/*******************************************************************
* File    : JSFX_ImageZoom.js  © JavaScript-FX.com
* Created : 2001/08/31
* Author  : Roy Whittle  (Roy@Whittle.com) www.Roy.Whittle.com
* Purpose : To create a zooming effect for images
* History
* Date         Version        Description
* 2001-08-09    1.0        First version
* 2001-08-31    1.1        Code split - others became JSFX_FadingRollovers,
*                             JSFX_ImageFader and JSFX_ImageZoom.
* 2002-01-27    1.2        Completed development by converting to JSFX namespace
* 2002-04-25    1.3        Added the functions stretchIn & expandIn
* 2004-01-06    1.4        Allowed for the image (tag) being forcibly sized
***********************************************************************/
/*** Create some global variables ***/
if(!window.JSFX)
    JSFX=new Object();
JSFX.ImageZoomRunning = false;
/*******************************************************************
*
* Function    : zoomIn
*
* Description : This function is based on the turn_on() function
*              of animate2.js (animated rollovers from www.roy.whittle.com).
*              Each zoom object is given a state.
*            OnMouseOver the state is switched depending on the current state.
*            Current state -> Switch to
*            ===========================
*            null        ->    OFF.
*            OFF        ->    ZOOM_IN + start timer
*            ZOOM_OUT    ->    ZOOM_IN
*            ZOOM_IN_OUT    ->    ZOOM_IN
*****************************************************************/
JSFX.zoomOn = function(img, zoomStep, maxZoom)
{
    if(img)
    {
        if(!zoomStep)
        {
            if(img.mode == "EXPAND")
                zoomStep = img.height/100;
            else
                zoomStep = img.width/100;
        }

        if(!maxZoom)
        {
            if(img.mode == "EXPAND")
                maxZoom = img.height/3;
            else
                maxZoom = img.width/3;
        }


        if(img.state == null)
        {
            img.state = "OFF";
            img.index = 0;
            img.orgWidth =  img.width;
            img.orgHeight = img.height;
            img.zoomStep = zoomStep;
            img.maxZoom  = maxZoom;
        }

        if(img.state == "OFF")
        {
            img.state = "ZOOM_IN";
            start_zooming();
        }
        else if( img.state == "ZOOM_IN_OUT"
            || img.state == "ZOOM_OUT")
        {
            img.state = "ZOOM_IN";
        }
    }
}
JSFX.zoomIn = function(img, zoomStep, maxZoom)
{
    img.mode = "ZOOM";
    JSFX.zoomOn(img, zoomStep, maxZoom);
}
JSFX.stretchIn = function(img, zoomStep, maxZoom)
{
    img.mode = "STRETCH";
    JSFX.zoomOn(img, zoomStep, maxZoom);
}
JSFX.expandIn = function(img, zoomStep, maxZoom)
{
    img.mode = "EXPAND";
    JSFX.zoomOn(img, zoomStep, maxZoom);
}
/*******************************************************************
*
* Function    : zoomOut
*
* Description : This function is based on the turn_off function
*              of animate2.js (animated rollovers from www.roy.whittle.com).
*              Each zoom object is given a state.
*            OnMouseOut the state is switched depending on the current state.
*            Current state -> Switch to
*            ===========================
*            ON        ->    ZOOM_OUT + start timer
*            ZOOM_IN    ->    ZOOM_IN_OUT.
*****************************************************************/
JSFX.zoomOut = function(img)
{
    if(img)
    {
        if(img.state=="ON")
        {
            img.state="ZOOM_OUT";
            start_zooming();
        }
        else if(img.state == "ZOOM_IN")
        {
            img.state="ZOOM_IN_OUT";
        }
    }
}
/*******************************************************************
*
* Function    : start_zooming
*
* Description : This function is based on the start_animating() function
*                of animate2.js (animated rollovers from www.roy.whittle.com).
*            If the timer is not currently running, it is started.
*            Only 1 timer is used for all objects
*****************************************************************/
function start_zooming()
{
    if(!JSFX.ImageZoomRunning)
        ImageZoomAnimation();
}

JSFX.setZoom = function(img)
{
    if(img.mode == "STRETCH")
    {
        img.width  = img.orgWidth  + img.index;
        img.height = img.orgHeight;
    }
    else if(img.mode == "EXPAND")
    {
        img.width  = img.orgWidth;
        img.height = img.orgHeight + img.index;
    }
    else
    {
        img.width  = img.orgWidth   + img.index;
        img.height = img.orgHeight  + (img.index * (img.orgHeight/img.orgWidth));
    }
}
/*******************************************************************
*
* Function    : ImageZoomAnimation
*
* Description : This function is based on the Animate function
*            of animate2.js (animated rollovers from www.roy.whittle.com).
*            Each zoom object has a state. This function
*            modifies each object and (possibly) changes its state.
*****************************************************************/
function ImageZoomAnimation()
{
    JSFX.ImageZoomRunning = false;
    for(i=0; i<document.images.length; i++)
    {
        var img = document.images[i];
        if(img.state)
        {
            if(img.state == "ZOOM_IN")
            {
                img.index+=img.zoomStep;
                if(img.index > img.maxZoom)
                    img.index = img.maxZoom;

                JSFX.setZoom(img);

                if(img.index == img.maxZoom)
                    img.state="ON";
                else
                    JSFX.ImageZoomRunning = true;
            }
            else if(img.state == "ZOOM_IN_OUT")
            {
                img.index+=img.zoomStep;
                if(img.index > img.maxZoom)
                    img.index = img.maxZoom;

                JSFX.setZoom(img);
    
                if(img.index == img.maxZoom)
                    img.state="ZOOM_OUT";
                JSFX.ImageZoomRunning = true;
            }
            else if(img.state == "ZOOM_OUT")
            {
                img.index-=img.zoomStep;
                if(img.index < 0)
                    img.index = 0;

                JSFX.setZoom(img);

                if(img.index == 0)
                    img.state="OFF";
                else
                    JSFX.ImageZoomRunning = true;
            }
        }
    }
    /*** Check to see if we need to animate any more frames. ***/
    if(JSFX.ImageZoomRunning)
        setTimeout("ImageZoomAnimation()", 40);
}




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НА ЭТОМ КОД ЗАКАНЧИВАЕТЬСЯ И хочу сказать что я понял из него:

Этот код отвечает за плавность увеличение, чем выше цифра тем плавнее увеличиваеться

zoomStep = img.height/100;
else
zoomStep = img.width/100;



А этот код за размер увеличение, чем меньше цифра тем больше увеличиваеться, если прописать Ноли  0  то увеличение бузагранично и не останавливаеться по высоте.

if(!maxZoom)
{
if(img.mode == "EXPAND")
maxZoom = img.height/3;
else
maxZoom = img.width/3;
}