An programmatically example on how to create a Triangle view in Android.

attr.xml

<?xml version="1.0" encoding="utf-8"?>
<resources>
    <declare-styleable name="TriangleShape">
        <attr name="triangleType">
            <enum name="centerTop" value="0" />
            <enum name="leftBottom" value="1" />
            <enum name="rightBottom" value="2" />
            <enum name="centerBottom" value="3" />
            <enum name="leftTop" value="4" />
        </attr>
        <attr name="triangleColor" format="color" />
    </declare-styleable>
</resources>

layout_example.xml

<?xml version="1.0" encoding="utf-8"?>
<FrameLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    android:layout_width="match_parent"
    android:layout_height="match_parent">

    <br.com.rsicarelli.example.Triangle
        android:id="@+id/markerTriangle"
        android:layout_width="48dp"
        android:layout_height="40dp"
        android:layout_gravity="center_horizontal"
        app:triangleColor="@android:color/black"
        app:triangleType="leftTop" />
</FrameLayout>

Triangle.java

public class Triangle extends View {

    private Path path;
    private Paint shapePaint;
    private int fillColor;
    private int type;

    public Triangle(Context context, AttributeSet attrs) {
        super(context, attrs);
        init(context, attrs);
    }

    private void init(Context context, AttributeSet attrs) {
        TypedArray attr = context.obtainStyledAttributes(attrs, R.styleable.TriangleShape, 0, 0);
        type = attr.getInt(R.styleable.TriangleShape_triangleType, Type.CENTER_TOP);
        fillColor = attr.getColor(R.styleable.TriangleShape_triangleColor, Color.WHITE);
        path = new Path();
        shapePaint = new Paint();
        attr.recycle();
    }

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

        switch (type) {
            case Type.LEFT_BOTTOM: {
                path.moveTo(0, 0);
                path.lineTo(0, getHeight());
                path.lineTo(getWidth(), getHeight());
                path.close();
                break;
            }
            case Type.RIGHT_BOTTOM: {
                path.moveTo(0, getHeight());
                path.lineTo(getWidth(), getHeight());
                path.lineTo(getWidth(), 0);
                path.close();
                break;
            }
            case Type.CENTER_BOTTOM: {
                path.moveTo(0, 0);
                path.lineTo(getWidth() / 2, getHeight());
                path.lineTo(getWidth(), 0);
                path.close();
                break;
            }
            case Type.LEFT_TOP: {
                path.moveTo(0, 0);
                path.lineTo(0, getHeight());
                path.lineTo(getWidth(), 0);
                break;
            }
            default: {
                path.moveTo(0, getHeight());
                path.lineTo(getWidth() / 2, 0);
                path.lineTo(getWidth(), getHeight());
                path.close();
                break;
            }
        }

        shapePaint.setStrokeJoin(Paint.Join.ROUND);
        shapePaint.setAntiAlias(true);
        shapePaint.setColor(getFillColor());
        shapePaint.setStyle(Paint.Style.FILL);

        canvas.drawPath(path, shapePaint);
    }

    public int getFillColor() {
        return fillColor;
    }

    public void setFillColor(@ColorRes int fillColor) {
        this.fillColor = fillColor;
    }

    static class Type {
        public static final int CENTER_TOP = 0;
        public static final int LEFT_BOTTOM = 1;
        public static final int RIGHT_BOTTOM = 2;
        public static final int CENTER_BOTTOM = 3;
        public static final int LEFT_TOP = 4;
    }
}