paint-ui/lib/canvas-utils.ts

/**
 * Create a new canvas element with specified dimensions
 */
export function createCanvas(width: number, height: number): HTMLCanvasElement {
  const canvas = document.createElement('canvas');
  canvas.width = width;
  canvas.height = height;
  return canvas;
}

/**
 * Get 2D context from canvas with error handling
 */
export function getContext(canvas: HTMLCanvasElement): CanvasRenderingContext2D {
  const ctx = canvas.getContext('2d', { willReadFrequently: true });
  if (!ctx) {
    throw new Error('Failed to get 2D context');
  }
  return ctx;
}

/**
 * Clear entire canvas
 */
export function clearCanvas(ctx: CanvasRenderingContext2D): void {
  ctx.clearRect(0, 0, ctx.canvas.width, ctx.canvas.height);
}

/**
 * Fill canvas with color
 */
export function fillCanvas(ctx: CanvasRenderingContext2D, color: string): void {
  ctx.fillStyle = color;
  ctx.fillRect(0, 0, ctx.canvas.width, ctx.canvas.height);
}

/**
 * Draw checkerboard pattern (for transparency)
 */
export function drawCheckerboard(
  ctx: CanvasRenderingContext2D,
  squareSize = 10,
  color1 = '#ffffff',
  color2 = '#cccccc',
  width?: number,
  height?: number
): void {
  const w = width ?? ctx.canvas.width;
  const h = height ?? ctx.canvas.height;

  for (let y = 0; y < h; y += squareSize) {
    for (let x = 0; x < w; x += squareSize) {
      const isEven = (Math.floor(x / squareSize) + Math.floor(y / squareSize)) % 2 === 0;
      ctx.fillStyle = isEven ? color1 : color2;
      ctx.fillRect(x, y, squareSize, squareSize);
    }
  }
}

/**
 * Clone a canvas
 */
export function cloneCanvas(source: HTMLCanvasElement): HTMLCanvasElement {
  const clone = createCanvas(source.width, source.height);
  const ctx = getContext(clone);
  ctx.drawImage(source, 0, 0);
  return clone;
}

/**
 * Resize canvas maintaining content
 */
export function resizeCanvas(
  canvas: HTMLCanvasElement,
  newWidth: number,
  newHeight: number
): void {
  const tempCanvas = cloneCanvas(canvas);
  canvas.width = newWidth;
  canvas.height = newHeight;
  const ctx = getContext(canvas);
  ctx.drawImage(tempCanvas, 0, 0);
}

/**
 * Get image data safely
 */
export function getImageData(
  ctx: CanvasRenderingContext2D,
  x: number,
  y: number,
  width: number,
  height: number
): ImageData | null {
  try {
    return ctx.getImageData(x, y, width, height);
  } catch (e) {
    console.error('Failed to get image data:', e);
    return null;
  }
}

/**
 * Put image data safely
 */
export function putImageData(
  ctx: CanvasRenderingContext2D,
  imageData: ImageData,
  x: number,
  y: number
): void {
  try {
    ctx.putImageData(imageData, x, y);
  } catch (e) {
    console.error('Failed to put image data:', e);
  }
}

/**
 * Convert canvas to blob
 */
export async function canvasToBlob(
  canvas: HTMLCanvasElement,
  type = 'image/png',
  quality = 1
): Promise<Blob | null> {
  return new Promise((resolve) => {
    canvas.toBlob((blob) => resolve(blob), type, quality);
  });
}

/**
 * Load image from URL
 */
export async function loadImage(url: string): Promise<HTMLImageElement> {
  return new Promise((resolve, reject) => {
    const img = new Image();
    img.crossOrigin = 'anonymous';
    img.onload = () => resolve(img);
    img.onerror = reject;
    img.src = url;
  });
}

/**
 * Load image from File
 */
export async function loadImageFromFile(file: File): Promise<HTMLImageElement> {
  const url = URL.createObjectURL(file);
  try {
    const img = await loadImage(url);
    URL.revokeObjectURL(url);
    return img;
  } catch (e) {
    URL.revokeObjectURL(url);
    throw e;
  }
}

/**
 * Draw grid on canvas
 */
export function drawGrid(
  ctx: CanvasRenderingContext2D,
  gridSize: number,
  color = 'rgba(0, 0, 0, 0.1)',
  width?: number,
  height?: number
): void {
  const w = width ?? ctx.canvas.width;
  const h = height ?? ctx.canvas.height;

  ctx.strokeStyle = color;
  ctx.lineWidth = 1;

  // Vertical lines
  for (let x = 0; x <= w; x += gridSize) {
    ctx.beginPath();
    ctx.moveTo(x + 0.5, 0);
    ctx.lineTo(x + 0.5, h);
    ctx.stroke();
  }

  // Horizontal lines
  for (let y = 0; y <= h; y += gridSize) {
    ctx.beginPath();
    ctx.moveTo(0, y + 0.5);
    ctx.lineTo(w, y + 0.5);
    ctx.stroke();
  }
}