CODEWITHSUNDEEP
windowsperformancewinapidirectx
Dylan_Programmer
Dylan_Programmer

Reputation: 31

Why does not calling `ValidateRect` cause a DirectX application to slow down tremendously?

I asked a related question earlier and realised that not calling ValidateRect in the application as response to WM_PAINT causes tremendous slowdown.

Why is this? How could this affect a DirectX application in such a manner?

// ----------------------------------------------------------------------------
// Name: MsgProc()
// Desc: The window's message handler
//-----------------------------------------------------------------------------
LRESULT WINAPI MsgProc( HWND hWnd, UINT msg, WPARAM wParam, LPARAM lParam ) {
    switch(msg) {
        case WM_DESTROY:
            Cleanup();
            PostQuitMessage( 0 );
            return 0;
        case WM_PAINT:
            Render();
            ValidateRect( hWnd, NULL );
            return 0;
    }
    return DefWindowProc( hWnd, msg, wParam, lParam );
}

Upvotes: 1

Views: 613

Answers (1)

Kenny Kerr
Kenny Kerr

Reputation: 3115

Your application is slowing down because it is rendering far more than necessary. It is receiving a furious stream of WM_PAINT messages.

Windows sends a WM_PAINT message to a window when it thinks the window should be painted. It makes this determination based on whether a window has been invalidated. Once you have rendered the window completely, you must tell Windows that this is the case by validating the window’s client area. As long as there is some invalidated area, Windows will continue to send your window WM_PAINT messages.

Before DirectX, application windows were validated when they called EndPaint. You can still call BeginPaint and EndPaint, wrapping whatever DirectX rendering you’re doing, or you can simply call ValidateRect when you’re done rendering.

Upvotes: 3

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