In previous tutorials, we introduced you to Scratch. We learned what are blocks and scripts, and how to make a script using blocks. In this chapter we will delve into more details about stage and sprite.
The Stage is the term for the background of the project. A stage has some restrictions as compared to sprites. Features of stage:
- A Stage is stationary, thus,
- Cannot use Motion Blocks
- Cannot use any Pen functions, other than Clear
- Has no size blocks
- Has no “touching” blocks in the Sensing category
- Has no “distance to” block in the Sensing category
- Cannot talk, thus,
- Has no “Say” or “Think” blocks in the Looks category
- When asking, places the question above the text box rather than in a speech bubble.
- Has backdrops instead of costumes
- Cannot be renamed
- Has no “show” or “hide” blocks in the Looks category
- Cannot change layers — it is always at the very back layer.
- Must have a 480×360 dimension
- Space in backgrounds left transparent becomes white automatically
In the above figure, you can see from where you can access stage and sprite. Once you select the stage you can make new scripts, backgrounds and sounds associated with stage. Background can be made, imported or selected from the library from the small menu given below the stage.
Stage in Scratch has a 2D coordinate system which uses 2 coordinates, “X position” and “Y position”, to determine the location of a sprite on the stage. The “X position” value determines the horizontal location of the sprite and the “Y position” value determines the vertical location or height. The screen is a 480×360 rectangle, such that: the X position can range from 240 to -240, where 240 is the rightmost a sprite can be and -240 is the leftmost, and the Yposition can range from 180 to -180, where 180 is the highest it can be and -180 is the lowest it can be. The coordinate system is shown in the figure given below.
Sprites, either user-created, uploaded, or found in the sprites library, are the objects that perform actions in a project. While the Stage can also be programmed in a project, most projects have at least one sprite as well because only sprites can move. You can make new sprite using the arrow tab below the stage.
When a sprite is created, it will place that sprite at a random location on the Stage, usually around the centre, and open the sprite in the tab you’re currently viewing.
Each sprite in a Scratch project has an area for scripts, called the scripts area. Users can give instructions to a sprite (such as telling the sprite to move) by snapping blocks together in the scripts area. Clicking on the block(s) in the script area will cause the sprite to react based on the function of the block(s) clicked (Just like we did it in previous chapter). Clicking on a sprite’s thumbnail in the sprite pane will bring up the script area of that sprite.
The look of a sprite can also be changed by using costumes. The current costume of a sprite can be changed by clicking on the “costumes” tab and clicking on the desired costume of choice, or by using blocks to select the sprite’s costume. New costumes for the sprite can be imported, created, and edited in the Scratch Paint Editor.
Some sprites additionally have at least one sound. Unlike costumes, sounds are an optional field, so you can have a sprite with no sounds. The sounds tab allows you to add, delete, and edit sounds. Sounds can be played in the sound editor or with blocks that play a specific sound.
Sprites (with all of their scripts, costumes, and sounds) can be exported, and then imported into another project if desired. This is achieved by right-clicking on a sprite’s thumbnail in the sprite pane and then selecting “save to local file” in the pop-up menu.