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HTML5: Graphics and Animation with Canvas
Illustration by John Hersey

Transforming objects using the translate tag


From:

HTML5: Graphics and Animation with Canvas

with Joe Marini

Video: Transforming objects using the translate tag

In this chapter, we're going to look at some pretty advanced canvas operations, and in fact some of these are not necessarily routines or features that cause any drawing to happen, but they certainly do have a profound effect on the results of drawing operations that you learned about earlier on in the course. And so we're going to start off by looking at transformations. Transformations are essentially a way that affect how objects are drawn to the canvas to achieve some pretty common, but yet difficult to program, effects.
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  1. 4m 54s
    1. Welcome
      1m 3s
    2. Using the exercise files
      2m 3s
    3. Using the HTML5 Canvas element in the real world
      1m 48s
  2. 10m 31s
    1. Real-world example: CanvasMol
      2m 9s
    2. Real-world example: Raphaël-JavaScript Library
      1m 47s
    3. Real-world example: The Wilderness Downtown
      4m 1s
    4. Real-world example: Sketchpad
      1m 10s
    5. Real-world example: Pirates Love Daisies
      1m 24s
  3. 3m 28s
    1. Installing the tools
      1m 29s
    2. Exploring the Canvas examples used in this course
      1m 59s
  4. 8m 58s
    1. Introducing the Canvas tag
      6m 30s
    2. Understanding the differences between Canvas and SVG
      2m 28s
  5. 5m 36s
    1. Identifying the Canvas element's methods and properties
      1m 40s
    2. Using the Canvas drawing context
      3m 56s
  6. 43m 14s
    1. Setting and using colors and styles
      3m 19s
    2. Drawing basic shapes: Rectangles and lines
      10m 21s
    3. Understanding the Canvas state
      5m 15s
    4. Drawing complex shapes: Arcs and paths
      9m 15s
    5. Drawing complex shapes: Bézier and quadratic curves
      5m 46s
    6. Rendering text
      9m 18s
  7. 32m 35s
    1. Creating shadows
      6m 41s
    2. Drawing with patterns
      7m 20s
    3. Drawing with gradients
      6m 18s
    4. Using clipping paths
      4m 46s
    5. Drawing images and video
      7m 30s
  8. 35m 42s
    1. Transforming objects using the translate tag
      4m 18s
    2. Scaling objects with the scale transformation
      4m 7s
    3. Rotating objects with the rotate transformation
      4m 33s
    4. Applying a custom transformation
      6m 58s
    5. Compositing in Canvas using globalAlpha
      6m 36s
    6. Manipulating raw pixels
      9m 10s
  9. 41m 23s
    1. Building an image slideshow control
      4m 24s
    2. Using smooth transitions in a slideshow
      4m 28s
    3. Creating a basic animation
      5m 42s
    4. Creating animation with double buffering
      13m 13s
    5. Incorporating Canvas into a real page
      13m 36s
  10. 48s
    1. Goodbye
      48s

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HTML5: Graphics and Animation with Canvas
3h 7m Intermediate Jun 03, 2011

Viewers: in countries Watching now:

One of the most exciting additions that HTML5 offers to designers is the ability to draw free-form graphics on a drawing surface known as the Canvas. In this course, author Joe Marini introduces the technical concepts behind Canvas and shows how to perform drawing operations directly in a web page. The course covers drawing basic and complex shapes, setting colors and styles, adding shadows, patterns, and gradients, more advanced techniques such as scaling, rotating, and compositing objects, and how to incorporate Canvas elements in a slideshow and an animation.

Topics include:
  • Understanding the differences between Canvas and SVG Graphics
  • Drawing shapes
  • Drawing arcs and paths
  • Rendering text
  • Using clipping paths
  • Drawing images and video
  • Transforming objects with the translate tag
  • Manipulating raw pixels
  • Applying a custom transformation
  • Creating an animation or slideshow control with Canvas
Subjects:
Developer Web Animation Web Design Web Development
Software:
HTML
Author:
Joe Marini

Transforming objects using the translate tag

In this chapter, we're going to look at some pretty advanced canvas operations, and in fact some of these are not necessarily routines or features that cause any drawing to happen, but they certainly do have a profound effect on the results of drawing operations that you learned about earlier on in the course. And so we're going to start off by looking at transformations. Transformations are essentially a way that affect how objects are drawn to the canvas to achieve some pretty common, but yet difficult to program, effects.

There's three basic transformations that the canvas provides. There's translate, scale and rotate, along with a way to define your own free-form transforms. Transforms affect all of the drawing operations that come after them, and they are additive. Each transform is added to the effects of the previous one. So just like other global canvas properties, like line width and so on, transforms affect everything.

You define a transform, you use it, and then you perform some drawing operations. Now, because they are additive, this is where saving and restoring the canvas state can really come in handy. Let's start by taking a look at the translate transform. It's the simplest one to use, and all it really does is moves the canvas origin to a new location. And the way you do it is by calling the translate function with an amount to move the origin in the X direction and an amount to move the origin in the Y direction.

So let's imagine for a moment you have a canvas and at the upper left of the canvas, that's the current origin point. That's where 0,0 is. If you use the translate function to move the origin by an amount X and Y, then all you have done is move the location of the origin. So now, anything drawn at 0,0 will be drawn at this point on the canvas instead of this point. So let's take a look at how that works. I'll go into the code. So here we are in my editor, and in the snippets file, I'm under the Translate Transform section.

So let's open up our example, and we're going to go to the Advanced folder, and we're going to go to the translate_start example. So what we're going to do is copy some code, and we're going to come in here and copy this over, copy, and we're going to paste. So before I show you what the example does, let me just comment out this call to translate, and we will save and we will go over the browser and look at the results.

So, let's bring this up. So you can see that I'm drawing a blue rectangle at the origin point 0,0 right here. So if we go look in the code, you can see that there it is. It's at 0,0. It's 100 pixels wide and 50 pixels high. Now, if I uncomment the call to translate, what I'm doing here is calling translate and I'm getting the width of the canvas and dividing it in half, and I'm getting the height of the canvas and dividing it in half. So this will pretty much move the origin of the canvas right to the middle, half the width and half the height.

So when I call fillRect again, even though I'm calling it to draw at the 0,0 location, the origin has now been moved to the middle of the canvas. So the second rectangle will be drawn at the middle point of the canvas. So let's save, and let's go back to the browser, and let's refresh. So you can see, I've got two rectangles. They are both drawn at 0,0. But in the first example, 0,0 is up here, and then after the call the translate, 0,0 moves to here.

So this can be pretty useful when you are creating a whole bunch of objects to be drawn on the canvas at different locations and the results of those locations are arrived at via various calculations and so on. Rather than having to keep track of all of those points, you can just simply move the origin to where you need it to move to, do your drawing, and then set it back to its previous state. So in this example, what we've seen is how to use a basic translate transform to move the origin around and affect where objects are drawn.

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