Set size to amount of space required

Fix sequencer expands to fill the space its in and pushing other
elements off below it.

The sequencer doesn't need to fill the space and it's likely that you
want to draw additional information about the selection below it.
Instead of filling available space, fill horizontal space and calculate
how much space we need.

ImSequencer.cpp

@@ -81,14 +81,20 @@ namespace ImSequencer
       ImDrawList* draw_list = ImGui::GetWindowDrawList();
       ImVec2 canvas_pos = ImGui::GetCursorScreenPos();            // ImDrawList API uses screen coordinates!
       ImVec2 canvas_size = ImGui::GetContentRegionAvail();        // Resize canvas to what's available
+      ImVec2 headerSize(canvas_size.x, (float)ItemHeight);
+      ImVec2 scrollBarSize(canvas_size.x, 14.f);
       int firstFrameUsed = firstFrame ? *firstFrame : 0;
 
 
+      const float spacer = 8.0f;
       int controlHeight = sequenceCount * ItemHeight;
       for (int i = 0; i < sequenceCount; i++)
          controlHeight += int(sequence->GetCustomHeight(i));
       int frameCount = ImMax(sequence->GetFrameMax() - sequence->GetFrameMin(), 1);
 
+      // Don't hide elements below. Limit our height to the space we use.
+      canvas_size.y = spacer + 10.0f + static_cast<float>(controlHeight) + headerSize.y + scrollBarSize.y;
+
       static bool MovingScrollBar = false;
       static bool MovingCurrentFrame = false;
       struct CustomDraw
@@ -155,12 +161,10 @@ namespace ImSequencer
          }
          */
          // test scroll area
-         ImVec2 headerSize(canvas_size.x, (float)ItemHeight);
-         ImVec2 scrollBarSize(canvas_size.x, 14.f);
          ImGui::InvisibleButton("topBar", headerSize);
          draw_list->AddRectFilled(canvas_pos, canvas_pos + headerSize, 0xFFFF0000, 0);
          ImVec2 childFramePos = ImGui::GetCursorScreenPos();
-         ImVec2 childFrameSize(canvas_size.x, canvas_size.y - 8.f - headerSize.y - (hasScrollBar ? scrollBarSize.y : 0));
+         ImVec2 childFrameSize(canvas_size.x, canvas_size.y - spacer - headerSize.y - (hasScrollBar ? scrollBarSize.y : 0));
          ImGui::PushStyleColor(ImGuiCol_FrameBg, 0);
          ImGui::BeginChildFrame(889, childFrameSize);
          sequence->focused = ImGui::IsWindowFocused();