Render drop shadow for active window

apps/multi.c

@@ -7,6 +7,7 @@
 #include "apps_multi.h"
 
 #define D(x) twin_double_to_fixed(x)
+#define ASSET_PATH "assets/"
 
 static void apps_line_start(twin_screen_t *screen, int x, int y, int w, int h)
 {
@@ -272,6 +273,50 @@ static void apps_flower_start(twin_screen_t *screen, int x, int y, int w, int h)
     twin_window_show(window);
 }
 
+static void apps_blur(twin_screen_t *screen, int x, int y, int w, int h)
+{
+    twin_pixmap_t *raw_background =
+        twin_pixmap_from_file(ASSET_PATH "tux.png", TWIN_ARGB32);
+    twin_window_t *window = twin_window_create(
+        screen, TWIN_ARGB32, TwinWindowApplication, x, y, w, h);
+    twin_window_set_name(window, "Blur");
+    twin_pixmap_t *scaled_background = twin_pixmap_create(
+        TWIN_ARGB32, window->pixmap->width, window->pixmap->height);
+    twin_fixed_t sx, sy;
+    sx = twin_fixed_div(
+        twin_int_to_fixed(raw_background->width),
+        twin_int_to_fixed(window->client.right - window->client.left));
+    sy = twin_fixed_div(
+        twin_int_to_fixed(raw_background->height),
+        twin_int_to_fixed(window->client.bottom - window->client.top));
+
+    twin_matrix_scale(&raw_background->transform, sx, sy);
+    twin_operand_t srcop = {
+        .source_kind = TWIN_PIXMAP,
+        .u.pixmap = raw_background,
+    };
+
+    twin_composite(scaled_background, 0, 0, &srcop, 0, 0, 0, 0, 0, TWIN_SOURCE,
+                   screen->width, screen->height);
+
+    twin_pointer_t src, dst;
+    for (int y = window->client.top; y < window->client.bottom; y++)
+        for (int x = window->client.left; x < window->client.right; x++) {
+            src =
+                twin_pixmap_pointer(scaled_background, x - window->client.left,
+                                    y - window->client.top);
+            dst = twin_pixmap_pointer(window->pixmap, x, y);
+            *dst.argb32 = *src.argb32 | 0xff000000;
+        }
+    twin_stack_blur(window->pixmap, 5, window->client.left,
+                    window->client.right, window->client.top,
+                    window->client.bottom);
+
+    twin_pixmap_destroy(scaled_background);
+    twin_pixmap_destroy(raw_background);
+    twin_window_show(window);
+}
+
 void apps_multi_start(twin_screen_t *screen,
                       const char *name,
                       int x,
@@ -286,4 +331,5 @@ void apps_multi_start(twin_screen_t *screen,
     apps_ascii_start(screen, x += 20, y += 20, w, h);
     apps_jelly_start(screen, x += 20, y += 20, w / 2, h);
     apps_flower_start(screen, x += 20, y += 20, w, h);
+    apps_blur(screen, x += 20, y += 20, w / 2, h / 2);
 }

configs/Kconfig

@@ -55,6 +55,10 @@ config CURSOR
     default n
     depends on !BACKEND_VNC
 
+config DROP_SHADOW
+    bool "Render drop shadow for active window"
+    default y
+
 endmenu
 
 menu "Image Loaders"

include/twin.h

@@ -194,6 +194,14 @@ typedef struct _twin_pixmap {
      * Pixels
      */
     twin_animation_t *animation;
+#if defined(CONFIG_DROP_SHADOW)
+    /*
+     * When the pixel map is within the active window, it will have a drop
+     * shadow to enhance its visual distinction.
+     */
+    bool shadow;
+#endif
+
     twin_pointer_t p;
     /*
      * When representing a window, this point
@@ -422,6 +430,13 @@ typedef void (*twin_destroy_func_t)(twin_window_t *window);
 struct _twin_window {
     twin_screen_t *screen;
     twin_pixmap_t *pixmap;
+
+#if defined(CONFIG_DROP_SHADOW)
+    /* Set the shadow range for horizontal and vertical directions. */
+    twin_coord_t shadow_x;
+    twin_coord_t shadow_y;
+#endif
+
     twin_window_style_t style;
     twin_rect_t client;
     twin_rect_t damage;
@@ -626,6 +641,14 @@ void twin_dispatch(twin_context_t *ctx);
  * draw.c
  */
 
+/* Blur the specified area in the pixel map. */
+void twin_stack_blur(twin_pixmap_t *px,
+                     int radius,
+                     twin_coord_t left,
+                     twin_coord_t right,
+                     twin_coord_t top,
+                     twin_coord_t bottom);
+
 void twin_composite(twin_pixmap_t *dst,
                     twin_coord_t dst_x,
                     twin_coord_t dst_y,
@@ -649,6 +672,15 @@ void twin_fill(twin_pixmap_t *dst,
 
 void twin_premultiply_alpha(twin_pixmap_t *px);
 
+/*
+ * Overwrite the original pixel values of the specified area in the pixel map.
+ */
+void twin_cover(twin_pixmap_t *dst,
+                twin_argb32_t color,
+                twin_coord_t x,
+                twin_coord_t y,
+                twin_coord_t width);
+
 /*
  * event.c
  */

include/twin_private.h

@@ -187,6 +187,25 @@ typedef int64_t twin_xfixed_t;
      ((((s) << 5) & 0xfc00) | (((s) >> 1) & 0x300)) | \
      ((((s) << 8) & 0xf80000) | (((s) << 3) & 0x70000)) | 0xff000000)
 
+#ifndef min
+#define min(x, y)            \
+    ({                       \
+        typeof(x) _x = (x);  \
+        typeof(y) _y = (y);  \
+        (void) (&_x == &_y); \
+        _x < _y ? _x : _y;   \
+    })
+#endif
+#ifndef max
+#define max(x, y)            \
+    ({                       \
+        typeof(x) _x = (x);  \
+        typeof(y) _y = (y);  \
+        (void) (&_x == &_y); \
+        _x > _y ? _x : _y;   \
+    })
+#endif
+
 typedef union {
     twin_pointer_t p;
     twin_argb32_t c;
@@ -467,7 +486,7 @@ void _twin_path_sfinish(twin_path_t *path);
 #define twin_glyph_snap_y(g) (twin_glyph_snap_x(g) + twin_glyph_n_snap_x(g))
 
 /*
- * dispatch stuff
+ * Dispatch stuff
  */
 typedef struct _twin_queue {
     struct _twin_queue *next;
@@ -592,6 +611,17 @@ void _twin_button_init(twin_button_t *button,
                        twin_style_t font_style,
                        twin_dispatch_proc_t dispatch);
 
+/*
+ * Visual effect stuff
+ */
+
+#if defined(CONFIG_DROP_SHADOW)
+void twin_shadow_border(twin_pixmap_t *shadow,
+                        twin_argb32_t color,
+                        twin_coord_t shift_x,
+                        twin_coord_t shift_y);
+#endif
+
 /* utility */
 
 #ifdef _MSC_VER