SetPixel(), then moving window

This is a discussion on SetPixel(), then moving window within the Windows Programming forums, part of the Platform Specific Boards category; I have a really basic program that's only job is to fill a window with pixels of random color in ...

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    SetPixel(), then moving window

    I have a really basic program that's only job is to fill a window with pixels of random color in random places. I do this with SetPixel() placed inside my windows procedure (just to make sure this happens a lot, probably not the best way, I know). Things seem to work fine, but when I move the window or resize it, etc. the entire screen clears and I don't understand why. Also, why is DirectX faster than GDI? What does DirectX use that makes it run faster and how can I access it?

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    >>when I move the window or resize it, etc. the entire screen clears and I don't understand why.

    Because the hdc you have drawn to has lost scope or been cleared by the OS.

    Have a look at the code I posted here. Should give you a good start.

    Device context woes

    If you create a single buffer then it should be fast enough. SetPixel() is slow and could be avoided.

    >>why is DirectX faster than GDI?

    AFAIK directx calls the graphics card to do some processing. GDI is called, then the graphics card.

    GDI is the tool to use for your app (IMO)
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    So why does moving it and resizing it make the DC out of its scope? How exactly is the appearance of the window stored?

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    >>How exactly is the appearance of the window stored?

    Thats the point, its not stored.........(Apart from in your resource script or winclass background brush)

    Unless you hold a copy in a buffer DC yourself and copy it back when a paint msg is received.
    "Man alone suffers so excruciatingly in the world that he was compelled to invent laughter."
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    "I spent a lot of my money on booze, birds and fast cars......the rest I squandered."
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    "If you are going through hell....keep going."
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    Aw, I think I gotcha. Should I store everything in a separate bitmap and only use a DC when I'm actually drawing it to the window? I've heard bad things happen when you have too many DC's open.

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    pronounced 'fib' FillYourBrain's Avatar
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    That's the idea. It's called back-buffering. You set the pixels in a bitmap and "blit" it to the screen in one GDI call. This is very fast. No need for DirectX for most applications.

    Where DirectX comes in to play is when you want to use hardware accelleration for certain common graphical operations such as matrix math, 3d texture mapping, etc.
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    pronounced 'fib' FillYourBrain's Avatar
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    as far as having too many DCs open. You don't really need any open until the moment of the WM_PAINT message. One method is to just get the paintDC and SetDIBits into it.
    "You are stupid! You are stupid! Oh, and don't forget, you are STUPID!" - Dexter

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    Cool, thanks guys. One more question: I tried to set the brush color of one of my DCs using SetDCBrushColor() and for whatever reason I got a compiler error saying that it was undeclared. This struck me as odd seeing as on MSDN it said that it was part of Wingdi.h which is included in Windows.h . I checked this out, and sure enough, there it was. I wasn't able to use this, and ended up doing a SelectObject() instead, which worked fine. Anybody have an idea as to why this error occurred?

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    Oh, also, is there a way to modify a bitmap without creating a DC for it? I've read in tutorials that this is the only way, but you just said that you only really need it when WM_PAINT is sent

  10. #10
    pronounced 'fib' FillYourBrain's Avatar
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    Quote Originally Posted by SgtMuffles
    Oh, also, is there a way to modify a bitmap without creating a DC for it? I've read in tutorials that this is the only way, but you just said that you only really need it when WM_PAINT is sent
    allocate a buffer big enough for the DIB. You'll have to look up the format. It's basically a bmp file without BITMAPFILEHEADER. That is what windows refers to as a DIB. Then just set the bytes. No DC or GDI calls necessary. On the WM_PAINT, SetDibits()
    "You are stupid! You are stupid! Oh, and don't forget, you are STUPID!" - Dexter

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