CollectCircles 1 - המסך, המחלקות והציור

binding = ActivityMainBinding.inflate(getLayoutInflater());
setContentView(binding.getRoot());

package com.example.collectcircles;

import android.graphics.Canvas;
import android.graphics.Paint;

public class Circle {
    private float centerX;
    private float centerY;
    private final float radius;
    private final int color;

    public Circle(float centerX, float centerY, float radius, int color) {
        this.centerX = centerX;
        this.centerY = centerY;
        this.radius = radius;
        this.color = color;
    }

    public float getCenterX() {
        return centerX;
    }

    public float getCenterY() {
        return centerY;
    }

    public float getRadius() {
        return radius;
    }

    public void setCenter(float centerX, float centerY) {
        this.centerX = centerX;
        this.centerY = centerY;
    }

    public double distanceTo(Circle other) {
        return distanceTo(other.centerX, other.centerY);
    }

    public double distanceTo(float pointX, float pointY) {
        float dx = centerX - pointX;
        float dy = centerY - pointY;
        return Math.sqrt(dx * dx + dy * dy);
    }

    public boolean contains(float pointX, float pointY) {
        return distanceTo(pointX, pointY) <= radius;
    }

    public boolean overlaps(Circle other) {
        return distanceTo(other) < radius + other.radius;
    }

    public void draw(Canvas canvas, Paint paint) {
        paint.setStyle(Paint.Style.FILL);
        paint.setColor(color);
        canvas.drawCircle(centerX, centerY, radius, paint);
    }
}

package com.example.collectcircles;

import android.graphics.Canvas;
import android.graphics.Paint;

public class Target extends Circle {
    private final int crossColor;
    private final float crossStrokeWidth;

    public Target(float centerX, float centerY, float radius, int color,
                  int crossColor, float crossStrokeWidth) {
        super(centerX, centerY, radius, color);
        this.crossColor = crossColor;
        this.crossStrokeWidth = crossStrokeWidth;
    }

    public boolean fullyContains(Circle circle) {
        return distanceTo(circle) + circle.getRadius() <= getRadius();
    }

    @Override
    public void draw(Canvas canvas, Paint paint) {
        super.draw(canvas, paint);

        paint.setStyle(Paint.Style.STROKE);
        paint.setStrokeWidth(crossStrokeWidth);
        paint.setColor(crossColor);

        canvas.drawLine(
                getCenterX(), getCenterY() - getRadius(),
                getCenterX(), getCenterY() + getRadius(), paint
        );
        canvas.drawLine(
                getCenterX() - getRadius(), getCenterY(),
                getCenterX() + getRadius(), getCenterY(), paint
        );
    }
}

public class GameBoardView extends View {
    private final Paint paint = new Paint(Paint.ANTI_ALIAS_FLAG);
    private Target target;
    private Circle[] previewCircles = new Circle[0];

    public GameBoardView(Context context) {
        this(context, null);
    }

    public GameBoardView(Context context, AttributeSet attrs) {
        this(context, attrs, 0);
    }

    public GameBoardView(Context context, AttributeSet attrs,
                         int defStyleAttr) {
        super(context, attrs, defStyleAttr);
        setBackgroundColor(color(R.color.board_background));
    }

    @Override
    protected void onSizeChanged(int width, int height,
                                 int oldWidth, int oldHeight) {
        float centerX = width / 2f;
        float centerY = height / 2f;
        float targetRadius = Math.min(
                dp(64f),
                Math.min(width, height) / 5f
        );
        float circleRadius = targetRadius / 2f;

        target = new Target(
                centerX, centerY, targetRadius,
                color(R.color.target_red),
                color(R.color.target_cross),
                dp(2f)
        );

        previewCircles = new Circle[] {
                new Circle(circleRadius * 1.5f, circleRadius * 1.5f,
                        circleRadius, color(R.color.circle_green)),
                new Circle(width - circleRadius * 1.5f, circleRadius * 2.2f,
                        circleRadius, color(R.color.circle_green)),
                new Circle(circleRadius * 1.8f, height - circleRadius * 1.7f,
                        circleRadius, color(R.color.circle_green))
        };
    }

    @Override
    protected void onDraw(Canvas canvas) {
        super.onDraw(canvas);
        if (target == null) {
            return;
        }

        target.draw(canvas, paint);
        for (Circle circle : previewCircles) {
            circle.draw(canvas, paint);
        }
    }

    private float dp(float value) {
        return value * getResources().getDisplayMetrics().density;
    }

    private int color(int colorResource) {
        return ContextCompat.getColor(getContext(), colorResource);
    }
}

// View Binding gives us a typed reference generated from activity_main.xml.
// The button becomes active in the next teaching step, when a playable game exists.
binding.startButton.setEnabled(false);