如何将控件绘制到位图上

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Article Metadata

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Tested with

Devices(s): S60 Emulator

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Compatibility

Platform(s): Symbian

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Article

Keywords: CWindowToBitmapMappingGc CCoeControl CFbsBitmap SetCustomGc CWsScreenDevice CFbsBitmapDevice CFbsBitGc

Created: chenziteng (08 Nov 2009)

Last edited: hamishwillee (26 Jul 2011)

概述

直接或间接继承自CCoeControl的控件在默认情况下使用系统GC（Graphics Context，图形上下文）将自己绘制到屏幕上，但在有些情况下开发人员需要将控件绘制到位图上，比如在实现视图切换特效时需要当前视图和目标视图的截图。本文展示了如何强制将控件绘制到位图上。

方案

CCoeControl::SetGc()和CCoeControl::SetCustomGc()可以将控件的绘制重定向到一个定制的图形GC上，但是这两个函数只接受窗口GC的指针，也就是说不能直接将位图GC作为它们的参数。Symbian OS 7.0中引入的CWindowToBitmapMappingGc可以解决这个问题，这个类可以将所有对窗口GC的操作映射到位图GC上。

// .mmp
...
// begin by chen
LIBRARY            egul.lib // CWindowToBitmapMappingGc
LIBRARY            bitgdi.lib // CFbsBitmapDevice
LIBRARY            imageconversion.lib // CImageEncoder
// end by chen
...

// .cpp
...
// begin by chen
#include <gulgcmap.h> // CWindowToBitmapMappingGc
#include <ImageConversion.h> // CImageEncoder
// end by chen
...
TBool CGoodbyeHellAppUi::HandleDummyDrawNowMenuItemSelectedL( TInt aCommand )
    {
    // TODO: implement selected event handler
// begin by chen
    RFs& fs = iCoeEnv->FsSession();
    CCoeControl* control = iGoodbyeHellContainer; // 待绘制的控件
    CWsScreenDevice* wsScreenDevice = iCoeEnv->ScreenDevice(); 
    CFbsBitmap* bitmap = new(ELeave) CFbsBitmap; // 绘制控件的位图
    CleanupStack::PushL(bitmap);
    TInt err = bitmap->Create(control->Size(), wsScreenDevice->DisplayMode());
    User::LeaveIfError(err);
        CFbsBitmapDevice* bitDevice = CFbsBitmapDevice::NewL(bitmap);
        CleanupStack::PushL(bitDevice);
            CFbsBitGc* bitGc = NULL;
            err = bitDevice->CreateContext(bitGc);
            User::LeaveIfError(err);
            CleanupStack::PushL(bitGc);
                CWindowToBitmapMappingGc* w2bGc = CWindowToBitmapMappingGc::NewL(*wsScreenDevice, *bitGc);
                CleanupStack::PushL(w2bGc);
                    control->SetCustomGc(w2bGc); // 将控件的GC替换成位图GC
                    control->DrawNow(); // 将控件绘制到位图上
                    control->SetCustomGc(NULL); // 恢复控件的GC
 
                    // 在本例中将位图保存成一个.bmp文件以方便查看效果
                    _LIT(KFileName, "c:\\data\\control.bmp");
                    _LIT8(KMIME, "image/bmp");
                    CImageEncoder* encoder = CImageEncoder::FileNewL(fs, KFileName, KMIME, CImageEncoder::EOptionAlwaysThread);
                    CleanupStack::PushL(encoder);
                        TRequestStatus status = KRequestPending;
                        encoder->Convert(&status, *bitmap);
                        User::WaitForRequest(status);
                        User::LeaveIfError(status.Int());
                    CleanupStack::PopAndDestroy(encoder);
 
                CleanupStack::PopAndDestroy(w2bGc);
            CleanupStack::PopAndDestroy(bitGc);
        CleanupStack::PopAndDestroy(bitDevice);
    CleanupStack::PopAndDestroy(bitmap);
// end by chen
    return ETrue;
    }
...

更多细节请查看完整的示例程序。

注：如果想将列表框控件绘制到位图上请参照论坛中的讨论

Source Code

完整的示例程序：

GoodbyeHell(DrawControlsOnBitmap).zip

模拟器截图：

示例程序绘制的位图（由于wiki不允许上传.bmp文件因此将它转换成了.png文件）：

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