SetScrollToPosHere() fixed imprecision + handling lower gap better fo…

…r bottom alignment (#150)

imgui.cpp

@@ -1412,7 +1412,7 @@ struct ImGuiWindow
  ImVec2 SizeContents; // Size of contents (== extents reach of the drawing cursor) from previous frame
  ImGuiID MoveID; // == window->GetID("#MOVE")
  float ScrollY;
- 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 ScrollTargetRelY; // 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()
@@ -1779,7 +1779,7 @@ ImGuiWindow::ImGuiWindow(const char* name)
  Size = SizeFull = ImVec2(0.0f, 0.0f);
  SizeContents = ImVec2(0.0f, 0.0f);
  ScrollY = 0.0f;
- ScrollTargetAbsY = -1.0f;
+ ScrollTargetRelY = -1.0f;
  ScrollTargetCenterRatioY = 0.5f;
  ScrollbarY = false;
  Active = WasActive = false;
@@ -3838,11 +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->ScrollTargetAbsY >= 0.0f)
+ if (window->ScrollTargetRelY >= 0.0f)
  {
  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 = window->ScrollTargetRelY - ((1.0f - center_ratio_y) * window->TitleBarHeight()) - (center_ratio_y * window->SizeFull.y);
+ window->ScrollTargetRelY = -1.0f;
  }
  window->ScrollY = ImMax(window->ScrollY, 0.0f);
  if (!window->Collapsed && !window->SkipItems)
@@ -4808,7 +4808,9 @@ 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->ScrollTargetAbsY = (float)(int)(window->ScrollY + window->DC.CursorPosPrevLine.y + (window->DC.PrevLineHeight) * center_y_ratio);
+ window->ScrollTargetRelY = (float)(int)(window->ScrollY + window->DC.CursorPosPrevLine.y - window->Pos.y + (window->DC.PrevLineHeight) * center_y_ratio);
+ float line_spacing = (window->DC.CursorPos.y - window->DC.CursorPosPrevLine.y) - (window->DC.PrevLineHeight);
+ window->ScrollTargetRelY += line_spacing * (center_y_ratio - 0.5f) * 2.0f;
  window->ScrollTargetCenterRatioY = center_y_ratio;
 }