libdmview: unseen boxes draw nothing; dmview keeps the splash screen

apps/dmview/src/main.c

@@ -392,6 +392,7 @@ static void show_view(service_t* s, char* path)
         Dmod_Free(path);
         return;
     }
+    bool was_shown = s->view != NULL;
     libdmview_close(s->view);
     s->view = NULL;
     if (s->view_path != NULL)
@@ -400,6 +401,8 @@ static void show_view(service_t* s, char* path)
     if (path == NULL)
     {
         DMOD_LOG_WARN("dmview: no view for %s (DMVIEW_VIEWS, DMVIEW_DEFAULT)\n", s->name);
+        if (!was_shown)
+            return;                     /* What the display shows - a splash screen - stays */
         dmdrvi_gfx_fill_rect_t all = { 0, 0, s->info.width, s->info.height, 0xFF000000u };
         (void)Dmod_Ioctl(s->gfx, DMDRVI_IOCTL_GFX_FILL_RECT, &all);
         present(s, NULL);

src/exec.c

@@ -744,6 +744,28 @@ static void redraw(struct libdmview* v, int32_t target, const rect_t* area)
     run(v, b->begin * DMV_CODE_WORD, true);
 }
 
+/*
+ * A box that changed but is not seen - a screen of a page behind the one
+ * shown, its opacity 0 - draws nothing, yet redrawing it redraws what is
+ * seen beneath it (a page's animations ran under the shown page all the
+ * time). Unseen: a box around it was not seen when last drawn (when that
+ * one's opacity changes, it is redrawn itself, with all inside it), or it
+ * was not seen itself and its OPACITY still makes it so.
+ */
+static bool stays_unseen(struct libdmview* v, const rbox_t* b)
+{
+    for (int32_t p = b->parent; p != ROOT; p = v->boxes[p].parent)
+    {
+        if (v->boxes[p].seen == 0)
+            return true;
+    }
+    if (b->seen != 0)
+        return false;
+    const uint8_t* insn = v->code + b->begin * DMV_CODE_WORD;
+    const uint8_t* next = insn + insn[1];
+    return next[0] == DMV_OP_OPACITY && v16(v, next, 0, OPOFF(OPACITY, 0)) <= 0;
+}
+
 void exec_draw(struct libdmview* v, rect_t* changed)
 {
     rect_t screen = { 0, 0, v->surface_w, v->surface_h };
@@ -766,7 +788,7 @@ void exec_draw(struct libdmview* v, rect_t* changed)
             rbox_t* b = &v->boxes[i];
             if ((b->flags & BOXF_DIRTY) == 0)
                 continue;
-            if ((b->flags & BOXF_VISIBLE) == 0)
+            if ((b->flags & BOXF_VISIBLE) == 0 || stays_unseen(v, b))
             {
                 b->flags &= (uint8_t)~BOXF_DIRTY;
                 continue;

tests/fixtures/hidden.dmvs

@@ -1,12 +1,14 @@
 ; Two screens one on another, as a page's views: the one below shown, with
 ; a button; the one on top hidden by its opacity ($top), with a box taking
-; no contact over the button - and a button of its own elsewhere.
+; no contact over the button - and a button of its own elsewhere. $tick
+; changes what the hidden screen shows: a bar's width, a box's place.
 .view   hidden
 .entry  draw
 
 .var    $top,    int, 0
 .var    $below,  int, 0
 .var    $above,  int, 0
+.var    $tick,   int, 1
 
 draw:
         FILL    #000000
@@ -25,6 +27,12 @@ draw:
         ON      CLICK, press_above
         FILL    #00FF00
         END
+        BOX     @bar, 0, 28, 64, 4
+        RECT    0, 0, $tick, 4, #FFFFFF
+        END
+        BOX     @mover, $tick, 24, 4, 4
+        FILL    #FFFF00
+        END
         END
         RET
 

tests/libdmview_test.c

@@ -742,6 +742,10 @@ DMOD_TEST_STEP(libdmview_hidden_boxes_take_no_contact)
         return;
     DMOD_TEST_EXPECT_EQ(libdmview_render(g_view, &g_s32, NULL), 1);
 
+    /* What the hidden screen shows changes: nothing is drawn */
+    DMOD_TEST_EXPECT_EQ(libdmview_set_int(g_view, "tick", 9), 0);
+    DMOD_TEST_EXPECT_EQ(libdmview_render(g_view, &g_s32, NULL), 0);
+
     /* The screen on top is not seen: the button beneath it is clicked */
     touch(1, 15, 15, 10);
     touch(0, 0, 0, 20);
@@ -755,6 +759,10 @@ DMOD_TEST_STEP(libdmview_hidden_boxes_take_no_contact)
     /* Shown: it covers the button, its own takes the contact */
     DMOD_TEST_EXPECT_EQ(libdmview_set_int(g_view, "top", 255), 0);
     DMOD_TEST_EXPECT_EQ(libdmview_render(g_view, &g_s32, NULL), 1);
+    DMOD_TEST_EXPECT_EQ(px(1, 29), 0xFFFFFFFFu);    /* The bar as $tick has it now */
+    DMOD_TEST_EXPECT_EQ(px(9, 25), 0xFFFFFF00u);
+    DMOD_TEST_EXPECT_EQ(libdmview_set_int(g_view, "tick", 20), 0);
+    DMOD_TEST_EXPECT_EQ(libdmview_render(g_view, &g_s32, NULL), 1);     /* Seen: drawn */
     touch(1, 15, 15, 50);
     touch(0, 0, 0, 60);
     DMOD_TEST_EXPECT_EQ(libdmview_get_int(g_view, "below", &value), 0);