visual feedback for drag-and-drop tab reordering (mintty#1283)

src/wintab.c

@@ -84,6 +84,7 @@ tabbar_update()
 #endif
   wchar_t title_fit[256];
   HDC tabdc = GetDC(tab_wnd);
+  //printf("tab DC %p\n", tabdc);
   SelectObject(tabdc, tabbar_font);
   tie.pszText = title_fit;
   SendMessage(tab_wnd, TCM_DELETEALLITEMS, 0, 0);
@@ -164,6 +165,7 @@ container_proc(HWND hwnd, UINT msg, WPARAM wp, LPARAM lp)
 static WORD dragmsg = 0;
 static int dragidx = -1;
 static int targidx = -1;
+static int targpro = -1;
 
   if (msg == WM_MOUSEACTIVATE) {
     //printf("WM_MOUSEACTIVATE lo %02X hi %02X\n", LOWORD(lp), HIWORD(lp));
@@ -211,16 +213,42 @@ static int targidx = -1;
         int x = p.x - xoff;
         int dropidx = x / curr_tab_width;
         //printf("%d:%d (pw %d) x %d drop %d\n", (int)p.y, (int)p.x, curr_tab_width, x, dropidx);
+        bool redraw_tab = false;
         if (dropidx != targidx && targidx >= 0) {
           // clear hover highlighting of previous drop target
-
+
+          // clear visual indication via RedrawWindow/WM_DRAWITEM
           targidx = -1;
+          redraw_tab = true;
         }
         if (dropidx != dragidx) {
           // visual indication of tab dragging: hover highlighting
-
+          // enquire tab rect to calculate relative cursor position
+          RECT tr;
+          SendMessage(tab_wnd, TCM_GETITEMRECT, dropidx, (LPARAM)&tr);
+          //printf("drop RECT %d %d %d %d\n", tr.left, tr.right, tr.top, tr.bottom);
+          int w = tr.right - tr.left;
+          int c = (tr.left + tr.right) / 2;
+          targpro = 100 - abs(x - c) * 100 / (w / 2);
+          //printf("drop %d [%d] %d: %d\n", tr.left, x, tr.right, targpro);
+#ifdef hover_tab_within_wm_setcursor
+#warning the RECT does not properly match what we have at WM_DRAWITEM ...
+          tr.right += xoff;  // tune tab position
+          tr.bottom += xoff;  // assuming yoff would be == xoff
+          HDC tabdc = GetDC(tab_wnd);
+          HBRUSH tabbr = CreateSolidBrush(RGB(50, 90, 200));
+          FillRect(tabdc, &tr, tabbr);
+          DeleteObject(tabbr);
+          ReleaseDC(tab_wnd, tabdc);
+#endif
+          // enquire tab rect to calculate relative cursor position
+
+          // render visual indication via RedrawWindow/WM_DRAWITEM
           targidx = dropidx;
+          redraw_tab = true;
         }
+        if (redraw_tab)
+          RedrawWindow(tab_wnd, 0, 0, RDW_INVALIDATE | RDW_UPDATENOW);
       }
     }
     else if (HIWORD(lp) == WM_LBUTTONUP) {
@@ -312,8 +340,10 @@ static int targidx = -1;
   else if (msg == WM_DRAWITEM) {
     //printf("tabbar con_proc WM_DRAWITEM\n");
     LPDRAWITEMSTRUCT dis = (LPDRAWITEMSTRUCT)lp;
+    int itemID = dis->itemID;
+
     HDC hdc = dis->hDC;
-    //printf("container received drawitem %llx %p\n", wp, dis);
+    //printf("WM_DRAWITEM %d DC %p RECT %d %d %d %d\n", itemID, hdc, dis->rcItem.left, dis->rcItem.right, dis->rcItem.top, dis->rcItem.bottom);
     int hcenter = (dis->rcItem.left + dis->rcItem.right) / 2;
     int vcenter = (dis->rcItem.top + dis->rcItem.bottom) / 2;
 
@@ -323,11 +353,11 @@ static int targidx = -1;
     tie.mask = TCIF_TEXT;
     tie.pszText = buf;
     tie.cchTextMax = 256;
-    SendMessage(tab_wnd, TCM_GETITEMW, dis->itemID, (LPARAM)&tie);
+    SendMessage(tab_wnd, TCM_GETITEMW, itemID, (LPARAM)&tie);
 
     HBRUSH tabbr;
     colour tabbg = (colour)-1;
-    if (tabinfo[dis->itemID].wnd == wnd) {
+    if (tabinfo[itemID].wnd == wnd) {
       //tabbr = GetSysColorBrush(COLOR_ACTIVECAPTION);
       //SetTextColor(hdc, GetSysColor(COLOR_CAPTIONTEXT));
       tabbr = GetSysColorBrush(COLOR_HIGHLIGHT);
@@ -353,6 +383,23 @@ static int targidx = -1;
       //tabbr = GetSysColorBrush(COLOR_INACTIVECAPTION);
       SetTextColor(hdc, GetSysColor(COLOR_CAPTIONTEXT));
       //printf("tab fg %06X\n", GetSysColor(COLOR_CAPTIONTEXT));
+
+      // drag-and-drop hover highlighting
+      if (itemID == targidx) {
+        colour bg1 = cfg.tab_bg_colour;
+        if (bg1 == (colour)-1)
+          bg1 = GetSysColor(COLOR_HIGHLIGHT);
+        colour bg0 = GetSysColor(COLOR_3DFACE);
+
+        //int p = targpro * 80 / 100 + 10;
+        int p = (100 - sqr(100 - targpro) / 100) * 80 / 100 + 10;
+        int r = red(bg0) + p * (red(bg1) - red(bg0)) / 100;
+        int g = green(bg0) + p * (green(bg1) - green(bg0)) / 100;
+        int b = blue(bg0) + p * (blue(bg1) - blue(bg0)) / 100;
+
+        tabbg = RGB(r, g, b);
+        tabbr = CreateSolidBrush(tabbg);
+      }
     }
     FillRect(hdc, &dis->rcItem, tabbr);
     if (tabbg != (colour)-1)