imgui: Clamp mouse y-coordinate in multi-line click/drag to text bounds (#15052)

* imgui: Clamp mouse y-coordinate in multi-line click/drag to text bounds

In single-line mode, click and drag already clamped y to the line's
y-coordinate so the cursor would continue to follow the x-position when
the mouse went off the top or bottom of the text.  Multi-line mode did
not clamp, so stb_text_locate_coord() would return 0 (above) or n
(below), snapping the cursor to the very start or end of text and
ignoring the x-coordinate entirely.

Now both modes walk the row layout to compute the top of the first row
(y_min) and bottom of the last row (y_max, minus half a line height to
add tolerance for rounding), then clamp y to that range before passing
it to stb_text_locate_coord().  This means dragging or clicking above
the text now places the cursor on the first line at the x-coordinate,
and dragging/clicking below places it on the last line at the
x-coordinate, matching the single-line precedent.

* Fix issue that cursor cannot be placed at the last empty line
This commit is contained in:
Noisyfox
2026-08-03 18:34:05 +08:00
committed by GitHub
parent 6b5c8af1c8
commit 66d3f3f9c3

View File

@@ -465,6 +465,57 @@ static void stb_textedit_click(STB_TEXTEDIT_STRING *str, STB_TexteditState *stat
STB_TEXTEDIT_LAYOUTROW(&r, str, 0);
y = r.ymin;
}
else
{
// In multi-line mode, clamp y to stay within the text vertical bounds.
// This lets the click still land at a valid location if the mouse is slightly
// above or below the text.
StbTexteditRow r;
int n = STB_TEXTEDIT_STRINGLEN(str);
int i = 0;
float base_y = 0, y_min, y_max;
// Get the first row to establish y_min and start the iteration
STB_TEXTEDIT_LAYOUTROW(&r, str, 0);
if (r.num_chars <= 0)
{
state->cursor = 0;
state->select_start = state->cursor;
state->select_end = state->cursor;
state->has_preferred_x = 0;
return;
}
y_min = r.ymin;
y_max = base_y + r.ymax;
i = r.num_chars;
base_y += r.baseline_y_delta;
// Walk the remaining rows to find the bottom of the last row
while (i < n)
{
STB_TEXTEDIT_LAYOUTROW(&r, str, i);
if (r.num_chars <= 0)
break;
y_max = base_y + r.ymax;
i += r.num_chars;
base_y += r.baseline_y_delta;
}
// If the text ends with a newline, account for the empty trailing line
// so the cursor can be placed on it
if (n > 0 && STB_TEXTEDIT_GETCHAR(str, n - 1) == STB_TEXTEDIT_NEWLINE)
{
STB_TEXTEDIT_LAYOUTROW(&r, str, n);
y_max = base_y + r.ymax;
}
// Subtract half the last line height to avoid rounding issues when the mouse
// is just barely below the last line (keep cursor on the last line, not after the text)
y_max -= (r.ymax - r.ymin) * 0.5f;
if (y < y_min) y = y_min;
if (y > y_max) y = y_max;
}
state->cursor = stb_text_locate_coord(str, x, y);
state->select_start = state->cursor;
@@ -485,6 +536,50 @@ static void stb_textedit_drag(STB_TEXTEDIT_STRING *str, STB_TexteditState *state
STB_TEXTEDIT_LAYOUTROW(&r, str, 0);
y = r.ymin;
}
else
{
// In multi-line mode, clamp y to stay within the text vertical bounds.
// This lets the drag keep working if the mouse goes off the top or bottom of the text.
StbTexteditRow r;
int n = STB_TEXTEDIT_STRINGLEN(str);
int i = 0;
float base_y = 0, y_min, y_max;
// Get the first row to establish y_min and start the iteration
STB_TEXTEDIT_LAYOUTROW(&r, str, 0);
if (r.num_chars <= 0)
return;
y_min = r.ymin;
y_max = base_y + r.ymax;
i = r.num_chars;
base_y += r.baseline_y_delta;
// Walk the remaining rows to find the bottom of the last row
while (i < n)
{
STB_TEXTEDIT_LAYOUTROW(&r, str, i);
if (r.num_chars <= 0)
break;
y_max = base_y + r.ymax;
i += r.num_chars;
base_y += r.baseline_y_delta;
}
// If the text ends with a newline, account for the empty trailing line
// so the cursor can be placed on it
if (n > 0 && STB_TEXTEDIT_GETCHAR(str, n - 1) == STB_TEXTEDIT_NEWLINE)
{
STB_TEXTEDIT_LAYOUTROW(&r, str, n);
y_max = base_y + r.ymax;
}
// Subtract half the last line height to avoid rounding issues when the mouse
// is just barely below the last line (keep cursor on the last line, not after the text)
y_max -= (r.ymax - r.ymin) * 0.5f;
if (y < y_min) y = y_min;
if (y > y_max) y = y_max;
}
if (state->select_start == state->select_end)
state->select_start = state->cursor;