SetScrollPosHere() takes a y centering ratio and can be used to aim t…

…he top or bottom of the window (relate #150)

imgui.cpp

@@ -1412,7 +1412,8 @@ struct ImGuiWindow
  ImVec2 SizeContents; // Size of contents (== extents reach of the drawing cursor) from previous frame
  ImGuiID MoveID; // == window->GetID("#MOVE")
  float ScrollY;
- float ScrollTargetCenterY; // position which we aim to center on
+ float ScrollTargetAbsY; // target scroll position. stored as cursor position with scrolling canceled out, so the highest point is always 0.0f. (-1.0f for no change)
+ float ScrollTargetCenterRatioY; // 0.0f = scroll so that target position is at top, 0.5f = scroll so that target position is centered
  bool ScrollbarY;
  bool Active; // Set to true on Begin()
  bool WasActive;
@@ -1778,7 +1779,8 @@ ImGuiWindow::ImGuiWindow(const char* name)
  Size = SizeFull = ImVec2(0.0f, 0.0f);
  SizeContents = ImVec2(0.0f, 0.0f);
  ScrollY = 0.0f;
- ScrollTargetCenterY = -1.0f;
+ ScrollTargetAbsY = -1.0f;
+ ScrollTargetCenterRatioY = 0.5f;
  ScrollbarY = false;
  Active = WasActive = false;
  Accessed = false;
@@ -3836,10 +3838,11 @@ bool ImGui::Begin(const char* name, bool* p_opened, const ImVec2& size_on_first_
  window->FocusIdxAllRequestNext = window->FocusIdxTabRequestNext = IM_INT_MAX;
 
  // Apply scrolling
- if (window->ScrollTargetCenterY >= 0.0f)
+ if (window->ScrollTargetAbsY >= 0.0f)
  {
- window->ScrollY = window->ScrollTargetCenterY - (window->Pos.y + (window->SizeFull.y + window->TitleBarHeight() + window->WindowPadding().y) * 0.5f);
- window->ScrollTargetCenterY = -1.0f;
+ float center_ratio_y = window->ScrollTargetCenterRatioY;
+ window->ScrollY = window->ScrollTargetAbsY - (window->Pos.y + (1.0f - center_ratio_y) * window->TitleBarHeight() + center_ratio_y * window->SizeFull.y);
+ window->ScrollTargetAbsY = -1.0f;
  }
  window->ScrollY = ImMax(window->ScrollY, 0.0f);
  if (!window->Collapsed && !window->SkipItems)
@@ -4800,10 +4803,13 @@ float ImGui::GetScrollMaxY()
  return window->SizeContents.y - window->SizeFull.y;
 }
 
-void ImGui::SetScrollPosHere()
+void ImGui::SetScrollPosHere(float center_y_ratio)
 {
+ // We store a target position so centering can occur on the next frame when we are guaranteed to have a known window size
+ IM_ASSERT(center_y_ratio >= 0.0f && center_y_ratio <= 1.0f);
  ImGuiWindow* window = GetCurrentWindow();
- window->ScrollTargetCenterY = (float)(int)(window->DC.CursorPos.y + window->ScrollY - window->DC.PrevLineHeight * 0.5f);
+ window->ScrollTargetAbsY = (float)(int)(window->ScrollY + window->DC.CursorPosPrevLine.y + (window->DC.PrevLineHeight) * center_y_ratio);
+ window->ScrollTargetCenterRatioY = center_y_ratio;
 }
 
 void ImGui::SetKeyboardFocusHere(int offset)

imgui.h

@@ -138,7 +138,7 @@ namespace ImGui
 
  IMGUI_API float GetScrollPosY(); // get scrolling position [0..GetScrollMaxY()]
  IMGUI_API float GetScrollMaxY(); // get maximum scrolling position == ContentSize.Y - WindowSize.Y
- IMGUI_API void SetScrollPosHere();   // adjust scrolling position to center into the current cursor position
+ IMGUI_API void SetScrollPosHere(float center_y_ratio = 0.5f); // adjust scrolling position to make the current cursor position visible. center_y_ratio=0.0: top, =0.5: center, =1.0: bottom.
  IMGUI_API void SetKeyboardFocusHere(int offset = 0); // focus keyboard on the next widget. Use positive 'offset' to access sub components of a multiple component widget
  IMGUI_API void SetStateStorage(ImGuiStorage* tree); // replace tree state storage with our own (if you want to manipulate it yourself, typically clear subsection of it)
  IMGUI_API ImGuiStorage* GetStateStorage();