GoSudaImplementing a Multi-File Listbox-Based Image Viewer with Go and Tcl/Tk 9.0
In the previous post, we briefly looked at the CGo-Free Tcl/Tk library. This time, we will build on the example from last time to create an image viewer.
Image Viewer Plan
- The image display from last time had no image deletion feature, so the window ran out of space as more images were loaded. Let's delete labels that are no longer used.
- If we are going to list multiple images in the image display, let's create a list.
- It would be good to load multiple images at once.
- Let's also implement removing images from the list that we no longer want to view.
- Let's create a feature that selects and displays a specific image from multiple images.
Modified Tcl/Tk 9.0 Library
The existing library's Listbox implementation is insufficient, making it difficult to display the image list. Let's download the modified library. If the Git CLI is not installed, you may download it as a tarball or zip file.
1git clone https://github.com/gg582/tk9.0
First, let's look at some of the added features.
Before looking at the new functions, let's briefly examine the structure of the existing functions through the Destroy function at line 1017 of tk.go.
1func Destroy(options ...Opt) {
2 evalErr(fmt.Sprintf("destroy %s", collect(options...)))
3}
This function is implemented by passing an action to the evalErr function in the form of a Tcl script. That means that to implement the desired functionality, you only need to pass the command in the corresponding Tcl script format.
As an example, let's implement a method that adds an item to a listbox. First, for Tcl scripting, let's look at insert, one of the commands available for listbox in the official manual.
Looking at the description page for the insert command, insert inserts the listed items at a specific index. Then, to implement this, we can write code like the following:
1func (l *ListboxWidget) AddItem(index int, items string) {
2 evalErr(fmt.Sprintf("%s insert %d %s", l.fpath, index, items))
3}
Now that we understand the general implementation principle, let's explain the additional features for Listbox.
List: Insertion/Deletion
1package main
2import . "modernc.org/tk9.0"
3
4func main() {
5 length := 3
6 l := Listbox()
7 l.AddItem(0, "item1 item2 item3")
8 b1 := TButton(Txt("Delete Multiple Items, index (0-1)"), Command( func(){
9 if length >= 2 {
10 l.DeleteItems(0,1)
11 length-=2
12 }
13 }))
14 b2 := TButton(Txt("Delete One Item, index (0)"), Command( func () {
15 if length > 0 {
16 l.DeleteOne(0)
17 length-=1
18 }
19 }))
20 Pack(TExit(),l,b1,b2)
21 App.Wait()
22}
23
In the program above, AddItem inserts the distinct items separated by spaces, starting from index 0 in order. item1 through item3 will have indices 0, 1, and 2, respectively. Let's run the example to see how item deletion works.
List: Getting Selected Items
Now let's retrieve the items selected in the Listbox and check them.
1package main
2
3import . "modernc.org/tk9.0"
4
5func main() {
6 l := Listbox()
7 l.SelectMode("multiple")
8 l.AddItem(0, "item1 item2 item3")
9 btn := TButton(Txt("Print Selected"), Command( func() {
10 sel := l.Selected()
11 for _, i := range sel {
12 println(l.GetOne(i))
13 }
14 }))
15
16 Pack(TExit(), l, btn)
17 App.Wait()
18}
The Selected method retrieves the indices of all items currently selected in the Listbox. The GetOne method retrieves the value of the item at the corresponding index. This can be confirmed by the result printed to the console. For reference, the similar Get method takes a start and end index and retrieves the values of all items within the range.
Next, let's change the colors of the listbox.
First, let's look at the example below.
1package main
2
3import . "modernc.org/tk9.0"
4
5func main() {
6 l := Listbox()
7 l.Background("blue")
8 l.Foreground("yellow")
9 l.SelectBackground("black")
10 l.SelectForeground("white")
11 l.Height(20)
12 l.Width(6)
13 l.AddItem(0, "item1 item2 item3")
14 l.ItemForeground(0,"red")
15 l.ItemBackground(0,"green")
16 l.ItemSelectBackground(0,"white")
17 l.ItemSelectForeground(0,"black")
18 l.Relief("ridged")
19 Pack(TExit(),l)
20 App.Wait()
21}
As written in the code above, the height has increased. You can also see that the colors have been applied correctly. Here, options that change colors only for specific items are set, so you can see that only the first line has a different color applied.
Also, although the difference is not large, using the Relief method allows you to change the border style of the widget to one of flat, groove, raise, ridge, solid, or sunken.
Image Viewer Example
Now, using the widgets we have just learned, let's create an image viewer. The example program is as follows:
1package main
2
3import (
4 "fmt"
5 "log"
6 "os"
7 "runtime"
8 "strings"
9 "path"
10
11 . "modernc.org/tk9.0"
12)
13
14var pbuttons []*TButtonWidget
15var extensions []FileType
16var pbutton *TButtonWidget = nil
17var listbox, listbox2 *ListboxWidget
18var cur *LabelWidget = nil
19var imagesLoaded []*LabelWidget
20func PhotoName(fileName string) string {
21 fileName = path.Base(fileName)
22 return fileName[:len(fileName)-len(path.Ext(fileName))]
23}
24
25func handleFileOpen() {
26 res := GetOpenFile(Multiple(true),Filetypes(extensions)) //๋ค์ค ์ ํ์ ํ์ฑํํ๊ณ ํํฐ๋ฅผ ์ผญ๋๋ค.
27 s := make([]string,0,1000)
28 for _, itm := range res {
29 if itm != "" {
30 tmp := strings.Split(itm," ")
31 s = append(s,tmp...)
32 }
33 }
34
35 for _, photo := range s {
36 formatCheck := strings.Split(photo, ".")
37 format := formatCheck[len(formatCheck)-1]
38
39 if (strings.Compare(format, "png") == 0) || (strings.Compare(format, "ico") == 0) {
40 picFile, err := os.Open(photo)
41 if err != nil {
42 log.Println("Error while opening photo, error is: ", err)
43 }
44
45 pictureRawData := make([]byte, 10000*10000)
46 picFile.Read(pictureRawData)
47
48 imageLabel := Label(Image(NewPhoto(Data(pictureRawData))))
49 imagesLoaded = append(imagesLoaded,imageLabel)
50 var deleteTestButton *TButtonWidget
51 deleteTestButton = TButton(
52 Txt("Unshow Image"),
53 Command(func() {
54 GridForget(imageLabel.Window)
55 GridForget(deleteTestButton.Window)
56 }))
57
58 pbuttons = append(pbuttons,deleteTestButton)
59
60 listbox.AddItem(len(imagesLoaded)-1,PhotoName(photo))
61 listbox2.AddItem(len(imagesLoaded)-1,PhotoName(photo))
62 picFile.Close()
63 }
64 }
65}
66
67func DeleteSelected () {
68 s:=listbox.Selected()
69 if len(s) == 0 {
70 return
71 }
72 for _, i := range s {
73 listbox.DeleteOne(i)
74 listbox2.DeleteOne(i)
75 if len(imagesLoaded)-1>i {
76 continue
77 }
78 if cur == imagesLoaded[i] {
79 pbutton = nil
80 cur = nil
81 }
82 Destroy(imagesLoaded[i])
83 Destroy(pbuttons[i])
84 imagesLoaded = append(imagesLoaded[:i],imagesLoaded[i+1:]...)
85 pbuttons = append(pbuttons[:i], pbuttons[i+1:]...)
86 }
87}
88
89func SelectImage() {
90 s:=listbox2.Selected()
91 if len(s) == 0 {
92 return
93 }
94
95 if len(imagesLoaded) -1 < s[0] {
96 return
97 }
98 if imagesLoaded[s[0]] == nil {
99 return
100 }
101 if cur != nil {
102 GridForget(cur.Window)
103 }
104 if pbutton != nil {
105 GridForget(pbutton.Window)
106 }
107
108 Grid(imagesLoaded[s[0]], Row(0), Column(2))
109 Grid(pbuttons[s[0]], Row(0), Column(3))
110 cur = imagesLoaded[s[0]]
111 pbutton = pbuttons[s[0]]
112}
113
114func SelectIndex(index int) {
115
116 if len(imagesLoaded) -1 <index {
117 return
118 }
119 if imagesLoaded[index] == nil {
120 return
121 }
122 if cur != nil {
123 GridForget(cur.Window)
124 }
125 if pbutton != nil {
126 GridForget(pbutton.Window)
127 }
128
129 Grid(imagesLoaded[index], Row(0), Column(2))
130 Grid(pbuttons[index], Row(0), Column(3))
131 cur = imagesLoaded[index]
132 pbutton = pbuttons[index]
133}
134
135func main() {
136 menubar := Menu()
137 //DefaultTheme("awdark","themes/awthemes-10.4.0")
138 //ํ
๋ง๋ฅผ ์ฌ์ฉํ๊ณ ์ถ์ ๋์๋ ํ
๋ง ๋ช
๊ณผ ๊ฒฝ๋ก๋ฅผ ์ง์ ํด ์ค๋๋ค.
139 fileMenu := menubar.Menu()
140 extensions = make([]FileType,0,1)
141 extensions = append(extensions, FileType{ "Supported Images", []string {".png",".ico"}, "" } )
142 //ํํฐ์ png์ ico๋ฅผ ๋ฃ์ด ์ค๋๋ค.
143 fileMenu.AddCommand(Lbl("Open..."), Underline(0), Accelerator("Ctrl+O"), Command(func () {
144 handleFileOpen()
145 SelectIndex(len(imagesLoaded)-1)
146 } ))
147 Bind(App, "<Control-o>", Command(func() { fileMenu.Invoke(0) }))
148 fileMenu.AddCommand(Lbl("Exit"), Underline(1), Accelerator("Ctrl+Q"), ExitHandler())
149 Bind(App, "<Control-q>", Command(func() { fileMenu.Invoke(1) }))
150 menubar.AddCascade(Lbl("File"), Underline(0), Mnu(fileMenu))
151 imagesLoaded = make([]*LabelWidget, 0, 10000)
152 pbuttons = make([]*TButtonWidget,0,10000)
153 var scrollx, scroll, scroll2, scrollx2 *TScrollbarWidget
154 listbox = Listbox(Yscrollcommand(func(e *Event) { e.ScrollSet(scroll)}) , Xscrollcommand( func(e *Event) { e.ScrollSet(scrollx)}))
155 listbox2 = Listbox(Yscrollcommand(func(e *Event) { e.ScrollSet(scroll2)}), Xscrollcommand(func(e *Event) { e.ScrollSet(scrollx2)}))
156 listbox.SelectMode("multiple")
157 listbox2 = Listbox()
158 listbox.Background("white")
159 listbox.SelectBackground("blue")
160 listbox.SelectForeground("yellow")
161 listbox2.Background("grey")
162 listbox2.SelectBackground("green")
163 listbox2.SelectForeground("blue")
164 listbox2.SelectBackground("brown")
165 listbox.Height(5)
166 listbox.Width(4)
167 listbox2.Height(5)
168 listbox2.Width(4)
169 delBtn := Button(Txt("Delete"), Command(func () { DeleteSelected() }))
170 selBtn := Button(Txt("Select"), Command(func () { SelectImage() }))
171 scroll = TScrollbar(Command(func(e *Event) { e.Yview(listbox) }))
172 scrollx = TScrollbar(Orient("horizontal"),Command(func(e *Event) { e.Xview(listbox) }))
173 scroll2 = TScrollbar(Command(func(e *Event) { e.Yview(listbox2) }))
174 scrollx2 = TScrollbar(Orient("horizontal"),Command(func(e *Event) { e.Xview(listbox2) }))
175 Grid(listbox,Row(1),Column(0), Sticky("nes"))
176 Grid(scroll,Row(1),Column(1), Sticky("nes"))
177 Grid(scrollx,Row(2),Column(0), Sticky("nes"))
178 Grid(delBtn,Row(3),Column(0), Sticky("nes"))
179 Grid(listbox2,Row(1),Column(2), Sticky("nes"))
180 Grid(scroll2,Row(1),Column(3), Sticky("nes"))
181 Grid(scrollx2,Row(2),Column(2), Sticky("nes"))
182 Grid(selBtn,Row(3),Column(2), Sticky("nes"))
183 App.WmTitle(fmt.Sprintf("%s on %s", App.WmTitle(""), runtime.GOOS))
184 App.Configure(Mnu(menubar), Width("80c"), Height("60c")).Wait()
185}
186
In this example, to keep the implementation simple, all image widgets are created in advance when loaded, and duplicate files are not checked. You may improve on the problems mentioned above, and you may also try changing the theme using the DefaultTheme method in the commented-out section. We encourage you to practice by writing a new program that improves these aspects.
Summary
In this post, we looked at how command invocation works in the Tcl/Tk library for Go, and created an image viewer with a listbox added.
- How Tcl/Tk library command invocation works
- How to use the listbox
- Changing listbox widget properties
- Writing an image viewer
We encourage you to apply this approach to modifying other libraries as well, and to write a complete program with the features you have added.