"

the freeze, at the end of my multithread job i added a Sleep(1);

"There will be major features. none to be thought of yet"

### #5Milla.M  Members

Posted 03 July 2012 - 12:01 AM

by this i mean, have your scenegraph updated at the secondary thread(s).