Scintilla Usage Notes

Implementing Auto-Indent

The key idea is to use the SCN_CHARADDED notification to add indentation after a newline.

The lParam on the notification is a pointer to a SCNotification structure whose ch member specifies the character added. If a newline was added, the previous line can be retrieved and the same indentation can be added to the new line.

Here is the relevant portion of code from SciTE: (SciTE.cxx SciTEWindow::CharAdded)

if (ch == '\r' || ch == '\n') {
     char linebuf[1000];
     int curLine = GetCurrentLineNumber();
     int lineLength = SendEditor(SCI_LINELENGTH, curLine);
     //Platform::DebugPrintf("[CR] %d len = %d\n", curLine, lineLength);
     if (curLine > 0 && lineLength <= 2) {
     int prevLineLength = SendEditor(SCI_LINELENGTH, curLine - 1);
     if (prevLineLength < sizeof(linebuf)) {
         WORD buflen = sizeof(linebuf);
         memcpy(linebuf, &buflen, sizeof(buflen));
         SendEditor(EM_GETLINE, curLine - 1,
                    reinterpret_cast<LPARAM>(static_cast<char *>(linebuf)));
         linebuf[prevLineLength] = '\0';
         for (int pos = 0; linebuf[pos]; pos++) {
             if (linebuf[pos] != ' ' && linebuf[pos] != '\t')
                 linebuf[pos] = '\0';
         }
         SendEditor(EM_REPLACESEL, 0, reinterpret_cast<LPARAM>(static_cast<char *>(linebuf)));
     }
}

Of course, fancier handling could be implemented. For example, if the previous line was the start of a control construct, the next line could be automatically indented one tab further. (Assuming that is your indenting style.)

Implementing Syntax Styling

Syntax styling is handled by the SCN_STYLENEEDED notification. Scintilla keeps track of the end of the styled text - this is retrieved with SCI_GETENDSTYLED. In response to the SCN_STYLENEEDED notification, you should apply styles to the text from ENDSTYLED to the position specified by the notification.

Here is the relevant portion of code from SciTE: (SciTE.cxx)

void SciTEWindow::Notify(SCNotification *notification) {
     switch (notification->nmhdr.code) {
     case SCN_STYLENEEDED: {
             if (notification->nmhdr.idFrom == IDM_SRCWIN) {
                 int endStyled = SendEditor(SCI_GETENDSTYLED);
                 int lineEndStyled = SendEditor(EM_LINEFROMCHAR, endStyled);
                 endStyled = SendEditor(EM_LINEINDEX, lineEndStyled);
                 Colourise(endStyled, notification->position);

Colourize(start, end) retrieves the specified range of text and then calls ColourizeDoc in keywords.cxx. It starts the process by calling:

SendMessage(hwnd, SCI_STARTSTYLING, startPos, 31);

and then for each token of the text, calling:

SendMessage(hwnd, SCI_SETSTYLING, length, style);

where style is a number from 0 to 31 whose appearance has been defined using the HTTP/1.1 200 OK Connection: keep-alive Connection: keep-alive Content-Disposition: inline; filename="ScintillaUsage.html" Content-Disposition: inline; filename="ScintillaUsage.html" Content-Length: 23412 Content-Length: 23412 Content-Security-Policy: default-src 'none' Content-Security-Policy: default-src 'none' Content-Type: text/plain; charset=UTF-8 Content-Type: text/plain; charset=UTF-8 Date: Wed, 21 Oct 2026 10:45:13 UTC ETag: "e0ffb0bfc404373771709278a46ab56f4e81f722" ETag: "e0ffb0bfc404373771709278a46ab56f4e81f722" Expires: Sat, 18 Oct 2036 10:45:12 GMT Expires: Sat, 18 Oct 2036 10:45:13 GMT Last-Modified: Wed, 21 Oct 2026 10:45:12 GMT Last-Modified: Wed, 21 Oct 2026 10:45:13 GMT Server: OpenBSD httpd Server: OpenBSD httpd X-Content-Type-Options: nosniff X-Content-Type-Options: nosniff Scintilla Usage Notes

Scintilla Usage Notes

Implementing Auto-Indent

The key idea is to use the SCN_CHARADDED notification to add indentation after a newline.

Here is the relevant portion of code from SciTE: (SciTE.cxx SciTEWindow::CharAdded)