public static WatermarkSettings FromConfig(WatermarkConfiguration config)
{
var settings = new WatermarkSettings
{
Position = config.Position ?? WatermarkPosition.BottomRight,
Text = config.Text
};
if (config.Colors is null || config.Colors.Count() == 0)
{
settings.Colors = new[] { SKColors.Red, SKColors.Purple };
}
public static IImageProcessingContext ApplyWatermark(this IImageProcessingContext processingContext, WatermarkConfiguration config)
{
if (config is null)
{
return(processingContext);
}
else if (!string.IsNullOrEmpty(config.SourceFile))
{
return(processingContext.ApplyWatermark(config.SourceFile, config.Opacity));
}
var settings = WatermarkSettings.FromConfig(config);
var size = processingContext.GetCurrentSize();
// Create a new image for the watermark layer.
using var watermark = new Image <Rgba32>(size.Width, size.Height);
var xOffeset = 0;
var yOffeset = 0;
watermark.Mutate(ctx =>
{
// Draw the watermark.
ctx.DrawWatermark(settings);
var angle = 0.0f;
if ((settings.Position == WatermarkPosition.BottomLeft) || (settings.Position == WatermarkPosition.TopRight))
{
angle = 45.0f;
// Calculate the x/y offsets for later when we draw the watermark on top of the source image.
xOffeset = -(int)((Math.Sin(angle) * (size.Width / 2)) / 2);
yOffeset = -(int)((Math.Sin(angle) * (size.Height / 2)) / 2);
}
else if ((settings.Position == WatermarkPosition.BottomRight) || (settings.Position == WatermarkPosition.TopLeft))
{
angle = -45.0f;
// Calculate the x/y offsets for later when we draw the watermark on top of the source image.
xOffeset = (int)((Math.Sin(angle) * (size.Width / 2)) / 2);
yOffeset = (int)((Math.Sin(angle) * (size.Height / 2)) / 2);
}
if (angle != 0)
{
ctx.Rotate(angle);
}
});
// Draw the watermark layer on top of the source image.
processingContext.DrawImage(watermark, new Point(xOffeset, yOffeset), 1);
return(processingContext);
}
private void DrawTextBanner(SKCanvas canvas, Context context)
{
// Undo the original scaling factor to simplify the rendering.
canvas.Scale(originalScale.X, originalScale.Y);
var settings = WatermarkSettings.FromConfig(configuration);
var bannerHeight = (float)(context.Size.Width / 4.5);
var(start, end) = GetBannerLocations(settings.Position, context.Size, (float)bannerHeight);
var shader = SKShader.CreateLinearGradient(
start,
end,
settings.Colors.Select(c => c.WithAlpha((byte)(0xFF * context.Opacity))).ToArray(),
null,
SKShaderTileMode.Clamp);
using var linePaint = new SKPaint
{
Shader = shader,
IsStroke = true,
StrokeWidth = bannerHeight,
Style = SKPaintStyle.Stroke
};
var path = new SKPath();
path.MoveTo(start);
path.LineTo(end);
canvas.DrawPath(path, linePaint);
using var textPaint = new SKPaint
{
Color = settings.TextColor.WithAlpha((byte)(0xFF * context.Opacity)),
TextAlign = SKTextAlign.Center,
Typeface = settings.Typeface
};
// Adjust TextSize property so text is 45% of the resulting image size.
var textWidth = textPaint.MeasureText(settings.Text);
textPaint.TextSize = 0.45f * context.Size.Width * textPaint.TextSize / textWidth;
// Find the text bounds
var textBounds = new SKRect();
// It may well be a Skia bug but it appears the measuring doesn't include the height of the descender characters in the measured height.
textPaint.MeasureText(StripDescenders(settings.Text), ref textBounds);
// Text drawn on the centre of the line so we need to bump it down to align the centre of the text.
canvas.DrawTextOnPath(settings.Text, path, 0, textBounds.Height / 2, textPaint);
}
// Colors: Red,Blue,Purple,#006666
private static IImageProcessingContext DrawWatermark(this IImageProcessingContext context, WatermarkSettings settings)
{
var imgSize = context.GetCurrentSize();
// measure the text size
var size = TextMeasurer.Measure(settings.Text, new RendererOptions(settings.TextFont));
//find out how much we need to scale the text to fill the space (up or down)
var scalingFactor = Math.Min(imgSize.Width / size.Width, imgSize.Height / size.Height) / 3;
//create a new settings.TextFont
var scaledFont = new Font(settings.TextFont, scalingFactor * settings.TextFont.Size);
var center = settings.Position switch
{
WatermarkPosition.Top => new PointF(imgSize.Width / 2, (imgSize.Height / 9)),
WatermarkPosition.TopLeft => new PointF(imgSize.Width / 2, (imgSize.Height / 9)),
WatermarkPosition.TopRight => new PointF(imgSize.Width / 2, (imgSize.Height / 9)),
_ => new PointF(imgSize.Width / 2, imgSize.Height - (imgSize.Height / 9)),
};
var textGraphicOptions = new TextGraphicsOptions(true)
{
HorizontalAlignment = HorizontalAlignment.Center,
VerticalAlignment = VerticalAlignment.Center,
};
// Apply Banner
context.DrawBanner(settings)
.DrawText(textGraphicOptions, settings.Text, scaledFont, settings.TextColor, center);
return(context);
}
private static IImageProcessingContext DrawBanner(this IImageProcessingContext context, WatermarkSettings settings)
{
var imgSize = context.GetCurrentSize();
var options = new GraphicsOptions(true, PixelColorBlendingMode.Normal, PixelAlphaCompositionMode.SrcOver, 1);
var points = new[] { new PointF(0, imgSize.Height), new PointF(imgSize.Width, imgSize.Height) };
var stop = 0;
IBrush brush = new LinearGradientBrush(
points[0],
points[1],
GradientRepetitionMode.Repeat,
settings.Colors.Select(x => new ColorStop(stop++, x)).ToArray());
var thickness = imgSize.Height / 4.5;
var center = imgSize.Height - thickness;
if ((settings.Position == WatermarkPosition.Top) || (settings.Position == WatermarkPosition.TopLeft) || (settings.Position == WatermarkPosition.TopRight))
{
points = new[] { new PointF(0, 0), new PointF(imgSize.Width, 0) };
}
var fullThickness = (float)(thickness * 2);
var pen = new Pen(brush, fullThickness);
var polygon = new Polygon(new LinearLineSegment(points));
return(context.Draw(options, pen, polygon));
}