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Rewrote in simple language. New example.

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Ron Hale-Evans 2016-06-20 13:18:41 -07:00
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docs/reference/images/scroll-image.md
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# Scroll Image
The scroll image function.
Scrolls the frames within an [Image](/reference/images/image) on the [LED screen](/device/screen).
### Block Editor
![](/static/mb/scroll-image-0.png)
### JavaScript
```
export function scrollImage(_this: micro_bit.Image, xOffsetPerStep: number, interval: number)
```
Scroll (slide) an [image](/reference/images/image) (picture) from one
side to the other of the [LED screen](/device/screen).
### Parameters
* x offset per step : [Number](/reference/types/number) - the number of columns to scroll at a time (horizontal offset). Use a positive number to scroll an image to the right and a negative number to scroll left. To jump from one image frame to the next, use an offset of 5 or -5.
* interval (ms) : [Number](/reference/types/number) - the time (in milliseconds) before scrolling by `x offset per step`; the larger the number, the slower the scroll.
* ``offset`` is a [number](/reference/types/number) that means
how many LEDs to scroll at a time, from right to left or
left to right. If you use a positive number like `2`, the image
will scroll from the right side of the screen to the left.
If you use a negative number like `-2`, the image will scroll
in the other direction. If you use `5` or `-5`, the image
will scroll one **frame** at a time. (A frame is a part of the
image. It is a square with five LEDs on a side). This is
useful for **animation**.
### ~hide
* ``interval (ms)`` is a [number](/reference/types/number) that means
how many milliseconds to wait before scrolling the amount that
``offset`` says. (1000 milliseconds is one second.) The bigger you
make this number, the slower the image will scroll.
```
let img = images.createImage(`
. . # . . . # # # . . # # # .
. . # . . . . . # . . . . # .
. . # . . . . # . . . # # # .
. . # . . . # . . . . . . # .
. . # . . . # # # . . # # # .
`)
```
### Example
### ~
This program scrolls an image of two arrows five LEDs at a time,
with a pause of 200 milliseconds between each time it scrolls.
Because each frame is five LEDs wide, that means this program
will look like it's animating one arrow flipping and flopping.
Of course, you can use any two frames you want instead.
To scroll an image 1 column at a time to the right:
```
img.scrollImage(1, 1000)
```
To scroll an image 5 columns at a time (skip from frame to frame):
```
img.scrollImage(5, 1000)
```
To scroll an image 1 column at a time to the left:
```
img.scrollImage(-1, 500)
```
### Example: scroll through frames
This example creates an image with 3 frames, then scrolls through the 3 frames:
```
img = images.createImage(`
. . # . . . # # # . . # # # .
. . # . . . . . # . . . . # .
. . # . . . . # . . . # # # .
. . # . . . # . . . . . . # .
. . # . . . # # # . . # # # .
`)
img.showImage(0)
img.scrollImage(5, 1000)
```blocks
let arrows = images.createBigImage(`
. . # . . . . # . .
. # # # . . . # . .
# . # . # # . # . #
. . # . . . # # # .
. . # . . . . # . .
`);
basic.forever(() => {
arrows.scrollImage(5, 200);
});
```
### See also