Improving nested scrolling regions behavior

[ggtucker]

When a scrolling region is nested within another, it would be nice if the following behavior existed:

• When the inner scroll region's scrollbar is at the top, and attempting to scroll up while hovering the inner region, the outer scroll region should take focus and scroll up.
• When the inner scroll region's scrollbar is at the bottom, and attempting to scroll down while hovering the inner region, the outer scroll region should take focus and scroll down.

Here's an example for quickly fiddling around with this yourself:

ImGui::Begin("WindowName");
ImGui::BeginChild("OuterRegion", ImVec2(0, -ImGui::GetItemsLineHeightWithSpacing()), false);
ImGui::Columns(2);
for (int i = 0; i < 40; ++i) {
    ImGui::Text("Entry %i", i);
    ImGui::NextColumn();
    ImGui::Text("Value %i", i);
    ImGui::NextColumn();
}
ImGui::Columns();
ImGui::BeginChild("InnerRegion", ImVec2(0, 300), false);
ImGui::Columns(2);
for (int i = 0; i < 40; ++i) {
    ImGui::Text("InnerEntry %i", i);
    ImGui::NextColumn();
    ImGui::Text("InnerValue %i", i);
    ImGui::NextColumn();
}
ImGui::Columns();
ImGui::EndChild();
ImGui::Columns(2);
for (int i = 40; i < 80; ++i) {
    ImGui::Text("Entry %i", i);
    ImGui::NextColumn();
    ImGui::Text("Value %i", i);
    ImGui::NextColumn();
}
ImGui::Columns();
ImGui::EndChild();
ImGui::End();

[ggtucker]

Tangentially related, it would be nice if, when using columns in a fixed-height child region, the dividers extended to the bottom of the region (in the case that there are not enough rows to fill the region).

See below for an example:

ImGui::Begin("WindowName");
ImGui::BeginChild("OuterRegion", ImVec2(0, -ImGui::GetItemsLineHeightWithSpacing()), false);
ImGui::Columns(2);
for (int i = 0; i < 40; ++i) {
    ImGui::Text("Entry %i", i);
    ImGui::NextColumn();
    ImGui::Text("Value %i", i);
    ImGui::NextColumn();
}
ImGui::Columns();
ImGui::Separator();
ImGui::BeginChild("InnerRegion", ImVec2(0, 150), false);
ImGui::Columns(2);
ImGui::Text("EntryHeader");
ImGui::NextColumn();
ImGui::Text("ValueHeader");
ImGui::NextColumn();
ImGui::Separator();
for (int i = 0; i < 3; ++i) {
    ImGui::Text("InnerEntry %i", i);
    ImGui::NextColumn();
    ImGui::Text("InnerValue %i", i);
    ImGui::NextColumn();
}
ImGui::Columns();
ImGui::EndChild();
ImGui::Columns(2);
ImGui::Separator();
for (int i = 40; i < 80; ++i) {
    ImGui::Text("Entry %i", i);
    ImGui::NextColumn();
    ImGui::Text("Value %i", i);
    ImGui::NextColumn();
}
ImGui::Columns();
ImGui::EndChild();
ImGui::End();

[ocornut]

Hi Geoffrey,

For the first request. I understand it in this context but I'm having a hard time figuring out it is desirable or would make sense in the general context. I think it might be but it'd be cautious. Moreover, different behavior might be desirable with mouse-wheel based scroll vs programmatic vs gamepad navigation scroll.

(Those changes are already a quite trickier than they sounds because there are a few subtle dependencies within the frame. Mouse-wheel are processed in NewFrame() and calling SetWindowScrollY() which sets ScrollY immediately - it is a rather unusual path but works since we're not in Begin/End. It may make more sense to store and defer the desirable relative scroll amount and process in Begin() once we have a contents size for the current frame, or move it all in Begin().)

Columns are a total mess at the moment, they barely changed since 1.0 and accumulating a pile of todos. What I would do right now is just to move your cursor to the bottom of the child window before closing the columns. I'm accumulating notes locally and in #513 #125 and that's one thing that will be automatically handled. Along with making it more natural and easy to line up stuff.

TL;DR; both doable, not high priority since I'm rather busy right now but I may have a look in particular at (1) since it seems less involved. Columns may need to wait for big update.

[ocornut]

For your second question, I tested this:
ImGui::SetCursorPosY(ImGui::GetWindowContentRegionMax().y);
Before the closing call to Columns() within InnerRegion and it does what you wanted.

The center column is still not horizontally aligned making everything looks a bit horrible but that's another problem.

[ocornut]

2. re-
   If you want the columns set width to match between parents and child and can't wait for hypothetical refactor of Columns system, you can possibly use this silly workaround (not particularly recommended, but throwing it out there):

ImGui::PushStyleVar(ImGuiStyleVar_WindowPadding, ImVec2(8,0));
ImGui::SetCursorPosX(0.0f);
ImGui::BeginChild("InnerRegion", ImVec2(ImGui::GetWindowWidth(), 150), false, ImGuiWindowFlags_AlwaysUseWindowPadding);

ImGui::EndChild();
ImGui::PopStyleVar();

Basically enforcing child pos and size to match.

[ggtucker]

Hi Omar!

Thanks for taking the time to answer my questions and looking into a solution for (1) despite your busy schedule. From an API perspective, would it make sense to pass a flag when creating the child region that determines whether or not it should pass scrolling focus to the parent? When configured, I imagine this behavior would only be associated with mouse-wheel (although maybe gamepad too?). I'm not sure it would make sense from a programmatic perspective.

As for (2), the workaround you mentioned works great for me.

Cheers,
Geoff

[ocornut]

Geoff,
Yes, a flag may be appropriate there. Would start by implementing the feature before figuring out if it needs a flag or if it can be the default. I agree that it probably doesn't make sense from the programmatic API either.

[ocornut]

Closing this old issue as it is handled by Tables and Columns are essentially legacy API at this point.