LlamaCasty/Services/ChatBoxRenderer.cs

using System.Globalization;
using System.Windows;
using System.Windows.Media;
using System.Windows.Media.Imaging;
using ytLive.Models;

namespace ytLive.Services;

/// <summary>
/// Renders chat messages into a VideoFrame for the chat overlay on stream.
/// Uses WPF's FormattedText + RenderTargetBitmap to produce BGRA8 output.
/// </summary>
public sealed class ChatBoxRenderer
{
    private static readonly CultureInfo InvariantCulture = CultureInfo.InvariantCulture;

    /// <summary>
    /// Render the last N messages into a VideoFrame at the specified dimensions.
    /// Messages are drawn bottom-up (newest at bottom, oldest at top) with
    /// configurable font, colors, and background.
    /// </summary>
    public VideoFrame Render(
        IReadOnlyList<ChatMessage> messages,
        int width,
        int height,
        double fontSize,
        string fontFamily,
        string fontColorHex,
        string backgroundColorHex,
        int maxMessages,
        bool showTimestamps,
        bool showBadges,
        string memberColorHex,
        string superChatColorHex)
    {
        var dpi = 96.0;
        var visual = new DrawingVisual();

        using (var ctx = visual.RenderOpen())
        {
            // Background
            var bgColor = ParseColor(backgroundColorHex);
            ctx.DrawRectangle(
                new SolidColorBrush(bgColor),
                null,
                new Rect(0, 0, width, height));

            if (messages.Count == 0)
                return CreateFrame(visual, width, height, dpi);

            // Layout parameters
            var lineHeight = fontSize * 1.4;
            var padding = 8.0;
            var maxVisibleLines = (int)((height - padding * 2) / lineHeight);
            if (maxVisibleLines < 1) maxVisibleLines = 1;

            // Take the last N messages that fit
            var visibleMessages = new List<(ChatMessage msg, string text, Brush brush)>();
            var totalLines = 0;

            for (var i = messages.Count - 1; i >= 0 && visibleMessages.Count < maxMessages; i--)
            {
                var msg = messages[i];
                var brush = GetMessageBrush(msg, fontColorHex, memberColorHex, superChatColorHex);
                var text = FormatMessage(msg, showTimestamps, showBadges);
                var lineCount = EstimateLineCount(text, fontSize, width - padding * 2);
                if (totalLines + lineCount > maxVisibleLines) break;
                totalLines += lineCount;
                visibleMessages.Add((msg, text, brush));
            }

            visibleMessages.Reverse();

            // Draw messages bottom-up
            var y = height - padding;
            for (var i = visibleMessages.Count - 1; i >= 0; i--)
            {
                var (_, text, brush) = visibleMessages[i];
                var formatted = new FormattedText(
                    text,
                    InvariantCulture,
                    FlowDirection.LeftToRight,
                    new Typeface(new FontFamily(fontFamily), FontStyles.Normal, FontWeights.Normal, FontStretches.Normal),
                    fontSize,
                    brush,
                    dpi);

                formatted.MaxTextWidth = width - padding * 2;
                formatted.Trimming = TextTrimming.CharacterEllipsis;

                y -= formatted.Height;
                ctx.DrawText(formatted, new Point(padding, y));
            }
        }

        return CreateFrame(visual, width, height, dpi);
    }

    private static string FormatMessage(ChatMessage msg, bool showTimestamps, bool showBadges)
    {
        var parts = new List<string>();

        if (showTimestamps)
            parts.Add($"[{msg.Timestamp:HH:mm}]");

        if (showBadges)
        {
            if (msg.IsSuperChat)
                parts.Add("💰");
            else if (msg.IsMember)
                parts.Add("⭐");
        }

        parts.Add($"{msg.AuthorName}: {msg.Message}");
        return string.Join(" ", parts);
    }

    private static int EstimateLineCount(string text, double fontSize, double maxWidth)
    {
        // Rough estimate: ~12 chars per 100px at font size 16
        var charsPerLine = (int)(maxWidth / (fontSize * 0.6));
        if (charsPerLine < 1) charsPerLine = 1;
        return Math.Max(1, (int)Math.Ceiling((double)text.Length / charsPerLine));
    }

    private static Brush GetMessageBrush(ChatMessage msg, string fontColorHex, string memberColorHex, string superChatColorHex)
    {
        if (msg.IsSuperChat)
            return new SolidColorBrush(ParseColor(superChatColorHex));
        if (msg.IsMember)
            return new SolidColorBrush(ParseColor(memberColorHex));
        return new SolidColorBrush(ParseColor(fontColorHex));
    }

    private static Color ParseColor(string hex)
    {
        hex = hex.Trim().TrimStart('#');
        if (hex.Length == 6)
        {
            var r = byte.Parse(hex.AsSpan(0, 2), NumberStyles.HexNumber);
            var g = byte.Parse(hex.AsSpan(2, 2), NumberStyles.HexNumber);
            var b = byte.Parse(hex.AsSpan(4, 2), NumberStyles.HexNumber);
            return Color.FromRgb(r, g, b);
        }
        if (hex.Length == 8)
        {
            var a = byte.Parse(hex.AsSpan(0, 2), NumberStyles.HexNumber);
            var r = byte.Parse(hex.AsSpan(2, 2), NumberStyles.HexNumber);
            var g = byte.Parse(hex.AsSpan(4, 2), NumberStyles.HexNumber);
            var b = byte.Parse(hex.AsSpan(6, 2), NumberStyles.HexNumber);
            return Color.FromArgb(a, r, g, b);
        }
        return Colors.White;
    }

    private static VideoFrame CreateFrame(DrawingVisual visual, int width, int height, double dpi)
    {
        var rtb = new RenderTargetBitmap(width, height, dpi, dpi, PixelFormats.Pbgra32);
        rtb.Render(visual);

        var stride = width * 4;
        var pixels = new byte[stride * height];
        rtb.CopyPixels(pixels, stride, 0);

        // Pbgra32 → Bgra8: swap R and B channels (Pbgra premultiplies alpha but
        // for opaque backgrounds the swap is all we need)
        for (var i = 0; i < pixels.Length; i += 4)
        {
            (pixels[i], pixels[i + 2]) = (pixels[i + 2], pixels[i]);
        }

        return new VideoFrame(width, height, pixels);
    }
}