Drawing Canvas Simple digital drawing canvas with color palette, brush sizes, and undo/redo support.

The Drawing Canvas tool utilizes the HTML5 Canvas API to render graphics in real-time, allowing users to interact with the canvas element using React event handlers such as `startDraw`, `draw`, and `endDraw`. When a user starts drawing, the `getPos` function calculates the position of the mouse or touch event relative to the canvas element, taking into account the bounding rectangle of the canvas. The `draw` function then uses this position data to draw lines on the canvas using the 2D drawing context's `strokeStyle`, `lineWidth`, and `lineCap` properties. The tool also employs a history stack to store previous states of the canvas as ImageData objects, which are used to implement undo and redo functionality.

The `saveHistory` function is called whenever the user makes a change to the canvas, and it trims the history stack to prevent it from exceeding 50 entries. This ensures that the tool remains responsive even after extensive use. When the user requests to undo or redo an action, the corresponding function (`undo` or `redo`) updates the `historyIndex` variable and uses the `putImageData` method to restore the canvas to its previous state. The tool also supports downloading the canvas as a PNG image using the `toDataURL` method, which generates a base64-encoded string representing the image data. Additionally, the color palette is implemented using a combination of predefined colors stored in the `COLORS` array and an HTML input element of type "color", allowing users to select custom colors using their browser's built-in color picker dialog.

The React library is used extensively throughout the tool to manage state changes and handle user interactions. Specifically, the `useState` hook is used to store the current drawing state, brush size, and selected color, while the `useCallback` hook is used to memoize functions such as `initCanvas`, `saveHistory`, `undo`, and `redo`. The `useRef` hook is used to create references to DOM elements, including the canvas element itself, allowing the tool to access and manipulate these elements directly. By leveraging these React features in conjunction with the HTML5 Canvas API, the Drawing Canvas tool provides a seamless and intuitive drawing experience for users.