Added SetNextWindowSizeConstraint() + demo code (#668)

imgui.cpp

@@ -457,7 +457,6 @@
  The list below consist mostly of notes of things to do before they are requested/discussed by users (at that point it usually happens on the github)
 
  - doc: add a proper documentation+regression testing system (#435)
- - window: maximum window size settings (per-axis). for large popups in particular user may not want the popup to fill all space.
  - window: add a way for very transient windows (non-saved, temporary overlay over hundreds of objects) to "clean" up from the global window list. perhaps a lightweight explicit cleanup pass.
  - window: calling SetNextWindowSize() every frame with <= 0 doesn't do anything, may be useful to allow (particularly when used for a single axis).
  - window: auto-fit feedback loop when user relies on any dynamic layout (window width multiplier, column) appears weird to end-user. clarify.
@@ -3416,7 +3415,7 @@ static inline void ClearSetNextWindowData()
 {
     ImGuiContext& g = *GImGui;
     g.SetNextWindowPosCond = g.SetNextWindowSizeCond = g.SetNextWindowContentSizeCond = g.SetNextWindowCollapsedCond = 0;
-    g.SetNextWindowFocus = false;
+    g.SetNextWindowSizeConstraint = g.SetNextWindowFocus = false;
 }
 
 static bool BeginPopupEx(const char* str_id, ImGuiWindowFlags extra_flags)
@@ -3731,6 +3730,31 @@ static ImGuiWindow* CreateNewWindow(const char* name, ImVec2 size, ImGuiWindowFl
     return window;
 }
 
+static void ApplySizeFullWithConstraint(ImGuiWindow* window, ImVec2 new_size)
+{
+    ImGuiContext& g = *GImGui;
+    if (g.SetNextWindowSizeConstraint)
+    {
+        // Using -1,-1 on either X/Y axis to preserve the current size.
+        ImRect cr = g.SetNextWindowSizeConstraintRect;
+        new_size.x = (cr.Min.x >= 0 && cr.Max.x >= 0) ? ImClamp(new_size.x, cr.Min.x, cr.Max.x) : window->SizeFull.x;
+        new_size.y = (cr.Min.y >= 0 && cr.Max.y >= 0) ? ImClamp(new_size.y, cr.Min.y, cr.Max.y) : window->SizeFull.y;
+        if (g.SetNextWindowSizeConstraintCallback)
+        {
+            ImGuiSizeConstraintCallbackData data;
+            data.UserData = g.SetNextWindowSizeConstraintCallbackUserData;
+            data.Pos = window->Pos;
+            data.CurrentSize = window->SizeFull;
+            data.DesiredSize = new_size;
+            g.SetNextWindowSizeConstraintCallback(&data);
+            new_size = data.DesiredSize;
+        }
+    }
+    if (!(window->Flags & (ImGuiWindowFlags_ChildWindow | ImGuiWindowFlags_AlwaysAutoResize)))
+        new_size = ImMax(new_size, g.Style.WindowMinSize);
+    window->SizeFull = new_size;
+}
+
 // Push a new ImGui window to add widgets to.
 // - A default window called "Debug" is automatically stacked at the beginning of every frame so you can use widgets without explicitly calling a Begin/End pair.
 // - Begin/End can be called multiple times during the frame with the same window name to append content.
@@ -3972,9 +3996,8 @@ bool ImGui::Begin(const char* name, bool* p_open, const ImVec2& size_on_first_us
             }
         }
 
-        // Apply window size constraints and final size
-        if (!(flags & (ImGuiWindowFlags_ChildWindow | ImGuiWindowFlags_AlwaysAutoResize)))
-            window->SizeFull = ImMax(window->SizeFull, style.WindowMinSize);
+        // Apply minimum/maximum window size constraints and final size
+        ApplySizeFullWithConstraint(window, window->SizeFull);
         window->Size = window->Collapsed ? window->TitleBarRect().GetSize() : window->SizeFull;
         
         // POSITION
@@ -4096,7 +4119,7 @@ bool ImGui::Begin(const char* name, bool* p_open, const ImVec2& size_on_first_us
                 if (g.HoveredWindow == window && held && g.IO.MouseDoubleClicked[0])
                 {
                     // Manual auto-fit when double-clicking
-                    window->SizeFull = size_auto_fit;
+                    ApplySizeFullWithConstraint(window, size_auto_fit);
                     if (!(flags & ImGuiWindowFlags_NoSavedSettings))
                         MarkSettingsDirty();
                     SetActiveID(0);
@@ -4104,7 +4127,7 @@ bool ImGui::Begin(const char* name, bool* p_open, const ImVec2& size_on_first_us
                 else if (held)
                 {
                     // We don't use an incremental MouseDelta but rather compute an absolute target size based on mouse position
-                    window->SizeFull = ImMax((g.IO.MousePos - g.ActiveIdClickOffset + resize_rect.GetSize()) - window->Pos, style.WindowMinSize);
+                    ApplySizeFullWithConstraint(window, (g.IO.MousePos - g.ActiveIdClickOffset + resize_rect.GetSize()) - window->Pos);
                     if (!(flags & ImGuiWindowFlags_NoSavedSettings))
                         MarkSettingsDirty();
                 }
@@ -4177,6 +4200,7 @@ bool ImGui::Begin(const char* name, bool* p_open, const ImVec2& size_on_first_us
 
         // Setup drawing context
         window->DC.IndentX = 0.0f + window->WindowPadding.x - window->Scroll.x;
+		window->DC.GroupOffsetX = 0.0f;
         window->DC.ColumnsOffsetX = 0.0f;
         window->DC.CursorStartPos = window->Pos + ImVec2(window->DC.IndentX + window->DC.ColumnsOffsetX, window->TitleBarHeight() + window->MenuBarHeight() + window->WindowPadding.y - window->Scroll.y);
         window->DC.CursorPos = window->DC.CursorStartPos;
@@ -4268,6 +4292,7 @@ bool ImGui::Begin(const char* name, bool* p_open, const ImVec2& size_on_first_us
     if (first_begin_of_the_frame)
         window->Accessed = false;
     window->BeginCount++;
+    g.SetNextWindowSizeConstraint = false;
 
     // Child window can be out of sight and have "negative" clip windows.
     // Mark them as collapsed so commands are skipped earlier (we can't manually collapse because they have no title bar).
@@ -4906,6 +4931,15 @@ void ImGui::SetNextWindowSize(const ImVec2& size, ImGuiSetCond cond)
     g.SetNextWindowSizeCond = cond ? cond : ImGuiSetCond_Always;
 }
 
+void ImGui::SetNextWindowSizeConstraint(const ImVec2& size_min, const ImVec2& size_max, ImGuiSizeConstraintCallback custom_callback, void* custom_callback_user_data)
+{
+    ImGuiContext& g = *GImGui;
+    g.SetNextWindowSizeConstraint = true;
+    g.SetNextWindowSizeConstraintRect = ImRect(size_min, size_max);
+    g.SetNextWindowSizeConstraintCallback = custom_callback;
+    g.SetNextWindowSizeConstraintCallbackUserData = custom_callback_user_data;
+}
+
 void ImGui::SetNextWindowContentSize(const ImVec2& size)
 {
     ImGuiContext& g = *GImGui;

imgui.h

@@ -52,7 +52,8 @@ struct ImGuiStorage;                // Simple custom key value storage
 struct ImGuiStyle;                  // Runtime data for styling/colors
 struct ImGuiTextFilter;             // Parse and apply text filters. In format "aaaaa[,bbbb][,ccccc]"
 struct ImGuiTextBuffer;             // Text buffer for logging/accumulating text
-struct ImGuiTextEditCallbackData;   // Shared state of ImGui::InputText() when using custom callbacks (advanced)
+struct ImGuiTextEditCallbackData;   // Shared state of ImGui::InputText() when using custom ImGuiTextEditCallback (rare/advanced use)
+struct ImGuiSizeConstraintCallbackData;// Structure used to constraint window size in custom ways when using custom ImGuiSizeConstraintCallback (rare/advanced use)
 struct ImGuiListClipper;            // Helper to manually clip large list of items
 struct ImGuiContext;                // ImGui context (opaque)
 
@@ -73,6 +74,7 @@ typedef int ImGuiInputTextFlags;    // flags for InputText*()               // e
 typedef int ImGuiSelectableFlags;   // flags for Selectable()               // enum ImGuiSelectableFlags_
 typedef int ImGuiTreeNodeFlags;     // flags for TreeNode*(), Collapsing*() // enum ImGuiTreeNodeFlags_
 typedef int (*ImGuiTextEditCallback)(ImGuiTextEditCallbackData *data);
+typedef void (*ImGuiSizeConstraintCallback)(ImGuiSizeConstraintCallbackData* data);
 
 // Others helpers at bottom of the file:
 // class ImVector<>                 // Lightweight std::vector like class.
@@ -138,6 +140,7 @@ namespace ImGui
     IMGUI_API void          SetNextWindowPos(const ImVec2& pos, ImGuiSetCond cond = 0);         // set next window position. call before Begin()
     IMGUI_API void          SetNextWindowPosCenter(ImGuiSetCond cond = 0);                      // set next window position to be centered on screen. call before Begin()
     IMGUI_API void          SetNextWindowSize(const ImVec2& size, ImGuiSetCond cond = 0);       // set next window size. set axis to 0.0f to force an auto-fit on this axis. call before Begin()
+    IMGUI_API void          SetNextWindowSizeConstraint(const ImVec2& size_min, const ImVec2& size_max, ImGuiSizeConstraintCallback custom_callback = NULL, void* custom_callback_data = NULL); // set next window size limits. use -1,-1 on either X/Y axis to preserve the current size. Use callback to apply non-trivial programmatic constraints.
     IMGUI_API void          SetNextWindowContentSize(const ImVec2& size);                       // set next window content size (enforce the range of scrollbars). set axis to 0.0f to leave it automatic. call before Begin()
     IMGUI_API void          SetNextWindowContentWidth(float width);                             // set next window content width (enforce the range of horizontal scrollbar). call before Begin()
     IMGUI_API void          SetNextWindowCollapsed(bool collapsed, ImGuiSetCond cond = 0);      // set next window collapsed state. call before Begin()
@@ -1029,6 +1032,16 @@ struct ImGuiTextEditCallbackData
     bool    HasSelection() const { return SelectionStart != SelectionEnd; }
 };
 
+// Resizing callback data to apply custom constraint. As enabled by SetNextWindowSizeConstraint(). Callback is called during the next Begin().
+// NB: For basic min/max size constraint on each axis you don't need to use the callback! The SetNextWindowSizeConstraint() parameters are enough.
+struct ImGuiSizeConstraintCallbackData
+{
+    void*   UserData;       // Read-only.   What user passed to SetNextWindowSizeConstraint()
+    ImVec2  Pos;            // Read-only.	Window position, for reference.
+    ImVec2  CurrentSize;    // Read-only.	Current window size.
+    ImVec2  DesiredSize;    // Read-write.  Desired size, based on user's mouse position. Write to this field to restrain resizing.
+};
+
 // ImColor() helper to implicity converts colors to either ImU32 (packed 4x1 byte) or ImVec4 (4x1 float)
 // Prefer using IM_COL32() macros if you want a guaranteed compile-time ImU32 for usage with ImDrawList API.
 // Avoid storing ImColor! Store either u32 of ImVec4. This is not a full-featured color class.

imgui_demo.cpp

@@ -46,6 +46,7 @@
 #endif
 
 #define IM_ARRAYSIZE(_ARR)  ((int)(sizeof(_ARR)/sizeof(*_ARR)))
+#define IM_MAX(_A,_B)       (((_A) >= (_B)) ? (_A) : (_B))
 
 //-----------------------------------------------------------------------------
 // DEMO CODE
@@ -59,6 +60,7 @@ static void ShowExampleAppLayout(bool* p_open);
 static void ShowExampleAppPropertyEditor(bool* p_open);
 static void ShowExampleAppLongText(bool* p_open);
 static void ShowExampleAppAutoResize(bool* p_open);
+static void ShowExampleAppConstrainedResize(bool* p_open);
 static void ShowExampleAppFixedOverlay(bool* p_open);
 static void ShowExampleAppManipulatingWindowTitle(bool* p_open);
 static void ShowExampleAppCustomRendering(bool* p_open);
@@ -105,6 +107,7 @@ void ImGui::ShowTestWindow(bool* p_open)
     static bool show_app_property_editor = false;
     static bool show_app_long_text = false;
     static bool show_app_auto_resize = false;
+    static bool show_app_constrained_resize = false;
     static bool show_app_fixed_overlay = false;
     static bool show_app_manipulating_window_title = false;
     static bool show_app_custom_rendering = false;
@@ -120,6 +123,7 @@ void ImGui::ShowTestWindow(bool* p_open)
     if (show_app_property_editor) ShowExampleAppPropertyEditor(&show_app_property_editor);
     if (show_app_long_text) ShowExampleAppLongText(&show_app_long_text);
     if (show_app_auto_resize) ShowExampleAppAutoResize(&show_app_auto_resize);
+    if (show_app_constrained_resize) ShowExampleAppConstrainedResize(&show_app_constrained_resize);
     if (show_app_fixed_overlay) ShowExampleAppFixedOverlay(&show_app_fixed_overlay);
     if (show_app_manipulating_window_title) ShowExampleAppManipulatingWindowTitle(&show_app_manipulating_window_title);
     if (show_app_custom_rendering) ShowExampleAppCustomRendering(&show_app_custom_rendering);
@@ -183,6 +187,7 @@ void ImGui::ShowTestWindow(bool* p_open)
             ImGui::MenuItem("Property editor", NULL, &show_app_property_editor);
             ImGui::MenuItem("Long text display", NULL, &show_app_long_text);
             ImGui::MenuItem("Auto-resizing window", NULL, &show_app_auto_resize);
+            ImGui::MenuItem("Constrained-resizing window", NULL, &show_app_constrained_resize);
             ImGui::MenuItem("Simple overlay", NULL, &show_app_fixed_overlay);
             ImGui::MenuItem("Manipulating window title", NULL, &show_app_manipulating_window_title);
             ImGui::MenuItem("Custom rendering", NULL, &show_app_custom_rendering);
@@ -1793,6 +1798,43 @@ static void ShowExampleAppAutoResize(bool* p_open)
     ImGui::End();
 }
 
+static void ShowExampleAppConstrainedResize(bool* p_open)
+{
+    struct CustomConstraints // Helper functions to demonstrate programmatic constraints
+    {
+        static void Square(ImGuiSizeConstraintCallbackData* data) { data->DesiredSize = ImVec2(IM_MAX(data->DesiredSize.x, data->DesiredSize.y), IM_MAX(data->DesiredSize.x, data->DesiredSize.y)); }
+        static void Step(ImGuiSizeConstraintCallbackData* data)   { float step = (float)(int)data->UserData; data->DesiredSize = ImVec2((int)(data->DesiredSize.x / step + 0.5f) * step, (int)(data->DesiredSize.y / step + 0.5f) * step); }
+    };
+
+    static int type = 0;
+    if (type == 0) ImGui::SetNextWindowSizeConstraint(ImVec2(-1, 0),    ImVec2(-1, FLT_MAX));      // Vertical only
+    if (type == 1) ImGui::SetNextWindowSizeConstraint(ImVec2(0, -1),    ImVec2(FLT_MAX, -1));      // Horizontal only
+    if (type == 2) ImGui::SetNextWindowSizeConstraint(ImVec2(100, 100), ImVec2(FLT_MAX, FLT_MAX)); // Width > 100, Height > 100
+    if (type == 3) ImGui::SetNextWindowSizeConstraint(ImVec2(300, 0),   ImVec2(400, FLT_MAX));     // Width 300-400
+    if (type == 4) ImGui::SetNextWindowSizeConstraint(ImVec2(0, 0),     ImVec2(FLT_MAX, FLT_MAX), CustomConstraints::Square);          // Always Square
+    if (type == 5) ImGui::SetNextWindowSizeConstraint(ImVec2(0, 0),     ImVec2(FLT_MAX, FLT_MAX), CustomConstraints::Step, (void*)100);// Fixed Step
+
+    if (ImGui::Begin("Example: Constrained Resize", p_open))
+    {
+        const char* desc[] = 
+        {
+            "Resize vertical only",
+            "Resize horizontal only",
+            "Width > 100, Height > 100",
+            "Width 300-400",
+            "Custom: Always Square",
+            "Custom: Fixed Steps (100)",
+        };
+        ImGui::Combo("Constraint", &type, desc, IM_ARRAYSIZE(desc)); 
+        if (ImGui::Button("200x200")) ImGui::SetWindowSize(ImVec2(200,200)); ImGui::SameLine();
+        if (ImGui::Button("500x500")) ImGui::SetWindowSize(ImVec2(500,500)); ImGui::SameLine();
+        if (ImGui::Button("800x200")) ImGui::SetWindowSize(ImVec2(800,200));
+        for (int i = 0; i < 10; i++) 
+            ImGui::Text("Hello, sailor! Making this line long enough for the example.");
+    }
+    ImGui::End();
+}
+
 static void ShowExampleAppFixedOverlay(bool* p_open)
 {
     ImGui::SetNextWindowPos(ImVec2(10,10));

imgui_internal.h

@@ -394,6 +394,10 @@ struct ImGuiContext
     ImGuiSetCond            SetNextWindowSizeCond;
     ImGuiSetCond            SetNextWindowContentSizeCond;
     ImGuiSetCond            SetNextWindowCollapsedCond;
+    ImRect                  SetNextWindowSizeConstraintRect;           // Valid if 'SetNextWindowSizeConstraint' is true
+    ImGuiSizeConstraintCallback SetNextWindowSizeConstraintCallback;
+    void*                       SetNextWindowSizeConstraintCallbackUserData;
+    bool                    SetNextWindowSizeConstraint;
     bool                    SetNextWindowFocus;
     bool                    SetNextTreeNodeOpenVal;
     ImGuiSetCond            SetNextTreeNodeOpenCond;
@@ -472,6 +476,8 @@ struct ImGuiContext
         SetNextWindowContentSizeCond = 0;
         SetNextWindowCollapsedCond = 0;
         SetNextWindowFocus = false;
+        SetNextWindowSizeConstraintCallback = NULL;
+        SetNextWindowSizeConstraintCallbackUserData = NULL;
         SetNextTreeNodeOpenVal = false;
         SetNextTreeNodeOpenCond = 0;