TRect type

TRect defines a rectangle.

Unit
Types

struct TRect
　{
　TRect() {}
　TRect(const TPoint& TL, const TPoint& BR)
　　{ left=TL.x; top=TL.y; right=BR.x; bottom=BR.y; }
　TRect(int l, int t, int r, int b)
　　{ left=l; top=t; right=r; bottom=b; }
　TRect(RECT& r)
　　{
　　left = r.left;
　　top = r.top;
　　right = r.right;
　　bottom = r.bottom;
　　}

int Width() const { return right - left; }
int Height() const { return bottom - top ; }
bool operator ==(const TRect& rc) const
　{
　return left == rc.left && top==rc.top &&
　right == rc.right && bottom==rc.bottom;
　}
bool operator !=(const TRect& rc) const
　{ return !(rc==*this); }
　__property LONG Left = { read=left, write=left };
　__property LONG Top = { read=top, write=top };
　__property LONG Right = { read=right, write=right };
　__property LONG Bottom = { read=bottom, write=bottom };
　};

Description
TRect represents the dimensions of a rectangle. The coordinates are specified as either four separate integers representing the left, top, right, and bottom sides, or as two points representing the locations of the top left and bottom right corners.

Typically, TRect values represent pixel locations, where the origin of the pixel coordinate system is in the top left corner of the screen (screen coordinates) or the top left corner of a control client area (client coordinates). When a TRect value represents a rectangle on the screen, by convention the top and left edges are considered inside the rectangle and the bottom and right edges are considered outside the rectangle. This convention allows the width of the rectangle to be Right - Left and the height to be Bottom - Top.

要特別注意的一點是 TRect 這個長方塊中所指明的區域並不包含 the bottom and right edges, 這是為了讓 rectangle 的長寬值剛好符合座標相減的緣故。
　

TCanvas::CopyRect method

Copies part of an image from another canvas into the canvas.

void __fastcall CopyRect(const TRect &Dest, TCanvas* Canvas, const TRect &Source);

Description
Use CopyRect to transfer part of the image on another canvas to the image of the TCanvas object. Dest specifies the rectangle on the canvas where the source image will be copied. The Canvas parameter specifies the canvas with the source image. Source specifies a rectangle bounding the portion of the source canvas that will be copied.

The portion of the source canvas is copied using the mode specified by CopyMode.

TCanvas::CopyRect method 可以將另外一個 Canvas ( 第二個輸入參數 ) 中的特定長方塊 (rectangle) ( 第三個輸入參數 ) 中的影像 copy 到自己這個 Canvas 的特定長方塊( 第一個輸入參數 ) 中。
　

VFW: 調整視訊畫面大小

調整視訊畫面大小主要有兩個步驟:
1. 使用VFW SDK 所提供的 capPreviewScale 函數設定畫面大小是否隨著視窗大小變化。
2. 使用 Win32 API 的 MoveWindow 函數來調整視訊擷取視窗的大小。

在 Preview 的顯示模式下, VFW SDK 提供 capPreviewScale 函數來允許視訊畫面大小隨著視窗大小變化而調整。

The capPreviewScale macro enables or disables scaling of the preview video images. If scaling is enabled, the captured video frame is stretched to the dimensions of the capture window.

BOOL capPreviewScale(
　hwnd,
　f
　);

Parameters
hwnd Handle of a capture window.
f Preview scaling flag.
Specify TRUE for this parameter to stretch preview frames to the size of the
capture window or FALSE to display them at their natural size.

Return Values
Returns TRUE if successful or FALSE otherwise.

Remarks
Scaling preview images controls the immediate presentation of captured frames within the capture window. It has no effect on the size of the frames saved to file. Scaling has no effect when using overlay to display video in the frame buffer.

設定擷取畫面隨著擷取視窗的位置, 大小而調整後, 我們就可以使用 Win32 API 所提供的 MoveWindow 函數來調整視窗, 達到調整視訊擷取畫面的目的

The MoveWindow function changes the position and dimensions of the specified window. For a top-level window, the position and dimensions are relative to the upper-left corner of the screen. For a child window, they are relative to the upper-left corner of the parent window's client area.

BOOL MoveWindow(
　HWND hWnd, 　// handle of window
　int X,　　　　　// horizontal position
　int Y,　　　　　// vertical position
　int nWidth,　　// width
　int nHeight, 　　// height
　BOOL bRepaint // repaint flag
　);

Parameters
hWnd Identifies the window.
X Specifies the new position of the left side of the window.
Y Specifies the new position of the top of the window.
nWidth Specifies the new width of the window.
nHeight Specifies the new height of the window.
bRepaint Specifies whether the window is to be repainted. If this parameter is TRUE, the window receives a WM_PAINT message. If the parameter is FALSE, no repainting of any kind occurs. This applies to the client area, the nonclient area (including the title bar and scroll bars), and any part of the parent window uncovered as a result of moving a child window. If this parameter is FALSE, the application must explicitly invalidate or redraw any parts of the window and parent window that need redrawing.

Return Values
If the function succeeds, the return value is nonzero.
If the function fails, the return value is zero.

Remarks
If the bRepaint parameter is TRUE, Windows sends the WM_PAINT message to the window procedure immediately after moving the window (that is, the MoveWindow function calls the UpdateWindow function). If bRepaint is FALSE, Windows places the WM_PAINT message in the message queue associated with the window. The message loop dispatches the WM_PAINT message only after dispatching all other messages in the queue.

VFW: 設定視訊畫面顯示速率

在Preview 顯示模式下, VFW SKD 提供 capPreviewRate 函數來設定視訊畫面的顯示速率。

The capPreviewRate macro sets the frame display rate in preview mode.

BOOL capPreviewRate(
　hwnd,
　wMS
　);

Parameters
hwnd Handle of a capture window.
wMS Rate, in milliseconds, at which new frames are captured and displayed.

Return Values
Returns TRUE if successful or FALSE if the capture window is not connected to a capture driver.

Remarks
The preview mode uses substantial CPU resources. Applications can disable preview or lower the preview rate when another application has the focus. During streaming video capture, the previewing task is lower priority than writing frames to disk, and preview frames are displayed only if no other buffers are available for writing.

注意: 這邊的 wMS 指的就是一個畫面 ( frame ) 要顯示多少毫秒 ( msec ), 單位是 msec/frame, 若要轉換成我們一般習慣的每秒顯示多少個畫面, 單位是 frame/sec, 則是 1sec. = 1000 msec. 例如: 每個畫面顯示 20 毫秒, 代表每秒種可以顯示 1000/20 = 50 個畫面。
　

VFW: 設定顯示模式

視訊顯示模式分成兩種:
一、Preview 顯示模式:
從視訊裝置取得的影像資料會先放在系統記憶體中, 然後再顯示於螢幕上。這些處理過程全都要仰賴 CPU 處理, 因此效率較差。在 Preview 模式下, 可以透過 capPreviewRate 函數設定視訊畫面的顯示速率與透過 capPreviewScale 調整顯示畫面尺寸。VFW SDK 提供了 capPreview 函數來啟動 Preview 顯示模式。

The capPreview macro enables or disables preview mode. In preview mode, frames are transferred from the capture hardware to system memory and then displayed in the capture window using GDI functions.

BOOL capPreview(
　hwnd,
　f
　);

Parameters
hwnd Handle of a capture window.
f Preview flag. Specify TRUE for this parameter to enable preview mode or FALSE to disable it.

Return Values
Returns TRUE if successful or FALSE otherwise.

Remarks
The preview mode uses substantial CPU resources. Applications can disable preview or lower the preview rate when another application has the focus. The fLiveWindow member of the CAPSTATUS structure indicates if preview mode is currently enabled. Enabling preview mode automatically disables overlay mode.

二、Overlay 顯示模式:
視訊裝置會直接將影像資料覆疊到螢幕上, 因此, 並不會佔用系統的 CPU 與記憶體資源, 所以顯示效率較好。不過, 並不是所有的視訊裝置都支援 Overlay 模式, 像 USB 攝影機就不支援 Overlay 顯示模式。 VFW SDK 提供 capOverlay 函數來啟動 Overlay 顯示模式。

The capOverlay macro enables or disables overlay mode. In overlay mode, video is displayed using hardware overlay.

BOOL capOverlay(
　hwnd,
　f
　);

Parameters
hwnd Handle of a capture window.
f Overlay flag. Specify TRUE for this parameter to enable overlay mode or FALSE to disable it.

Return Values
Returns TRUE if successful or FALSE otherwise.

Remarks
Using an overlay does not require CPU resources. The fHasOverlay member of the CAPDRIVERCAPS structure indicates whether the device is capable of overlay. The fOverlayWindow member of the CAPSTATUS structure indicates whether overlay mode is currently enabled. Enabling overlay mode automatically disables preview mode.

註: USB 攝影機將類比影像訊號轉成數位資料, 透過 USB 傳輸介面傳送到系統記憶體中, 然後 CPU 再將影像資料顯示於螢幕上。至於影像擷取卡, 透過 A/D 轉換模組, 將類比影像訊號轉成數位資料, 並儲存於影像擷取卡的記憶體中。某些較高階的影像擷取卡還包含了影像處理晶片, 提供一些基本的影像處理功能。
　

VFW: 取得視訊裝置驅動程式的效能

由於各家視訊裝置所提供的驅動程式功能並不完全相同, 因此, 我們開發的應用程式有必要了解自己所安裝的驅動程式到底提供了什麼功能。VFW SDK 提供了 capDriverGetCaps 函數來讓你了解自己的視訊系統。

The capDriverGetCaps macro returns the hardware capabilities of the capture driver currently connected to a capture window.

capDriverGetCaps(
　hwnd,
　psCaps,
　wSize
　);

Parameters
hwnd Handle of a capture window.
psCaps Address of the CAPDRIVERCAPS structure to contain the hardware capabilities.
wSize Size, in bytes, of the structure referenced by s.

Return Values
Returns TRUE if successful or FALSE if the capture window is not connected to a capture driver.

Remarks
The capabilities returned in CAPDRIVERCAPS are constant for a given capture driver. Applications need to retrieve this information once when the capture driver is first connected to a capture window.

呼叫了這個函數後, 我們的應用程式就會得知你的電腦中代表該視訊驅動程式的索引值, 你的視訊裝置有沒有提供影像 Overlay 模式, 提供了哪些對話盒供你呼叫使用...等等。

既然這個函數要告訴我們這麼多資料, 顯然呼叫時, 就要設定很多個輸入或輸出的參數。為了方便我們使用, VFW 所採用的作法就是在 vfw.h, line 3493 起, 宣告了 tagCapDriverCaps 結構資料型態攻供我們使用:

typedef struct tagCapDriverCaps {
　UINT wDeviceIndex; // Driver index in system.ini
　BOOL fHasOverlay; // Can device overlay?
　BOOL fHasDlgVideoSource; // Has Video source dlg?
　BOOL fHasDlgVideoFormat; // Has Format dlg?
　BOOL fHasDlgVideoDisplay; // Has External out dlg?
　BOOL fCaptureInitialized; // Driver ready to capture?
　BOOL fDriverSuppliesPalettes; // Can driver make palettes?
　// following always NULL on Win32.
　HANDLE hVideoIn; // Driver In channel
　HANDLE hVideoOut; // Driver Out channel
　HANDLE hVideoExtIn; // Driver Ext In channel
　HANDLE hVideoExtOut; // Driver Ext Out channel
　} CAPDRIVERCAPS, *PCAPDRIVERCAPS, FAR *LPCAPDRIVERCAPS;

因此, 我們只要在程式中宣告一個變數 s 屬於 tagCapDriverCaps 資料型態, 我們就可以將 s 的位址 &s 放到 capDriverGetCaps 的參數之中來用了。

範例程式:
// 宣告部份:
tagCapDriverCaps s;

// 呼叫與傳回值使用部份
if (capDriverGetCaps(hwndVideo,&s,sizeof(s)))
　{
　if ( s.fHasOverlay )
　　lblOverlay->Caption = AnsiString("Overlay: Yes");
　else
　　lblOverlay->Caption = AnsiString("Overlay: No");
　}
　

VFW: 連結視訊擷取視窗與視訊裝置

The capDriverConnect macro connects a capture window to a capture driver.

BOOL capDriverConnect(
　hwnd,
　iIndex
　);

Parameters
hwnd Handle of a capture window.
iIndex Index of the capture driver. The index can range from 0 through 9.

Return Values
Returns TRUE if successful or FALSE if the specified capture driver cannot be connected to the capture window.

Remarks
Connecting a capture driver to a capture window automatically disconnects any previously connected capture driver.

當我們的應用程式建立一個視訊擷取視窗時, 視窗的畫面仍然會黑壓壓的一片, 這是由於視訊裝置所拍攝的資料並沒有餵進所建立之視訊擷取視窗的緣故。我們可以用 capDriverConnect 這個函數將兩者連結起來。很自然而然地, 輸入參數一個是之前建立視窗時傳回的 handle 值, 另一個是視訊裝置驅動程式的編號 iIndex。不過, 要中斷兩者的連結 capDriverDisconnect , 只要指出哪個視訊擷取視窗要中斷連結即可, 並不需要指出兩邊的參數。

The capDriverDisconnect macro disconnects a capture driver from a capture window.

BOOL capDriverDisconnect(
　hwnd
　);

Return Values
Returns TRUE if successful or FALSE if the capture window is not connected to a capture driver.

注意: 連結成功後, 視訊擷取視窗的影像仍然是靜態的, 並不是即時動態的視訊資料, 這是由於尚未 設定顯示模式 的緣故。
　

VFW: 如何建立一個視訊擷取視窗

The capCreateCaptureWindow function creates a capture window.

HWND VFWAPI capCreateCaptureWindow(
LPCSTR lpszWindowName,
DWORD dwStyle,
int x,
int y,
int nWidth,
int nHeight,
HWND hWnd,
int nID
);

Parameters
lpszWindowName Null-terminated string containing the name used for the capture window.
dwStyle Window styles used for the capture window.
( Note: Window styles are described with the CreateWindowEx function.)
x and y The x- and y-coordinates of the upper left corner of the capture window.
nWidth and nHeight Width and height of the capture window.
hWnd Handle of the parent window.
nID Window identifier.

Return Values
Returns a handle of the capture window if successful or NULL otherwise.

看完 BCB Help 的說明後, 我們一樣也來看看 vfw.h 之中, capCreateCaptureWindow 是如何宣告的:

HWND VFWAPI capCreateCaptureWindowA (
LPCSTR lpszWindowName,
DWORD dwStyle,
int x, int y, int nWidth, int nHeight,
HWND hwndParent, int nID);

HWND VFWAPI capCreateCaptureWindowW (
LPCWSTR lpszWindowName,
DWORD dwStyle,
int x, int y, int nWidth, int nHeight,
HWND hwndParent, int nID);

我們要建立一個視訊擷取視窗, 自然要告訴電腦要把視窗建立在哪邊? 是要直接放在 Form 上呢? 還是放在 Form 上的 Panel 物件上呢? 因此, 我們必須透過 handleParent 這個參數來告訴電腦, 也就是需要告訴電腦一個代碼, 這個代碼表示了所產生的視窗將要顯示在哪個物件之上。除此, 要放在這個物件的何處, 則是透過 x, y 來指定視窗的左上角要放這個物件的哪一個 ( x, y ) 座標上; 至於所建立的擷取視窗大小則是透過 nWidth 與 nHeight 兩個參數來表示。

capCreateCaptureWindow 的傳回值的資料型態為 HWND, 也就是所建立的視訊擷取視窗的代碼 ( handle ), 將來我們程式中要提到或針對此視窗的相關處理時, 只要指明這個代碼即可。

要關閉視訊擷取視窗的方法, 如同要關閉一般視窗一樣, 只要利用 Win32 API 的 DestroyWindow 函數, 並告訴電腦你要關閉的視窗代碼 ( handle ) 即可。

程式範例:
HWND hwndVideo;

hwndVideo = capCreateCaptureWindow(
(LPSTR) "My Capture Window", WS_CHILD | WS_VISIBLE,
0, 0, iImageWidth, iImageHeight, Form1->pnlCapture1->Handle, 1 );

RGB macro

The RGB macro selects a red, green, blue (RGB) color based on the arguments supplied and the color capabilities of the output device.

COLORREF RGB(
BYTE bRed, // red component of color
BYTE bGreen, // green component of color
BYTE bBlue // blue component of color
);

Parameters
cRed Specifies the intensity of the red color.
cGreen Specifies the intensity of the green color.
cBlue Specifies the intensity of the blue color.

Return Values
The return value is the resultant RGB color.

Remarks
The intensity for each argument is in the range 0 through 255. If all three intensities are zero, the result is black. If all three intensities are 255, the result is white.

The RGB macro is defined as follows:

#define RGB(r, g ,b) ((DWORD) (((BYTE) (r) | \
((WORD) (g) << 8)) | (((DWORD) (BYTE) (b)) << 16)))

TCanvas

TCanvas 這個類別是用來處理 Window 繪圖的介面, 負責與 Window 的裝置驅動程式溝通, 透過裝置驅動程式將資料顯示在顯示器上面。

C++ Builder 中, 具有 Canvas 的元件有 TForm, TImage, TbitButton ... 等等, 換句話說, 你可以在這些元件上繪圖。

TCanvas 透過畫筆 (TPen) 和 畫刷 (TBrush) 兩個類別來進行繪圖。除此, 也可以直接透過 Pixels property 對畫布上的像素色彩值進行存取。

TCanvas provides an abstract drawing space for objects that must render their own images.

Hierarchy
TObject -> TPersistent -> TCanvas

Unit
Graphics

Description
Use TCanvas as a drawing surface for objects that draw an image of themselves. Standard window controls such as edit controls or list boxes do not require a canvas, as they are drawn by the system.

TCanvas provides properties, events and methods that assist in creating an image by
。Specifying the type of brush, pen and font to use.
。Drawing and filling a variety of shapes and lines.
。Writing text.
。Rendering graphic images.
。Enabling a response to changes in the current image.

TCanvas has two descendants, TControlCanvas and TMetafileCanvas, which assist in drawing images of controls and in creating metafile images for objects.

TColor type

TColor is used to specify the color of an object.

Unit
Graphics

enum TColor {clMin=-0x7fffffff-1, clMax=0x7fffffff};

Description
TColor is used to specify the color of an object. It is used by the Color property of many components and by a number of other properties that specify color values.

The Graphics unit contains definitions of useful constants for TColor. These constants map either directly to the closest matching color in the system palette (for example, clBlue maps to blue) or to the corresponding system screen element color defined in the Color section of the Windows Control panel (for example, clBtnFace maps to the system color for button faces).

If you specify TColor as a specific 4-byte hexadecimal number instead of using the constants defined in the Graphics unit, the low three bytes represent RGB color intensities for blue, green, and red, respectively. The value 0x00FF0000 represents full-intensity, pure blue, 0x0000FF00 is pure green, and 0x000000FF is pure red. 0x00000000 is black and 0x00FFFFFF is white.

If the highest-order byte is zero (0x00), the color obtained is the closest matching color in the system palette. If the highest-order byte is one (0x01), the color obtained is the closest matching color in the currently realized palette. If the highest-order byte is two (0x02), the value is matched with the nearest color in the logical palette of the current device context.

注意: TColor 本身已經是一個最底層的資料型態了, 本身是一個 enum 的型態, 長度為 4 個位元組(bytes) 的整數。