Infcanvas

A drawing app with unlimited canvas size and scriptable brush pipeline

Because of default flutter engine not exposing relevant skia resources (SkImage, GPU Backed SkCanvas, SkRuntimeEffect, etc.), a modified flutter engine is used. Please follown the instructions to compile and use a custom built engine.

Because of iOS sandbox restrictions,JIT based interpreters (C# Mono, dotnet, even DartVM) cannot be used. A Direct Call Threading interpreter is implemented to run the scriptable brush pipeline, targeting resonable performance and easy host integration.

Quadtree

children index

 tl | tr
 00 | 01
----+---->
 bl | br
 10 | 11
    V


canvas size = 2^3 = 8
          tree          LoD   depth                    offsets
       ____+____               0  <--root                +0    1 << (0-1)
      /         \		   	   
    _+_         _+_            1                         +1    1 << (1-1)
   /   \       /   \	   	   
  +     +     +     +          2                         +2    1 << (2-1)
 / \   / \   / \   / \	   	   
#   # #   # #   # #   #   0    3  <--originDepth         +4    1 << (3-1)
|   | |   | |   | |   |   1       <--subdivide nodes
|   | |   | |   | |   |   2
|   | |   | |   | |   |   3..
indices:                       index + offset = tree path
-4  -3-2  -1 0   1 2   3
MSB:                       
 2   2 1   0 0   1 2   2

Interpreter

A direct call threading interpreter with generational GC. goto repo.

Screenshots

Scriptable Brush Pipeline

Unlimited Canvas Size

File Structure

• utilities : Self contained function blocks, no dependencies outside its own folder
  • async : async guards, task schedulers, etc.
  • serializer : simple object serializer
  • storage : Application state saving and loading, amongst other io related functions
• widgets : Reusable visual elements
  • functional : Parts that serves a specific functional need, like tree view
  • visual : Vanilla widgets that are customized visually
• scripting : Visual scripting module
  • editor : VM Code editor and compilers
  • shader_editor : Shader code editor and compilers
• canvas : The work horse of the canvas UI system frontends
  • tools : Canvas UI tool plugins, like brush system, color palette, canvas viewer. Other tools like line guides, color picker, paint bucket are to be added.
• brush_manager : Glue logic between file system and tree viewer widget to
  manage brush data saved on disk

TODO

Please refer to TODO.md

ISSUES

• Canvas viewport zooming mechanism is not accurate enough during LoD changes
• Increase VM robustness, capture VM errors as complete as possible ( No exception support in flutter engine project, sadly ), or the whole application will crash.
• Handle VM null access scenarios during script execution. Maybe exception handling needs to be added to VM?
• Since flutter 2.2, the cross-context image passing trick no longer works. Currently viewport snapshot images needs to be transfered GPU -> CPU -> GPU to be used from dart safely, which tanked performance. Currently SkPictureRecorder is used to record tree node layout during snapshot generation.

Stretch Goals

• Freeform transforming
• Selection and masking
• Cut Copy Paste pixels
• Other sophisticated image processing (e.g. flood fill) tools which requires CPU support
• PSD file format support?
• Custom plugin support, since we already have a VM script runtime for brush pipeline. A major overhaul of the vm interpreter is needed though, as well as a compiler frontend and a well-ish defined scripting api are needed.

Flutter Application

This project is a starting point for a Flutter application.

A few resources to get you started if this is your first Flutter project:

• Lab: Write your first Flutter app
• Cookbook: Useful Flutter samples

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