Pan/Zoom

The CartesianChart and PolarChart components have opt-in support for "pan/zoom" gestures simply by using the useChartTransformState hook.

useChartTransformState

The useChartTransformState hook provides the necessary state management for pan and zoom gestures. It accepts an optional configuration object and returns an object with a state property.

Configuration

The hook accepts a configuration object with the following options:

type ChartTransformStateConfig = {
  scaleX?: number; // Initial X-axis scale
  scaleY?: number; // Initial Y-axis scale
};

Return Value

The hook returns an object with a state property that contains:

{
  state: {
    panActive: SharedValue<boolean>; // Whether a pan gesture is currently active
    zoomActive: SharedValue<boolean>; // Whether a zoom gesture is currently active
    origin: SharedValue<{ x: number; y: number }>; // The origin point for transformations
    matrix: SharedValue<Matrix4>; // The current transformation matrix
    offset: SharedValue<Matrix4>; // The offset transformation matrix
  };
}

Basic Usage

To enable pan and zoom gestures on a chart, pass the transform state to the chart's transformState prop:

import { CartesianChart, useChartTransformState } from "victory-native";

function MyChart() {
  const transformState = useChartTransformState({
    scaleX: 1.5, // Initial X-axis scale
    scaleY: 1.0, // Initial Y-axis scale
  });

return (
  <CartesianChart
      transformState={transformState}
      // ... other props
    >
      {/* chart content */}
    </CartesianChart>
  )
}

If no configuration is provided, the chart will initialize with a scale of 1.0 for both axes.

Transform Gesture Configuration

You can customize the pan gesture behavior using the transformConfig prop:

<CartesianChart
  transformState={state}
  transformConfig={{
    pan: {
      activateAfterLongPress: 100, // Delay in ms before pan gesture activates
    },
  }}
>
  {/* chart content */}
</CartesianChart>

Utility Functions

Several utility functions are available to help work with chart transformations:

getTransformComponents

Extracts the scale and translation components from a transformation matrix:

const { scaleX, scaleY, translateX, translateY } = getTransformComponents(matrix);

setScale

Updates the scale components of a transformation matrix:

// Set uniform scale
const newMatrix = setScale(matrix, 2.0); // scales both X and Y by 2.0

// Set different X and Y scales
const newMatrix = setScale(matrix, 2.0, 1.5); // scaleX = 2.0, scaleY = 1.5

setTranslate

Updates the translation components of a transformation matrix:

const newMatrix = setTranslate(matrix, 100, 50); // moves 100 units in X, 50 in Y

These utility functions are particularly useful when you need to programmatically modify chart transformations or read the current transformation state.