The FreehandDrawingAnnotationCreationModifier

The FreehandDrawingModifier is a chart modifier that allows for freehand creation of FreehandDrawingAnnotation instances.

Overview

When this modifier is enabled and added to a SciChartSurface, users can draw freehand strokes directly on the chart using touch gestures. The modifier automatically creates a new FreehandDrawingAnnotation and populates it with points based on the user's movement.

Properties

The following properties can be used to configure the FreehandDrawingModifier:

Property	Description
brushColor	Sets the color of the brush stroke for the annotations created by this modifier.
brushThickness	Sets the thickness of the brush stroke for the annotations created by this modifier.
xAxisId	Sets the ID of the X-Axis that the created annotations should be measured against.
yAxisId	Sets the ID of the Y-Axis that the created annotations should be measured against.

Event Listeners

You can receive a notification when an annotation is created by setting an OnAnnotationCreatedListener:

setAnnotationCreationListener(OnAnnotationCreatedListener listener): Passes the newly created annotation instance to the listener.

Using FreehandDrawingModifier

The following code demonstrates how to add and configure a FreehandDrawingModifier:

Java
Kotlin

// Create a FreehandDrawingModifier
final FreehandDrawingModifier freehandModifier = new FreehandDrawingModifier();

// Configure the modifier
freehandModifier.setBrushColor(Color.WHITE);
freehandModifier.setBrushThickness(4f);

// Optional: Set a listener to be notified when an annotation is created
freehandModifier.setAnnotationCreationListener(newAnnotation -> {
    // Configure the newly created annotation if needed
    newAnnotation.setIsEditable(true);
});

// Add the modifier to the surface
surface.getChartModifiers().add(freehandModifier);

// Create a FreehandDrawingModifier
val freehandModifier = FreehandDrawingModifier().apply {
    // Configure the modifier
    brushColor = Color.WHITE
    brushThickness = 4f

    // Optional: Set a listener to be notified when an annotation is created
    setAnnotationCreationListener { newAnnotation ->
        // Configure the newly created annotation if needed
        newAnnotation.setIsEditable(true)
    }
}

// Add the modifier to the surface
surface.chartModifiers.add(freehandModifier)

Customizing the Modifier

You can customize the behavior of the FreehandDrawingModifier by extending it and overriding its touch event methods. This allows you to add custom logic before or after an annotation is created.

Java
Kotlin

// Define a custom FreehandDrawingModifier
private static class CustomFreehandDrawingModifier extends FreehandDrawingModifier {
    @Override
    protected boolean onTouchDown(ModifierTouchEventArgs args) {
        // Custom logic before creation
        return super.onTouchDown(args);
    }

    @Override
    protected boolean onTouchMove(ModifierTouchEventArgs args) {
        // Custom logic during creation
        return super.onTouchMove(args);
    }

    @Override
    protected boolean onTouchUp(ModifierTouchEventArgs args) {
        // Custom logic after creation
        return super.onTouchUp(args);
    }
}

void useCustomFreehandDrawingModifier(@NonNull SciChartSurface surface) {
    // Use the custom modifier
    final CustomFreehandDrawingModifier customModifier = new CustomFreehandDrawingModifier();
    customModifier.setBrushColor(Color.YELLOW);
    
    surface.getChartModifiers().add(customModifier);
}

// Define a custom FreehandDrawingModifier
private class CustomFreehandDrawingModifier : FreehandDrawingModifier() {
    override fun onTouchDown(args: ModifierTouchEventArgs): Boolean {
        // Custom logic before creation
        return super.onTouchDown(args)
    }

    override fun onTouchMove(args: ModifierTouchEventArgs): Boolean {
        // Custom logic during creation
        return super.onTouchMove(args)
    }

    override fun onTouchUp(args: ModifierTouchEventArgs): Boolean {
        // Custom logic after creation
        return super.onTouchUp(args)
    }
}

fun useCustomFreehandDrawingModifier(surface: SciChartSurface) {
    // Use the custom modifier
    val customModifier = CustomFreehandDrawingModifier()
    customModifier.brushColor = Color.YELLOW
    
    surface.chartModifiers.add(customModifier)
}

Note

To learn more about other Annotation Types, available out of the box in SciChart, please find the comprehensive list in the Annotation APIs article.