go-fltk

---

A simple wrapper around FLTK 1.4 library, which is a lightweight GUI library which allows creating small, self-contained and fast gui applications.

Requirements

For building go-fltk, besides Golang compiler, you will also need a C++11 compiler, such as GCC or Clang on Linux, MinGW on Windows and XCode on MacOS.

go-fltk comes with prebuilt FLTK libraries for some architectures (linux/amd64, windows/amd64), but you can easily rebuild them yourself or build them for other architectures. To build FLTK libraries for your platform it should be enough to call go generate from the root of the go-fltk source tree.

If the build procedure doesn't work for you, you can modify fltk-build.sh or fltk-build.bat yourself or ask a question on https://github.com/pwiecz/go-fltk/discussions.

For running programs built using go-fltk you will need some system libs which are normally available on operating systems with a graphical user interfaces:

• Windows: No external dependencies, besides a (for mingw64)
• MacOS: No external dependencies
• Linux (and other Unix systems - not tested): You need:
  • X11
  • Xrender
  • Xcursor
  • Xfixes
  • Xext
  • Xft
  • Xinerama
  • XKBCommon
  • Wayland
  • libdecor
  • DBus
  • OpenGL

Usage

package main

import "github.com/pwiecz/go-fltk"

func main() {
    win := fltk.NewWindow(400, 300)
    win.SetLabel("Main Window")
    btn := fltk.NewButton(160, 200, 80, 30, "Click")
    btn.SetCallback(func() {
        btn.SetLabel("Clicked")
    })
    win.End()
    win.Show()
    fltk.Run()
}

Widgets are created using the fltk.New<WidgetType> functions, modified for whatever widget you're instantiating. Function and method names resemble the original C++ names, while however, following the Golang convention of PascalCase. Setter methods are also preceded by a Set prefix.

Styling

FLTk offers 4 builtin schemes:

• base (default)
• gtk+
• gleam
• plastic These can be set using fltk.SetScheme("gtk+") for example.

FLTK also allows custom styling of your widgets:

package main

import (
	"strconv"

	"github.com/pwiecz/go-fltk"
)

// FLTK uses an RGBI color representation, the I is an index into FLTK's color map
// Passing 00 as I will use the RGB part of the value
const GRAY = 0x75757500
const LIGHT_GRAY = 0xeeeeee00
const BLUE = 0x42A5F500
const SEL_BLUE = 0x2196F300
const WIDTH = 600
const HEIGHT = 400

func main() {
	curr := 0
	fltk.InitStyles()
	win := fltk.NewWindow(WIDTH, HEIGHT)
	win.SetLabel("Flutter-like")
	win.SetColor(fltk.WHITE)
	bar := fltk.NewBox(fltk.FLAT_BOX, 0, 0, WIDTH, 60, "    FLTK App!")
	bar.SetDrawHandler(func() { // Shadow under the bar
		fltk.DrawBox(fltk.FLAT_BOX, 0, 0, WIDTH, 63, LIGHT_GRAY)
	})
	bar.SetAlign(fltk.ALIGN_INSIDE | fltk.ALIGN_LEFT)
	bar.SetLabelColor(255) // this uses the index into the color map, here it's white
	bar.SetColor(BLUE)
	bar.SetLabelSize(22)
	text := fltk.NewBox(fltk.NO_BOX, 250, 180, 100, 40, "You have pushed the button this many times:")
	text.SetLabelSize(18)
	text.SetLabelFont(fltk.TIMES)
	count := fltk.NewBox(fltk.NO_BOX, 250, 180+40, 100, 40, "0")
	count.SetLabelSize(36)
	count.SetLabelColor(GRAY)
	btn := fltk.NewButton(WIDTH-100, HEIGHT-100, 60, 60, "@+6plus") // this translates into a plus sign
	btn.SetColor(BLUE)
	btn.SetSelectionColor(SEL_BLUE)
	btn.SetLabelColor(255)
	btn.SetBox(fltk.OFLAT_BOX)
	btn.ClearVisibleFocus()
	btn.SetCallback(func() {
		curr += 1
		count.SetLabel(strconv.Itoa(curr))
	})
	win.End()
	win.Show()
	fltk.Run()
}

Label attributes can be seen here

Image support

FLTK supports vector and raster graphics, via several image types:

• SvgImage
• RgbImage
• JpegImage
• PngImage
• BmpImage
• SharedImage

Some of these can be instantiated from an image file or from data:

package main

import (
	"fmt"

	"github.com/pwiecz/go-fltk"
)

func main() {
	win := fltk.NewWindow(400, 300)
	box := fltk.NewBox(fltk.FLAT_BOX, 0, 0, 400, 300, "")
	image, err := fltk.NewJpegImageLoad("image.jpg")
	if err != nil {
		fmt.Printf("An error occured: %s\n", err)
	} else {
		box.SetImage(image)
	}
	win.End()
	win.Show()
	fltk.Run()
}

Resources

• Link to the official FLTK 1.4 documentation.
• Link to go-fltk documentation.