Graphics Utilizing Jetpack Compose | Kodeco

Android has quite a lot of graphics-based objects to position on the app’s display screen. A few of these graphics objects embody textual content, buttons and checkboxes. What for those who needed to attract customized graphics? Like rectangles, traces, triangles and different shapes? Video video games, portray apps or chart drawing applications want customized graphics. Once you need a good avatar to your subsequent sport, customized graphics with Jetpack Compose would be the approach to create it.

You draw customized graphics on a particular view known as a Canvas with a Paint interface. When working with Jetpack Compose, you employ the Graphics API. The Graphics API makes use of an method known as the declarative programming paradigm. On this tutorial, you’ll be taught this less complicated method to make use of the Graphics API on Canvas.

On this tutorial, you’ll use Jetpack Compose to:

• Draw primitive shapes with customized graphics.
• Create complicated customized graphics by combining graphics objects.
• Show textual content utilizing Paint.
• Rework objects.

Getting Began

Begin through the use of the Obtain Supplies button on the high or backside of this tutorial to obtain the venture.

Open the venture in Android Studio Bumblebee or later and get conversant in the recordsdata. You’ll discover a starter venture and a last venture. Open and run the starter venture. The app – Pacman – comprises a clean, white display screen.

Humble beginnings up to now, proper? In case you’re questioning in regards to the finish results of the venture, open and run the ultimate venture. You’ll see the Pacman display screen:

Hopefully, seeing the ultimate app will get you fired as much as begin drawing some superior Pacman graphics. So with that, waka, waka, chomp, chomp. Time to get to it!

Creating Jetpack Compose Customized Graphics

You draw graphics like buttons, textual content fields and pickers by putting them on a view. “Graphics” on this tutorial refers to customized drawings like rectangles, triangles and contours. The graphics right here, known as primitives, aren’t like subtle shapes like buttons. You may create graphics utilizing bitmap or SVG, however the Graphics API in Android offers you an alternate approach to do it. As an alternative of drawing graphics utilizing instruments like Adobe Illustrator and importing them as bitmap or SVG, you’ll be able to create uncooked graphics instantly by way of code.

Utilizing solely code, you continue to create a bitmap with pixels and can see the identical pictures on the Android display screen. Your code makes use of Canvas to attract objects utilizing a bitmap. As an alternative of placing sure colours in particular x and y areas, you employ helper strategies to attract widespread shapes like traces, rectangles and circles. Lastly, to vary the bitmap’s fashion and colours, you employ the Paint interface.

Utilizing Declarative Graphics API

The Graphics API has been within the Android SDK since its inception, API degree 1, in 2008. What’s new is a declarative method to make use of this API: It makes managing Canvas and Paint a straightforward job. You don’t have to set technique or different configurations on the Paint object. As an alternative, all of the configuration and execution occur in a single place: the composable operate. Earlier than Jetpack Compose, working with the Paint API required meticulous element since code group selections may trigger noticeable efficiency inefficiencies. Moreover, working with Canvas may be complicated. However with Compose, it’s a breeze to create graphics.

Understanding Canvas

What’s Canvas?

To attract an object on the Android display screen, first you want a Drawable to carry your drawing. Drawings are composed of pixels. In case you’ve labored in Android very lengthy, you’ll find out about Drawable. You employ this class if you wish to show a picture. Canvas holds the strategies to attract shapes. So, with Drawable, you override the draw technique. The draw technique accepts Canvas because the argument. This connection means that you can draw shapes utilizing code in Drawable to place them on the Canvas.

What are you able to do with Canvas?

Canvas means that you can draw many primitive shapes, from circles to clipping the shapes. You may say that Canvas is an abstraction of Drawable. You load up a picture with Drawable by inflating SVG or PNG recordsdata. Inflating doesn’t want Canvas. However for those who needed to attract a primitive form dynamically, you’d use Canvas.

Consider Canvas as a layer on high of Drawable the place you possibly can draw quite a lot of shapes.

Making a Canvas

Making a Canvas is simple. Within the starter venture, open MainActivity.kt and take a look at CanvasApp:

  Canvas(modifier = Modifier
    .fillMaxHeight()
    .fillMaxWidth()
  ) {
...
  }

Canvas accepts a modifier that permits you to modify the Canvas’s measurement, for instance. On this instance, you set the dimensions to the utmost measurement of the mother or father.

Once you ran the starter venture, you didn’t see something, however it’s time to vary that. Take a look at the primary two traces contained in the Canvas block:

    val canvasWidth = measurement.width
    val canvasHeight = measurement.peak

Contained in the Canvas block, you possibly can question the dimensions of Canvas from measurement. Bear in mind the modifier above that extends to the utmost width and peak? That’s the dimensions of Canvas.

Drawing on a Canvas With Jetpack Compose

Following the primary two traces is a name to drawBlackScreen:

    drawBlackScreen(scope = this, canvasWidth, canvasHeight)

Go inside drawBlackScreen. It’s empty proper now. Put the next code inside it:

scope.drawRect(Shade.Black,
    measurement=Dimension(canvasWidth, canvasHeight))

As its identify suggests, drawRect attracts a rectangle. It’s price noting that considerate technique names are an amazing assist in code growth. You understand what drawRect does by its identify: It attracts a rectangle. However what are its parameters? The primary is the colour of the rectangle and the second parameter is the dimensions of the rectangle.

By calling Dimension, Android Studio assists you in including the required import, androidx.compose.ui.geometry.Dimension.

Construct and run the app. You’ll see a black rectangle over the complete display screen:

In your utilization, you omitted the Paint object argument, however you possibly can provide one to vary the fashion of the drawn rectangle. You’ll see how one can assemble Paint later. You additionally omitted the place argument. This implies you used the default worth for the place, which is 0 for x and y coordinates. Different parameters outline coloration and measurement, that are widespread to all objects. Different object strategies require completely different parameters in keeping with the thing form. drawCircle wants an argument for radius, however the line object doesn’t.

Utilizing Modifier

You’ve seen Modifier within the Canvas operate. However you’ve gotten different arsenals as nicely. Suppose you need to add some padding. Change the Modifier inside Canvas to:

  Canvas(modifier = Modifier
    .fillMaxHeight()
    .fillMaxWidth()
    .padding(50.dp)
  ) {

Don’t overlook to import padding. Every technique on the modifier returns an up to date Modifier occasion. So by chaining the tactic calls, you’re progressively constructing the Canvas. The order by which you name the strategies matter.

Rebuild the venture and run it. You’ll see the black display screen now has white padding:

Now that you just’ve seen how padding works for customized graphics in Jetpack Compose, you’ll be able to take away that code.

Creating Objects With Jetpack Compose

It’s lastly time to strive to attract some shapes! You’ll see that every of those shapes has its personal traits.

Drawing Traces

Now that you just’ve created a rectangle, it’s time to create different shapes. You’ll begin by drawing a part of the Pacman maze. Go inside drawBlueLines. You discover that there’s an annotation on high of this technique, @OptIn(ExperimentalGraphicsApi::class). It’s wanted since you use Shade.hsv, which is experimental. So what is that this technique? It will get a coloration that you just’ll use to attract on Canvas. HSV (hue, saturation, worth) is without doubt one of the coloration areas moreover RGB (pink, inexperienced, blue). You may learn extra about HSV in Picture Processing in iOS Half 1: Uncooked Bitmap Modification. Shade.hsv accepts three arguments: hue, saturation and worth. The saturation and worth ranges from 0 to 1. It’s a float which represents the share worth.

On this technique, you could draw 4 traces. You’ve already bought the positions outlined for you.

Add the next code at // 2. Use the drawLine technique:

    scope.drawLine(
      blue, // 1
      Offset(0f, line), // 2
      Offset(canvasWidth, line), // 2
      strokeWidth = 8.dp.worth // 3
    )

Right here’s what is going on:

1. blue is the colour you bought from Shade.hsv.
2. These outline the dot positions that make a line when linked. Every dot wants an Offset. Mainly, it’s an object that accepts two values, the x and y positions.
3. This units the width of the stroke. The upper the worth, the thicker your line turns into. You outline a line by two factors. That’s why the tactic to attract a line wants two Offset arguments. It’s completely different from the tactic for drawing a rectangle.

Rebuild the venture and run the app. You’ll see 4 blue traces:

Discover that you just’ve drawn traces after drawing a rectangle — the order issues. In case you draw traces first, then draw a rectangle, the massive rectangle will cowl your traces.

Drawing Circles

Subsequent, you’ll draw an influence pellet. The circle represents an object that, if eaten by Pacman, makes him resistant to ghosts for a sure time period. Go to // 3. Use the drawCircle technique, and add the next:

  scope.drawCircle(purple, // 1
    middle = Offset(pacmanOffset.x + 600.dp.worth, dotYPos), // 2
    radius = radius) // 3

Right here’s what this code does:

1. This specifies the colour of the circle.
2. The middle argument refers back to the place of the middle of the circle in Canvas.
3. The radius refers to how massive your circle is.

As you’ll be able to see, each strategies — whether or not drawing a rectangle, line or circle — settle for a coloration argument. Nevertheless, they differ in different arguments as a result of each form is a bit completely different. All of the strategies settle for an optionally available Paint object.

Construct the venture and run the app. You’ll see a purple circle:

With that, your energy pellet is able to give ol’ Blinky — spoiler — a run for his cash! :]

Drawing Level Traces

Within the Pacman video video games, this line of factors consult with the dots that Pacman must eat to complete the sport. You may create all of the factors one after the other, however you possibly can additionally use a technique to create a line consisting of factors. Discover // 4. Use the drawPoints technique, and add the next:

  scope.drawPoints(factors, // 1
    PointMode.Factors, // 2
    purple, // 3
    strokeWidth = 16.dp.worth) // 4

This code defines:

1. The listing of Offsets the place you outlined the place of factors.
2. The mode or fashion of the purpose. Right here, you render small squares. There are different PointMode choices. Attempt them out earlier than shifting on. Press Ctrl (or CMD on a Mac) + Area in your keyboard to see the opposite choices.
3. Shade.
4. Line thickness.

Construct the venture and run the app. You’ll see a line of factors:

Drawing Arcs

Now, right here comes probably the most thrilling a part of the tutorial: drawing Pacman himself! Pacman is a not-quite-full circle. You name this form a sector. You name 1 / 4 of a circle an arc. Pacman seems to be like a circle with an arc taken out!

Beneath // 5. Use the drawArc technique inside drawPacman, add the next code:

  scope.drawArc(
    Shade.Yellow, // 1
    45f, // 2
    270f, // 3
    true, // 4
    pacmanOffset,
    Dimension(200.dp.worth, 200.dp.worth)
  )

This code specifies:

1. Yellow because the arc’s coloration.
2. Begin angle, which refers back to the backside a part of Pacman’s mouth.
3. Sweep angle. Sum the beginning angle and the sweep angle, and also you’ll get the place of the highest a part of the mouth. Zero levels begins on the proper facet of the circle. In case you consider the highest as north and backside as south, then zero levels is within the west path. You may change the beginning angle to zero and redraw Pacman to see the placement of zero levels.
4. Whether or not you draw a line between the beginning angle and the top angle utilizing the middle. If not, you draw a direct line between the beginning and finish angles. In your case, you need to use the middle since you create a mouth by making a line from the beginning angle to the middle after which from the middle to the top angle.

Construct the venture and run the app. You’ll see Pacman:

You may see the distinction between utilizing the middle or not in drawing an arc within the image under:

Drawing Advanced Shapes: Blinky the Ghost

The ghosts that chase your Pacman have a fancy form, and Jetpack Compose doesn’t have any “ghost” shapes in its customized graphics. :] So, you’ll draw a customized ghost form. To do that, you could divide a ghost into just a few easy shapes and draw them every utilizing the strategies you’ve discovered.

You may separate a ghost into completely different primitive shapes:

Drawing the Ghost’s Toes

Breaking down the ghost customized graphic, separate the ft. What do you see? Three arcs or half-circles lined up horizontally.

Go inside drawGhost and add the next code:

    val ghostXPos = canvasWidth / 4
    val ghostYPos = canvasHeight / 2
    val threeBumpsPath = Path().let {
      it.arcTo( // 1
        Rect(Offset(ghostXPos - 50.dp.worth, ghostYPos + 175.dp.worth),
          Dimension(50.dp.worth, 50.dp.worth)),
        startAngleDegrees = 0f,
        sweepAngleDegrees = 180f,
        forceMoveTo = true
      )
      it.arcTo( // 2
        Rect(Offset(ghostXPos - 100.dp.worth, ghostYPos + 175.dp.worth),
          Dimension(50.dp.worth, 50.dp.worth)),
        startAngleDegrees = 0f,
        sweepAngleDegrees = 180f,
        forceMoveTo = true
      )
      it.arcTo( // 3
        Rect(Offset(ghostXPos - 150.dp.worth, ghostYPos + 175.dp.worth),
          Dimension(50.dp.worth, 50.dp.worth)),
        startAngleDegrees = 0f,
        sweepAngleDegrees = 180f,
        forceMoveTo = true
      )
      it.shut()
      it
    }
    scope.drawPath( // 4
      path = threeBumpsPath,
      Shade.Pink,
      fashion = Fill
    )

By calling Rect, Android Studio assists you in including the required import, androidx.compose.ui.geometry.Rect.

1. arcTo is just like drawArc above: the startAngleDegrees and sweepAngleDegrees arguments are like begin and sweep angles the place the first argument is the rectangle that defines or bounds the dimensions of the arc. The final argument strikes the Path level to the top of the trail earlier than drawing one other arc. In any other case, you’d at all times draw different arcs from the identical beginning place or starting of the primary arc.
2. You probably did precisely the identical as above, solely you’re beginning on the finish of the primary one.
3. For the final leg, you begin on the finish of the second leg.
4. path argument is the trail you’ve created, and the second argument is the colour of your path. The third argument, fill, is whether or not you need to fill the trail with the chosen coloration.

Rebuild the venture and run the app. You’ll see the ghost’s ft:

Observe: As an alternative of utilizing drawPath, you possibly can use drawArc 3 times. Experiment with drawArc and see which one is extra handy for you.

Drawing the Ghost’s Physique

Now, you’ll draw a rectangle as the principle a part of the ghost’s physique. You already know how one can construct a rectangle, so add the next code on the backside of drawGhost:

    scope.drawRect(
      Shade.Pink,
      Offset(ghostXPos - 150.dp.worth, ghostYPos + 120.dp.worth),
      Dimension(150.dp.worth, 82.dp.worth)
    )

Rebuild the venture and launch the app. You’ll see the ghost’s physique:

A ghost with a physique? Solely in Pacman. :]

Drawing the Ghost’s Head

The ghost’s head is a half-circle arc, however greater and in the wrong way of the ghost’s ft. Add the next code on the backside of drawGhost:

    scope.drawArc(
      Shade.Pink,
      startAngle = 180f,
      sweepAngle = 180f,
      useCenter = false,
      topLeft = Offset(ghostXPos - 150.dp.worth, ghostYPos + 50.dp.worth),
      measurement = Dimension(150.dp.worth, 150.dp.worth)
    )

Beginning on the high left nook of the ghost’s physique, you draw an arc 180 levels to the proper. Rebuild the venture and run the app. You’ll see the ghost’s head:

Drawing the Ghost’s Eyes

Wow, all you’re lacking now are the eyes! The ghost has two eyes, with every eye composed of a white outer circle and a black inside circle for the iris. So now, you’ll draw 4 circles similar to you’ve already completed with the ability pellet. Add the next code on the backside of drawGhost:

    scope.drawCircle(
      Shade.White,
      middle = Offset(ghostXPos - 100.dp.worth, ghostYPos + 100.dp.worth),
      radius = 20f
    )
    scope.drawCircle(
      Shade.Black,
      middle = Offset(ghostXPos - 90.dp.worth, ghostYPos + 100.dp.worth),
      radius = 10f
    )

Rebuild the venture and run the app. You’ll see a one-eyed ghost:

Now, strive to attract the ghost’s left eye. Gotta have two eyes to catch Pacman. :]

Drawing Textual content With Jetpack Compose

To attract textual content, you could entry the native Canvas object as a result of you’ll be able to’t draw textual content on high of Jetpack Compose’s Canvas. Inside drawScore, you’ll see that you’ve textPaint:

  val textPaint = Paint().asFrameworkPaint().apply {
    isAntiAlias = true
    textSize = 80.sp.worth
    coloration = android.graphics.Shade.WHITE
    typeface = Typeface.create(Typeface.MONOSPACE, Typeface.BOLD)
    textAlign = android.graphics.Paint.Align.CENTER
  }

Textual content is drawn as a customized graphic utilizing Jetpack Compose with Paint. You modify the color and style of the textual content by way of this interface. Usually with Canvas, you employ the bottom Paint object, however since you’re utilizing the native Canvas object, you want the framework Paint technique known as asFrameworkPaint. Contained in the asFrameworkPaint.apply block above, you configure the Paint object’s textual content for font, fashion, measurement and coloration.

Moreover, there’s no drawText contained in the DrawingScope for the traditional Canvas object. You could name into the nativeCanvas interface to entry its drawText technique. To attract textual content on the native Canvas, add the next code under // 7. Draw a textual content:

  scope.drawIntoCanvas {
    it.nativeCanvas.drawText( // 1
      "HIGH SCORE", // 2
      canvasWidth / 2, // 3
      canvasHeight / 3, // 3
      textPaint // 4
    )
    it.nativeCanvas.drawText( // 1
      "360", // 2
      canvasWidth / 2, // 3
      canvasHeight / 3 + 100.dp.worth, // 3
      textPaint // 4
    )
  }

Right here’s what’s taking place:

1. Just like the Path in arcTo earlier, it is the Canvas object contained in the drawIntoCanvas block. You reference the native Canvas object after which use drawText to attract the textual content.
2. That is the textual content you need to write.
3. These are the x and y coordinates for textual content placement.
4. That is the framework Paint object representing the textual content’s coloration, measurement and font.

Construct the venture and run the app. You’ll see the next textual content on the display screen:

Scaling, Translating and Rotating Objects With Jetpack Compose

You’ve completed plenty of drawing! Generally, after drawing objects, you would possibly want to remodel them. For instance, you would possibly need to make them greater or change their place or path. You might also have to rotate Pacman as he strikes by way of the maze: When he strikes north, his mouth ought to level north.

Scaling and Translating Objects

Take a look at the ghost, and also you’ll see he’s smaller than Pacman. Additionally, the ghost’s place is barely decrease than Pacman’s. You may repair this by remodeling the ghost, which you’ll do now.

DrawingScope has the withTransform technique. Inside this technique, add the scale and translate modifiers. Inside drawGhost wrap each code there with the next snippet under:

  scope.withTransform({ // 1
    scale(1.2f) // 2
    translate(high=-50.dp.worth, left=50.dp.worth) // 3
  }) {
    ...
  }

Right here’s what this code does:

1. A scope block makes use of the tactic withTransform. Contained in the block, withTransform makes use of two strategies, or modifiers, to remodel the thing.
2. scale modifications the dimensions of the thing. The argument 1.2f means the thing can be 20% greater.
3. translate has two arguments, high and left. high modifications the vertical place of the thing. The damaging worth, -50.dp.worth, means the thing rises upward. A optimistic worth pushes the thing downward. The horizontal place of the thing modifications with the left argument. The damaging worth, -50.dp.worth, means object strikes to the left. A optimistic worth would transfer the thing to the proper.

Construct the venture and run the app. You’ll see the ghost has moved barely up and turn out to be greater:

Effectively, take a look at that! A Blinky duplicate. Blinky could be proud. Waka do you suppose? :]

Rotating Objects

The Pacman sport has a lives indicator, and including one will make this entire. The indicator is the Pacman form itself. So, if the indicator has three Pacman shapes, it means you’ve gotten three lives. You already know the way to attract Pacman. Now, you could duplicate him. However that’s not sufficient. You additionally want to maneuver the clones, make them smaller, after which rotate them.

Go into drawPacmanLives, and add the next code:

  scope.withTransform({
    scale(0.4f)
    translate(high=1200.dp.worth, left=-1050.dp.worth)
    rotate(180f)
  }) {
    drawArc(
      Shade.Yellow,
      45f,
      270f,
      true,
      pacmanOffset,
      Dimension(200.dp.worth, 200.dp.worth)
    )
  }

You’ve seen the drawArc code earlier than. It’s the code you used while you drew the unique Pacman. withTransform will scale, translate, and eventually, rotate Pacman. rotate accepts the angle argument in levels.

Construct the venture and run the app. You’ll see one other Pacman however smaller and in a special place:

Now, strive to attract one other Pacman beside this clone to point that you’ve two lives left within the sport.

The place to Go From Right here?

Obtain the ultimate venture by clicking Obtain Supplies on the high or backside of this tutorial.

You’ve discovered in regards to the Graphics API in Jetpack Compose. You discovered how one can arrange Canvas and modify it utilizing a modifier. You’ve drawn many shapes and reworked them. You additionally used the native Canvas to attract textual content on it.

However there are extra belongings you haven’t explored, reminiscent of animation. You may transfer Pacman and make his mouth open to simulate consuming the dots. In fact, you possibly can give life to the ghost, make it flash blue, and have it chase Pacman.

Be happy to checkout this excellent Getting Began with Jetpack Compose Animations tutorial adopted by the extra superior Jetpack Compose Animations tutorial.

We hope you loved this tutorial! You probably have any feedback or questions, please be a part of the discussion board dialogue under.