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<H1 ALIGN="RIGHT"><A NAME="editor">4 - Designing a Simple Text Editor</A></H1>
<P>This chapter takes you through the design of a simple
pyFLTK-based text editor.
<H2>Determining the Goals of the Text Editor</H2>
<P>Since this will be the first big project you'll be doing with pyFLTK,
lets define what we want our text editor to do:
<OL>
<LI>Provide a menubar/menus for all functions.</LI>
<LI>Edit a single text file, possibly with multiple views.</LI>
<LI>Load from a file.</LI>
<LI>Save to a file.</LI>
<LI>Cut/copy/delete/paste functions.</LI>
<LI>Search and replace functions.</LI>
<LI>Keep track of when the file has been changed.</LI>
</OL>
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<H2>Designing the Main Window</H2>
<P>Now that we've outlined the goals for our editor, we can begin with
the design of our GUI. Obviously the first thing that we need is a
window, which we'll place inside a class called <TT>EditorWindow</TT>:
<UL><PRE>
class EditorWindow(Fl_Double_Window):
search = ""
def __init__(self, w, h, label):
Fl_Double_Window.__init__(self, w, h, label)
</PRE></UL>
<H2>Variables</H2>
<P>Our text editor will need some global variables to keep track of
things:
<UL><PRE>
changed = False
filename = ""
title = ""
textbuf = None
editor = None
</PRE></UL>
<P>The <TT>textbuf</TT> variable is the text editor buffer for
our window class described previously. We'll cover the other
variables as we build the application.</P>
<H2>Menubars and Menus</H2>
<P>The first goal requires us to use a menubar and menus that
define each function the editor needs to perform. The <A
href="fltk.html#Fl_Menu_Item"><TT>Fl_Menu_Item</TT></A> structure is
used to define the menus and items in a menubar:</P>
<UL><PRE>
menuitems = (( "&File", 0, 0, 0, FL_SUBMENU ),
( "&New File", 0, new_cb ),
( "&Open File...", FL_CTRL + ord('o'), open_cb ),
( "&Insert File...", FL_CTRL + ord('i'), insert_cb, 0, FL_MENU_DIVIDER ),
( "&Save File", FL_CTRL + ord('s'), save_cb ),
( "Save File &As...", FL_CTRL + FL_SHIFT + ord('s'), saveas_cb, 0, FL_MENU_DIVIDER ),
( "New &View", FL_ALT + ord('v'), view_cb, 0 ),
( "&Close View", FL_CTRL + ord('w'), close_cb, 0, FL_MENU_DIVIDER ),
( "E&xit", FL_CTRL + ord('q'), quit_cb, 0 ),
( None, 0 ),
( "&Edit", 0, 0, 0, FL_SUBMENU ),
( "Cu&t", FL_CTRL + ord('x'), cut_cb ),
( "&Copy", FL_CTRL + ord('c'), copy_cb ),
( "&Paste", FL_CTRL + ord('v'), paste_cb ),
( "&Delete", 0, delete_cb ),
( None, 0 ),
( "&Search", 0, 0, 0, FL_SUBMENU ),
( "&Find...", FL_CTRL + ord('f'), find_cb ),
( "F&ind Again", FL_CTRL + ord('g'), find2_cb ),
( "&Replace...", FL_CTRL + ord('r'), replace_cb ),
( "Re&place Again", FL_CTRL + ord('t'), replace2_cb ),
( None, 0 ),
( None, 0 )
)
</PRE></UL>
<P>Once we have the menus defined we can create the
<TT>Fl_Menu_Bar</TT> widget and assign the menus to it with:</P>
<UL><PRE>
m = Fl_Menu_Bar(0, 0, 660, 30);
m.copy(menuitems)
</PRE></UL>
<P>We'll define the callback functions later.
<H2>Editing the Text</H2>
<P>To keep things simple our text editor will use the
<A HREF="fltk.html#Fl_Text_Editor"><TT>Fl_Text_Editor</TT></A>
widget to edit the text:
<UL><PRE>
w.editor = Fl_Text_Editor(0, 30, 660, 370)
w.editor.buffer(textbuf)
</PRE></UL>
<P>So that we can keep track of changes to the file, we also want to add
a "modify" callback:</P>
<UL><PRE>
textbuf.add_modify_callback(changed_cb, w)
textbuf.call_modify_callbacks()
</PRE></UL>
<P>Finally, we want to use a mono-spaced font like <TT>FL_COURIER</TT>:
<UL><PRE>
w.editor.textfont(FL_COURIER)
</PRE></UL>
<H2>The Replace Dialog</H2>
<P>We can use the pyFLTK convenience functions for many of the
editor's dialogs, however the replace dialog needs its own
custom window. To keep things simple we will have a
"find" string, a "replace" string, and
"replace all", "replace next", and
"cancel" buttons. The strings are just
<TT>Fl_Input</TT> widgets, the "replace all" and
"cancel" buttons are <TT>Fl_Button</TT> widgets, and
the "replace next " button is a
<TT>Fl_Return_Button</TT> widget:</P>
<P ALIGN="CENTER"><IMG src="editor-replace.jpg" ALT="The search and replace dialog."><BR>
<I>Figure 4-1: The search and replace dialog.</I></P>
<UL><PRE>
self.replace_dlg = Fl_Window(300, 105, "Replace")
self.replace_find = Fl_Input(80, 10, 210, 25, "Find:")
self.replace_with = Fl_Input(80, 40, 210, 25, "Replace:")
self.replace_all = Fl_Button(10, 70, 90, 25, "Replace All")
self.replace_next = Fl_Return_Button(105, 70, 120, 25, "Replace Next")
self.replace_cancel = Fl_Button(230, 70, 60, 25, "Cancel")
</PRE></UL>
<H2>Callbacks</H2>
<P>Now that we've defined the GUI components of our editor, we
need to define our callback functions.</P>
<H3>changed_cb()</H3>
<P>This function will be called whenever the user changes any text in the
<TT>editor</TT> widget:
<UL><PRE>
def changed_cb(i1, nInserted, nDeleted, i2, c1, editor):
global changed, loading
if (nInserted != 0 or nDeleted != 0) and loading == False:
changed = True
set_title(editor);
if loading:
editor.editor.show_insert_position()
</PRE></UL>
<P>The <TT>set_title()</TT> function is one that we will write to set
the changed status on the current file. We're doing it this way
because we want to show the changed status in the window's
title bar.
<H3>copy_cb()</H3>
<P>This callback function will call <A
href="fltk.html#Fl_Text_Editor-kf_copy"><TT>kf_copy()</TT></A>
to copy the currently selected text to the clipboard:</P>
<UL><PRE>
def copy_cb(widget):
global editor
Fl_Text_Editor.kf_copy(0, editor.editor)
</PRE></UL>
<H3>cut_cb()</H3>
<P>This callback function will call <A
href="fltk.html#Fl_Text_Editor-kf_cut"><TT>kf_cut()</TT></A>
to cut the currently selected text to the clipboard:</P>
<UL><PRE>
def cut_cb(widget):
global editor
Fl_Text_Editor.kf_cut(0, editor.editor)
</PRE></UL>
<H3>delete_cb()</H3>
<P>This callback function will call <A
href="fltk.html#Fl_Text_Buffer-remove_selection"><TT>remove_selection()</TT></A>
to delete the currently selected text to the clipboard:</P>
<UL><PRE>
def delete_cb(widget):
global textbuf
textbuf.remove_selection()
</PRE></UL>
<H3>find_cb()</H3>
<P>This callback function asks for a search string using the <A
href="fltk.html#-fl_input2"><TT>fl_input()</TT></A>
convenience function and then calls the <TT>find2_cb()</TT>
function to find the string:
<UL><PRE>
def find_cb(widget):
global editor
val = fl_input("Search String:", editor.search)
if val != None:
# User entered a string - go find it!
editor.search = val
find2_cb(widget)
</PRE></UL>
<H3>find2_cb()</H3>
<P>This function will find the next occurrence of the search
string. If the search string is blank then we want to pop up the
search dialog:
<UL><PRE>
def find2_cb(widget):
global editor
if editor.search[0] == 0:
# Search string is blank; get a new one...
find_cb(widget, editor)
return
pos = editor.editor.insert_position();
(found, pos) = textbuf.search_forward(pos, editor.search);
if found!= 0:
# Found a match; select and update the position...
textbuf.select(pos, pos+len(editor.search))
editor.editor.insert_position(pos+len(editor.search))
editor.editor.show_insert_position()
else:
fl_alert("No occurrences of %s found!"%editor.search)
</PRE></UL>
<P>If the search string cannot be found we use the <A
href="fltk.html#-fl_alert"><TT>fl_alert()</TT></A>
convenience function to display a message to that effect.
<H3>new_cb()</H3>
<P>This callback function will clear the editor widget and current
filename. It also calls the <TT>check_save()</TT> function to give the
user the opportunity to save the current file first as needed:
<UL><PRE>
def new_cb(widget):
global filename, changed
if check_save() == 0:
return
filename = ""
textbuf.select(0, textbuf.length())
textbuf.remove_selection()
changed = False
textbuf.call_modify_callbacks()
</PRE></UL>
<H3>open_cb()</H3>
<P>This callback function will ask the user for a filename and then load
the specified file into the input widget and current filename. It also
calls the <TT>check_save()</TT> function to give the user the
opportunity to save the current file first as needed:
<UL><PRE>
def open_cb(widget):
global filename
if check_save() == 0:
return
newfile = fl_file_chooser("Open File?", "*", filename)
if newfile != None:
load_file(newfile, -1)
</PRE></UL>
<P>We call the <TT>load_file()</TT> function to actually load the file.
<H3>paste_cb()</H3>
<P>This callback function will call <A
href="fltk.html#Fl_Text_Editor-kf_paste"><TT>kf_paste()</TT></A>
to paste the clipboard at the current position:</P>
<UL><PRE>
def paste_cb(widget):
global editor
Fl_Text_Editor.kf_paste(0, editor.editor)
</PRE></UL>
<H3>quit_cb()</H3>
<P>The quit callback will first see if the current file has been
modified, and if so give the user a chance to save it. It then exits
from the program:
<UL><PRE>
def quit_cb(widget, data):
global changed
if changed and check_save() == 0:
return
sys.exit(0)
</PRE></UL>
<H3>replace_cb()</H3>
<P>The replace callback just shows the replace dialog:
<UL><PRE>
def replace_cb(widget):
global editor
editor.replace_dlg.show()
</PRE></UL>
<H3>replace2_cb()</H3>
<P>This callback will replace the next occurence of the replacement
string. If nothing has been entered for the replacement string, then
the replace dialog is displayed instead:
<UL><PRE>
def replace2_cb(widget):
global editor
find = editor.replace_find.value()
replace = editor.replace_with.value()
if len(find) == 0:
editor.replace_dlg.show()
return
editor.replace_dlg.hide()
pos = editor.editor.insert_position()
(found, pos) = textbuf.search_forward(pos, find)
if found != 0:
# Found a match; update the position and replace text...
textbuf.select(pos, pos+len(find))
textbuf.remove_selection()
textbuf.insert(pos, replace)
textbuf.select(pos, pos+len(replace))
editor.editor.insert_position(pos+len(replace))
editor.editor.show_insert_position()
else:
fl_alert("No occurrences of %s found!"%find)
</PRE></UL>
<H3>replall_cb()</H3>
<P>This callback will replace all occurences of the search
string in the file:
<UL><PRE>
def replall_cb(widget):
global editor
find = editor.replace_find.value()
replace = editor.replace_with.value()
if len(find) == 0:
editor.replace_dlg.show()
return
editor.replace_dlg.hide()
editor.editor.insert_position(0)
times = 0
found = 1
while found != 0:
pos = editor.editor.insert_position()
(found, pos) = textbuf.search_forward(pos, find)
if found != 0:
# Found a match; update the position and replace text...
textbuf.select(pos, pos+len(find))
textbuf.remove_selection()
textbuf.insert(pos, replace)
editor.editor.insert_position(pos+len(replace))
editor.editor.show_insert_position()
times += 1
if times > 0:
fl_message("Replaced %d occurrences."%times)
else:
fl_alert("No occurrences of %s found!"%find)
</PRE></UL>
<H3>replcan_cb()</H3>
<P>This callback just hides the replace dialog:
<UL><PRE>
def replcan_cb(widget):
global editor
editor.replace_dlg.hide()
</PRE></UL>
<H3>save_cb()</H3>
<P>This callback saves the current file. If the current filename is
blank it calls the "save as" callback:
<UL><PRE>
def save_cb(widget):
global filename
if len(filename) == 0:
# No filename - get one!
saveas_cb()
return
else:
save_file(filename)
</PRE></UL>
<P>The <TT>save_file()</TT> function saves the current file to the
specified filename.
<H3>saveas_cb()</H3>
<P>This callback asks the user for a filename and saves the current file:
<UL><PRE>
def saveas_cb(widget, data):
global filename
newfile = fl_file_chooser("Save File As?", "*", filename)
if newfile != None:
save_file(newfile)
</PRE></UL>
<P>The <TT>save_file()</TT> function saves the current file to the
specified filename.
<H2>Other Functions</H2>
<P>Now that we've defined the callback functions, we need our support
functions to make it all work:
<H3>check_save()</H3>
<P>This function checks to see if the current file needs to be saved. If
so, it asks the user if they want to save it:
<UL><PRE>
def check_save():
global changed
if not changed:
return
r = fl_choice("The current file has not been saved.\n"
"Would you like to save it now?",
"Cancel", "Save", "Don't Save")
if r == 1:
save_cb()
return not changed
if r == 2:
return 1
else:
return 0
}
</PRE></UL>
<H3>load_file()</H3>
<P>This function loads the specified file into the <TT>textbuf</TT> class:
<UL><PRE>
loading = False
def load_file(newfile, ipos):
global changed, loading, filename
loading = True
if ipos != -1:
insert = 1
changed = True
else:
insert = 0
changed = False
if insert == 0:
filename = ""
r = textbuf.loadfile(newfile)
else:
r = textbuf.insertfile(newfile, ipos)
if r != 0:
fl_alert("Error reading from file %s."%newfile)
else:
if insert == 0:
filename = newfile
loading = False
textbuf.call_modify_callbacks()
</PRE></UL>
<P>When loading the file we use the <A
href="fltk.html#Fl_Text_Buffer-loadfile"><TT>loadfile()</TT></A>
method to "replace" the text in the buffer, or the <A
href="fltk.html#Fl_Text_Buffer-insertfile"><TT>insertfile()</TT></A>
method to insert text in the buffer from the named file.
<H3>save_file()</H3>
<P>This function saves the current buffer to the specified file:
<UL><PRE>
def save_file(newfile):
global changed, filename
if textbuf.savefile(newfile) != 0:
fl_alert("Error writing to file %s."%newfile)
else:
filename = newfile
changed = False
textbuf.call_modify_callbacks()
</PRE></UL>
<H3>set_title()</H3>
<P>This function checks the <TT>changed</TT> variable and updates the
window label accordingly:
<UL><PRE>
def set_title(win):
global filename, title
if len(filename) == 0:
title = "Untitled"
else:
title = os.path.basename(filename)
if changed:
title = title+" (modified)"
win.label(title)
</PRE></UL>
<H2>The main code</H2>
<P>Once we've created all of the support functions, the only thing left
is to tie them all together. What remains is to create a new text buffer, create a
new view (window) for the text, show the window, load the file on
the command-line (if any), and then enter the FLTK event loop:
<UL><PRE>
textbuf = Fl_Text_Buffer()
style_init()
window = new_view()
window.show(1, sys.argv)
if len(sys.argv) > 1:
load_file(sys.argv[1], -1)
Fl.run()
</PRE></UL>
<H2>Running the Editor</H2>
<P>The complete source for our text editor can be found in the <TT>test/editor.py</TT> source file. You can run the program as:
<UL><PRE>
python editor.py
</PRE></UL>
<P>Congratulations, you've just built your own text editor!</P>
<H2>The Final Product</H2>
The final editor window should look like the image in Figure 4-2.
<P ALIGN="CENTER"><IMG src="editor.jpg" ALT="The completed editor window."><BR>
<I>Figure 4-2: The completed editor window</I></P>
<H2>Advanced Features</H2>
<P>Now that we've implemented the basic functionality, it is
time to show off some of the advanced features of the
<CODE>Fl_Text_Editor</CODE> widget.
<H3>Syntax Highlighting</H3>
<P>The <CODE>Fl_Text_Editor</CODE> widget supports highlighting
of text with different fonts, colors, and sizes. The
implementation is based on the excellent <A
HREF="http://www.nedit.org/">NEdit</A> text editor core, which
uses a parallel "style" buffer which tracks the font, color, and
size of the text that is drawn.
<P>Styles are defined using Python arrays of the form:
<CODE>Fl_Text_Display::Style_Table_Entry</CODE> structure
defined in <CODE><FL/Fl_Text_Display.H></CODE>:
<UL><PRE>
[[color, font, size], ...]
</PRE></UL>
<P>The <CODE>color</CODE> member sets the color for the text,
the <CODE>font</CODE> member sets the FLTK font index to use,
and the <CODE>size</CODE> member sets the pixel size of the
text. The <CODE>attr</CODE> member is currently not used.
<P>For our text editor we'll define 7 styles for plain code,
comments, keywords, and preprocessor directives:
<UL><PRE>
styletable = [ # Style table
[ FL_BLACK, FL_COURIER, 14 ], # A - Plain
[ FL_DARK_GREEN, FL_COURIER_ITALIC, 14 ], # B - Line comments
[ FL_DARK_GREEN, FL_COURIER_ITALIC, 14 ], # C - Block comments
[ FL_BLUE, FL_COURIER, 14 ], # D - Strings
[ FL_DARK_RED, FL_COURIER, 14 ], # E - Directives
[ FL_DARK_RED, FL_COURIER_BOLD, 14 ], # F - Types
[ FL_BLUE, FL_COURIER_BOLD, 14 ] # G - Keywords
]
</PRE></UL>
<P>You'll notice that the comments show a letter next to each
style - each style in the style buffer is referenced using a
character starting with the letter 'A'.
<P>You call the <CODE>highlight_data()</CODE> method to associate the
style data and buffer with the text editor widget:
<UL><PRE>
w.editor.highlight_data(stylebuf, styletable,
len(styletable),
'A', style_unfinished_cb, None)
</PRE></UL>
<P>Finally, you need to add a callback to the main text buffer so
that changes to the text buffer are mirrored in the style buffer:
<UL><PRE>
textbuf.add_modify_callback(style_update, w.editor)
</PRE></UL>
<P>The <CODE>style_update()</CODE> function, like the <CODE>change_cb()</CODE>
function described earlier, is called whenever text is added or removed from
the text buffer. It mirrors the changes in the style buffer and then updates
the style data as necessary:
<UL><PRE>
#
# 'style_update()' - Update the style buffer...
#
def style_update(pos, nInserted, nDeleted, nRestyled, deletedText, e):
global stylebuf, editor
if nInserted == 0 and nDeleted == 0:
stylebuf.unselect()
else:
if nInserted > 0:
style = 'A'*nInserted
stylebuf.replace(pos, pos+nDeleted, style)
else:
# Just delete characters in the style buffer...
stylebuf.remove(pos, pos+nDeleted)
# Select the area that was just updated to avoid unnecessary
# callbacks...
stylebuf.select(pos, pos + nInserted - nDeleted)
# Re-parse the changed region; we do this by parsing from the
# beginning of the previous line of the changed region to the end of
# the line of the changed region... Then we check the last
# style character and keep updating if we have a multi-line
# comment character...
start = textbuf.line_start(pos)
end = textbuf.line_end(pos + nInserted)
text = textbuf.text_range(start, end)
style = stylebuf.text_range(start, end)
if start==end:
last = 0
else:
last = style[end - start - 1]
style = style_parse(text, style, end - start)
stylebuf.replace(start, end, style)
editor.editor.redisplay_range(start, end)
if start == end or last != style[end - start - 1]:
# Either the user deleted some text, or the last character
# on the line changed styles, so reparse the
# remainder of the buffer...
end = textbuf.length()
text = textbuf.text_range(start, end)
style = stylebuf.text_range(start, end)
style_parse(text, style, end - start)
stylebuf.replace(start, end, style)
editor.editor.redisplay_range(start, end)
</PRE></UL>
<P>The <CODE>style_parse()</CODE> function scans a copy of the
text in the buffer and generates the necessary style characters
for display. It assumes that parsing begins at the start of a line:
<UL><PRE>
//
// 'style_parse()' - Parse text and produce style data.
//
#
# 'style_parse()' - Parse text and produce style data.
#
def style_parse(text, style, length):
# Style letters:
#
# A - Plain
# B - Line comments
# C - Block comments
# D - Strings
# E - Directives
# F - Types
# G - Keywords
col = 0
new_style = ""
isComment = False
isString = False
pos = 0
last = False
while pos < length:
current = style[pos]
if isComment:
current = 'B'
if text[pos] == '\n':
isComment = False
elif isString:
current = 'D'
if text[pos] == '"' or text[pos] == "'":
isString = False
elif current in ['B', 'F', 'G']:
current = 'A'
if current == 'A':
# Check for directives, comments, strings, and keywords...
if text[pos] == '#':
current = 'B'
isComment = True
elif text[pos] == '"' or text[pos] == "'":
current = 'D'
isString = True
elif not last and text[pos].islower() or text[pos] == '_':
pos1 = pos
while pos1 < length:
if text[pos1].islower() or text[pos1] == '_':
pos1 += 1
else:
break
kw = text[pos:pos1]
if iskeyword(kw):
new_style = new_style+'F'*(pos1-pos)
current = 'F'
if pos1 >= length:
pos1 -= 1
pos = pos1
last = True
last = text[pos].isalnum() or text[pos] == '_' or text[pos] == '.'
if text[pos] == '\n':
col = 0
if current == 'B' or current == 'E':
current = 'A'
new_style = new_style+current
pos += 1
return new_style
</PRE></UL>
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