從回調函數的參數中獲取值

Question

我正在使用biometrics SDK。我將頭文件轉換爲delphi以使用dll。

它看起來是這樣的：

const 
{VrBio_EventType} 
    VRBIO_CAPTURE_EVENT_UNPLUG    = $001; {Fingerprint scanner unplugged from the computer.} 
    VRBIO_CAPTURE_EVENT_PLUG     = $002; {Fingerprint scanner plugged on the computer.} 
    VRBIO_CAPTURE_EVENT_REMOVED    = $004; {Finger removed from the fingerprint scanner.} 
    VRBIO_CAPTURE_EVENT_PLACED    = $008; {Finger placed on the fingerprint scanner.} 
    VRBIO_CAPTURE_EVENT_IMAGE_FRAME   = $10; {A fingerprint frame was captured on the fingerprint scanner.} 
    VRBIO_CAPTURE_EVENT_IMAGE_CAPTURED  = $020; {A fingerprint image was captured on the fingerprint scanner.} 
    VRBIO_CAPTURE_EVENT_FAKE_FINGER_DETECTED = $400; {A false finger has been detected on the sensor} 
    VRBIO_CAPTURE_EVENT_FAKE_FINGER_REMOVED = $800; {A false finger has been removed from the sensor} 

type 

(* Stores the parameters of the ISO 19794-4 image format. @see VGetReaderProperties @see VrBio_ReaderProperty 
typedef struct 
{ 
    /** @see VrBio_ISO197944CompressionMode*/ 
    int compressionMode; 
    /** @see VrBio_ISO197944ImpressionType*/ 
    int impressionType; 
    /** @see VrBio_ISO197944FingerPosition*/  
    int fingerPosition; 

}VrBio_ISO197944Parameters; 
*) 

    PISO197944Parameters = ^TISO197944Parameters; 
    TISO197944Parameters = record 
     compressionMode: Integer; { @see VrBio_ISO197944CompressionMode} 
     impressionType: Integer; { @see VrBio_ISO197944ImpressionType} 
     fingerPosition: Integer; { @see VrBio_ISO197944FingerPosition} 
    end; 

(* Represents a biometric image. @see VrBio_CaptureEventCallback \ref VSyncCapture 
struct VrBio_BiometricImage 
{ 
    /** Image width.*/ 
    int width; 
    /**Image height*/ 
    int height; 
    /**Image resolution in dpi. For the obsolete functions, use pixels/cm.*/ 
    int resolution; 
    /**Number of channels in the image. Fingerprint images should always be grayscale, so this value is always 1.*/ 
    int channels; 
    /**Biometric modality. 
    * Always use VRBIO_BIOMETRIC_MODALITY_FINGERPRINT. 
    * \ref VrBio_BiometricModality. 
    */ 
    int biometricModality; 
    /**Scanner type. 
    * \ref VrBio_ScannerType. 
    */ 
    int scannerType; 
    /**Formato de imagem: Formato da imagem. 
    *\ ref VrBio_ImageFormat.*/ 
    int imageFormat; 
    /**Size of the buffer*/ 
    int bufferSize; 
    /**Compression rate. Valid for images that allow compression. 
    * \ref VrBio_CompressionRate 
    */ 
    int compressionRate; 
/**Quality of the fingerprint image. 
    * \ref VrBio_FingerQuality 
    */ 
    int fingerQuality; 

    /** Only valid if the image if imageFormat is \ref VrBio_ImageFormat::VRBIO_IMAGEFORMAT_ISO19794_4 
    *\ref VrBio_ISO197944Parameters 
    */ 
    VrBio_ISO197944Parameters* ISO197944_parameters; 

    /** Buffer storing the pixels of the image. 
    The position(x,y,c) of a pixel is y*width*channels+x*channels+c. 
    */ 
    unsigned char* buffer; 

    /**Reserved for future use*/ 
    void* reserved; 
}; 

typedef struct VrBio_BiometricImage VrBio_BiometricImage; 
*) 
    PBiometricImage = ^TBiometricImage; 
    TBiometricImage = record 
    width: Integer;        { Image width. } 
    height: Integer;       { Image height } 
    resolution: Integer;      { Image resolution in dpi. For the obsolete functions, use pixels/cm.} 
    channels: Integer;       { Number of channels in the image. Fingerprint images should always be grayscale, so this value is always 1. } 
    biometricModality: Integer;     { Biometric modality. Always use VRBIO_BIOMETRIC_MODALITY_FINGERPRINT. \ref VrBio_BiometricModality. } 
    scannerType: Integer;      { Scanner type. \ref VrBio_ScannerType. } 
    imageFormat: Integer;      { Formato de imagem: Formato da imagem. \ ref VrBio_ImageFormat. } 
    bufferSize: Integer;      { Size of the buffer } 
    compressionRate: Integer;     { Compression rate. Valid for images that allow compression. \ref VrBio_CompressionRate } 
    fingerQuality: Integer;      { Quality of the fingerprint image. \ref VrBio_FingerQuality } 
    ISO197944_parameters: PISO197944Parameters; { Only valid if the image if imageFormat is \ref VrBio_ImageFormat::VRBIO_IMAGEFORMAT_ISO19794_4 \ref VrBio_ISO197944Parameters } 
    buffer: PByte;        { Buffer storing the pixels of the image. The position(x,y,c) of a pixel is y*width*channels+x*channels+c. } 
    reserved: Pointer;       { Reserved for future use } 
    end; 

(* 
#include "VTypes.h" 

#ifdef WIN32 
#define DLLIMPORT extern "C" __declspec(dllimport) int __stdcall 
#else 
#define DLLIMPORT extern "C" 
#endif 
*) 

{ Callback function that receives events.. 
typedef void (*VrBio_CaptureEventCallback) (
        int eventType, 
      const char* readerName, 
    VrBio_BiometricImage* image, 
      const void* userData) 
} 
    TCaptureEventCallback = procedure(eventType: Integer; readerName: PAnsiChar; image: PBiometricImage; userData: Pointer); stdcall; 

{ Function responsible for initializing the SDK. This function MUST be called before calling any other method, except \ref VInstallLicense 
    DLLIMPORT VStartSDK(VrBio_CaptureEventCallback eventCallback); 
} 
    function VStartSDK(eventCallback: TCaptureEventCallback): Integer; stdcall; 

{ Function responsible for finalizing the SDK. This function should be called when the SDK is not needed in the application anymore. 
    DLLIMPORT VStopSDK(); 
} 
    function VStopSDK(): Integer; stdcall; 

{ Function responsible for starting the capture on a specific fingerprint reader. 
    After calling this function, the application is able to receive events. 
    DLLIMPORT VStartReader(const char* readerName); 
} 
    function VStartReader(readerName: PAnsiChar): Integer; stdcall; 

使用它看起來像這樣：

implementation 

{$R *.dfm} 

procedure EventCallback(eventType: Integer; readerName: PAnsiChar; image: PBiometricImage; userData: Pointer); stdcall; 
begin 
    case eventType of 
    VRBIO_CAPTURE_EVENT_UNPLUG:    Form1.Memo1.Lines.Add('Leitor desconectado!'); 
    VRBIO_CAPTURE_EVENT_REMOVED:    Form1.Memo1.Lines.Add('Dedo removido!'); 
    VRBIO_CAPTURE_EVENT_PLACED:    Form1.Memo1.Lines.Add('Dedo detectado!'); 
    VRBIO_CAPTURE_EVENT_IMAGE_FRAME:   Form1.Memo1.Lines.Add('Frame capturado!'); 
    VRBIO_CAPTURE_EVENT_IMAGE_CAPTURED:  Form1.Memo1.Lines.Add('Imagem capturada!'); 
    VRBIO_CAPTURE_EVENT_FAKE_FINGER_DETECTED: Form1.Memo1.Lines.Add('Dedo falso detectado!'); 
    VRBIO_CAPTURE_EVENT_FAKE_FINGER_REMOVED: Form1.Memo1.Lines.Add('Dedo falso removido!'); 

    VRBIO_CAPTURE_EVENT_PLUG: 
    begin 
     VStartReader(readerName); 
     Form1.Memo1.Lines.Add('Leitor conectado!'); 
    end; 

    end; 
end; 

procedure TForm1.Button2Click(Sender: TObject); 
begin 
    VStartSDK(EventCallback); 
end; 

我的問題：

我可以使用該應用程序並獲得Plug，Unplug和Placed事件，但當我得到Image Captured事件時，我有一個acces vilation。 在正在運行的事件中，EventCallback參數圖像爲nil。 TBiometricImage記錄轉換是否正確？

如何將TBiometricImage緩衝區轉換爲TBitmap並在TImage中顯示捕獲的圖像？

Answer 1

當我得到圖像捕捉事件我有一個acces vilation。在正在運行的事件中，EventCallback參數圖像爲零。 TBiometricImage記錄轉換是否正確？

單個字段被宣佈爲正常，但請仔細檢查Delphi記錄的對齊和填充是否與C/C++中結構使用的對齊和填充匹配。

而且，更重要的是，VrBio_CaptureEventCallback的typedef在C/C++聲明沒有指定的任何調用約定，所以它會使用編譯器的默認慣例，這是通常__cdecl代替__stdcall（可在編譯器設置來配置）。在Delphi中，您聲明TCaptureEventCallback使用stdcall而不是cdecl。你必須確保你正確匹配調用約定（導出的DLL函數使用stdcall，所以你沒問題）。

如何將TBiometricImage緩衝區轉換爲TBitmap並在TImage中顯示捕獲的圖像？

SDK文檔沒有說明如何處理各種圖像格式。但是，僅查看結構聲明，buffer字段指向實際圖像數據，而imageFormat字段指示該數據的格式（還有一個VrBio_ImageFormat枚舉，您尚未翻譯）。因此，您首先需要查看imageFormat以瞭解如何解釋buffer。

我確實看到VConvertImage()功能可用。所以你應該能夠將圖像轉換爲BMP格式，如果它們還沒有。根據SDK中的示例，看起來buffer數據可能是標準BMP文件格式，因此您可以嘗試將buffer複製到TMemoryStream，然後使用TBitmap.LoadFromStream()方法。

也有可用的GIF和JPG圖片格式，這可能是TGIFImage和TJPEGImage，分別進行處理，甚至TWICImage，如果你想而無需將它們首先轉換爲BMP顯示掃描GIF/JPG圖片。還有一個RAW圖像格式可用（顯然你的圖像正在使用），但沒有標準的VCL TGraphic類來處理RAW圖像，但我認爲如果你環顧四周，可能會出現一些第三方類。

否則，你可以嘗試將圖像數據轉換爲BMP，如果需要的話，然後傳遞到buffer Win32 API的CreateBitmap/Indirect()或CreateDibSection()功能，然後如果成功分配產生HBITMAP到TBitmap.Handle財產。