menu_sdl: Implement the string-input dialog

The text field is hand-drawn and IME-aware: SDL_TEXTINPUT /
SDL_TEXTEDITING / BACKSPACE are handled directly (mirroring editor.c)
instead of using a microui textbox.

src/menu_sdl.c

@@ -23,6 +23,7 @@
 
 #include <stdio.h>
 #include <stdlib.h>
+#include <string.h>
 
 #include "portab.h"
 #include "system.h"
@@ -32,6 +33,7 @@
 #include "gfx_private.h"
 #include "msgskip.h"
 #include "modal.h"
+#include "utfsjis.h"
 #ifdef _WIN32
 #include "win/dialog.h"
 #endif
@@ -157,11 +159,180 @@ void menu_resetmenu_open(void) {
 	}
 }
 
+// The string-input dialog.
+// The input field is not a microui textbox: to support IME (SDL_TEXTEDITING)
+// composition we keep our own buffer (str_buf) and feed it from the handler,
+// mirroring editor.c.
+struct string_state {
+	modal base;
+	INPUTSTRING_PARAM *param;
+	char composing[SDL_TEXTEDITINGEVENT_TEXT_SIZE];  // IME preedit text
+	bool done;
+	bool accepted;
+};
+
+// Heap buffer holding the string dialog's edited text. It must outlive the
+// modal loop because the caller reads p->newstring after menu_inputstring()
+// returns; it is freed and reallocated on the next call.
+static char *str_buf;
+
+// Append `add` to str_buf, truncating so the total stays within
+// st->param->max characters (counted as UTF-8 code points).
+static void str_append(struct string_state *st, const char *add) {
+	int room = st->param->max;
+	for (const char *p = str_buf; *p; p = advance_char(p, UTF8))
+		room--;
+	const char *end = add;
+	while (room > 0 && *end) {
+		end = advance_char(end, UTF8);
+		room--;
+	}
+	strncat(str_buf, add, end - add);
+}
+
+// Delete the last UTF-8 character of str_buf.
+static void str_backspace(void) {
+	if (!*str_buf)
+		return;
+	char *p = str_buf + strlen(str_buf) - 1;
+	while (p > str_buf && UTF8_TRAIL_BYTE(*p))
+		p--;
+	*p = '\0';
+}
+
+static bool menu_string_handler(const SDL_Event *e, modal *modal) {
+	struct string_state *st = (struct string_state *)modal;
+	switch (e->type) {
+	case SDL_KEYDOWN:
+		// While an IME composition is active, let it consume the key.
+		if (!*st->composing) {
+			switch (e->key.keysym.sym) {
+			case SDLK_RETURN:
+				st->accepted = true;
+				st->done = true;
+				break;
+			case SDLK_ESCAPE:
+				st->base.cancelled = true;
+				break;
+			case SDLK_BACKSPACE:
+				str_backspace();
+				break;
+			}
+		}
+		return true;  // never forward keys to microui (there is no textbox)
+	case SDL_TEXTINPUT:
+		str_append(st, e->text.text);
+		st->composing[0] = '\0';
+		return true;
+	case SDL_TEXTEDITING:
+		strncpy(st->composing, e->edit.text, sizeof(st->composing) - 1);
+		st->composing[sizeof(st->composing) - 1] = '\0';
+		return true;
+	}
+	return modal_default_handler(e, modal);
+}
+
+// Tell SDL where the text input is, so the IME candidate window is positioned
+// near the field. `box` is in logical (view) coordinates; convert to window
+// pixels for SDL_SetTextInputRect.
+static void set_text_input_rect(mu_Rect box) {
+	SDL_Rect r = { box.x, box.y, box.w, box.h };
+#if SDL_VERSION_ATLEAST(2, 0, 18)
+	int x2, y2;
+	SDL_RenderLogicalToWindow(gfx_renderer, box.x, box.y, &r.x, &r.y);
+	SDL_RenderLogicalToWindow(gfx_renderer, box.x + box.w, box.y + box.h, &x2, &y2);
+	r.w = x2 - r.x;
+	r.h = y2 - r.y;
+#endif
+	SDL_SetTextInputRect(&r);
+}
+
+// Draw the IME-aware text field (committed text, preedit with underline, caret).
+static void draw_string_field(mu_Context *ctx, mu_Rect box, const struct string_state *st) {
+	mu_draw_rect(ctx, box, ctx->style->colors[MU_COLOR_BASE]);
+	mu_draw_box(ctx, box, ctx->style->colors[MU_COLOR_BORDER]);
+
+	mu_Font font = ctx->style->font;
+	mu_Color col = ctx->style->colors[MU_COLOR_TEXT];
+	int th = ctx->text_height(font);
+	int x = box.x + ctx->style->padding;
+	int y = box.y + (box.h - th) / 2;
+
+	mu_push_clip_rect(ctx, box);
+	if (*str_buf) {
+		mu_draw_text(ctx, font, str_buf, -1, mu_vec2(x, y), col);
+		x += ctx->text_width(font, str_buf, -1);
+	}
+	if (*st->composing) {
+		mu_draw_text(ctx, font, st->composing, -1, mu_vec2(x, y), col);
+		int cw = ctx->text_width(font, st->composing, -1);
+		mu_draw_rect(ctx, mu_rect(x, y + th, cw, 1), col);  // preedit underline
+		x += cw;
+	}
+	mu_draw_rect(ctx, mu_rect(x, y, 1, th), col);  // caret
+	mu_pop_clip_rect(ctx);
+
+	set_text_input_rect(box);
+}
+
+static bool inputstring_build(mu_Context *ctx, modal *modal) {
+	struct string_state *st = (struct string_state *)modal;
+	const char *title = (st->param->title && *st->param->title)
+	                        ? st->param->title : _("Enter a string");
+	int row_h = ctx->text_height(ctx->style->font) + ctx->style->padding * 2;
+	int w = 320;
+	int h = 3 * (row_h + ctx->style->spacing) + ctx->style->padding * 2
+	        + ctx->style->title_height;
+	mu_Rect r = mu_rect((view_w - w) / 2, (view_h - h) / 2, w, h);
+
+	if (mu_begin_window_ex(ctx, title, r,
+	        MU_OPT_NORESIZE | MU_OPT_NOCLOSE | MU_OPT_NOSCROLL)) {
+		mu_layout_row(ctx, 1, (int[]){ -1 }, 0);
+
+		char info[64];
+		snprintf(info, sizeof(info), _("Up to %d characters"), st->param->max);
+		mu_label(ctx, info);
+
+		draw_string_field(ctx, mu_layout_next(ctx), st);
+
+		int content = w - ctx->style->padding * 2;
+		int half = (content - ctx->style->spacing) / 2;
+		mu_layout_row(ctx, 2, (int[]){ half, -1 }, 0);
+		if (mu_button(ctx, _("OK"))) {
+			st->accepted = true;
+			st->done = true;
+		}
+		if (mu_button(ctx, _("Cancel"))) {
+			st->accepted = false;
+			st->done = true;
+		}
+		mu_end_window(ctx);
+	}
+
+	if (st->base.cancelled) {  // Esc
+		st->accepted = false;
+		st->done = true;
+	}
+	return !st->done;
+}
+
 bool menu_inputstring(INPUTSTRING_PARAM *p) {
 #ifdef _WIN32
 	return input_string(p);
 #else
-	p->newstring = p->oldstring;
+	struct string_state st = {
+		.base = { .build = inputstring_build, .handler = menu_string_handler },
+		.param = p,
+	};
+	free(str_buf);
+	str_buf = malloc(p->max * MAX_UTF8_BYTES_PAR_CHAR + 1);
+	strcpy(str_buf, p->oldstring ? p->oldstring : "");
+
+	SDL_StartTextInput();
+	modal_run(&st.base);
+	SDL_StopTextInput();
+
+	p->newstring = st.accepted ? str_buf : p->oldstring;
 	return true;
 #endif
 }