Panic When Using canvas.Image

[Seanld]

I had been using canvas.Image instead of image.Image in my code because the documentation mentioned possible decrease in encoding/decoding overhead. It worked for a long time, but I pulled a new version of this project while managing dependencies, and it started panicking telling me hash of unhashable type canvas.Image.

It seems to be a problem with embedImage using image.Image as a key in a map, but not expecting canvas.Image to be used in its place. I'm not sure what changed to break this, but it must be a library-side regression.

I changed my code to use image.Image and now it works exactly as intended.

Full stack trace:

panic: panic: runtime error: hash of unhashable type canvas.Image
       stacktrace:
       goroutine 5 [running]:
       runtime/debug.Stack()
               /usr/local/go/src/runtime/debug/stack.go:26 +0x67
       github.com/sourcegraph/conc/panics.NewRecovered(0x1, {0x12346c0, 0xc000198350})
               /go/pkg/mod/github.com/sourcegraph/[email protected]/panics/panics.go:59 +0xc7
       github.com/sourcegraph/conc/panics.(*Catcher).tryRecover(0xc00019cbb0)
               /go/pkg/mod/github.com/sourcegraph/[email protected]/panics/panics.go:28 +0x7b
       panic({0x12346c0?, 0xc000198350?})
               /usr/local/go/src/runtime/panic.go:785 +0x132
       github.com/tdewolff/canvas/renderers/pdf.(*pdfPageWriter).embedImage(0xc0001b2280, {0x14ad080, 0xc0001a07c0}, 0x0)
               /go/pkg/mod/github.com/tdewolff/[email protected]/renderers/pdf/writer.go:1172 +0xb0
       github.com/tdewolff/canvas/renderers/pdf.(*pdfPageWriter).DrawImage(0xc0001b2280, {0x14ad080, 0xc0001a07c0}, 0x0, {{0x3c57e8960d3791cb, 0xbfb5acb6f46508e0, 0x406396f9db22d0e6}, {0x3fb5acb6f46508e0, 0x3c57e8960d3791cb, 0x403560da740da73e}})
               /go/pkg/mod/github.com/tdewolff/[email protected]/renderers/pdf/writer.go:1159 +0x890
       github.com/tdewolff/canvas/renderers/pdf.(*PDF).RenderImage(0xc000172120, {0x14ad080, 0xc0001a07c0}, {{0x3c57e8960d3791cb, 0xbfb5acb6f46508e0, 0x406396f9db22d0e6}, {0x3fb5acb6f46508e0, 0x3c57e8960d3791cb, 0x403560da740da73e}})
               /go/pkg/mod/github.com/tdewolff/[email protected]/renderers/pdf/pdf.go:256 +0xcb
       github.com/tdewolff/canvas.(*Canvas).RenderViewTo(0xc0001a5120, {0x14aea50, 0xc000172120}, {{0x3ff0000000000000, 0x0, 0x0}, {0x0, 0x3ff0000000000000, 0x0}})
               /go/pkg/mod/github.com/tdewolff/[email protected]/canvas.go:831 +0x492
       github.com/tdewolff/canvas.(*Canvas).RenderTo(...)
               /go/pkg/mod/github.com/tdewolff/[email protected]/canvas.go:812
       github.com/tdewolff/canvas/renderers.PDF.func1({0x14a5c40, 0xc00013e038}, 0xc0001a5120)
               /go/pkg/mod/github.com/tdewolff/[email protected]/renderers/renderers.go:239 +0x12c
       github.com/tdewolff/canvas.(*Canvas).WriteFile(0xc0001a5120, {0xc00023b5c0, 0x1f}, 0xc000138060)
               /go/pkg/mod/github.com/tdewolff/[email protected]/canvas.go:852 +0x77
       github.com/tdewolff/canvas/renderers.Write({0xc00023b5c0, 0x1f}, 0xc0001a5120, {0x0, 0x0, 0x0})
               /go/pkg/mod/github.com/tdewolff/[email protected]/renderers/renderers.go:49 +0x34c
       everyname-renderer/lib/pagemaker.(*Page).RenderToFile(0xc00014c9c0, {0xc00023b5c0, 0x1f}, {0x14b0a68, 0x1b87560}, 0xc0001a5100)
               /renderer/lib/pagemaker/page.go:63 +0x5a5
       everyname-renderer/lib/renderer.Renderer.RenderBatch.func1()
               /renderer/lib/renderer/batch.go:57 +0xf2
       everyname-renderer/lib/renderer.Renderer.RenderBatch.(*ErrorPool).Go.func2()
               /go/pkg/mod/github.com/sourcegraph/[email protected]/pool/error_pool.go:30 +0x34
       github.com/sourcegraph/conc/pool.(*Pool).worker(0xc00019cba0)
               /go/pkg/mod/github.com/sourcegraph/[email protected]/pool/pool.go:154 +0xde
       github.com/sourcegraph/conc/panics.(*Catcher).Try(0xc00019cbb0, 0xc000036b50)
               /go/pkg/mod/github.com/sourcegraph/[email protected]/panics/panics.go:23 +0x78
       github.com/sourcegraph/conc.(*WaitGroup).Go.func1()
               /go/pkg/mod/github.com/sourcegraph/[email protected]/waitgroup.go:32 +0x90
       created by github.com/sourcegraph/conc.(*WaitGroup).Go in goroutine 34
               /go/pkg/mod/github.com/sourcegraph/[email protected]/waitgroup.go:30 +0xe5

[tdewolff]

You should probably use a pointer to canvas.Image, i.e. allocate it. I believe this only speeds up the SVG renderer.