Added examples for group layout

Author: jannst

cmd/nk-example-layout/nk-group-layout/README.md

@@ -0,0 +1,27 @@
+## nk-group-layout
+
+This example shows, how to use group layout provided by nuklear API.
+
+Please note, that the following explanations are taken from the nuklear doc, available [here](https://github.com/vurtun/nuklear/tree/master/doc)
+
+## Groups
+Groups are basically windows inside windows. They allow to subdivide space in a window to layout widgets as a group. Almost all more complex widget layouting requirements can be solved using groups and basic layouting fuctionality. Groups just like windows are identified by an unique name and internally keep track of scrollbar offsets by default. However additional versions are provided to directly manage the scrollbar. 
+
+To create a group you have to call one of the three `nk.NkGroupBegin` functions to start group declarations and `nk.NkGroupEnd` at the end. Furthermore it is required to check the return value of `nk.NkGroupBegin` and only process widgets inside the window if the value is not 0. Nesting groups is possible and even encouraged since many layouting schemes can only be achieved by nesting. Groups, unlike windows, need `nk.NkGroupEnd` to be only called if the corosponding `nk.NkGroupBegin` call does not return 0.
+Note that group names should be unique.
+//TODO
+## Install
+Make sure, that the following packages are installed
+  - github.com/go-gl/gl/v3.2-core/gl
+  - github.com/go-gl/glfw/v3.2/glfw
+  - github.com/golang-ui/nuklear/nk
+  - github.com/xlab/closer
+
+Then run
+```
+$ go run main.go
+```
+Now a runnable binary should have been created in your $GOBIN path
+
+### Maintainer
+jannst <mkawaganga@gmail.com>

cmd/nk-example-layout/nk-group-layout/main.go

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+package main
+
+import (
+	"log"
+	"runtime"
+	"time"
+
+	"github.com/go-gl/gl/v3.2-core/gl"
+	"github.com/go-gl/glfw/v3.2/glfw"
+	"github.com/golang-ui/nuklear/nk"
+	"github.com/xlab/closer"
+)
+
+const (
+	winWidth  = 800
+	winHeight = 550
+
+	maxVertexBuffer  = 512 * 1024
+	maxElementBuffer = 128 * 1024
+)
+
+func init() {
+	runtime.LockOSThread()
+}
+
+func main() {
+	if err := glfw.Init(); err != nil {
+		closer.Fatalln(err)
+	}
+	glfw.WindowHint(glfw.ContextVersionMajor, 3)
+	glfw.WindowHint(glfw.ContextVersionMinor, 2)
+	glfw.WindowHint(glfw.OpenGLProfile, glfw.OpenGLCoreProfile)
+	glfw.WindowHint(glfw.OpenGLForwardCompatible, glfw.True)
+	win, err := glfw.CreateWindow(winWidth, winHeight, "Nuklear Demo", nil, nil)
+	if err != nil {
+		closer.Fatalln(err)
+	}
+	win.MakeContextCurrent()
+
+	width, height := win.GetSize()
+	log.Printf("glfw: created window %dx%d", width, height)
+
+	if err := gl.Init(); err != nil {
+		closer.Fatalln("opengl: init failed:", err)
+	}
+	gl.Viewport(0, 0, int32(width), int32(height))
+
+	ctx := nk.NkPlatformInit(win, nk.PlatformInstallCallbacks)
+
+	atlas := nk.NewFontAtlas()
+	nk.NkFontStashBegin(&atlas)
+	//Use default font so we dont have to manage assets
+	sansFont := nk.NkFontAtlasAddDefault(atlas, 14, nil)
+	nk.NkFontStashEnd()
+	if sansFont != nil {
+		nk.NkStyleSetFont(ctx, sansFont.Handle())
+	}
+
+	exitC := make(chan struct{}, 1)
+	doneC := make(chan struct{}, 1)
+	closer.Bind(func() {
+		close(exitC)
+		<-doneC
+	})
+
+	state := &State{
+		bgColor:     nk.NkRgba(28, 48, 62, 255),
+		groupStates: make([]int32, 16),
+	}
+	fpsTicker := time.NewTicker(time.Second / 30)
+	for {
+		select {
+		case <-exitC:
+			nk.NkPlatformShutdown()
+			glfw.Terminate()
+			fpsTicker.Stop()
+			close(doneC)
+			return
+		case <-fpsTicker.C:
+			if win.ShouldClose() {
+				close(exitC)
+				continue
+			}
+			glfw.PollEvents()
+			gfxMain(win, ctx, state)
+		}
+	}
+}
+
+func gfxMain(win *glfw.Window, ctx *nk.Context, state *State) {
+	nk.NkPlatformNewFrame()
+
+	// Layout
+	bounds := nk.NkRect(10, 10, 700, 500)
+	//Begin Window
+	if nk.NkBegin(ctx, "Group Layout Demo", bounds, nk.WindowBorder|nk.WindowMovable|nk.WindowScalable|nk.WindowMinimizable|nk.WindowTitle) > 0 {
+
+		nk.NkLayoutRowStatic(ctx, 300, 200, 2)
+		//create group with border and title
+		if nk.NkGroupBegin(ctx, "Group 1", nk.WindowBorder|nk.WindowTitle) > 0 {
+			//create row with dynamic calculated height and 1 column
+			nk.NkLayoutRowDynamic(ctx, 0, 1)
+			//add 16 widgets
+			for i := 0; i < 16; i++ {
+				nk.NkSelectableLabel(ctx, getGroupStatus(state.groupStates[i]), nk.TextCentered, &state.groupStates[i])
+			}
+			//Do not forget to end group
+			nk.NkGroupEnd(ctx)
+		}
+
+		//lets create a floating group. Therefore we need to use layout space api
+		nk.NkLayoutSpaceBegin(ctx, nk.Static, 150, 10000)
+		//Define the rectangle, in which our group will be placed
+		nk.NkLayoutSpacePush(ctx, nk.NkRect(150, 10, 300, 100))
+		//try to add the group
+		if nk.NkGroupBegin(ctx, "Group 2", nk.WindowBorder|nk.WindowTitle) > 0 {
+			//create row with dynamic calculated height and 1 column
+			nk.NkLayoutRowDynamic(ctx, 0, 1)
+			//add 16 widgets
+			for i := 0; i < 16; i++ {
+				//add selector widget
+				nk.NkSelectableLabel(ctx, getGroupStatus(state.groupStates[i]), nk.TextCentered, &state.groupStates[i])
+			}
+			//Do not forget to end group
+			nk.NkGroupEnd(ctx)
+		}
+		nk.NkLayoutSpaceEnd(ctx)
+
+	}
+	//End Window
+	nk.NkEnd(ctx)
+
+	// Render
+	bg := make([]float32, 4)
+	nk.NkColorFv(bg, state.bgColor)
+	width, height := win.GetSize()
+	gl.Viewport(0, 0, int32(width), int32(height))
+	gl.Clear(gl.COLOR_BUFFER_BIT)
+	gl.ClearColor(bg[0], bg[1], bg[2], bg[3])
+	nk.NkPlatformRender(nk.AntiAliasingOn, maxVertexBuffer, maxElementBuffer)
+	win.SwapBuffers()
+}
+
+func getGroupStatus(b int32) string {
+	if b != 0 {
+		return "selected"
+	} else {
+		return "not selected"
+	}
+}
+
+type State struct {
+	bgColor     nk.Color
+	prop        int32
+	groupStates []int32
+}