Change color theme in Xamarin.iOS viewer

PDFViewCtrl has three special color modes: night mode, inverted color mode, and custom color mode. In night mode, colors are adjusted to improve reading at night, in inverted color mode, all colors are inverted, and in custom color mode, you can set a custom color for text and the background color.

To set the color mode:

1. Find the constant value of the color mode

   Color mode	Constant value
   Normal color mode	PDFRasterizer.ColorPostProcessMode.e_postprocess_none
   Night mode	PDFRasterizer.ColorPostProcessMode.e_postprocess_night_mode
   Inverted color mode	PDFRasterizer.ColorPostProcessMode.e_postprocess_invert
   Custom color mode	PDFRasterizer.ColorPostProcessMode.e_postprocess_gradient_map

2. Call SetColorPostProcessMode.

3. Optionally, set the PDFViewCtrl background color for the best visual result. You can set background color by calling SetClientBackgroundColor (Xamarin.Android) or SetBackgroundColor (Xamarin.iOS).

   

   For example, set the background color to black for night mode:

   // Xamarin.Android
   mPdfViewCtrl.SetClientBackgroundColor(0, 0, 0, false);
   
   // Xamarin.iOS
   mPdfViewCtrl.SetBackgroundColor(0, 0, 0, false);

4. If you are using postprocess_gradient_map, call PDFViewCtrl.SetColorPostProcessColors to set the white and black points. For example, for a sepia effect, try:

   // Xamarin.Android
   var darkBrown = Android.Graphics.Color.Rgb(61, 38, 10);
   var lightBrown = Android.Graphics.Color.Rgb(245, 224, 202);
   mPdfViewCtrl.SetColorPostProcessColors(lightBrown, darkBrown);
   
   // Xamarin.iOS
   var darkBrown = new UIKit.UIColor(0.24f, 0.15f, 0.04f, 1.0f);
   var lightBrown = new UIKit.UIColor(0.96f, 0.88f, 0.79f, 1.0f);
   mPdfViewCtrl.SetColorPostProcessColors(lightBrown, darkBrown);

5. Update PDFViewCtrl to redraw the contents:

   mPdfViewCtrl.Update(true);

   Sample result when using postprocess_gradient_map and a light/dark brown for the white/black color: