improve cursor positioning in mouse selections

Author: mike-ward

event_handlers.v

@@ -6,16 +6,6 @@ module gui
 //
 import arrays
 
-// MouseLockCfg stores callback functions for mouse event handling in a locked state.
-// When mouse is locked, these callbacks intercept normal mouse event processing.
-// Used for implementing drag operations and modal behaviors.
-pub struct MouseLockCfg {
-pub:
-	mouse_down ?fn (&Layout, mut Event, mut Window)
-	mouse_move ?fn (&Layout, mut Event, mut Window)
-	mouse_up   ?fn (&Layout, mut Event, mut Window)
-}
-
 fn char_handler(layout &Layout, mut e Event, mut w Window) {
 	for child in layout.children {
 		if child.shape.disabled {

examples/multiline_input.v

@@ -1,6 +1,6 @@
 import gui
 
-// Multiline Text Demo
+// Multiline Input Demo
 // =============================
 
 @[heap]
@@ -11,7 +11,7 @@ mut:
 
 fn main() {
 	mut window := gui.window(
-		title:        'Multiline Text Test'
+		title:        'Multiline Input Demo'
 		state:        &MultilineApp{}
 		width:        400
 		height:       300

view_state.v

@@ -2,8 +2,8 @@ module gui
 
 import sokol.sapp
 
-// Generating views and immediate mode means there is no place to
-// store view states. This is gui's solution.
+// Generating views and immediate mode means there is no place to store view
+// states. This is v-gui's  solution.
 struct ViewState {
 mut:
 	input_state       map[u32]InputState         // [id_focus] -> InputState
@@ -18,12 +18,25 @@ mut:
 	select_state      map[string]bool            // [id select] -> open/close state
 	tree_state        map[string]map[string]bool // [tree id] -> [node id ] -> open/closed
 	date_picker_state map[string]DatePickerState // [id date_picker -> DatePickerState
-	mouse_lock        MouseLockCfg               // mouse down/move/up methods to call when locked
+	mouse_lock        MouseLockCfg               // mouse down/move/up/scroll/sliders, etc. use this
 	id_focus          u32                        // current view that has focus
 	cursor_on_sticky  bool                       // keeps the cursor visible during cursor movement
 	input_cursor_on   bool = true // used by cursor blink animation
 }
 
+// MouseLockCfg stores callback functions for mouse event handling in a locked state.
+// When mouse is locked, these callbacks intercept normal mouse event processing.
+// Used for implementing drag operations and modal behaviors.
+pub struct MouseLockCfg {
+pub:
+	cursor_pos int
+	mouse_down ?fn (&Layout, mut Event, mut Window)
+	mouse_move ?fn (&Layout, mut Event, mut Window)
+	mouse_up   ?fn (&Layout, mut Event, mut Window)
+}
+
+// clear releases all stored view state maps and resets the window's ViewState.
+// Call this when a window is destroyed or needs its GUI state fully reinitialized.
 fn (mut vs ViewState) clear(mut w Window) {
 	unsafe {
 		vs.input_state.free()

view_text.v

@@ -130,8 +130,10 @@ fn (tv &TextView) on_click(layout &Layout, mut e Event, mut w Window) {
 	}
 	if e.mouse_button == .left && w.is_focus(layout.shape.id_focus) {
 		id_focus := layout.shape.id_focus
+		cursor_pos := tv.mouse_cursor_pos(layout.shape, e, mut w)
 		// Init mouse lock to handle dragging selection (mouse move) and finishing selection (mouse up)
 		w.mouse_lock(
+			cursor_pos: cursor_pos
 			mouse_move: fn [tv, id_focus] (layout &Layout, mut e Event, mut w Window) {
 				// The layout in mouse locks is always the root layout.
 				if ly := layout.find_layout(fn [id_focus] (ly Layout) bool {
@@ -153,7 +155,6 @@ fn (tv &TextView) on_click(layout &Layout, mut e Event, mut w Window) {
 			}
 		)
 		// Set cursor position and reset text selection
-		cursor_pos := tv.mouse_cursor_pos(layout.shape, e, mut w)
 		cursor_offset := offset_from_cursor_position(layout.shape, cursor_pos, w)
 		input_state := w.view_state.input_state[layout.shape.id_focus]
 		w.view_state.input_state[layout.shape.id_focus] = InputState{
@@ -181,17 +182,23 @@ fn (tv &TextView) mouse_move_locked(layout &Layout, mut e Event, mut w Window) {
 		}
 		ev := event_relative_to(layout.shape, e)
 		input_state := w.view_state.input_state[layout.shape.id_focus]
-		cursor_pos := u32(input_state.cursor_pos)
+		start_cursor_pos := u32(w.view_state.mouse_lock.cursor_pos)
 		mouse_cursor_pos := u32(tv.mouse_cursor_pos(layout.shape, ev, mut w))
 
-		// Update selection range: start is the original cursor pos, end is the current mouse pos
 		w.view_state.input_state[layout.shape.id_focus] = InputState{
 			...input_state
-			select_beg: if cursor_pos < mouse_cursor_pos { cursor_pos } else { mouse_cursor_pos }
-			select_end: if cursor_pos < mouse_cursor_pos { mouse_cursor_pos } else { cursor_pos }
+			cursor_pos:    int(mouse_cursor_pos)
+			cursor_offset: -1
+			select_beg:    match start_cursor_pos < mouse_cursor_pos {
+				true { start_cursor_pos }
+				else { mouse_cursor_pos }
+			}
+			select_end:    match start_cursor_pos < mouse_cursor_pos {
+				true { mouse_cursor_pos }
+				else { start_cursor_pos }
+			}
 		}
 
-		// Ensure the cursor being dragged to is visible
 		scroll_cursor_into_view(int(mouse_cursor_pos), layout, ev, mut w)
 		e.is_handled = true
 	}

xtra_window.v

@@ -21,7 +21,7 @@ fn (mut window Window) blinky_cursor_animation() {
 }
 
 // color_background returns the window background color
-pub fn (window &Window) color_background() Color {
+pub fn (_ &Window) color_background() Color {
 	return gui_theme.color_background
 }