Coordinate Transformation

Overview of Coordinate Systems

Understanding different coordinate systems and their transformations is crucial in graph visualization. G6 involves multiple coordinate systems, each used for different scenarios:

• Client Coordinate System: Origin is at the top-left corner of the browser viewport, measured in pixels. Typically used for handling browser events.
• Screen Coordinate System: Origin is at the top-left corner of the screen, affected by page scrolling.
• Page Coordinate System: Origin is at the top-left corner of the document, considering document scrolling.
• Canvas Coordinate System: Also known as the world coordinate system, used for drawing and layout, with the origin at the top-left corner of the canvas element.
• Viewport Coordinate System: The visible area of the canvas, with the origin at the top-left corner of the viewport. The viewport can be panned and zoomed to view different areas of the Canvas.

In this example, moving the mouse shows the position in various coordinate systems:

When the canvas is not panned or zoomed, the Viewport and Canvas coordinate systems coincide. With user interactions like dragging or zooming, the two systems may shift.

G6 provides a series of APIs for converting between different coordinate systems, detailed below.

API Reference

Graph.getCanvasByClient(point)

Convert browser coordinates (client coordinates) to canvas coordinates.

getCanvasByClient(point: Point): Point;

Parameters

Return Value

• Type: [number, number] | [number, number, number]
• Description: Coordinate point in the canvas coordinate system

Graph.getCanvasByViewport(point)

Convert viewport coordinates to canvas coordinates.

getCanvasByViewport(point: Point): Point;

Parameters

Return Value

• Type: [number, number] | [number, number, number]
• Description: Coordinate point in the canvas coordinate system

Graph.getClientByCanvas(point)

Convert canvas coordinates to browser client coordinates.

getClientByCanvas(point: Point): Point;

Parameters

Return Value

• Type: [number, number] | [number, number, number]
• Description: Coordinate point in the browser client coordinate system

Graph.getViewportByCanvas(point)

Convert canvas coordinates to viewport coordinates.

getViewportByCanvas(point: Point): Point;

Parameters

Return Value

• Type: [number, number] | [number, number, number]
• Description: Coordinate point in the viewport coordinate system