Is the cursor in CudaText custom-drawn?

[Autumn-one]

Hello, I am developing software that displays some information at the cursor position (not the mouse pointer, but the text cursor). Therefore, I need to be able to get the exact coordinates of the cursor in the editor relative to the entire system interface. My software works well in many other editors, but it does not work in the CudaText editor. I am wondering if the cursor in CudaText is custom-drawn? If so, is there a way to access the coordinates of the editor's cursor relative to the system interface?

[Alexey-T]

Do you need to read caret coord from Python API? or other way? it is possible only from Py API. App don't use Win32 API to paint the caret.

[Autumn-one]

To be honest, I don't have much experience with how applications handle SendMessage messages, but I feel that it should be possible to register a listener to listen for messages sent externally via SendMessage by calling a method like OnMessage (not necessarily called this) in Python. If you need to test how the SendMessage is sent, I can provide the relevant AHK code for you.

[Alexey-T]

I cannot make the SendMessage API in the near month, because not on Windows PC. Maybe in a month I can see it. Relevant AHK code won't help me. I need description of the API (which I will read in a month).

[Autumn-one]

Here is the answer I got from GPT, not sure if it helps:

import ctypes
from ctypes import wintypes

# Define some constants
WM_COPYDATA = 0x004A

# Define COPYDATASTRUCT structure
class COPYDATASTRUCT(ctypes.Structure):
    _fields_ = [("dwData", wintypes.LPARAM),
                ("cbData", wintypes.DWORD),
                ("lpData", wintypes.LPVOID)]

# Define window procedure
def wnd_proc(hWnd, message, wParam, lParam):
    if message == WM_COPYDATA:
        pCDS = ctypes.cast(lParam, ctypes.POINTER(COPYDATASTRUCT)).contents
        data = ctypes.string_at(pCDS.lpData, pCDS.cbData)
        print("Received message:", data.decode('utf-8'))
    return ctypes.windll.user32.DefWindowProcW(hWnd, message, wParam, lParam)

# Register window class
WNDPROCTYPE = ctypes.WINFUNCTYPE(ctypes.c_long, wintypes.HWND, wintypes.UINT, wintypes.WPARAM, wintypes.LPARAM)
wnd_proc_c = WNDPROCTYPE(wnd_proc)

wc = wintypes.WNDCLASS()
wc.lpfnWndProc = wnd_proc_c
wc.lpszClassName = "MyWindowClass"
ctypes.windll.user32.RegisterClassW(ctypes.byref(wc))

# Create window
hWnd = ctypes.windll.user32.CreateWindowExW(0, wc.lpszClassName, "MyWindow", 0, 0, 0, 0, 0, 0, 0, 0, None)

# Message loop
msg = wintypes.MSG()
while ctypes.windll.user32.GetMessageW(ctypes.byref(msg), 0, 0, 0) != 0:
    ctypes.windll.user32.TranslateMessage(ctypes.byref(msg))
    ctypes.windll.user32.DispatchMessageW(ctypes.byref(msg))

[Autumn-one]

Okay, thank you for your reply. If you plan to start this a month later, please remind me.

[Alexey-T]

@Autumn-one How does your software detect caret position in most of other editors, using what method? Is it win32 api for getting OS caret coords?

[Alexey-T]

@dinkumoil Hello. My editor misses some SendMessage API to help other apps to read the caret postion from AHK scripts. I am not on Windows PC so cannot add it in the near month. Can you help?

[dinkumoil]

@Alexey-T Sorry, I'm not able to help in coding, but I can provide some knowledge to solve the task.

SendMessage is a Windows API that directly calls a program's main message loop (in contrast to PostMessage that only queues a message to the program's message queue where it stays until Windows assigns the CPU to the program and the program calls some Windows API that reads messages from that queue).

In order to be able to process WM_COPYDATA messages you have to declare a so called message method in your main form like the following:

procedure TMainForm.WMCopyDataHandler(var Msg); message WM_COPYDATA;

The parameter Msg is a record like that:

TMsg = record 
  Msg: cardinal;
  WParam: WPARAM;
  LParam: LPARAM;
  Result: LRESULT;
end;

WPARAM, LPARAM and LRESULT are data types from the Windows API.

The message handler method WMCopyDataHandler can handle the record's fields like specified in the documentation of WM_COPYDATA. The important part here is field LParam which holds a pointer to a COPYDATASTRUCT record. The data that should be passed from one program to the other has to be in a buffer that is referenced by the lpData member of that record.

IMPORTANT (from the docs):

The data being passed must not contain pointers or other references to objects not accessible to the application receiving the data.

That's because the receiving process cannot access memory that is in the address space of the sending process. Windows marshalls the buffer whose pointer is provided in lpData and makes it possible that the receiving process can access its contained data but not the very same buffer!

Follow >> this link << for an example in C++ that shows how to use WM_COPYDATA.