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CSS: Page Layouts introduces basic layout concepts, gives advice on how to create properly structured HTML based on prototypes and mockups, and goes into critical page layout skills such as floats and positioning. Author James Williamson shows how to combine these techniques to create fixed, fluid, and responsive layouts. Designers are also shown how to enhance their pages through the creative use of CSS techniques like multi-column text, opacity, and the background property. Exercise files are included with this course.
One of the things that absolutely positioned elements allow us to do that we can't do with other element types is to use the clip property. Now the clip property allows us to essentially crop an element and its contents. Let's take a look at that by opening up clipping.htm, which you can find in the 04_05 directory. And the page structure of this one has changed a little bit. Instead of our normal three div tags that we have been using, essentially we have a section with a class of container, and now inside of that we have a div that has a paragraph inside of it as well. So we want a little bit more content inside of this so that you can actually see the clipping taking place.
So essentially we are just going to crop that content down a little bit. I am going to preview that in the browser for you, so you can see what's kind of going on here, and here is the content that we are going to be clipping. You can see it's being positioned using absolute positioning. So what values can we use for the clip property? Well, there are not too many. The clipping property has three values that we can use. We have Shape, Auto, and Inherit. Now Inherit and Auto are pretty much the same as doing nothing. Inherit is asking the parent what's your clipping property, whereas Auto is just nothing.
Now Shape, on the other hand, that is something. Shape allows us to pass a shape and some offsets into it that describe the shape of the clipping. Now, currently the only shape that browsers will accept is a rectangle. You can see the syntax right here. So the only shape that it allow us to pass into it right now is rectangle. There's hope that in the future we will be able use different shapes, like ovals, or polygons, but for right now rectangle is it. Now that is followed by a series of offsets. Now these offsets basically start at the top, so the first offset is top, then we have right, bottom, and left.
So if you're looking for a way to remember that, you can think of trouble, top, right, bottom, left. Or you can think of starting with top and going in a clockwise fashion. So what we want to do is we want to take this element and clip it using offset values such as these. So I am going to go back into my code and I want to go up and find element1, so this is who we are going to clip. Remember, this is only available for absolutely positioned elements. So I am going to go down on the next line here and I am going to type in clip, and then I am going to do the rectangular shape, and then inside the parentheses, I am going to give it an offset of 50 pixels for the top, comma, 200 pixels for the right-hand side, comma, 150 pixels for the bottom, and then after another comma, finally 50 pixels for the left-hand side.
Then I am going to remember my semicolon. I will go ahead and save that. I am going to go back out to the browser and refresh the page, and now you can see our content is clipped. Given the values that I just gave you, 50, 200, 150 and 50, is that what you were expecting? I'm betting not. And most of the time people get really, really confused about clipping properties. Basically, let's just practice using these values right here. Most people would assume that a top offset of 10 pixels means that it would come down and start clipping here, and then a 10-pixel offset from the right, they assume it comes to the right- hand side, it comes 10 pixels in.
25 pixels, 25 pixels up and then 10 pixels, 10 pixels over. But actually nothing could be further from the truth. Really what happens is top and bottom offsets start from the top. Right and left offsets start from the left-hand side. So a top offset of 10 would start here and go down 10, just like you would expect, but then a bottom offset of 25 would go down 25 pixels and start clipping here. So it creates a sort of inner frame from those edges, and although once you think about it, it makes sense, it's still kind of hard to calculate exactly what you're going to be clipping, to be quite honest with you.
So in order to really control the clip property, you need to know what the width and height of the element that you are working with is; otherwise, you've got no real way of controlling what content gets clipped. So I am going to go back into my code, and I don't see any height or width on element1, but it's a div tag, so if I go up, I can see that in the div tag, I've got 400 pixels' worth of width. In most cases that's pretty much what your elements are going to be like, and the height is generally created by the content and the padding and that sort of thing. But in this case if you are going to do clipping, one thing is that it only happens on absolutely positioned elements.
So for those, you generally are going to be setting element width and height probably more frequently than you would on elements that are on normal flow. But here we don't have a height, so I am going to go ahead and set one. So right after our width, I am going to go ahead and set a height value of 150 pixels. So let's think about this for a moment. We have 400 pixels' worth of width, 150 pixels' worth of height. We have 25 pixels' worth of padding all the way around, so the true height is 200 pixels and the true width is 450 pixels.
Then we have this 2-pixel border. So let's give ourselves a little exercise here. Let's say we want to take the clip property and just clip the 2-pixel border off. Why would you ever do that? Well, you could do something really cool. You could take the border off and then based on user interactivity or something like that, you could undo the clip property and make the border come back up. You could make elements sort of expand and contract. I mean there's all sorts of really kind of cool stuff you can do with clip if you're using it with absolutely positioned elements. So I am going to go down to element1 and I am going to change our clip here.
I am going to change the top clip to 2 pixels. Remember, that's 2 pixels down from the top. And then I'm going to show you different way to write this syntax. Instead of using commas, I am just going to use white space between them, so no comma, but I do need a white space there. The next thing I am going to do is I am going to go ahead and give this offset at 452 pixels. Now, why 452? Remember, this is the right-hand offset. That means it's going go all the way over from the left edge to the right, 452 pixels. Think about the width of our element. 450 pixels of width, with 4 pixels of total border, so two on the left-hand side, 2 on the right-hand side, so this is going to clip off the two that's on the right-hand side.
Now our bottom offset is going to be 200 pixels. Again, remember that the bottom offset starts at the top of the element and then comes down. I am going to get rid of the comma, make sure I have my white space, and then the very last one, which is the left- hand side, is also going to be just 2 pixels, because it's going to start at left- hand side and go over 2 pixels and clip it. Again, I've got to remember the white space there. Okay, so what's the difference in the two syntaxes? The first syntax we used had commas; the second syntax does not.
Well, the first syntax, the one with commas in it, that is the one that the W3C specification says is the proper syntax. The syntax you are seeing here is the one that older versions of Internet Explorer actually support. Now because all the modern browsers support this as well, just to be backwards compatible, because back in the day, Internet Explorer 8 and above now support the standard syntax, but older versions of IE, IE7 and 6, for example, in order to get it to work, designers would use this syntax. So all the other browsers, like Chrome and Firefox and browsers like that, said, okay, we will support that too, whatever. So if you want to support older versions of IE use this syntax.
If you want to use it in the standards- compliant way, use the previous syntax. So if I save this, go back out to the browser, and refresh, you can see that it is doing exactly what we wanted it to do, it's clipping off just the border and nothing else. Remember, this clip property works for any element that is absolutely positioned, and that means that any element that's considered to be in the absolute positioning model. So if we go back to element1 and change its position from absolute to fixed, remember, fixed elements are also considered to be part of the absolute positioning positioning model. That sounds weird to say.
But the absolute positioning model, if I save that, and preview it again, yes, it changes the position of that, but again, the clip property is still working. If I change the position relative, the clip property wouldn't work. Now I doubt that you are going to need to use clipping very often, but it is nice to know that you have yet another way to control absolutely positioned elements within your layouts.
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