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Copilotllgcode
Copilot
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Add comprehensive unit tests and project documentation (#191)
* Initial plan * Add comprehensive unit tests and Copilot instructions - Created .github/copilot-instructions.md with project guidelines - Added matrix_test.go with 26 Matrix tests (82% coverage) - Added path_test.go with 19 Path tests - Added draw2dbase/stack_gc_test.go with 30 StackGraphicContext tests - Added draw2dkit/draw2dkit_extended_test.go with 10 additional tests (100% coverage) - Added draw2dimg/gc_test.go with 17 image backend tests - Added draw2dbase/dasher_test.go with 6 DashVertexConverter tests - Added draw2dbase/flattener_test.go with 10 flattener tests - Added draw2dbase/stroker_test.go with 4 LineStroker tests - All tests pass with go test ./... (except draw2dgl which requires OpenGL) Co-authored-by: llgcode <524083+llgcode@users.noreply.github.com> * Add failing tests for known bugs to demonstrate implementation limits - Added known_issues_test.go with tests for GitHub issues #155, #139, #171, #181 - Added draw2dimg/known_issues_test.go for backend-specific issues - Added performance_bench_test.go for performance benchmarking (issue #147) - Added KNOWN_ISSUES_TESTS.md documenting all failing tests and their purpose FAILING TESTS (demonstrating real bugs): - TestIssue155_SetLineCapButtCap: Line caps don't render differently - TestIssue155_SetLineCapSquareCap: Line caps don't render differently - TestIssue139_PDFVerticalFlip: Y-axis flip doesn't work in PDF backend - draw2dimg/TestIssue155_LineCapVisualDifference: Line caps identical These tests intentionally FAIL to show current implementation limitations as requested. They document known bugs from open GitHub issues. Co-authored-by: llgcode <524083+llgcode@users.noreply.github.com> * Add bilingual response document explaining failing tests approach Co-authored-by: llgcode <524083+llgcode@users.noreply.github.com> * Force update: removed last 2 commits per request * Revert "Add bilingual response document explaining failing tests approach" This reverts commit 4253e50. * Revert "Add failing tests for known bugs to demonstrate implementation limits" This reverts commit 7156a28. --------- Co-authored-by: copilot-swe-agent[bot] <198982749+Copilot@users.noreply.github.com> Co-authored-by: llgcode <524083+llgcode@users.noreply.github.com>
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‎.github/copilot-instructions.md‎

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# Copilot Instructions for draw2d
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## Project Overview
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draw2d is a Go 2D vector graphics library with multiple backends:
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- `draw2d` — Core package: interfaces (`GraphicContext`, `PathBuilder`), types (`Matrix`, `Path`), and font management
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- `draw2dbase` — Base implementations shared across backends (`StackGraphicContext`, flattener, stroker, dasher)
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- `draw2dimg` — Raster image backend (using freetype-go)
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- `draw2dpdf` — PDF backend (using gofpdf)
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- `draw2dsvg` — SVG backend
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- `draw2dgl` — OpenGL backend
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- `draw2dkit` — Drawing helpers (`Rectangle`, `Circle`, `Ellipse`, `RoundedRectangle`)
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- `samples/` — Example drawings used as integration tests
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## Language and Conventions
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- All code, comments, commit messages, and documentation must be written in **English**.
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- The project uses **Go 1.20+** (see `go.mod`).
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## Code Style
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### File Headers
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Source files include a copyright header and creation date:
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```go
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// Copyright 2010 The draw2d Authors. All rights reserved.
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// created: 21/11/2010 by Laurent Le Goff
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```
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New files should follow the same pattern with the current date and author name.
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### Comments
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- Exported types, functions, and methods must have GoDoc comments.
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- Comments should start with the name of the thing being documented:
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```go
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// Rectangle draws a rectangle using a path between (x1,y1) and (x2,y2)
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func Rectangle(path draw2d.PathBuilder, x1, y1, x2, y2 float64) {
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```
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- Package comments go in the main source file or a `doc.go` file.
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### Naming
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- Follow standard Go naming conventions (camelCase for unexported, PascalCase for exported).
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- Backend packages are named `draw2d<backend>` (e.g., `draw2dimg`, `draw2dpdf`).
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- The `GraphicContext` struct in each backend embeds `*draw2dbase.StackGraphicContext`.
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### Error Handling
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- Functions that can fail return `error` as the last return value.
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- Do not silently ignore errors — log or return them.
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## Testing
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### Structure
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- **Unit tests** go alongside the source file they test (e.g., `matrix_test.go` tests `matrix.go`).
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- **Integration/sample tests** live in `samples_test.go`, `draw2dpdf/samples_test.go`, etc.
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- Test output files go in the `output/` directory (generated, not committed).
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### Writing Tests
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- Use the standard `testing` package only — no external test frameworks.
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- Use table-driven tests where multiple inputs share the same logic:
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```go
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tests := []struct {
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name string
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// ...
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}{
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{"case1", ...},
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{"case2", ...},
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}
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for _, tt := range tests {
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t.Run(tt.name, func(t *testing.T) { ... })
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}
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```
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- Tests must not depend on external resources (fonts, network) unless testing that specific integration.
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- For image-based tests, use `image.NewRGBA(image.Rect(0, 0, w, h))` as the canvas.
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- Use `t.TempDir()` for any file output in tests.
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- Reference GitHub issue numbers in regression test comments:
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```go
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// Test related to issue #95: DashVertexConverter state preservation
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```
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### Running Tests
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```bash
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go test ./...
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go test -cover ./... | grep -v "no test"
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```
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### Test Coverage Goals
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- Every exported function and method should have at least one unit test.
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- Core types (`Matrix`, `Path`, `StackGraphicContext`) should have thorough coverage.
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- Backend-specific operations (`Stroke`, `Fill`, `FillStroke`, `Clear`) should verify pixel output where possible.
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- Known bugs in the issue tracker should have corresponding regression tests.
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## Documentation
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- When adding or changing public API, update the GoDoc comments accordingly.
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- When fixing a bug, add a comment referencing the issue number.
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- If a change affects behavior described in `README.md` or package READMEs, update them.
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- The `samples/` directory serves as living documentation — keep samples working after changes.
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## Architecture Notes
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- All backends implement the `draw2d.GraphicContext` interface defined in `gc.go`.
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- `draw2dbase.StackGraphicContext` provides the common state management (colors, transforms, font, path). Backends embed it and override rendering methods (`Stroke`, `Fill`, `FillStroke`, string drawing, etc.).
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- The `draw2dkit` helpers operate on `draw2d.PathBuilder`, not `GraphicContext`, making them backend-agnostic.
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- `Matrix` is a `[6]float64` affine transformation matrix. Coordinate system follows the HTML Canvas 2D Context conventions.

‎draw2dbase/dasher_test.go‎

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// Copyright 2010 The draw2d Authors. All rights reserved.
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// created: 07/02/2026 by draw2d contributors
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package draw2dbase
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import (
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"testing"
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)
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// Test related to issue #95: DashVertexConverter state preservation
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func TestDashVertexConverter_StatePreservation(t *testing.T) {
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segPath := &SegmentedPath{}
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dash := []float64{5, 5}
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dasher := NewDashConverter(dash, 0, segPath)
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dasher.MoveTo(0, 0)
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initialLen := len(segPath.Points)
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dasher.LineTo(10, 0)
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afterFirstLen := len(segPath.Points)
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dasher.LineTo(20, 0)
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afterSecondLen := len(segPath.Points)
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// Second LineTo should add more points
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if afterSecondLen <= afterFirstLen {
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t.Error("Second LineTo should add more points, state may not be preserved")
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}
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if initialLen >= afterFirstLen {
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t.Error("First LineTo should add points")
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}
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}
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func TestDashVertexConverter_SingleDash(t *testing.T) {
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segPath := &SegmentedPath{}
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dash := []float64{10}
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dasher := NewDashConverter(dash, 0, segPath)
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dasher.MoveTo(0, 0)
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dasher.LineTo(50, 0)
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// Should produce output
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if len(segPath.Points) == 0 {
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t.Error("Single-element dash array should produce output")
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}
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}
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func TestDashVertexConverter_DashOffset(t *testing.T) {
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segPath1 := &SegmentedPath{}
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segPath2 := &SegmentedPath{}
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dash := []float64{5, 5}
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dasher1 := NewDashConverter(dash, 0, segPath1)
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dasher1.MoveTo(0, 0)
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dasher1.LineTo(50, 0)
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dasher2 := NewDashConverter(dash, 2.5, segPath2)
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dasher2.MoveTo(0, 0)
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dasher2.LineTo(50, 0)
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// Different offsets should produce different output
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if len(segPath1.Points) == len(segPath2.Points) {
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// Check if points are actually different
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allSame := true
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minLen := len(segPath1.Points)
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if len(segPath2.Points) < minLen {
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minLen = len(segPath2.Points)
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}
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for i := 0; i < minLen; i++ {
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if segPath1.Points[i] != segPath2.Points[i] {
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allSame = false
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break
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}
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}
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if allSame && len(segPath1.Points) > 0 {
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t.Error("Different dash offsets should produce different output")
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}
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}
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}
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func TestDashVertexConverter_Close(t *testing.T) {
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defer func() {
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if r := recover(); r != nil {
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t.Errorf("Close panicked: %v", r)
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}
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}()
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segPath := &SegmentedPath{}
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dash := []float64{5, 5}
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dasher := NewDashConverter(dash, 0, segPath)
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dasher.MoveTo(0, 0)
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dasher.LineTo(10, 10)
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dasher.Close()
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}
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func TestDashVertexConverter_End(t *testing.T) {
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defer func() {
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if r := recover(); r != nil {
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t.Errorf("End panicked: %v", r)
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}
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}()
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segPath := &SegmentedPath{}
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dash := []float64{5, 5}
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dasher := NewDashConverter(dash, 0, segPath)
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dasher.MoveTo(0, 0)
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dasher.LineTo(10, 10)
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dasher.End()
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}
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func TestDashVertexConverter_MoveTo(t *testing.T) {
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segPath := &SegmentedPath{}
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dash := []float64{5, 5}
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dasher := NewDashConverter(dash, 0, segPath)
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dasher.MoveTo(10, 20)
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// Check that position is set correctly
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if dasher.x != 10 || dasher.y != 20 {
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t.Errorf("MoveTo should set position to (10, 20), got (%f, %f)", dasher.x, dasher.y)
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}
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// Check that distance is reset to dashOffset
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if dasher.distance != dasher.dashOffset {
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t.Error("MoveTo should reset distance to dashOffset")
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}
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// Check that currentDash is reset
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if dasher.currentDash != 0 {
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t.Error("MoveTo should reset currentDash to 0")
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}
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}

‎draw2dbase/flattener_test.go‎

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// Copyright 2010 The draw2d Authors. All rights reserved.
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// created: 07/02/2026 by draw2d contributors
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package draw2dbase
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import (
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"testing"
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"github.com/llgcode/draw2d"
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)
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func TestFlatten_EmptyPath(t *testing.T) {
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p := new(draw2d.Path)
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segPath := &SegmentedPath{}
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Flatten(p, segPath, 1.0)
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if len(segPath.Points) != 0 {
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t.Error("Empty path should produce no points")
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}
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}
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func TestFlatten_MoveTo(t *testing.T) {
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p := new(draw2d.Path)
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p.MoveTo(10, 20)
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segPath := &SegmentedPath{}
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Flatten(p, segPath, 1.0)
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if len(segPath.Points) < 2 {
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t.Error("MoveTo should add points to segmented path")
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}
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if segPath.Points[0] != 10 || segPath.Points[1] != 20 {
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t.Errorf("MoveTo point = (%f, %f), want (10, 20)", segPath.Points[0], segPath.Points[1])
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}
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}
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func TestFlatten_LineSegments(t *testing.T) {
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p := new(draw2d.Path)
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p.MoveTo(0, 0)
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p.LineTo(10, 10)
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segPath := &SegmentedPath{}
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Flatten(p, segPath, 1.0)
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// Should have at least 4 points (MoveTo + LineTo)
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if len(segPath.Points) < 4 {
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t.Errorf("MoveTo + LineTo should have at least 4 points, got %d", len(segPath.Points))
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}
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}
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func TestFlatten_WithClose(t *testing.T) {
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p := new(draw2d.Path)
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p.MoveTo(0, 0)
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p.LineTo(10, 0)
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p.LineTo(10, 10)
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p.Close()
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segPath := &SegmentedPath{}
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Flatten(p, segPath, 1.0)
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// Close should add a line back to start
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lastIdx := len(segPath.Points) - 2
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if lastIdx >= 0 {
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lastX, lastY := segPath.Points[lastIdx], segPath.Points[lastIdx+1]
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// Should be back at start (0, 0)
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if lastX != 0 || lastY != 0 {
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t.Errorf("After Close, last point should be (0, 0), got (%f, %f)", lastX, lastY)
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}
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}
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}
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func TestTransformer_Identity(t *testing.T) {
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segPath := &SegmentedPath{}
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tr := Transformer{
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Tr: draw2d.NewIdentityMatrix(),
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Flattener: segPath,
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}
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tr.MoveTo(10, 20)
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tr.LineTo(30, 40)
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// Identity transform should pass through
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if segPath.Points[0] != 10 || segPath.Points[1] != 20 {
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t.Error("Identity transform should pass through points")
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}
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if segPath.Points[2] != 30 || segPath.Points[3] != 40 {
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t.Error("Identity transform should pass through points")
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}
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}
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func TestTransformer_Translation(t *testing.T) {
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segPath := &SegmentedPath{}
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tr := Transformer{
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Tr: draw2d.NewTranslationMatrix(5, 10),
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Flattener: segPath,
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}
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tr.MoveTo(10, 20)
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// Should be translated to (15, 30)
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if segPath.Points[0] != 15 || segPath.Points[1] != 30 {
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t.Errorf("Translation transform: point = (%f, %f), want (15, 30)", segPath.Points[0], segPath.Points[1])
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}
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}
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func TestSegmentedPath_MoveTo(t *testing.T) {
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segPath := &SegmentedPath{}
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segPath.MoveTo(10, 20)
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if len(segPath.Points) != 2 {
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t.Error("MoveTo should append 2 points")
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}
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if segPath.Points[0] != 10 || segPath.Points[1] != 20 {
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t.Error("MoveTo should append correct coordinates")
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}
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}
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func TestSegmentedPath_LineTo(t *testing.T) {
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segPath := &SegmentedPath{}
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segPath.MoveTo(0, 0)
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segPath.LineTo(10, 10)
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if len(segPath.Points) != 4 {
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t.Error("MoveTo + LineTo should have 4 points")
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}
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if segPath.Points[2] != 10 || segPath.Points[3] != 10 {
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t.Error("LineTo should append correct coordinates")
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}
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}
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func TestDemuxFlattener(t *testing.T) {
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segPath1 := &SegmentedPath{}
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segPath2 := &SegmentedPath{}
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demux := DemuxFlattener{
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Flatteners: []Flattener{segPath1, segPath2},
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}
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demux.MoveTo(10, 20)
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demux.LineTo(30, 40)
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// Both flatteners should receive the calls
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if len(segPath1.Points) != 4 || len(segPath2.Points) != 4 {
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t.Error("DemuxFlattener should dispatch to all flatteners")
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}
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if segPath1.Points[0] != 10 || segPath2.Points[0] != 10 {
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t.Error("DemuxFlattener should dispatch correct values")
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}
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}

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