[Skia][Wasm] Missing methods in current Skia implementation

[jeromelaban]

Description

Mono provides two ways for interoperating with native WebAssembly: Dynamic Linking for interpreter-only builds and Static Linking for AOT enabled builds.

Static linking is currently not working, and is being tracked by this issue [link].

Dynamic linking relies on a generated table of method invocations, to give the ability to invoke wasm methods, which the signatures must be known in advance.

Problem

The list of methods used by SkiaSharp to interop with the C++ Skia API contains signatures that are not provided by this mono file. Modifiying this file to add missing signatures is currently not an option because of this emscripten issue: emscripten-core/emscripten#8770, which breaks the compilation of the release-dynamic runtime configuration in mono,

Workaround

The workaround consist in adjusting the signatures of the Skia API to match known signatures of the m2n wrapper, and transform parameters into structures if no signature adjustment is possible.

Methods to adjust

Signatures to transform into structures

• FIIII :
  System.Single SkiaSharp.SkiaApi::sk_paint_measure_text(System.IntPtr,System.IntPtr,System.IntPtr,SkiaSharp.SKRect&)
• FIIII :
  System.Single SkiaSharp.SkiaApi::sk_paint_measure_text(System.IntPtr,System.IntPtr,System.IntPtr,System.IntPtr)
• FIIF :
  System.Single SkiaSharp.SkiaApi::sk_paint_get_fontmetrics(System.IntPtr,SkiaSharp.SKFontMetrics&,System.Single)
• FIIF :
  System.Single SkiaSharp.SkiaApi::sk_paint_get_fontmetrics(System.IntPtr,System.IntPtr,System.Single)
• VIFFFIIFF :
  System.Void SkiaSharp.SkiaApi::sk_path_arc_to(System.IntPtr,System.Single,System.Single,System.Single,SkiaSharp.SKPathArcSize,SkiaSharp.SKPathDirection,System.Single,System.Single)
• VIFFFIIFF :
  System.Void SkiaSharp.SkiaApi::sk_path_rarc_to(System.IntPtr,System.Single,System.Single,System.Single,SkiaSharp.SKPathArcSize,SkiaSharp.SKPathDirection,System.Single,System.Single)
• IFFFFIIII :
  System.IntPtr SkiaSharp.SkiaApi::sk_imagefilter_new_drop_shadow(System.Single,System.Single,System.Single,System.Single,System.UInt32,SkiaSharp.SKDropShadowImageFilterShadowMode,System.IntPtr,System.IntPtr)
• IFFFFIIII :
  System.IntPtr SkiaSharp.SkiaApi::sk_imagefilter_new_arithmetic(System.Single,System.Single,System.Single,System.Single,System.Boolean,System.IntPtr,System.IntPtr,System.IntPtr)
• IIFIFIIIII :
  System.IntPtr SkiaSharp.SkiaApi::sk_shader_new_two_point_conical_gradient(SkiaSharp.SKPoint&,System.Single,SkiaSharp.SKPoint&,System.Single,SkiaSharp.SKColor[],System.Single[],System.Int32,SkiaSharp.SKShaderTileMode,SkiaSharp.SKMatrix&)
• IIFIFIIIII :
  System.IntPtr SkiaSharp.SkiaApi::sk_shader_new_two_point_conical_gradient(SkiaSharp.SKPoint&,System.Single,SkiaSharp.SKPoint&,System.Single,SkiaSharp.SKColor[],System.Single[],System.Int32,SkiaSharp.SKShaderTileMode,System.IntPtr)
• IIFIFIIIII :
  System.IntPtr SkiaSharp.SkiaApi::sk_shader_new_two_point_conical_gradient(SkiaSharp.SKPoint&,System.Single,SkiaSharp.SKPoint&,System.Single,SkiaSharp.SKColor[],System.IntPtr,System.Int32,SkiaSharp.SKShaderTileMode,SkiaSharp.SKMatrix&)
• IIFIFIIIII :
  System.IntPtr SkiaSharp.SkiaApi::sk_shader_new_two_point_conical_gradient(SkiaSharp.SKPoint&,System.Single,SkiaSharp.SKPoint&,System.Single,SkiaSharp.SKColor[],System.IntPtr,System.Int32,SkiaSharp.SKShaderTileMode,System.IntPtr)
• IIIFFFII :
  System.IntPtr SkiaSharp.SkiaApi::sk_imagefilter_new_distant_lit_specular(SkiaSharp.SKPoint3&,System.UInt32,System.Single,System.Single,System.Single,System.IntPtr,System.IntPtr)
• IIIFFFII :
  System.IntPtr SkiaSharp.SkiaApi::sk_imagefilter_new_point_lit_specular(SkiaSharp.SKPoint3&,System.UInt32,System.Single,System.Single,System.Single,System.IntPtr,System.IntPtr)
• FIII :
  System.Single SkiaSharp.SkiaApi::sk_matrix44_get(System.IntPtr,System.Int32,System.Int32)
• IIIFFIFFFII :
  System.IntPtr SkiaSharp.SkiaApi::sk_imagefilter_new_spot_lit_specular(SkiaSharp.SKPoint3&,SkiaSharp.SKPoint3&,System.Single,System.Single,System.UInt32,System.Single,System.Single,System.Single,System.IntPtr,System.IntPtr)
• IIIFFIIIII :
  System.IntPtr SkiaSharp.SkiaApi::sk_imagefilter_new_matrix_convolution(SkiaSharp.SKSizeI&,System.Single[],System.Single,System.Single,SkiaSharp.SKPointI&,SkiaSharp.SKMatrixConvolutionTileMode,System.Boolean,System.IntPtr,System.IntPtr)
• FIFFF :
  System.Single SkiaSharp.SkiaApi::sk_3dview_dot_with_normal(System.IntPtr,System.Single,System.Single,System.Single)
• VIIIFFIIII :
  System.Void SkiaSharp.SkiaApi::sk_textblob_builder_alloc_run_text(System.IntPtr,System.IntPtr,System.Int32,System.Single,System.Single,System.Int32,System.IntPtr,SkiaSharp.SKRect*,SkiaSharp.SKTextBlobBuilderRunBuffer&)
• VIIIFIIII :
  System.Void SkiaSharp.SkiaApi::sk_textblob_builder_alloc_run_text_pos_h(System.IntPtr,System.IntPtr,System.Int32,System.Single,System.Int32,System.IntPtr,SkiaSharp.SKRect*,SkiaSharp.SKTextBlobBuilderRunBuffer&)

Object based signatures

• IIIO :
  System.Boolean SkiaSharp.SkiaApi::sk_webpencoder_encode(System.IntPtr,System.IntPtr,SkiaSharp.SKWebpEncoderOptions)
• IIIO :
  System.Boolean SkiaSharp.SkiaApi::sk_jpegencoder_encode(System.IntPtr,System.IntPtr,SkiaSharp.SKJpegEncoderOptions)
• IIIO :
  System.Boolean SkiaSharp.SkiaApi::sk_pngencoder_encode(System.IntPtr,System.IntPtr,SkiaSharp.SKPngEncoderOptions)

[gritsenko]

sk_paint_measure_text and sk_pngencoder_encode are pretty important also...

[jeromelaban]

sk_paint_measure_text is now in the latest nuget package.

pngencoder has a particularity with the way parameters are passed in, it'll have to be handled differently.

[jeromelaban]

This issue can now be closed as the support for mono has improved for those scenarios.