How do I change the background image in Code.org?

Changing the background image in Code.org's App Lab is a straightforward process that involves either using the Design mode for static backgrounds or coding blocks for dynamic changes.

Understanding Backgrounds in Code.org App Lab

In Code.org's App Lab, each "screen" in your app acts as a container that can have its own background. You can set a solid color or an image as the background for any screen. This allows you to visually customize your app's interface.

Step-by-Step: Changing a Background Image in Design Mode

For a static background image that loads with your screen, the Design tab is the easiest place to make the change.

1. Navigate to the Design Tab

Open your project in Code.org's App Lab.
Click on the "Design" tab located at the top of the workspace.

2. Select Your Screen

In the Design workspace, click on the specific screen ID (e.g., screen1) whose background you wish to change. This will display its properties in the "Properties" panel on the right.

3. Set the Image Property

In the "Properties" panel, scroll down to find the "image" property.
Click the "Choose" button next to the "image" field.
A new window will appear, allowing you to:
- Upload File: Upload an image directly from your computer.
- Browse Assets: Select an image you've previously uploaded or one from Code.org's built-in library.
- Image Selection & Usage Rights: When choosing an image, it's important to consider its usage rights. Many images online are protected by copyright. Look for images shared under licenses like Creative Commons or those explicitly free for use. Your teacher might also provide specific guidance on acceptable image sources for your projects. Choose an image you like that fits your app's theme.
After selecting or uploading your desired image, click "Choose" or "Select". The image will now appear as the background of your selected screen.

4. Adjust Image Display (Optional)

Back in the "Properties" panel, you might see an "image_mode" property (or similar). This property controls how the image is scaled and displayed on the screen. Common options include:
- fit: Resizes the image to fit within the screen, maintaining its aspect ratio.
- fill: Resizes the image to fill the screen, maintaining its aspect ratio, potentially cropping parts of the image.
- stretch: Stretches the image to completely fill the screen, potentially distorting its aspect ratio.

Advanced: Dynamically Changing Backgrounds with Code

For scenarios where you want the background image to change based on user interaction or other events, you'll use coding blocks in the "Code" tab.

Using `setImageURL` or `setProperty` Blocks

Switch to the Code Tab: Click on the "Code" tab at the top of the workspace.
Identify the Event: Determine when you want the background to change (e.g., when a button is clicked, after a certain time). Use an event handler block like onEvent().
Use setProperty(): The most common way to change an image dynamically is using the setProperty() block.
- Drag a setProperty() block into your event handler.
- Set the id parameter to the ID of your screen (e.g., "screen1").
- Set the property parameter to "image".
- Set the value parameter to the URL or asset ID of your new background image. You can get asset IDs from the "Animation" tab or by uploading images in the "Design" tab and noting their path.
Example Code Block:
```
onEvent("myButton", "click", function() {
  setProperty("screen1", "image", "asset://myNewBackground.png");
  // Or if using a URL from the web:
  // setProperty("screen1", "image", "https://example.com/new_background.jpg");
});
```
Note: When using external image URLs, ensure they are publicly accessible and have appropriate usage rights.

Key Properties for Background Images

Property Name	Description	Usage in Code
`image`	The URL or asset ID of the image to display as the background.	`setProperty("screen1", "image", "asset://image.png");`
`image_mode`	Controls how the background image scales (e.g., "fit", "fill").	`setProperty("screen1", "image_mode", "fill");`

Tips for Choosing Background Images

Consider Usage Rights: Always ensure you have permission to use an image. Public domain, Creative Commons, or images provided by Code.org are generally safe choices.
Readability: Choose backgrounds that don't make your text or other UI elements hard to read. High contrast is usually best.
Resolution and File Size: Use images with appropriate resolution for your app to avoid pixelation, but also keep file sizes small for faster loading times.
Thematic Relevance: Select images that align with the overall theme and purpose of your app to create a cohesive user experience.

For more detailed information on App Lab functions, you can refer to the official Code.org App Lab Documentation.