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Graphics Utilizing Jetpack Compose | Kodeco

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Android has a wide range of graphics-based objects to put on the app’s display. A few of these graphics objects embody textual content, buttons and checkboxes. What in case you needed to attract customized graphics? Like rectangles, traces, triangles and different shapes? Video video games, portray apps or chart drawing packages want customized graphics. Whenever you desire a good avatar on your subsequent recreation, customized graphics with Jetpack Compose would be the technique 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 utilize the Graphics API. The Graphics API makes use of an strategy known as the declarative programming paradigm. On this tutorial, you’ll study this less complicated means 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 advanced customized graphics by combining graphics objects.
  • Show textual content utilizing Paint.
  • Rework objects.
Word: This tutorial assumes you’ve got expertise with Android and Kotlin. If that’s not the case, try the Starting Android Improvement with Kotlin sequence and different Kotlin and Android tutorials to get familiarized first.

Getting Began

Begin by utilizing the Obtain Supplies button on the prime or backside of this tutorial to obtain the challenge.

Open the challenge in Android Studio Bumblebee or later and get acquainted with the recordsdata. You’ll discover a starter challenge and a remaining challenge. Open and run the starter challenge. The app – Pacman – incorporates a clean, white display.

Humble beginnings to date, proper? For those who’re questioning in regards to the finish results of the challenge, open and run the ultimate challenge. You’ll see the Pacman display:

Full Pacman App custom graphics with Jetpack Compose

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 would create graphics utilizing bitmap or SVG, however the Graphics API in Android offers you another technique to do it. As a substitute of drawing graphics utilizing instruments like Adobe Illustrator and importing them as bitmap or SVG, you possibly can create uncooked graphics immediately via code.

Utilizing solely code, you continue to create a bitmap with pixels and can see the identical photographs on the Android display. Your code makes use of Canvas to attract objects utilizing a bitmap. As a substitute of placing sure colours in particular x and y areas, you utilize helper strategies to attract frequent shapes like traces, rectangles and circles. Lastly, to vary the bitmap’s type and colours, you utilize 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 means to make use of this API: It makes managing Canvas and Paint a straightforward activity. You don’t have to set methodology or different configurations on the Paint object. As a substitute, all of the configuration and execution occur in a single place: the composable perform. Earlier than Jetpack Compose, working with the Paint API required meticulous element since code group selections might 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, first you want a Drawable to carry your drawing. Drawings are composed of pixels. For those who’ve labored in Android very lengthy, you’ll learn 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 methodology. The draw methodology accepts Canvas because the argument. This connection permits you to draw shapes utilizing code in Drawable to place them on the Canvas.

What are you able to do with Canvas?

Canvas permits you to draw many primitive shapes, from circles to clipping the shapes. You would 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 in case you needed to attract a primitive form dynamically, you’d use Canvas.

Consider Canvas as a layer on prime of Drawable the place you could possibly draw a wide range of shapes.

Making a Canvas

Making a Canvas is easy. Within the starter challenge, 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 dimension, for instance. On this instance, you set the scale to the utmost dimension of the dad or mum.

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

    val canvasWidth = dimension.width
    val canvasHeight = dimension.top

Contained in the Canvas block, you could possibly question the scale of Canvas from dimension. Keep in mind the modifier above that extends to the utmost width and top? That’s the scale 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(Coloration.Black,
    dimension=Dimension(canvasWidth, canvasHeight))

As its identify suggests, drawRect attracts a rectangle. It’s value noting that considerate methodology names are an incredible assist in code improvement. You already know 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 scale 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:

Black rectangle on Pacman app, custom graphics with Jetpack Compose

In your utilization, you omitted the Paint object argument, however you could possibly provide one to vary the type of the drawn rectangle. You’ll see learn how to 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 colour and dimension, that are frequent to all objects. Different object strategies require completely different parameters in accordance with the article form. drawCircle wants an argument for radius, however the line object doesn’t.

Utilizing Modifier

You’ve seen Modifier within the Canvas perform. However you’ve got different arsenals as effectively. Suppose you wish 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 methodology on the modifier returns an up to date Modifier occasion. So by chaining the strategy calls, you’re progressively constructing the Canvas. The order by which you name the strategies matter.

Rebuild the challenge and run it. You’ll see the black display now has white padding:
Black rectangle with white padding

Now that you simply’ve seen how padding works for customized graphics in Jetpack Compose, you possibly can 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 Strains

Now that you simply’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 prime of this methodology, @OptIn(ExperimentalGraphicsApi::class). It’s wanted since you use Coloration.hsv, which is experimental. So what is that this methodology? It will get a colour that you simply’ll use to attract on Canvas. HSV (hue, saturation, worth) is without doubt one of the colour areas in addition to RGB (pink, inexperienced, blue). You’ll be able to learn extra about HSV in Picture Processing in iOS Half 1: Uncooked Bitmap ModificationColoration.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 methodology, you could draw 4 traces. You’ve already obtained the positions outlined for you.

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

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

Right here’s what is occurring:

  1. blue is the colour you bought from Coloration.hsv.
  2. These outline the dot positions that make a line when related. 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 strategy to attract a line wants two Offset arguments. It’s completely different from the strategy for drawing a rectangle.

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

Four blue lines, custom graphics with Jetpack Compose

Discover that you simply’ve drawn traces after drawing a rectangle — the order issues. For those who 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 methodology, and add the next:

  scope.drawCircle(purple, // 1
    heart = 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 heart argument refers back to the place of the middle of the circle in Canvas.
  3. The radius refers to how large your circle is.

As you possibly can see, each strategies — whether or not drawing a rectangle, line or circle — settle for a colour argument. Nonetheless, they differ in different arguments as a result of each form is a bit completely different. All of the strategies settle for an non-compulsory Paint object.

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

Purple circle, custom graphics with Jetpack Compose

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

Drawing Level Strains

Within the Pacman video video games, this line of factors check with the dots that Pacman must eat to complete the sport. You’ll be able to create all of the factors one after the other, however you could possibly additionally use a way to create a line consisting of factors. Discover // 4. Use the drawPoints methodology, and add the next:

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

This code defines:

  1. The checklist of Offsets the place you outlined the place of factors.
  2. The mode or type 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) + House in your keyboard to see the opposite choices.
  3. Coloration.
  4. Line thickness.

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

A Line of points, custom graphics with Jetpack Compose

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!

Under // 5. Use the drawArc methodology inside drawPacman, add the next code:

  scope.drawArc(
    Coloration.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 colour.
  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. For those who consider the highest as north and backside as south, then zero levels is within the west course. You would 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 wish 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 challenge and run the app. You’ll see Pacman:

Pacman eating dots, custom graphics with Jetpack Compose

You’ll be able to see the distinction between utilizing the middle or not in drawing an arc within the image under:

Using the center in drawing an arc, custom graphics with Jetpack Compose

Drawing Complicated Shapes: Blinky the Ghost

The ghosts that chase your Pacman have a posh 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’ll be able to separate a ghost into completely different primitive shapes:

Ghost Dissected, custom graphics with jetpack compose

Drawing the Ghost’s Ft

Breaking down the ghost customized graphic, separate the toes. 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,
      Coloration.Pink,
      type = 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 scale 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 must fill the trail with the chosen colour.

Rebuild the challenge and run the app. You’ll see the ghost’s toes:

Ghost's feet, custom graphics with Jetpack Compose

Word: As a substitute of utilizing drawPath, you could possibly use drawArc thrice. 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 learn how to construct a rectangle, so add the next code on the backside of drawGhost:

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

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

Ghost's body, custom graphics with Jetpack Compose

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 other way of the ghost’s toes. Add the next code on the backside of drawGhost:

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

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

Ghost's full body, custom graphics with Jetpack Compose

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 internal circle for the iris. So now, you’ll draw 4 circles identical to you’ve already carried out with the facility pellet. Add the next code on the backside of drawGhost:

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

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

One-eyed ghost, custom graphics with Jetpack Compose

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 possibly can’t draw textual content on prime of Jetpack Compose’s Canvas. Inside drawScore, you’ll see that you’ve got textPaint:

  val textPaint = Paint().asFrameworkPaint().apply {
    isAntiAlias = true
    textSize = 80.sp.worth
    colour = android.graphics.Coloration.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 alter the color and style of the textual content via this interface. Usually with Canvas, you utilize the bottom Paint object, however since you’re utilizing the native Canvas object, you want the framework Paint methodology known as asFrameworkPaint. Contained in the asFrameworkPaint.apply block above, you configure the Paint object’s textual content for font, type, dimension and colour.

Moreover, there’s no drawText contained in the DrawingScope for the conventional Canvas object. It’s essential name into the nativeCanvas interface to entry its drawText methodology. 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 occurring:

  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 wish 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 colour, dimension and font.

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

Score text, custom graphics with Jetpack Compose

Scaling, Translating and Rotating Objects With Jetpack Compose

You’ve carried out a whole lot of drawing! Generally, after drawing objects, you may want to remodel them. For instance, you may wish to make them greater or change their place or course. You might also have to rotate Pacman as he strikes via 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’ll be able to repair this by remodeling the ghost, which you’ll do now.

DrawingScope has the withTransform methodology. Inside this methodology, 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(prime=-50.dp.worth, left=50.dp.worth) // 3
  }) {
    ...
  }

Right here’s what this code does:

  1. scope block makes use of the strategy withTransform. Contained in the block, withTransform makes use of two strategies, or modifiers, to remodel the article.
  2. scale modifications the scale of the article. The argument 1.2f means the article will likely be 20% greater.
  3. translate has two arguments, prime and left. prime modifications the vertical place of the article. The adverse worth, -50.dp.worth, means the article rises upward. A constructive worth pushes the article downward. The horizontal place of the article modifications with the left argument. The adverse worth, -50.dp.worth, means object strikes to the left. A constructive worth would transfer the article to the appropriate.

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

Bigger ghost, custom graphics with Jetpack Compose

Properly, have a look at that! A Blinky reproduction. Blinky can be proud. Waka do you suppose? :]

Rotating Objects

The Pacman recreation 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 got three lives. You already understand how 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(prime=1200.dp.worth, left=-1050.dp.worth)
    rotate(180f)
  }) {
    drawArc(
      Coloration.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 at last, rotate Pacman. rotate accepts the angle argument in levels.

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

One Life of Pacman, custom graphics with Jetpack Compose

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

The place to Go From Right here?

Obtain the ultimate challenge by clicking Obtain Supplies on the prime or backside of this tutorial.

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

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

Be at liberty 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! If in case you have any feedback or questions, please be part of the discussion board dialogue under.

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