check texture smart pointer, center window on monitor where mouse is

Author: aloneguid

grey/backends/win32dx11app.hpp

@@ -240,11 +240,23 @@ namespace grey::backends {
         }
 
         void get_screen_center(int width, int height, int& x, int& y) {
-            int sw = ::GetSystemMetrics(SM_CXFULLSCREEN);
-            int sh = ::GetSystemMetrics(SM_CYFULLSCREEN);
-
-            x = sw / 2 - width / 2;
-            y = sh / 2 - height / 2;
+            // get center of the screen where mouse cursor is, not just the primary monitor
+
+            // mouse cursor position
+            POINT cursor;
+            ::GetCursorPos(&cursor);
+
+            // get monitor and it's info
+            HMONITOR hMonitor = ::MonitorFromPoint(cursor, MONITOR_DEFAULTTONEAREST);
+            MONITORINFO mi = {sizeof(mi)};
+            ::GetMonitorInfo(hMonitor, &mi);
+            RECT& wa = mi.rcWork;
+
+            // calculate it
+            int sw = wa.right - wa.left;
+            int sh = wa.bottom - wa.top;
+            x = wa.left + (sw - width) / 2;
+            y = wa.top + (sh - height) / 2;
         }
 
         void resize_main_viewport(int width, int height) {

grey/widgets.cpp

@@ -808,7 +808,7 @@ namespace grey::widgets {
     void image_rounded(app& app, const std::string& key, size_t width, size_t height, float rounding,
         float uv0_x, float uv0_y, float uv1_x, float uv1_y) {
         auto tex = app.get_texture(key);
-        if (tex->data) {
+        if (tex && tex->data) {
             ImDrawList* dl = ImGui::GetWindowDrawList();
             ImVec2 p_min = ImGui::GetCursorScreenPos();
             ImVec2 p_max = ImVec2(p_min.x + width, p_min.y + height);