![]() ![]() Something beyond two dimensional, but all the graphics I've ever done and that will ask you to do are the 2D graphics. So I'm going to call git context and I have to specify that I'm getting the 2d context, in other examples we might see. It's kind of hitting the keyboard and so annoying to me, might be annoying to you. So excuse me, while I remove it and put it right there. I'm actually going to take off my bracelet because it's kind of jangly. The way we do that is create another variable, I'll call it ctx for context and I'll get the context from the canvas which is stored in variable dd1. That's a new concept for canvases, that the graphics are actually displayed in the canvas's context. The first step is going to be that rather than drawing in the canvas, we're going to have to access the context of the canvas. So, let's look at the doyellow JavaScript function and see how to make yellow rectangles appear by using the canvas. That's why when we start with the page blank, we see that the canvas is here with nothing in it, a little narrow border that's one pixel wide as we can see here specified in this CSS and these two buttons. But I'm going to make it white in preparation for making some yellow rectangles, let's also just review very quickly that there's some CSS for the canvas that styles it have a specific width, a specific height and a border. So, right now making yellow actually turns it white. In the make yellow function, which is the button that calls doyellow, I get the element by it's ID and I make the background white. And then I make the background color lime, that's why the function is called dolime. I use the standard document.getElementByid to grab the element whose id is d1 as a reminder, that's this canvas. We can come over here and just review a couple of concepts. The functionality that we have that we start with, which I've already coded, is make lime. One that says make yellow and calls a doyellow( ) javascript function. And we have two buttons, one that says make lime and calls a dolime( ) JavaScript function. We see that we've got the canvas element here. As we saw in the recent lesson, I'm going to have a canvas that's going to make both color background changes and draw using the graphics element. Let's look at an example of using CodePen to combine HTML, CSS, and JavaScript to make an interactive webpage using a canvas. And the other will draw yellow squares and create text in the canvas all with JavaScript. Each button will change a different feature of the HTML canvas element. We'll create a webpage with two buttons, using HTML, CSS, and JavaScript. We'll show a simple interactive page using a canvas element. There are several methods that you use to create these graphic tasks such as drawing paths, boxes, circles, text, and adding images. You should think of it like a container for graphics where the container needs to be filled in which you do by writing a script. As we explore this functionality in more detail. We'll see more closely how to program with a canvas. But as you can see here with the canvas, the background color changes work the same as they did with HTML div elements. It turns out that special methods are necessary to write text in a canvas. When we use canvas, the hello text disappeared. You'll see that we have to make a few changes to the CSS, and to the HTML panels. Let's try using canvas element instead of div. ![]() And the Make Ybutton changes the background color to yellow. On this page, the Make Lime button changes the background color to lime. So, the background color or other attributes can be changed programmatically by referring to the element ID. Previously you have seen the div element used to specify a section of a web page. You'll see how it's accessed via JavaScript and you'll be able to do more if you explore additional resources. We'll only explore basic functionality of this HTML element. ![]() As you'll see, it's possible to draw shapes, lines, and more. A canvas has a different functionality than a div. The canvas HTML element is used to store images in the Duke Learn to Program, or DLTP environment that you've seen before. ![]() Rather than using elements, we'll use a new HTML element named. Hi, let's see how to create a webpage and write code that will move us closer to the green screen page. ![]()
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