Manipulate mouse cursor with a minimal image

This commit makes mouse cursor manipulation configurable, allowing it to
be turned off completely for the SDL backend and to be featured in the
upcoming Linux framebuffer backend with a minimal mouse image rendered.
Currently, only one minimalist dot is provided, but the default cursor
image should be improved later.

Makefile

@@ -56,6 +56,9 @@ libtwin.a_includes-y := \
 	include \
 	src
 
+# Features
+libtwin.a_files-$(CONFIG_CURSOR) += src/cursor.c
+
 # Image loaders
 
 ifeq ($(CONFIG_LOADER_JPEG), y)

apps/main.c

@@ -101,6 +101,13 @@ int main(void)
     atexit(cleanup);
     signal(SIGINT, sigint_handler);
 
+#if defined(CONFIG_CURSOR)
+    int hx, hy;
+    twin_pixmap_t *cursor = twin_make_cursor(&hx, &hy);
+    if (cursor)
+        twin_screen_set_cursor(tx->screen, cursor, hx, hy);
+#endif
+
     twin_screen_set_background(
         tx->screen, load_background(tx->screen, ASSET_PATH "/tux.png"));
 

configs/Kconfig

@@ -16,6 +16,14 @@ config BACKEND_SDL
 
 endchoice
 
+menu "Features"
+
+config CURSOR
+    bool "Manipulate cursor"
+    default n
+
+endmenu
+
 menu "Image Loaders"
 
 config LOADER_PNG

include/twin.h

@@ -578,6 +578,12 @@ void twin_path_convolve(twin_path_t *dest,
                         twin_path_t *stroke,
                         twin_path_t *pen);
 
+/*
+ * cursor.c
+ */
+
+twin_pixmap_t *twin_make_cursor(int *hx, int *hy);
+
 /*
  * dispatch.c
  */

src/cursor.c

@@ -0,0 +1,27 @@
+/*
+ * Twin - A Tiny Window System
+ * Copyright (c) 2024 National Cheng Kung University, Taiwan
+ * All rights reserved.
+ */
+
+/* Manipulating cursor images */
+
+#include <stddef.h>
+#include <twin.h>
+
+/* FIXME: Improve the default cursor instead of using a minimalist dot. */
+static uint32_t _twin_cursor_default[] = {
+    0x00000000, 0x88ffffff, 0x88ffffff, 0x00000000, 0x88ffffff, 0xff000000,
+    0xff000000, 0x88ffffff, 0x88ffffff, 0xff000000, 0xff000000, 0x88ffffff,
+    0x00000000, 0x88ffffff, 0x88ffffff, 0x00000000,
+};
+
+twin_pixmap_t *twin_make_cursor(int *hx, int *hy)
+{
+    twin_pointer_t data = {.argb32 = _twin_cursor_default};
+    twin_pixmap_t *cur = twin_pixmap_create_const(TWIN_ARGB32, 4, 4, 16, data);
+    if (!cur)
+        return NULL;
+    *hx = *hy = 4;
+    return cur;
+}

src/screen.c

@@ -210,9 +210,11 @@ void twin_screen_update(twin_screen_t *screen)
                 twin_screen_span_pixmap(screen, span, p, y, left, right, pop16,
                                         pop32);
 
+#if defined(CONFIG_CURSOR)
             if (screen->cursor)
                 twin_screen_span_pixmap(screen, span, screen->cursor, y, left,
                                         right, pop16, pop32);
+#endif
 
             (*screen->put_span)(left, y, right, span, screen->closure);
         }
@@ -253,6 +255,7 @@ twin_pixmap_t *twin_screen_get_background(twin_screen_t *screen)
     return screen->background;
 }
 
+#if defined(CONFIG_CURSOR)
 static void twin_screen_damage_cursor(twin_screen_t *screen)
 {
     twin_screen_damage(screen, screen->cursor->x, screen->cursor->y,
@@ -302,6 +305,7 @@ static void twin_screen_update_cursor(twin_screen_t *screen,
 
     twin_screen_enable_update(screen);
 }
+#endif /* CONFIG_CURSOR */
 
 static void _twin_adj_mouse_evt(twin_event_t *event, twin_pixmap_t *pixmap)
 {
@@ -320,9 +324,11 @@ bool twin_screen_dispatch(twin_screen_t *screen, twin_event_t *event)
     case TwinEventMotion:
     case TwinEventButtonDown:
     case TwinEventButtonUp:
+#if defined(CONFIG_CURSOR)
         /* update mouse cursor */
         twin_screen_update_cursor(screen, event->u.pointer.screen_x,
                                   event->u.pointer.screen_y);
+#endif
 
         /* if target is tracking the mouse, check for mouse up, if not,
          * just pass the event along