Animation Controls

An animation control is a window that displays an Audio-Video Interleaved (AVI) clip. An AVI clip is a series of bitmap frames like a movie. Animation controls can only display AVI clips that do not contain audio.

About Animation Controls

One common use for an animation control is to indicate system activity during a lengthy operation. This is possible because the operation thread continues executing while the AVI clip is displayed. For example, the Find dialog box of Microsoft® Windows® Explorer displays a moving magnifying glass as the system searches for a file.

Note If you are using ComCtl32.dll version 6 the thread is not supported, therefore make sure that your application does not block the UI or the animation will not occur.

An animation control can display an AVI clip originating from either an uncompressed AVI file or from an AVI file that was compressed using run-length (BI_RLE8) encoding. You can add the AVI clip to your application as an AVI resource, or the clip can accompany your application as a separate AVI file.

Note The AVI file, or resource, must not have a sound channel. The capabilities of the animation control are very limited and are subject to change. If you need a control to provide multimedia playback and recording capabilities for your application, you can use the MCIWnd control. For more information about the MCIWnd control, see the multimedia documentation in the Platform SDK.

Animation Control Creation

An animation control belongs to the ANIMATE_CLASS window class. You create an animation control by using the CreateWindow function or the Animate_Create macro. The macro positions the animation control in the upper-left corner of the parent window and, if the ACS_CENTER style is not specified, sets the width and height of the control based on the dimensions of a frame in the AVI clip. If ACS_CENTER is specified, Animate_Create sets the width and height of the control to zero. You can use the SetWindowPos function to set the position and size of the control.

If you create an animation control within a dialog box or from a dialog box resource, the control is automatically destroyed when the user closes the dialog box. If you create an animation control within a window, you must explicitly destroy the control.

About Animation Control Messages

An application sends messages to an animation control to open, play, stop, and close the corresponding AVI clip. Each message has one or more macros that you can use instead of sending the message explicitly.

After creating an animation control, an application sends the ACM_OPEN message to open an AVI clip and load it into memory. The message specifies either the path of an AVI file or the name of an AVI resource. The system loads the AVI resource from the module that created the animation control.

If the animation control has the ACS_AUTOPLAY style, the control begins playing the AVI clip immediately after the AVI file or AVI resource is opened. Otherwise, an application can use the ACM_PLAY message to start the AVI clip. An application can stop the clip at any time by sending the ACM_STOP message. The last frame played remains displayed when the control finishes playing the AVI clip or when ACM_STOP is sent.

An animation control can send two notification messages, ACN_START and ACN_STOP , to its parent window. Most applications do not handle either notification.

To close the AVI file or AVI resource and remove it from memory, an application can use the Animate_Close macro, which sends ACM_OPEN with the file name or resource name set to NULL.

Default Message Processing

This section describes the window messages handled by the window procedure for the ANIMATE_CLASS window class.

Message	Processing performed
WM_CLOSE	Frees the AVI file or AVI resource associated with the animation control.
WM_DESTROY	Frees the AVI file or AVI resource, frees an internal data structure, and then calls the DefWindowProc function.
WM_ERASEBKGND	Erases the window background using the current background color for static controls.
WM_NCCREATE	Allocates and initializes an internal data structure and then calls DefWindowProc.
WM_NCHITTEST	Returns the HTTRANSPARENT hit test value.
WM_PAINT	Draws an AVI frame in the animation control.
WM_SIZE	Checks if the control has the ACS_CENTER style. If the control does not, it calls DefWindowProc. Otherwise, it centers the animation in the control, invalidates the control, and then calls DefWindowProc.

Creating an Animation Control

The following function creates an animation control in a dialog box. The animation control is positioned below the specified control, and the dimensions of the animation control are based on the dimensions of a frame in the AVI clip.

		
// CreateAnimationCtrl - creates an animation control, positions it 
//                       below the specified control in a dialog box, 
//                       and opens the AVI clip for the animation control. 
// Returns the handle to the animation control. 
// hwndDlg             - handle to the dialog box. 
// nIDCtl              - identifier of the control below which the animation control 
//                       is to be positioned. 
// 
// Constants 
//     IDC_ANIMATE - identifier of the animation control. 
//     CX_FRAME, CY_FRAME - width and height of the frames 
//     in the AVI clip. 

HWND CreateAnimationCtrl(HWND hwndDlg, int nIDCtl) 
{ 
    HWND hwndAnim = NULL; 
    RECT rc; 
    POINT pt; 

    // Create the animation control. 
    hwndAnim = Animate_Create(hwndDlg, IDC_ANIMATE, 
        WS_BORDER | WS_CHILD, g_hinst); 

    // Get the screen coordinates of the specified control button. 
    GetWindowRect(GetDlgItem(hwndDlg, nIDCtl), &rc); 

    // Convert the coordinates of the lower-left corner to 
    // client coordinates. 
    pt.x = rc.left; 
    pt.y = rc.bottom; 
    ScreenToClient(hwndDlg, &pt); 

    // Position the animation control below the Stop button. 
    SetWindowPos(hwndAnim, 0, pt.x, pt.y + 20, 
        CX_FRAME, CY_FRAME, 
        SWP_NOZORDER | SWP_DRAWFRAME); 

    // Open the AVI clip, and show the animation control. 
    Animate_Open(hwndAnim, "SEARCH.AVI"); 
    ShowWindow(hwndAnim, SW_SHOW); 

    return hwndAnim; 
}

Controlling the AVI Clip

The following function uses the animation control macros to control the display of the AVI clip in an animation control.

	
// DoAnimation - plays, stops, or closes an animation control's 
//               AVI clip, depending on the value of an action flag. 
// hwndAnim    - handle to an animation control 
// nAction     - flag that determines whether to play, stop, or close 
//               the AVI clip. 

void DoAnimation(HWND hwndAnim, int nAction) 
{ 
    switch (nAction) { 
        case PLAYIT: 
         // Play the clip continuously starting with the 
         // first frame. 
            Animate_Play(hwndAnim, 0, -1, -1); 
            break; 

        case STOPIT: 
            Animate_Stop(hwndAnim); 
            break; 

        case CLOSEIT: 
            Animate_Close(hwndAnim); 
            break; 

        default: 

            break; 

    } 

    return; 
}