draw2d: Instructions file for GitHub Copilot

Copilot Instructions for draw2d

Project Overview

draw2d is a Go 2D vector graphics library with multiple backends:

• draw2d — Core package: interfaces (GraphicContext, PathBuilder), types (Matrix, Path), and font management
• draw2dbase — Base implementations shared across backends (StackGraphicContext, flattener, stroker, dasher)
• draw2dimg — Raster image backend (using freetype-go)
• draw2dpdf — PDF backend (using gofpdf)
• draw2dsvg — SVG backend
• draw2dgl — OpenGL backend
• draw2dkit — Drawing helpers (Rectangle, Circle, Ellipse, RoundedRectangle)
• samples/ — Example drawings used as integration tests

Language and Conventions

• All code, comments, commit messages, and documentation must be written in English.
• The project uses Go 1.20+ (see go.mod).

Code Style

File Headers

Source files include a copyright header and creation date:

// Copyright 2010 The draw2d Authors. All rights reserved.
// created: 21/11/2010 by Laurent Le Goff

New files should follow the same pattern with the current date and author name.

Comments

• Exported types, functions, and methods must have GoDoc comments.
• Comments should start with the name of the thing being documented:

  // Rectangle draws a rectangle using a path between (x1,y1) and (x2,y2)
  func Rectangle(path draw2d.PathBuilder, x1, y1, x2, y2 float64) {
  

• Package comments go in the main source file or a doc.go file.

Naming

• Follow standard Go naming conventions (camelCase for unexported, PascalCase for exported).
• Backend packages are named draw2d<backend> (e.g., draw2dimg, draw2dpdf).
• The GraphicContext struct in each backend embeds *draw2dbase.StackGraphicContext.

Error Handling

• Functions that can fail return error as the last return value.
• Do not silently ignore errors — log or return them.

Testing

Structure

• Unit tests go alongside the source file they test (e.g., matrix_test.go tests matrix.go).
• Integration/sample tests live in samples_test.go, draw2dpdf/samples_test.go, etc.
• Test output files go in the output/ directory (generated, not committed).