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Using smooth transitions in a slideshow

From: HTML5: Graphics and Animation with Canvas

Video: Using smooth transitions in a slideshow

In this example, we are going to see how to use smooth transitions to improve upon the previous example where we built an image slideshow control. So what I am going to do is open up the SlideShowSmooth_finished example and show you what I mean. In the other example, the transitions between the images were pretty abrupt, but you can see that what we are doing here is gradually fading in each image to create a nice smooth transition. So let's see how to do that. So I am going to open up my SlideShowSmooth_start example.

Using smooth transitions in a slideshow

In this example, we are going to see how to use smooth transitions to improve upon the previous example where we built an image slideshow control. So what I am going to do is open up the SlideShowSmooth_finished example and show you what I mean. In the other example, the transitions between the images were pretty abrupt, but you can see that what we are doing here is gradually fading in each image to create a nice smooth transition. So let's see how to do that. So I am going to open up my SlideShowSmooth_start example.

This is our starting point. And let's go back to the snippets. So the setup code is the first few lines we are going to copy over. So let's paste that in. So I have an array of all the image paths and then variables that refer to the canvas and the canvas context. Then I create an image that's going to be responsible for loading each one of the images from the local folder or from the web. I have an indexer here that keeps track of which image we are looking at, and then finally, a variable that's going to be the timer that smoothly reveals each image.

So it is called the revealTimer. So let's go ahead and copy over the initialization logic, and that's this function here. So let's paste that in. So when the window loads--and that's this function right here. So when the window loads up, we are going to get a reference to the canvas and the canvas context. Then, on the image, we are going to set the height and width to be the height and widths of the images that we are going to be loading. Then we call the switchImage function, which shows the first image, and then we have we have an animation that waits every three seconds, which is 3,000 milliseconds, to change to the next image.

So we will save that. Now we need to copy over the two functions that are the meat of how this works. So let's copy over switchImage, and I'll explain that one. Now the switchImage function basically looks at the current image index, gets its path from the images array, and then sets the source attribute of the image object that we created up here using the DOM, right there, to be pointing at the source for whatever the current image index is.

Then we have a little check right here to see if that current image counter, which we're incrementing each time, if it's bigger than the array that contains the paths, we just need to set it back to 0. Then we set the globalAlpha of the canvas context to 0.1, or 10%--and we covered this back in the globalAlpha movie. Then we set the revealTimer to be an interval of 100 milliseconds, or a 10th of a second. So, every 10th of a second we are going to call this revealImage function, which we need to copy over.

Let's copy and we'll paste. So let's take a look what the revealImage does. So every three seconds, switchImage will be called. Then we have another subInterval down here. So revealImage saves the current context of the canvas, and it then draws the current image onto the canvas at the upper-left corner using the width and height. Then it increments the globalAlpha by 10%.

If the globalAlpha reaches 100%, then we stop the revealTimer. So what's going to happen is every 10th of a second this revealImage is going to be called. So because we are incrementing the globalAlpha by .1 each time, it's going to be called 10 times. So over a full second, we are going to slowly fade the image onto the canvas on top of what's already there. After we do that, we will restore the context, and then the function ends. So we got two timers going on. We've got one that's three seconds long and we've got one that's 100 milliseconds but executes 10 times, which is 1 second.

So let's save, and let's go back to the browser and take a look of this. Now I can see that over a course of a second, the image fades in. Then we wait a few seconds and the next one fades in. So the way that we are accomplishing this is is by setting the globalAlpha to an increment of 10% each time and then just redrawing the image in place. That gives the effect of fading in over a smooth transition. So now we have seen how to create smooth transitions using the globalAlpha and a JavaScript timer.

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This video is part of

Image for HTML5: Graphics and Animation with Canvas
HTML5: Graphics and Animation with Canvas

37 video lessons · 18446 viewers

Joe Marini
Author

 
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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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