Image Space Dust Filter Effect Creator

function processImage(originalImg, dustColor = "rgba(255, 255, 255, 0.8)", dustDensity = 0.05, dustSizeMin = 1, dustSizeMax = 3) {
    const canvas = document.createElement('canvas');
    const ctx = canvas.getContext('2d');

    const imgWidth = originalImg.naturalWidth || originalImg.width;
    const imgHeight = originalImg.naturalHeight || originalImg.height;

    if (imgWidth === 0 || imgHeight === 0) {
        console.error("Image Space Dust Filter Effect: Original image has zero dimensions. Is it loaded correctly?");
        // Return a tiny, effectively empty canvas to avoid errors downstream.
        canvas.width = 1;
        canvas.height = 1;
        return canvas;
    }

    canvas.width = imgWidth;
    canvas.height = imgHeight;

    // Draw the original image onto the canvas
    ctx.drawImage(originalImg, 0, 0, canvas.width, canvas.height);

    // --- Parameter Sanitization and Processing ---
    // Default values are set by the JavaScript engine if corresponding parameters are `undefined`.
    // This section validates and finalizes the parameters, handling cases like:
    // - Explicitly passed `null` or values of incorrect types (e.g., string for a number).
    // - Numeric values that are outside acceptable ranges (e.g., negative density).

    let finalDustColor;
    let finalDustDensity;
    let finalDustSizeMin;
    let finalDustSizeMax;

    // Validate dustColor: must be a non-empty string.
    if (typeof dustColor === 'string' && dustColor.trim() !== "") {
        finalDustColor = dustColor;
    } else {
        finalDustColor = "rgba(255, 255, 255, 0.8)"; // Default from signature
    }
    
    // Validate dustDensity: must be a non-negative number.
    const numDustDensity = Number(dustDensity); // Attempt to convert to number
    if (!isNaN(numDustDensity) && numDustDensity >= 0) {
        finalDustDensity = numDustDensity;
    } else {
        finalDustDensity = 0.05; // Default from signature
    }

    // Validate dustSizeMin: must be a positive number.
    const numDustSizeMin = Number(dustSizeMin); // Attempt to convert
    if (!isNaN(numDustSizeMin) && numDustSizeMin > 0) {
        finalDustSizeMin = numDustSizeMin;
    } else {
        finalDustSizeMin = 1; // Default from signature
    }

    // Validate dustSizeMax: must be a positive number.
    const numDustSizeMax = Number(dustSizeMax); // Attempt to convert
    if (!isNaN(numDustSizeMax) && numDustSizeMax > 0) {
        finalDustSizeMax = numDustSizeMax;
    } else {
        finalDustSizeMax = 3; // Default from signature
    }
    
    // Ensure min size is not greater than max size. If so, swap them.
    if (finalDustSizeMin > finalDustSizeMax) {
        [finalDustSizeMin, finalDustSizeMax] = [finalDustSizeMax, finalDustSizeMin];
    }
    // --- End Parameter Processing ---

    // Calculate the total number of dust particles based on density and image area.
    const numDustParticles = Math.floor(canvas.width * canvas.height * finalDustDensity);
    
    ctx.fillStyle = finalDustColor;

    for (let i = 0; i < numDustParticles; i++) {
        // Generate a random position for the dust particle
        const x = Math.random() * canvas.width;
        const y = Math.random() * canvas.height;
        
        // Generate a random size for the dust particle within the specified range.
        // Size is in [finalDustSizeMin, finalDustSizeMax).
        // If finalDustSizeMin equals finalDustSizeMax, particleSize will be exactly finalDustSizeMin.
        const particleSize = Math.random() * (finalDustSizeMax - finalDustSizeMin) + finalDustSizeMin;
        
        // Draw the dust particle (a small square).
        // Offset x and y by half the particle size to center the particle at (x, y).
        ctx.fillRect(x - particleSize / 2, y - particleSize / 2, particleSize, particleSize);
    }

    return canvas;
}