ImGuiTabBarFlags_NoSeparator flag

[Mewiof]

👋.

The problem
Tab bars in dock nodes draw the bottom line (separator). Tabs trim the top and bottom pixels.

The only solution for disabling that I could find was to hide the bottom line (separator) by pushing a transparent color (see #4859, #5022, and #5239). This doesn't remove trimming, leaving 2 pixels of space at the top and bottom, and adds unnecessary calls, "drawing" a transparent line.

The solution

• Added a new public flag, "ImGuiTabBarFlags_NoSeparator";
• An internal ("ImGuiTabItemFlags_Preview") flag already existed and was used once to remove trimming by "DockNodePreviewDockRender". It was renamed to "ImGuiTabItemFlags_NoTrimming" and is now also assigned by "TabItemEx" when the new "ImGuiTabBarFlags_NoSeparator" flag is present at its tab bar;
• The "ImGuiTabBarFlags_NoSeparator" flag is assigned to tab bars in dock nodes for a better user experience. Previously, users who wanted to disable the line could not do it normally. Now users who want to keep the line can draw it themselves, as shown in the screenshot above.

Result

Thanks for your time~

[ocornut]

I would rather ensure that style-related parameters are all based on shared Style data rather than per-instance, hence my past answer in the styles you linked above.

I believe it can be realized in a more simple manner by:

// new field in ImGuiTabBar
bool                VisibleSeparator;

// in BeginTabBar()
tab_bar->VisibleSeparator = (col & IM_COL32_A_MASK) != 0.0f;

// in TabItem()
if (tab_bar->VisibleSeparator == false)
    flags |= ImGuiTabItemFlags_Preview;

What do you think?
This doesn't create unnecessary draw commands as the commands with Alpha=0 are stripped.

I also agree that in this case ImGuiTabItemFlags_Preview should be renamed to e.g. ImGuiTabItemFlags_HeightForNoTabBarSeparator. I'll do that separately if you agree on the premise of my proposed change.

Let me know.

[Mewiof]

This seems more reasonable and preferable.

However, unfortunately, it appears that for detached windows, the pushed colors are not considered. I used the following solution to one of the issues mentioned above:

ImGui::PushStyleColor(ImGuiCol_TabActive, ImVec4());
ImGui::PushStyleColor(ImGuiCol_TabUnfocusedActive, ImVec4());
ImGui::DockSpaceOverViewport(..., ...);
ImGui::PopStyleColor(2);

Not very familiar with the source code, but my guess is that the detached windows are drawn in "NewFrame" before the user code is called (see "DockContextNewFrameUpdateDocking")~

[ocornut]

Not very familiar with the source code, but my guess is that the detached windows are drawn in "NewFrame" before the user code is called,

Correct, the solution is currently to modify that style when calling NewFrame().

[ocornut]

I decided to solve this differently and added a style.TabBarBorderSize variable.
master : ef8ff1b, docking : 64b1e44
Removed ImGuiTabItemFlags_Preview.

Thanks for the feedback and help!

[Mewiof]

What about the top pixel (see the first screenshot here)?

[ocornut]

Presently it is being too distracting to add minor/custom styling features for everything. Best to wait until a larger refactor of the styling system.