When resizing from an edge, the border is more visible and better follow the rounded corners. Border rendering moved to RenderOuterBorders so it can be called in a different order for docking. (#1495, #822)

docs/CHANGELOG.txt

@@ -36,6 +36,7 @@ HOW TO UPDATE?
 Other Changes:
 - Added .editorconfig file for text editors to standardize using spaces. (#2038) [@kudaba]
 - Fixed range-version of PushID() and GetID() not honoring the ### operator to restart from the seed value.
+- Window: When resizing from an edge, the border is more visible and better follow the rounded corners.
 - ImDrawList: Fixed AddCircle(), AddCircleFilled() angle step being off, which was visible when drawing a "circle"
   with a small number of segments (e.g. an hexagon). (#2287) [@baktery]
 - ImGuiTextBuffer: Added append() function (unformatted).

imgui.cpp

@@ -1033,6 +1033,8 @@ static ImGuiWindow*     NavRestoreLastChildNavWindow(ImGuiWindow* window);
 static void             UpdateMouseInputs();
 static void             UpdateMouseWheel();
 static void             UpdateManualResize(ImGuiWindow* window, const ImVec2& size_auto_fit, int* border_held, int resize_grip_count, ImU32 resize_grip_col[4]);
+static void             RenderOuterBorders(ImGuiWindow* window, int border_held);
+
 }
 
 //-----------------------------------------------------------------------------
@@ -4637,12 +4639,12 @@ static void CalcResizePosSizeFromAnyCorner(ImGuiWindow* window, const ImVec2& co
 
 struct ImGuiResizeGripDef
 {
-    ImVec2  CornerPos;
+    ImVec2  CornerPosN;
     ImVec2  InnerDir;
     int     AngleMin12, AngleMax12;
 };
 
-const ImGuiResizeGripDef resize_grip_def[4] =
+static const ImGuiResizeGripDef resize_grip_def[4] =
 {
     { ImVec2(1,1), ImVec2(-1,-1), 0, 3 }, // Lower right
     { ImVec2(0,1), ImVec2(+1,-1), 3, 6 }, // Lower left
@@ -4654,10 +4656,10 @@ static ImRect GetResizeBorderRect(ImGuiWindow* window, int border_n, float perp_
 {
     ImRect rect = window->Rect();
     if (thickness == 0.0f) rect.Max -= ImVec2(1,1);
-    if (border_n == 0) return ImRect(rect.Min.x + perp_padding, rect.Min.y - thickness,    rect.Max.x - perp_padding, rect.Min.y + thickness);
-    if (border_n == 1) return ImRect(rect.Max.x - thickness,    rect.Min.y + perp_padding, rect.Max.x + thickness,    rect.Max.y - perp_padding);
-    if (border_n == 2) return ImRect(rect.Min.x + perp_padding, rect.Max.y - thickness,    rect.Max.x - perp_padding, rect.Max.y + thickness);
-    if (border_n == 3) return ImRect(rect.Min.x - thickness,    rect.Min.y + perp_padding, rect.Min.x + thickness,    rect.Max.y - perp_padding);
+    if (border_n == 0) return ImRect(rect.Min.x + perp_padding, rect.Min.y - thickness,    rect.Max.x - perp_padding, rect.Min.y + thickness);      // Top
+    if (border_n == 1) return ImRect(rect.Max.x - thickness,    rect.Min.y + perp_padding, rect.Max.x + thickness,    rect.Max.y - perp_padding);   // Right
+    if (border_n == 2) return ImRect(rect.Min.x + perp_padding, rect.Max.y - thickness,    rect.Max.x - perp_padding, rect.Max.y + thickness);      // Bottom
+    if (border_n == 3) return ImRect(rect.Min.x - thickness,    rect.Min.y + perp_padding, rect.Min.x + thickness,    rect.Max.y - perp_padding);   // Left
     IM_ASSERT(0);
     return ImRect();
 }
@@ -4685,7 +4687,7 @@ static void ImGui::UpdateManualResize(ImGuiWindow* window, const ImVec2& size_au
     for (int resize_grip_n = 0; resize_grip_n < resize_grip_count; resize_grip_n++)
     {
         const ImGuiResizeGripDef& grip = resize_grip_def[resize_grip_n];
-        const ImVec2 corner = ImLerp(window->Pos, window->Pos + window->Size, grip.CornerPos);
+        const ImVec2 corner = ImLerp(window->Pos, window->Pos + window->Size, grip.CornerPosN);
 
         // Using the FlattenChilds button flag we make the resize button accessible even if we are hovering over a child window
         ImRect resize_rect(corner - grip.InnerDir * grip_hover_outer_size, corner + grip.InnerDir * grip_hover_inner_size);
@@ -4707,8 +4709,8 @@ static void ImGui::UpdateManualResize(ImGuiWindow* window, const ImVec2& size_au
         {
             // Resize from any of the four corners
             // We don't use an incremental MouseDelta but rather compute an absolute target size based on mouse position
-            ImVec2 corner_target = g.IO.MousePos - g.ActiveIdClickOffset + ImLerp(grip.InnerDir * grip_hover_outer_size, grip.InnerDir * -grip_hover_inner_size, grip.CornerPos); // Corner of the window corresponding to our corner grip
-            CalcResizePosSizeFromAnyCorner(window, corner_target, grip.CornerPos, &pos_target, &size_target);
+            ImVec2 corner_target = g.IO.MousePos - g.ActiveIdClickOffset + ImLerp(grip.InnerDir * grip_hover_outer_size, grip.InnerDir * -grip_hover_inner_size, grip.CornerPosN); // Corner of the window corresponding to our corner grip
+            CalcResizePosSizeFromAnyCorner(window, corner_target, grip.CornerPosN, &pos_target, &size_target);
         }
         if (resize_grip_n == 0 || held || hovered)
             resize_grip_col[resize_grip_n] = GetColorU32(held ? ImGuiCol_ResizeGripActive : hovered ? ImGuiCol_ResizeGripHovered : ImGuiCol_ResizeGrip);
@@ -4722,16 +4724,17 @@ static void ImGui::UpdateManualResize(ImGuiWindow* window, const ImVec2& size_au
         if ((hovered && g.HoveredIdTimer > WINDOWS_RESIZE_FROM_EDGES_FEEDBACK_TIMER) || held)
         {
             g.MouseCursor = (border_n & 1) ? ImGuiMouseCursor_ResizeEW : ImGuiMouseCursor_ResizeNS;
-            if (held) *border_held = border_n;
+            if (held) 
+                *border_held = border_n;
         }
         if (held)
         {
             ImVec2 border_target = window->Pos;
             ImVec2 border_posn;
-            if (border_n == 0) { border_posn = ImVec2(0, 0); border_target.y = (g.IO.MousePos.y - g.ActiveIdClickOffset.y + WINDOWS_RESIZE_FROM_EDGES_HALF_THICKNESS); }
-            if (border_n == 1) { border_posn = ImVec2(1, 0); border_target.x = (g.IO.MousePos.x - g.ActiveIdClickOffset.x + WINDOWS_RESIZE_FROM_EDGES_HALF_THICKNESS); }
-            if (border_n == 2) { border_posn = ImVec2(0, 1); border_target.y = (g.IO.MousePos.y - g.ActiveIdClickOffset.y + WINDOWS_RESIZE_FROM_EDGES_HALF_THICKNESS); }
-            if (border_n == 3) { border_posn = ImVec2(0, 0); border_target.x = (g.IO.MousePos.x - g.ActiveIdClickOffset.x + WINDOWS_RESIZE_FROM_EDGES_HALF_THICKNESS); }
+            if (border_n == 0) { border_posn = ImVec2(0, 0); border_target.y = (g.IO.MousePos.y - g.ActiveIdClickOffset.y + WINDOWS_RESIZE_FROM_EDGES_HALF_THICKNESS); } // Top
+            if (border_n == 1) { border_posn = ImVec2(1, 0); border_target.x = (g.IO.MousePos.x - g.ActiveIdClickOffset.x + WINDOWS_RESIZE_FROM_EDGES_HALF_THICKNESS); } // Right
+            if (border_n == 2) { border_posn = ImVec2(0, 1); border_target.y = (g.IO.MousePos.y - g.ActiveIdClickOffset.y + WINDOWS_RESIZE_FROM_EDGES_HALF_THICKNESS); } // Bottom
+            if (border_n == 3) { border_posn = ImVec2(0, 0); border_target.x = (g.IO.MousePos.x - g.ActiveIdClickOffset.x + WINDOWS_RESIZE_FROM_EDGES_HALF_THICKNESS); } // Left
             CalcResizePosSizeFromAnyCorner(window, border_target, border_posn, &pos_target, &size_target);
         }
     }
@@ -4772,6 +4775,41 @@ static void ImGui::UpdateManualResize(ImGuiWindow* window, const ImVec2& size_au
     window->Size = window->SizeFull;
 }
 
+static void ImGui::RenderOuterBorders(ImGuiWindow* window, int border_held)
+{
+    ImGuiContext& g = *GImGui;
+    float rounding = window->WindowRounding;
+    float border_size = window->WindowBorderSize;
+    if (border_size > 0.0f && !(window->Flags & ImGuiWindowFlags_NoBackground))
+        window->DrawList->AddRect(window->Pos, window->Pos + window->Size, GetColorU32(ImGuiCol_Border), rounding, ImDrawCornerFlags_All, border_size);
+    if (border_held != -1)
+    {
+        struct ImGuiResizeBorderDef
+        {
+            ImVec2 InnerDir;
+            ImVec2 CornerPosN1, CornerPosN2;
+            float  OuterAngle;
+        };
+        static const ImGuiResizeBorderDef resize_border_def[4] =
+        {
+            { ImVec2(0,+1), ImVec2(0,0), ImVec2(1,0), IM_PI*1.50f }, // Top
+            { ImVec2(-1,0), ImVec2(1,0), ImVec2(1,1), IM_PI*0.00f }, // Right
+            { ImVec2(0,-1), ImVec2(1,1), ImVec2(0,1), IM_PI*0.50f }, // Bottom
+            { ImVec2(+1,0), ImVec2(0,1), ImVec2(0,0), IM_PI*1.00f }  // Left
+        };
+        const ImGuiResizeBorderDef& def = resize_border_def[border_held];
+        ImRect border_r = GetResizeBorderRect(window, border_held, rounding, 0.0f);
+        window->DrawList->PathArcTo(ImLerp(border_r.Min, border_r.Max, def.CornerPosN1) + ImVec2(0.5f, 0.5f) + def.InnerDir * rounding, rounding, def.OuterAngle - IM_PI*0.25f, def.OuterAngle);
+        window->DrawList->PathArcTo(ImLerp(border_r.Min, border_r.Max, def.CornerPosN2) + ImVec2(0.5f, 0.5f) + def.InnerDir * rounding, rounding, def.OuterAngle, def.OuterAngle + IM_PI*0.25f);
+        window->DrawList->PathStroke(GetColorU32(ImGuiCol_SeparatorActive), false, ImMax(2.0f, border_size)); // Thicker than usual
+    }
+    if (g.Style.FrameBorderSize > 0 && !(window->Flags & ImGuiWindowFlags_NoTitleBar))
+    {
+        float y = window->Pos.y + window->TitleBarHeight() - 1;
+        window->DrawList->AddLine(ImVec2(window->Pos.x + border_size, y), ImVec2(window->Pos.x + window->Size.x - border_size, y), GetColorU32(ImGuiCol_Border), g.Style.FrameBorderSize);
+    }
+}
+
 void ImGui::UpdateWindowParentAndRootLinks(ImGuiWindow* window, ImGuiWindowFlags flags, ImGuiWindow* parent_window)
 {
     window->ParentWindow = parent_window;
@@ -5193,7 +5231,7 @@ bool ImGui::Begin(const char* name, bool* p_open, ImGuiWindowFlags flags)
                 for (int resize_grip_n = 0; resize_grip_n < resize_grip_count; resize_grip_n++)
                 {
                     const ImGuiResizeGripDef& grip = resize_grip_def[resize_grip_n];
-                    const ImVec2 corner = ImLerp(window->Pos, window->Pos + window->Size, grip.CornerPos);
+                    const ImVec2 corner = ImLerp(window->Pos, window->Pos + window->Size, grip.CornerPosN);
                     window->DrawList->PathLineTo(corner + grip.InnerDir * ((resize_grip_n & 1) ? ImVec2(window_border_size, grip_draw_size) : ImVec2(grip_draw_size, window_border_size)));
                     window->DrawList->PathLineTo(corner + grip.InnerDir * ((resize_grip_n & 1) ? ImVec2(grip_draw_size, window_border_size) : ImVec2(window_border_size, grip_draw_size)));
                     window->DrawList->PathArcToFast(ImVec2(corner.x + grip.InnerDir.x * (window_rounding + window_border_size), corner.y + grip.InnerDir.y * (window_rounding + window_border_size)), window_rounding, grip.AngleMin12, grip.AngleMax12);
@@ -5202,15 +5240,7 @@ bool ImGui::Begin(const char* name, bool* p_open, ImGuiWindowFlags flags)
             }
 
             // Borders
-            if (window_border_size > 0.0f && !(flags & ImGuiWindowFlags_NoBackground))
-                window->DrawList->AddRect(window->Pos, window->Pos + window->Size, GetColorU32(ImGuiCol_Border), window_rounding, ImDrawCornerFlags_All, window_border_size);
-            if (border_held != -1)
-            {
-                ImRect border = GetResizeBorderRect(window, border_held, grip_draw_size, 0.0f);
-                window->DrawList->AddLine(border.Min, border.Max, GetColorU32(ImGuiCol_SeparatorActive), ImMax(1.0f, window_border_size));
-            }
-            if (style.FrameBorderSize > 0 && !(flags & ImGuiWindowFlags_NoTitleBar))
-                window->DrawList->AddLine(title_bar_rect.GetBL() + ImVec2(style.WindowBorderSize, -1), title_bar_rect.GetBR() + ImVec2(-style.WindowBorderSize, -1), GetColorU32(ImGuiCol_Border), style.FrameBorderSize);
+            RenderOuterBorders(window, border_held);
         }
 
         // Draw navigation selection/windowing rectangle border