Demo: Added extra demo in the Basic Horizontal Layout section. (#1977) + PR guidelines

.github/pull_request_template.md

@@ -1,6 +1,7 @@
 - When adding a feature, please describe the usage context (how you intend to use it, why you need it, etc.).
 - When fixing a warning or compilation problem, please post the compiler log and specify the version and OS you are using.
 - Try to attach screenshots to clarify the context and demonstrate the feature at a glance.
+- Make sure your code follows the coding style already used in imgui (spaces instead of tabs, "local_variable", "FunctionName", "MemberName", etc.).
 - Make sure you create a branch for the pull request. In Git, 1 PR is associated to 1 branch. If you keep pushing to the same branch after you submitted the PR, your new commits will appear in the PR.
 - You can read [CONTRIBUTING.md](https://github.com/ocornut/imgui/blob/master/.github/CONTRIBUTING.md) for more details.
 

imgui_demo.cpp

@@ -1533,10 +1533,26 @@ void ImGui::ShowDemoWindow(bool* p_open)
             ImGui::PopItemWidth();
 
             // Dummy
-            ImVec2 sz(30,30);
-            ImGui::Button("A", sz); ImGui::SameLine();
-            ImGui::Dummy(sz); ImGui::SameLine();
-            ImGui::Button("B", sz);
+            ImVec2 button_sz(40,40);
+            ImGui::Button("A", button_sz); ImGui::SameLine();
+            ImGui::Dummy(button_sz); ImGui::SameLine();
+            ImGui::Button("B", button_sz);
+
+            // Manually wrapping (we should eventually provide this as an automatic layout feature, but for now you can do it manually)
+            ImGui::Text("Manually wrapping:");
+            ImGuiStyle& style = ImGui::GetStyle();
+            int buttons_count = 20;
+            float window_visible_x2 = ImGui::GetWindowPos().x + ImGui::GetWindowContentRegionMax().x;
+            for (int n = 0; n < buttons_count; n++)
+            {
+                ImGui::PushID(n);
+                ImGui::Button("Box", button_sz);
+                float last_button_x2 = ImGui::GetItemRectMax().x;
+                float next_button_x2 = last_button_x2 + style.ItemSpacing.x + button_sz.x; // Expected position if next button was on same line
+                if (n + 1 < buttons_count && next_button_x2 < window_visible_x2)
+                    ImGui::SameLine();
+                ImGui::PopID();
+            }
 
             ImGui::TreePop();
         }