Photo Popsicle Melt Filter Effect Tool

function processImage(originalImg, dripChanceParam = "0.005", minDripLengthParam = "10", maxDripLengthParam = "50") {
    // 1. Parameter parsing and sanitization
    // Parameters from the function signature might be strings (if default) or could be numbers/strings if passed by user.
    // parseFloat/parseInt conveniently handle both numbers and string representations of numbers.

    let dripChance = parseFloat(dripChanceParam);
    // Validate dripChance: should be a probability between 0 and 1.
    if (isNaN(dripChance) || dripChance < 0 || dripChance > 1) {
        dripChance = 0.005; // Default value if parsing fails or value is out of range.
    }

    let minDripLength = parseInt(minDripLengthParam);
    // Validate minDripLength: should be at least 1.
    if (isNaN(minDripLength) || minDripLength < 1) {
        minDripLength = 10; // Default value if parsing fails or value is less than 1.
    }

    let maxDripLength = parseInt(maxDripLengthParam);
    // Validate maxDripLength: should be a number.
    if (isNaN(maxDripLength)) {
        maxDripLength = 50; // Default value if parsing fails.
    }
    
    // Ensure maxDripLength is not less than minDripLength.
    if (maxDripLength < minDripLength) {
        maxDripLength = minDripLength; // Adjust maxDripLength if it's smaller than the (potentially adjusted) minDripLength.
    }

    // 2. Canvas setup
    const canvas = document.createElement('canvas');
    // Add willReadFrequently attribute for potential performance optimization on repeated getImageData calls.
    const ctx = canvas.getContext('2d', { willReadFrequently: true }); 
    
    // Use naturalWidth/naturalHeight to get the original image dimensions, not CSS-scaled dimensions.
    const width = originalImg.naturalWidth || originalImg.width;
    const height = originalImg.naturalHeight || originalImg.height;

    // Handle cases where the image might not have loaded or has zero dimensions.
    if (width === 0 || height === 0) {
        canvas.width = 0;
        canvas.height = 0;
        return canvas; // Return an empty, zero-size canvas.
    }

    canvas.width = width;
    canvas.height = height;

    // 3. Image data processing
    // Draw the original image onto the canvas. This is the surface we'll read pixels from.
    ctx.drawImage(originalImg, 0, 0, width, height);
    
    let sourceImageData;
    try {
        // Attempt to get the pixel data from the canvas.
        sourceImageData = ctx.getImageData(0, 0, width, height);
    } catch (e) {
        // This error can occur if the image is loaded from a different origin (CORS issue)
        // and the server's CORS policy doesn't allow cross-origin data access.
        console.error("Failed to get image data, possibly due to CORS policy. The effect cannot be applied.", e);
        // In this scenario, return the canvas with only the original image drawn, as the effect cannot proceed.
        return canvas;
    }
    
    // Create a new ImageData object to store the pixels of the modified image.
    const targetImageData = ctx.createImageData(width, height);
    
    // Initialize targetImageData by copying all pixels from sourceImageData.
    // This ensures that pixels not affected by a "drip" will retain their original color from the source image.
    targetImageData.data.set(sourceImageData.data);

    const sourceData = sourceImageData.data; // A Uint8ClampedArray view of the source image's pixel data.
    const targetData = targetImageData.data; // A Uint8ClampedArray view for the target image's pixel data.

    // 4. Apply the "Popsicle Melt" (drip) effect
    // Iterate over each column of pixels in the image.
    for (let x = 0; x < width; x++) {
        // Iterate over each row of pixels in the current column.
        for (let y = 0; y < height; y++) {
            // With a certain probability (dripChance), a drip will start from the current pixel (x, y).
            if (Math.random() < dripChance) {
                // Calculate a random length for this specific drip, within the min/max bounds.
                const currentDripLength = Math.floor(Math.random() * (maxDripLength - minDripLength + 1)) + minDripLength;
                
                // Get the color (RGBA) of the source pixel that initiates this drip.
                // The index calculation maps 2D (x,y) coordinates to a 1D array index. Each pixel uses 4 array elements (R,G,B,A).
                const srcPixelIndex = (y * width + x) * 4; 
                const r = sourceData[srcPixelIndex];     // Red component
                const g = sourceData[srcPixelIndex + 1]; // Green component
                const b = sourceData[srcPixelIndex + 2]; // Blue component
                const a = sourceData[srcPixelIndex + 3]; // Alpha (transparency) component

                // "Paint" the drip downwards from the current pixel (x,y) using its color.
                for (let offsetY = 0; offsetY < currentDripLength; offsetY++) {
                    const dripY = y + offsetY; // Calculate the Y-coordinate for the current segment of the drip.
                    
                    // Ensure the drip segment is still within the image's vertical bounds.
                    if (dripY < height) {
                        const targetPixelIndex = (dripY * width + x) * 4;
                        targetData[targetPixelIndex]     = r;
                        targetData[targetPixelIndex + 1] = g;
                        targetData[targetPixelIndex + 2] = b;
                        targetData[targetPixelIndex + 3] = a;
                    } else {
                        // The drip has extended beyond the bottom edge of the image; stop this drip.
                        break; 
                    }
                }
            }
        }
    }

    // 5. Put the modified image data (targetImageData) back onto the canvas.
    ctx.putImageData(targetImageData, 0, 0);

    // 6. Return the canvas element with the applied effect.
    return canvas;
}