Android: Simple trigonometric formula for calculating cascading joint rotations for an arm joint system.

CraneView.java

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import android.content.Context;
import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.Paint;
import android.graphics.RectF;
import android.support.annotation.NonNull;
import android.support.annotation.Nullable;
import android.util.AttributeSet;
import android.view.MotionEvent;
import android.view.View;

/**
 * Hard coded the distances in pixels and stuff, it's just realized pseudocode so expect to sanitize the code
 * for the Android realm. "Buttons" are also hard coded into the view for simplicity.
 *
 * @author Pär Amsen 07/2017
 */
public class CraneView extends View {
    float[] parent; //0: posX, 1: posY, 2: rot
    float[] child1; //0: offset, 1: rot
    float[] child2; //0: offset

    RectF button1;
    RectF button2;

    Paint linePaint;
    Paint textPaint;

    public CraneView(@NonNull Context context, @Nullable AttributeSet attrs) {
        super(context, attrs);

        parent = new float[]{200, 500, -200};
        child1 = new float[]{100, 45};
        child2 = new float[]{75};

        button1 = new RectF(300, 200, 300 + 300, 200 + 50);
        button2 = new RectF(300, 300, 300 + 300, 300 + 50);

        linePaint = new Paint();
        linePaint.setColor(Color.BLACK);
        linePaint.setStyle(Paint.Style.STROKE);
        linePaint.setStrokeWidth(10);
        linePaint.setTextSize(20);

        textPaint = new Paint();
        textPaint.setColor(Color.BLACK);
        textPaint.setTextSize(20);
    }

    @Override
    protected void onDraw(Canvas canvas) {
        super.onDraw(canvas);

        float c1X = parent[0] + child1[0] * ((float) Math.sin(Math.toRadians(parent[2])));
        float c1Y = parent[1] + child1[0] * ((float) Math.cos(Math.toRadians(parent[2])));

        float c2X = c1X + child2[0] * (((float) Math.sin(Math.toRadians(child1[1] + parent[2]))));
        float c2Y = c1Y + child2[0] * (((float) Math.cos(Math.toRadians(child1[1] + parent[2]))));

        canvas.drawLine(parent[0],
                parent[1],
                c1X,
                c1Y,
                linePaint);

        canvas.drawLine(c1X,
                c1Y,
                c2X,
                c2Y,
                linePaint);

        canvas.drawRect(button1, linePaint);
        canvas.drawText("Rotate parent joint", button1.left, button1.bottom - 25, textPaint);
        canvas.drawRect(button2, linePaint);
        canvas.drawText("Rotate first joint", button2.left, button2.bottom - 25, textPaint);
    }

    @Override
    public boolean onTouchEvent(MotionEvent event) {
        float x = event.getX();
        float y = event.getY();

        if (button1.contains(x, y))
            parent[2] += 10;

        if (button2.contains(x, y))
            child1[1] += 10;

        postInvalidate();

        return super.onTouchEvent(event);
    }
}