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);
}
