To properly scale a 2D texture to the screen size, we may need to make it bordered. This allows us to force the resolution, but not scale all the parts of our image, in order to maintain the original appearance of the image. Buttons are often bordered because their appearance depends strongly on how corners are scaled, and we don't generally want them to scale.
To begin, we need to import our image. We can do this by right-clicking on the Project panel and then selecting Import new asset....
Using the navigation menu on your computer, locate an image and import it. As a result, the image will be in our project and it can be used everywhere within the current project.
Next, we need to select our image in the Project panel. In fact, this allows us to display all the import settings in the Inspector window, which we can then tweak.
In order to use images as part of the UI, Texture Type must to be set in Sprite (2D and UI). This can be changed through the Inspector window after we have selected them. However, if our project is set as a 2D project, the image in the project will have already been imported with Texture Type set correctly.
Once we have done this, we click on the Sprite Editor button.
In each side of the figure, we can find four green points. By dragging them, it is possible to divide the image into sections. By doing this, we create the borders of our image. Therefore, let's drag them a bit inside the picture so that we can see the borders. We have to pay attention when we have curved corners, which can be the case if we are working on a button. In fact, we need to ensure that all the green lines that belong to the border are beyond the curvatures of the corners. Otherwise, they will not be scaled as they should.
Finally, we can click on the Apply button in the top-right corner of the Sprite Editor to save all our changes. After this, we can close the Sprite Editor, since we don't need it anymore.
As a result, the image has borders, and therefore can be scaled as it should. How to properly place this inside our UI, since it requires us to set the Image (Script) component to Sliced.
Sometimes, some components of our UI need to be scaled. However, not all of them can be scaled freely. Otherwise, it could look different from what we thought it should be. Therefore, bordered images are used to scale everything as it should be. Borders tell Unity how it has to scale the picture. When we drag the green points in the Sprite Editor, we are dividing the image into nine sections. Each of these sections is scaled differently. The central sections are scaled in both x and y directions (vertically and horizontally). The side sections are scaled in only one direction: vertically for the right/left sections and horizontally for the upper/lower sections). Finally, the corners do not scale at all. You can see these nine sections and the scales in the following image:
Let's consider an example to understand why a bordered sprite is important for the UI. Imagine that we have a button like the one in the preceding image and we have placed it on the screen. When the game runs on different devices, the resolutions will be different and Unity will scale our UI accordingly (see the next recipe for more information). Ideally, we want the button to look like the original one that we have designed as much as possible. This means, for instance, that we want to preserve the original curvatures of the corners, and therefore, we need to force them not to scale. This can be communicated to Unity using borders. In this way, the rest of the button can scale along with the screen size in order to fit it, but as a result, the button will look like the original one.
The next subtopic will show us how to slice the sprite without using all of the nine sections.
As you have learned so far, we can use the nine sections of the border to define the scaling setting of an image properly. But we are not constrained to use all of them. In fact, it is possible to segment the image into fewer sections. This is useful when we have some UI elements that are attached to the border of the screen. In fact, in this case, the image will scale differently according to only those sections that have been defined. To do this, we need to drag only some of the green points from the corners, instead of what we did in steps 5 and 6, where we dragged all them. By tweaking these, we can achieve different ways of scaling our UI, and the right one depends on how we want our game to look in different resolutions. For instance, we can create something similar to this:
Since having a bordered image is very important when the UI is scaled on different resolutions and platforms, maybe it could be worthwhile taking a deeper look at resolution scaling. The following recipe, Resizing the UI according to the screen size and resolution, will explain how to resize the UI according to the screen resolution.
Moreover, it is possible to learn more about how to place an image in the UI in the Adding and placing an image in the UI recipe.