Nolans-Air:dual-bifilar-coil nolansingroy$ ls
README.md main.go
dual-bifilar-coil-diagram.png view.sh
dual-bifilar-coil-layers.gif
Nolans-Air:dual-bifilar-coil nolansingroy$ go run main.go
go: extracting github.com/gmlewis/go-fonts v0.0.6
-> unzip /Users/nolansingroy/go/pkg/mod/cache/download/github.com/gmlewis/go-fonts/@v/v0.0.6.zip: malformed file path "fonts/airstream/Nick's Fonts License.txt": invalid char '''
build command-line-arguments: cannot load github.com/gmlewis/go-fonts/fonts: unzip /Users/nolansingroy/go/pkg/mod/cache/download/github.com/gmlewis/go-fonts/@v/v0.0.6.zip: malformed file path "fonts/airstream/Nick's Fonts License.txt": invalid char '''
Nolans-Air:dual-bifilar-coil nolansingroy$

i should say that im new to go, but not to other languages.
I found this little gem of yours searching for gerber files of bifilar coils, installed go and tried to do one of the examples ..
i get some errors, i wonder is this a go or gcc version issue ?

C:\Users\Mårten Sundling>cd C:\Users\Mårten Sundling\Documents\go-gerber-master\examples\bifilar-with-capacitor

C:\Users\Mårten Sundling\Documents\go-gerber-master\examples\bifilar-with-capacitor>go run main.go

github.com/go-gl/glfw/v3.3/glfw

In file included from ........\go\pkg\mod\github.com\go-gl\glfw\v3.3\[email protected]\c_glfw.go:4:
C:\Users\M�rten Sundling\go\pkg\mod\github.com\go-gl\glfw\v3.3\[email protected]/glfw/src/context.c: In function 'glfwSwapBuffers':
C:\Users\M�rten Sundling\go\pkg\mod\github.com\go-gl\glfw\v3.3\[email protected]/glfw/src/context.c:646:1: error: converting to execution character set: Illegal byte sequence
assert(window != NULL);
^ ~~~~~~~~~~~~~~~~~~~~~~~
C:\Users\M�rten Sundling\go\pkg\mod\github.com\go-gl\glfw\v3.3\[email protected]/glfw/src/context.c: In function 'glfwExtensionSupported':
C:\Users\M�rten Sundling\go\pkg\mod\github.com\go-gl\glfw\v3.3\[email protected]/glfw/src/context.c:680:1: error: converting to execution character set: Illegal byte sequence
assert(extension != NULL);
^ ~~~~~~~~~~~~~~~~~~~~~~~~~~
C:\Users\M�rten Sundling\go\pkg\mod\github.com\go-gl\glfw\v3.3\[email protected]/glfw/src/context.c: In function 'glfwGetProcAddress':
C:\Users\M�rten Sundling\go\pkg\mod\github.com\go-gl\glfw\v3.3\[email protected]/glfw/src/context.c:746:1: error: converting to execution character set: Illegal byte sequence
assert(procname != NULL);
^ ~~~~~~~~~~~~~~~~~~~~~~~~~
In file included from ........\go\pkg\mod\github.com\go-gl\glfw\v3.3\[email protected]\c_glfw.go:6:
C:\Users\M�rten Sundling\go\pkg\mod\github.com\go-gl\glfw\v3.3\[email protected]/glfw/src/input.c: In function 'glfwGetInputMode':
C:\Users\M�rten Sundling\go\pkg\mod\github.com\go-gl\glfw\v3.3\[email protected]/glfw/src/input.c:476:1: error: converting to execution character set: Illegal byte sequence
assert(window != NULL);
^ ~~~~~~~~~~~~~~~~~~~~~~~
C:\Users\M�rten Sundling\go\pkg\mod\github.com\go-gl\glfw\v3.3\[email protected]/glfw/src/input.c: In function 'glfwSetInputMode':
C:\Users\M�rten Sundling\go\pkg\mod\github.com\go-gl\glfw\v3.3\[email protected]/glfw/src/input.c:501:1: error: converting to execution character set: Illegal byte sequence
assert(window != NULL);
^ ~~~~~~~~~~~~~~~~~~~~~~~
C:\Users\M�rten Sundling\go\pkg\mod\github.com\go-gl\glfw\v3.3\[email protected]/glfw/src/input.c: In function 'glfwGetKey':
C:\Users\M�rten Sundling\go\pkg\mod\github.com\go-gl\glfw\v3.3\[email protected]/glfw/src/input.c:632:1: error: converting to execution character set: Illegal byte sequence
assert(window != NULL);
^ ~~~~~~~~~~~~~~~~~~~~~~~
C:\Users\M�rten Sundling\go\pkg\mod\github.com\go-gl\glfw\v3.3\[email protected]/glfw/src/input.c: In function 'glfwGetMouseButton':
C:\Users\M�rten Sundling\go\pkg\mod\github.com\go-gl\glfw\v3.3\[email protected]/glfw/src/input.c:655:1: error: converting to execution character set: Illegal byte sequence
assert(window != NULL);
^ ~~~~~~~~~~~~~~~~~~~~~~~
C:\Users\M�rten Sundling\go\pkg\mod\github.com\go-gl\glfw\v3.3\[email protected]/glfw/src/input.c: In function 'glfwGetCursorPos':
C:\Users\M�rten Sundling\go\pkg\mod\github.com\go-gl\glfw\v3.3\[email protected]/glfw/src/input.c:678:1: error: converting to execution character set: Illegal byte sequence
assert(window != NULL);
^ ~~~~~~~~~~~~~~~~~~~~~~~
C:\Users\M�rten Sundling\go\pkg\mod\github.com\go-gl\glfw\v3.3\[email protected]/glfw/src/input.c: In function 'glfwSetCursorPos':
C:\Users\M�rten Sundling\go\pkg\mod\github.com\go-gl\glfw\v3.3\[email protected]/glfw/src/input.c:701:1: error: converting to execution character set: Illegal byte sequence
assert(window != NULL);
^ ~~~~~~~~~~~~~~~~~~~~~~~
C:\Users\M�rten Sundling\go\pkg\mod\github.com\go-gl\glfw\v3.3\[email protected]/glfw/src/input.c: In function 'glfwCreateCursor':
C:\Users\M�rten Sundling\go\pkg\mod\github.com\go-gl\glfw\v3.3\[email protected]/glfw/src/input.c:734:1: error: converting to execution character set: Illegal byte sequence
assert(image != NULL);
^ ~~~~~~~~~~~~~~~~~~~~~~
C:\Users\M�rten Sundling\go\pkg\mod\github.com\go-gl\glfw\v3.3\[email protected]/glfw/src/input.c: In function 'glfwSetCursor':
C:\Users\M�rten Sundling\go\pkg\mod\github.com\go-gl\glfw\v3.3\[email protected]/glfw/src/input.c:820:1: error: converting to execution character set: Illegal byte sequence
assert(window != NULL);
^ ~~~~~~~~~~~~~~~~~~~~~~~
C:\Users\M�rten Sundling\go\pkg\mod\github.com\go-gl\glfw\v3.3\[email protected]/glfw/src/input.c: In function 'glfwSetKeyCallback':
C:\Users\M�rten Sundling\go\pkg\mod\github.com\go-gl\glfw\v3.3\[email protected]/glfw/src/input.c:832:1: error: converting to execution character set: Illegal byte sequence
assert(window != NULL);
^ ~~~~~~~~~~~~~~~~~~~~~~~
C:\Users\M�rten Sundling\go\pkg\mod\github.com\go-gl\glfw\v3.3\[email protected]/glfw/src/input.c: In function 'glfwSetCharCallback':
C:\Users\M�rten Sundling\go\pkg\mod\github.com\go-gl\glfw\v3.3\[email protected]/glfw/src/input.c:842:1: error: converting to execution character set: Illegal byte sequence
assert(window != NULL);
^ ~~~~~~~~~~~~~~~~~~~~~~~
C:\Users\M�rten Sundling\go\pkg\mod\github.com\go-gl\glfw\v3.3\[email protected]/glfw/src/input.c: In function 'glfwSetCharModsCallback':
C:\Users\M�rten Sundling\go\pkg\mod\github.com\go-gl\glfw\v3.3\[email protected]/glfw/src/input.c:852:1: error: converting to execution character set: Illegal byte sequence
assert(window != NULL);
^ ~~~~~~~~~~~~~~~~~~~~~~~
C:\Users\M�rten Sundling\go\pkg\mod\github.com\go-gl\glfw\v3.3\[email protected]/glfw/src/input.c: In function 'glfwSetMouseButtonCallback':
C:\Users\M�rten Sundling\go\pkg\mod\github.com\go-gl\glfw\v3.3\[email protected]/glfw/src/input.c:863:1: error: converting to execution character set: Illegal byte sequence
assert(window != NULL);
^ ~~~~~~~~~~~~~~~~~~~~~~~
C:\Users\M�rten Sundling\go\pkg\mod\github.com\go-gl\glfw\v3.3\[email protected]/glfw/src/input.c: In function 'glfwSetCursorPosCallback':
C:\Users\M�rten Sundling\go\pkg\mod\github.com\go-gl\glfw\v3.3\[email protected]/glfw/src/input.c:874:1: error: converting to execution character set: Illegal byte sequence

Describe the bug

reproducible segfault in gerber.Gerber.WriteGerber if empty text objects are included.

• if text supplied: no segfault
• if only whitespace supplied: no segfault
• if empty string supplied: segfault

To Reproduce

The below code reproduces the issue. If text is supplied via the -text flag, should have no segfault.

package main

import (
	"flag"
	"fmt"
	"os"

	"github.com/gmlewis/go-fonts/fonts"
	_ "github.com/gmlewis/go-fonts/fonts/bitstreamverasansmono_bold"
	"github.com/gmlewis/go-gerber/gerber"
)

func main() {
	var text string
	flag.StringVar(&text, "text", "", "text to render on the panel")
	flag.Parse()
	g := gerber.New("textbug")
	g.TopSilkscreen().Add(
		gerber.Text(
			25, 25,
			1.0,    // for top silk
			text,
			"bitstreamverasansmono_bold",
			12,
			&gerber.TextOpts{XAlign: fonts.XCenter, YAlign: fonts.YCenter},
		),
	)
	if err := g.WriteGerber(); err != nil {
		fmt.Printf("write: %v", err)
		os.Exit(1)
	}
}

Expected behavior

gerber.Text API does not return errors, so perhaps log a warning instead? Not really sure what's best here.

Screenshots

$ go build && rm -f textbug.* && ./gerber-empty-text-bug -text='' && gerbv textbug*
panic: runtime error: invalid memory address or nil pointer dereference
[signal SIGSEGV: segmentation violation code=0x2 addr=0x10 pc=0x102be9270]

goroutine 1 [running]:
github.com/gmlewis/go-fonts/fonts.TextMBB(0x4039000000000000, 0x4039000000000000, 0x4010eeeeeeeeeeef, 0x4010eeeeeeeeeeef, {0x16d4139e9, 0x0}, {0x102bf9091?, 0x1029f54cc?})
	/Users/jslee/go/pkg/mod/github.com/gmlewis/[email protected]/fonts/text.go:196 +0x2a0
github.com/gmlewis/go-fonts/fonts.Text(0x4039000000000000, 0x4039000000000000, 0x4010eeeeeeeeeeef, 0x4010eeeeeeeeeeef, {0x16d4139e9, 0x0}, {0x102bf9091, 0x1a}, 0x14000126078)
	/Users/jslee/go/pkg/mod/github.com/gmlewis/[email protected]/fonts/text.go:221 +0x7c
github.com/gmlewis/go-gerber/gerber.(*TextT).renderText(0x140001009b0)
	/Users/jslee/go/pkg/mod/github.com/gmlewis/[email protected]/gerber/text.go:109 +0x64
github.com/gmlewis/go-gerber/gerber.(*TextT).WriteGerber(0x140001009b0, {0x102ccd5c8, 0x14000100a00}, 0x7?)
	/Users/jslee/go/pkg/mod/github.com/gmlewis/[email protected]/gerber/text.go:143 +0x2c
github.com/gmlewis/go-gerber/gerber.(*Layer).WriteGerber(0x140003685a0, {0x102ccd5c8, 0x14000100a00})
	/Users/jslee/go/pkg/mod/github.com/gmlewis/[email protected]/gerber/layers.go:56 +0x220
github.com/gmlewis/go-gerber/gerber.(*Gerber).WriteGerber(0x14000141f30)
	/Users/jslee/go/pkg/mod/github.com/gmlewis/[email protected]/gerber/gerber.go:43 +0x1bc
main.main()
	/Users/jslee/vc/jsleeio/experiments/gerber/gerber-empty-text-bug/main.go:28 +0x358

Additional context
Am using macOS and Go 1.19.4. Also reproduced on Linux.

Thanks for making this library; it solved a problem for me :-)