dragonruby-book/src/09-background.md

# Background

We're eight chapters in and haven't even touched upon a simple and useful piece of functionality that DragonRuby GTK gives us: drawing rectangles! Rectangles are great for backgrounds, text boxes and more. Layer some sprites on top, and you can get pretty fancy.

## Blue Sky

Up until now, our dragon has been flying around in a gray sky. Let's make the sky blue to start.

DragonRuby provides `args.outputs.solids` to easy display filled rectangles.

At the top of `#tick`, below where we start the music, create a solid rectangle that's the size of the screen and placed at 0, 0:

``` ruby
{{#include code/chapter_09/01_blue_sky/app/main.rb:102:115}}
```

We're familiar with a lot of the shape hash keys for the position and size, but `r`, `g`, and `b` are new. They specify the values for the red, green, and blue color values for the rectangle we're drawing. Their values can be set to anything between 0 and 255, inclusive. Adjust the values to see a different color displayed. The higher the value for a given color, the more it'll be part of the mix. So our color has a blue of 230, meaning blue comes through more than the others. You can also specify `a`, the alpha value, between 0 and 100, inclusive, to get transparency in our shape.

Now we've got our dragon flying over a blue sky. That looks quite a bit better.

![game with dragon and three targets and blue background](./img/c09-blue-sky.jpg)

## Extra Credit

- Make (or find) some cloud sprites and render those in the sky. Put them in the `args.outputs.sprites` _before_ the other sprites to have them render behind.
- Move the clouds, randomly placing at a different position and with a different size when they go off the screen.
- Draw some more rectangles under the score and timer to make them easier to read.

## What's Next