Editor: Add canvas size mode (#170)

Config can now decide how editor should resize view when changing size.

Author: thedmd

Diff for: docs/CHANGELOG.txt

@@ -141,6 +141,14 @@ v0.9.1 (WIP):
         New API:
             ImVector<float> Config::CustomZoomLevels;
 
+    NEW: Editor: Add canvas size mode (#170)
+
+        Config can now decide how editor should resize view when changing size.
+
+        New API:
+            enum class CanvasSizeMode;
+            Config::CanvasSizeMode;
+
     BUGFIX: Avoid crash while destroying editor.
 
     BUGFIX: Save draw list used by editor between Begin() and End()

Diff for: imgui_node_editor.cpp

@@ -1186,15 +1186,33 @@ void ed::EditorContext::Begin(const char* id, const ImVec2& size)
     {
         m_NavigateAction.FinishNavigation();
 
+        auto centerX            = (previousVisibleRect.Max.x + previousVisibleRect.Min.x) * 0.5f;
+        auto centerY            = (previousVisibleRect.Max.y + previousVisibleRect.Min.y) * 0.5f;
         auto currentVisibleRect = m_Canvas.ViewRect();
         auto currentAspectRatio = currentVisibleRect.GetHeight() ? (currentVisibleRect.GetWidth() / currentVisibleRect.GetHeight()) : 0.0f;
+        auto width              = previousVisibleRect.GetHeight();
+        auto height             = previousVisibleRect.GetHeight();
 
-        auto centerX = (previousVisibleRect.Max.x + previousVisibleRect.Min.x) * 0.5f;
-        auto height  = previousVisibleRect.GetHeight();
-        auto width   = currentAspectRatio * height;
+        if (m_Config.CanvasSizeMode == ax::NodeEditor::CanvasSizeMode::FitVerticalView)
+        {
+            height  = previousVisibleRect.GetHeight();
+            width   = height * currentAspectRatio;
+        }
+        else if (m_Config.CanvasSizeMode == ax::NodeEditor::CanvasSizeMode::FitHorizontalView)
+        {
+            width   = previousVisibleRect.GetWidth();
+            height  = width / currentAspectRatio;
+        }
+        else if (m_Config.CanvasSizeMode == ax::NodeEditor::CanvasSizeMode::CenterOnly)
+        {
+            width  = currentVisibleRect.GetWidth();
+            height = currentVisibleRect.GetHeight();
+        }
 
         previousVisibleRect.Min.x = centerX - 0.5f * width;
         previousVisibleRect.Max.x = centerX + 0.5f * width;
+        previousVisibleRect.Min.y = centerY - 0.5f * height;
+        previousVisibleRect.Max.y = centerY + 0.5f * height;
 
         m_NavigateAction.NavigateTo(previousVisibleRect, Detail::NavigateAction::ZoomMode::Exact, 0.0f);
     }

Diff for: imgui_node_editor.h

@@ -31,6 +31,27 @@ struct LinkId;
 struct PinId;
 
 
+//------------------------------------------------------------------------------
+enum class PinKind
+{
+    Input,
+    Output
+};
+
+enum class FlowDirection
+{
+    Forward,
+    Backward
+};
+
+enum class CanvasSizeMode
+{
+    FitVerticalView,        // Previous view will be scaled to fit new view on Y axis
+    FitHorizontalView,      // Previous view will be scaled to fit new view on X axis
+    CenterOnly,             // Previous view will be centered on new view
+};
+
+
 //------------------------------------------------------------------------------
 enum class SaveReasonFlags: uint32_t
 {
@@ -66,6 +87,7 @@ struct Config
     ConfigLoadNodeSettings  LoadNodeSettings;
     void*                   UserPointer;
     ImVector<float>         CustomZoomLevels;
+    typename CanvasSizeMode CanvasSizeMode;
     int                     DragButtonIndex;        // Mouse button index drag action will react to (0-left, 1-right, 2-middle)
     int                     SelectButtonIndex;      // Mouse button index select action will react to (0-left, 1-right, 2-middle)
     int                     NavigateButtonIndex;    // Mouse button index navigate action will react to (0-left, 1-right, 2-middle)
@@ -81,6 +103,7 @@ struct Config
         , LoadNodeSettings(nullptr)
         , UserPointer(nullptr)
         , CustomZoomLevels()
+        , CanvasSizeMode(CanvasSizeMode::FitVerticalView)
         , DragButtonIndex(0)
         , SelectButtonIndex(0)
         , NavigateButtonIndex(1)
@@ -90,20 +113,6 @@ struct Config
 };
 
 
-//------------------------------------------------------------------------------
-enum class PinKind
-{
-    Input,
-    Output
-};
-
-enum class FlowDirection
-{
-    Forward,
-    Backward
-};
-
-
 //------------------------------------------------------------------------------
 enum StyleColor
 {