feat: add RenderSingleSeriesToPng for standalone underlying chart

CertReports.Syncfusion/Services/Implementations/SkiaChartRendererV2.cs

@@ -187,6 +187,130 @@ public static class SkiaChartRendererV2
         return imgData.ToArray();
     }
 
+    // ═══════════════════════════════════════════════════════════════════
+    // Entry point — grafico standalone singolo sottostante (no certificato)
+    // ═══════════════════════════════════════════════════════════════════
+
+    public static byte[] RenderSingleSeriesToPng(UnderlyingChartData data, int width = 1100, int height = 700, bool jpeg = false)
+    {
+        using var surface = SKSurface.Create(new SKImageInfo(width, height));
+        var canvas = surface.Canvas;
+        canvas.Clear(SKColors.White);
+
+        float titleBottom = DrawUnderlyingTitle(canvas, width, data.Nome);
+
+        float marginLeft   = 70;
+        float marginRight  = 40;
+        float marginTop    = titleBottom + 10;
+        float marginBottom = 45;
+
+        var plotArea = new SKRect(marginLeft, marginTop, width - marginRight, height - marginBottom);
+
+        var points = data.Points.OrderBy(p => p.Date).ToList();
+        if (points.Count == 0)
+            return Array.Empty<byte>();
+
+        DateTime minDate = points[0].Date;
+        DateTime maxDate = points[^1].Date;
+        double minY = (double)points.Min(p => p.Px);
+        double maxY = (double)points.Max(p => p.Px);
+        double range = maxY - minY;
+        if (range == 0) range = Math.Max(minY * 0.1, 1);
+        double margin = range * 0.1;
+        minY -= margin;
+        maxY += margin;
+
+        DrawGrid(canvas, plotArea, minDate, maxDate, minY, maxY);
+        DrawUnderlyingAxisLabels(canvas, plotArea, minDate, maxDate, minY, maxY);
+        DrawUnderlyingSeries(canvas, plotArea, points, minDate, maxDate, minY, maxY);
+
+        using var borderPaint = new SKPaint
+        {
+            Color = SKColors.Gray, StrokeWidth = 1,
+            Style = SKPaintStyle.Stroke, IsAntialias = true,
+        };
+        canvas.DrawRect(plotArea, borderPaint);
+
+        using var image = surface.Snapshot();
+        using var imgData = jpeg
+            ? image.Encode(SKEncodedImageFormat.Jpeg, 90)
+            : image.Encode(SKEncodedImageFormat.Png, 95);
+        return imgData.ToArray();
+    }
+
+    private static float DrawUnderlyingTitle(SKCanvas canvas, int width, string nome)
+    {
+        float y = 15f;
+        var boldFont = CreateFont(13f, bold: true);
+        using var titlePaint = new SKPaint { Color = TitleColor, IsAntialias = true };
+        canvas.DrawText(nome, width / 2f, y + 13, SKTextAlign.Center, boldFont, titlePaint);
+        return y + 22 + 5;
+    }
+
+    private static void DrawUnderlyingAxisLabels(SKCanvas canvas, SKRect area,
+        DateTime minDate, DateTime maxDate, double minY, double maxY)
+    {
+        var font = CreateFont(11);
+        using var paint = new SKPaint { Color = SKColors.DimGray, IsAntialias = true };
+
+        int ySteps = 8;
+        for (int i = 0; i <= ySteps; i++)
+        {
+            double val = maxY - ((maxY - minY) / ySteps) * i;
+            float y = area.Top + (area.Height / ySteps) * i;
+            canvas.DrawText($"{val:F2}", area.Left - 55, y + 4, SKTextAlign.Left, font, paint);
+        }
+
+        double totalDays = (maxDate - minDate).TotalDays;
+        int intervalMonths = XAxisIntervalMonths(minDate, maxDate);
+        string fmt = totalDays > 365 ? "MMM yy" : "dd/MM/yy";
+
+        if (intervalMonths > 0)
+        {
+            var d = XAxisStart(minDate, intervalMonths);
+            while (d <= maxDate)
+            {
+                float x = DateToX(d, area, minDate, maxDate);
+                if (x >= area.Left && x <= area.Right)
+                    canvas.DrawText(d.ToString(fmt), x, area.Bottom + 20, SKTextAlign.Center, font, paint);
+                d = d.AddMonths(intervalMonths);
+            }
+        }
+        else
+        {
+            canvas.DrawText(minDate.ToString("dd/MM/yy"), area.Left,  area.Bottom + 20, SKTextAlign.Left,  font, paint);
+            canvas.DrawText(maxDate.ToString("dd/MM/yy"), area.Right, area.Bottom + 20, SKTextAlign.Right, font, paint);
+        }
+    }
+
+    private static void DrawUnderlyingSeries(SKCanvas canvas, SKRect area,
+        List<UnderlyingChartPoint> points,
+        DateTime minDate, DateTime maxDate, double minY, double maxY)
+    {
+        using var paint = new SKPaint
+        {
+            Color = CertColor, StrokeWidth = 2f,
+            Style = SKPaintStyle.Stroke, IsAntialias = true,
+            StrokeCap = SKStrokeCap.Round, StrokeJoin = SKStrokeJoin.Round,
+        };
+
+        using var path = new SKPath();
+        bool first = true;
+        foreach (var pt in points)
+        {
+            float x = DateToX(pt.Date, area, minDate, maxDate);
+            float y = ValueToY((double)pt.Px, area, minY, maxY);
+            y = Math.Max(area.Top, Math.Min(area.Bottom, y));
+            if (first) { path.MoveTo(x, y); first = false; }
+            else path.LineTo(x, y);
+        }
+
+        canvas.Save();
+        canvas.ClipRect(area);
+        canvas.DrawPath(path, paint);
+        canvas.Restore();
+    }
+
     // ═══════════════════════════════════════════════════════════════════
     // Titolo
     // ═══════════════════════════════════════════════════════════════════