Spindrop

Note: Like many of my tutorials, you don’t need [symfony], just [PHP]. However, I develop in [symfony] and take advantage of the MVC-support that it offers.

Years ago when I was working on a photo gallery for davedash.com I got the art of making tumbnails down fairly well. It was automated and didn’t allow for specifying how the thumbnail should be made. With dozens of photos (which was a lot back then), when would I find that kind of time.

Flashback to today, for my company… we want users with avatars… but nothing too large. Maybe a nice 80×80 picture. Well the coolest UI I’ve seen was Apple’s Address Book which let you use this slider mechanism to crop a fixed sized image from a larger image.

Here’s a demo.

Overview

The front-end GUI is based on code from [digg] which is based on the look and feel (as near as I can tell) from Apple.

The GUI provides a clever visual way of telling the server how to chop the image. The gist is this, sliding the image around and zooming in and out change a few form values that get passed to another script which uses this data to produce the image.

Frontend: What would you like to crop?

In this tutorial, we’re going to be cropping an 80×80 avatar from an uploaded image. The front-end requires the correct mix of Javascript, CSS, HTML and images. The Javascript sets up the initial placements of the image and the controls. The CSS presents some necessary styling. The images makeup some of the controls. The HTML glues everything together.

HTML

Let’s work on our HTML first. Since I used [symfony], I created a crop action for a userpics module. So in our cropSuccess.php template:

<div id="ava">
    <?php echo form_tag("userpics/crop") ?>
        <div id="ava_img">
            <div id="ava_overlay"></div>
            <div id="ava_drager"></div>
            <img src="<?php echo $image ?>" id="avatar" />
        </div>
        <div id="ava_slider"><div id="ava_handle"></div></div>
        <input type="hidden" id="ava_width" name="width" value="80" />
        <input type="hidden" id="ava_x" name="x" value="100" />
        <input type="hidden" id="ava_y" name="y" value="100" />
        <input type="hidden" id="ava_image" name="file" value="<?php echo $image ?>" />
        </div>
        <input type="submit" name="submit" id="ava_submit" value="Crop" style="width: auto; font-size: 105%; font-weight: bold; margin: 1em 0;" />
    </form>
</div>

Right now a lot of this doesn’t quite make sense. If you attempt to render it, you will just see only the image. As we add the corresponding CSS and images it will make some more sense.

CSS and corresponding images

We’ll go through each style individually and explain what purpose it serves in terms of the GUI.

#ava is our container.

#ava {
    border: 1px solid gray;
     width: 200px;
}

#ava_img is the area that contains our image. Our window for editing this image 200×200 pixels. If we drag out image out of bounds we just want the overflowing image to be clipped. We also want our position to be relative so any child elements can be positioned absolutely with respect to #ava_img.

#ava_img {
    width: 200px;
    height: 200px;
    overflow: hidden;
    position: relative;
}

#ava_overlay is a window we use to see what exactly will be our avatar. If it’s in the small 80×80 window in the center of the image, then it’s part of the avatar. If it’s in the fuzzy region, then it’s getting cropped out. This overlay of course needs to be positioned absolutely.

#ava_overlay {
    width: 200px;
    height: 200px;
    position: absolute;
    top: 0px;
    left: 0px;
    background: url('/images/overlay.png');
    z-index: 50;
}

#ava_drager is probably the least intuitive element (Heck, I’m not even sure if I’ve even got it right). In our demo you’re not actually dragging the image, because you can drag anywhere within the #ava_img container and move the image around. You’re using dragging an invisible handle. It’s a 400×400 pixel square that can be dragged all over the container and thusly move the image as needed.

#ava_drager {
    width: 400px;
    height: 400px;
    position: absolute;
    z-index: 100;
    color: #fff;
    cursor: move;
}

#avatar is our image, and since it will be moving all around the window, it requires absolute positioning.

#avatar {
    position: absolute;
}

#ava_slider and #ava_handle are our slider components. They should be self-explanatory.

#ava_slider {
    width: 200px;
    height: 27px;
    background: #eee;
    position: relative;
    border-top: 1px solid gray; 
    background: url('/images/slider_back.png');
}
#ava_handle {
    width: 19px;
    height: 20px;
    background: blue;
    position: absolute;
    background: url('/images/handle.png');
}

Internet Explorer

PNG do not work so well in Internet Explorer, but there is a small trick, adding these components into a style sheet that only IE can read will make things work:

#ava_overlay {
  background: none;
  filter:progid:DXImageTransform.Microsoft.AlphaImageLoader(src='/images/ui/cropper/overlay.png', sizingMethod='crop');
}

#ava_handle {
  background: none;
  filter:progid:DXImageTransform.Microsoft.AlphaImageLoader(src='/images/ui/cropper/handle.png', sizingMethod='crop');
}

The Javascript

The Javascript is actually not as complicated as you’d expect thanks to the wonder of [prototype]. This framework provides so much so easily. You’ll need to include prototype.js and dom-drag.js.

So let’s take a look.

<script type="text/javascript" language="javascript" charset="utf-8">
// <![CDATA[
function setupAva() {
    if ($("avatar")) {
        var handle = $("ava_handle");
        var avatar = $("avatar");
        var drager = $("ava_drager");
        var slider = $("ava_slider");
        var ava_width = $("ava_width");
        var ava_x = $("ava_x");
        var ava_y = $("ava_y");
        // four numbers are minx, maxx, miny, maxy
        Drag.init(handle, null, 0, 134, 0, 0);
        Drag.init(drager, avatar, -100, 350, -100, 350);
        var start_w = avatar.width;
        var start_h = avatar.height;
        var ratio = (start_h / start_w);
        var new_h;
        var new_w;
        if (ratio > 1) {
            new_w = 80;
            new_h = (80*start_h)/start_w;
        } else {
            new_h = 80;
            new_w = (80*start_w)/start_h;
        }
        // these need to be set after we init
        avatar.style.top = '100px';
        avatar.style.left = '100px';
        avatar.style.width = new_w + 'px';
        avatar.style.height = new_h + 'px';
        avatar.style.margin = '-' + (new_h / 2) + 'px 0 0 -' + (new_w / 2) + 'px';
        handle.style.margin = '3px 0 0 20px';
        avatar.onDrag = function(x, y) {
            ava_x.value = x;
            ava_y.value = y;
        }
        handle.onDrag = function(x, y) {
            var n_width = (new_w + (x * 2));
            var n_height = (new_h + ((x * 2) * ratio));         
            avatar.style.width = n_width + 'px';
            avatar.style.height = n_height+ 'px';
            ava_width.value = n_width;  
            avatar.style.margin = '-' + (n_height / 2) + 'px 0 0 -' + (n_width / 2) + 'px';
        }
    }
}
Event.observe(window,'load',setupAva, false);
// ]]>
</script>

If this isn’t exactly crystal clear, I can explain. If you’re new to [prototype], $() is the same as doucment.getElementByID() (at least for our purposes).

We need to initialize two draggable elements, one is our slider for zooming and the other is our avatar itself. We initialize the draggers using Drag.init(). We specify what to drag, if another element should be used as a handle and then the range of motion in xy coordinates. In the second call we use that #dragger to move around the image in this manner.

Drag.init(handle, null, 0, 134, 0, 0);
Drag.init(drager, avatar, -100, 350, -100, 350);

We want to initialize the the size and placement of the avatar. We do that using maths. First we want it in our 80×80 pixel box. So it should be roughly 80×80. I’ve set the math up so that the smallest side is 80 pixels (there’s reasons for doing this the other way around).

    if (ratio > 1) {
        new_w = 80;
        new_h = (80*start_h)/start_w;
    } else {
        new_h = 80;
        new_w = (80*start_w)/start_h;
    }

We then place the avatar element. We initialize it to be in the center of the screen (top: 100px;left:100px) and then nudge the image using margins.

    avatar.style.top = '100px';
    avatar.style.left = '100px';
    avatar.style.width = new_w + 'px';
    avatar.style.height = new_h + 'px';
    avatar.style.margin = '-' + (new_h / 2) + 'px 0 0 -' + (new_w / 2) + 'px';

We also use margins to place the handle.

    handle.style.margin = '3px 0 0 20px';

#ava_x and #ava_y tell us where the center of the avatar is. So when the avatar is moved we need to set these again:

    avatar.onDrag = function(x, y) {
        ava_x.value = x;
        ava_y.value = y;
    }

That was easy. Slighly more complicated is the zoomer function. We are basically adjusting the width and the height proportionately based on roughly where the slider is. Note that we’re still using that ratio variable that we calculated earlier. We basically take the new x-coordinate of the handle and allow our image to get just slightly larger than the #ava_image container.

    handle.onDrag = function(x, y) {
        var n_width = (new_w + (x * 2));
        var n_height = (new_h + ((x * 2) * ratio));         
        avatar.style.width = n_width + 'px';
        avatar.style.height = n_height+ 'px';
        ava_width.value = n_width;  
        avatar.style.margin = '-' + (n_height / 2) + 'px 0 0 -' + (n_width / 2) + 'px';
    }

We want to load initialize the slider right away when the page loads: Event.observe(window,'load',setupAva, false);

Not terribly hard or complicated. Once these elements are all in place you have a working functioning slider. It returns the x and y coordinates of the center of the image with respect to our 200×200 pixel #ava_image. It also tells us the new width of our image. We feed this information into a new script and out should pop a new image which matches exactly what we see in our GUI.

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