Add TableBuilder::drag_to_scroll

[KYovchevski]

Closes #3097

[vvv]

@KYovchevski If I understand #3097 correctly, you want to be able to set drag_to_scroll = false.

ScrollArea gets the default behavior, which is drag_to_scroll = true, but I may not want that behavior.

I gave TableBuilder::drag_to_scroll a try, but failed to notice any difference from the default behaviour.

I ran 3 versions of the demo app (cargo run -p egui_demo_app --release):

1. master (9478e50)
2. your branch (e8865d1)
3. your branch with the patch below

diff --git a/crates/egui_demo_lib/src/demo/table_demo.rs b/crates/egui_demo_lib/src/demo/table_demo.rs
index 8fdea420..ceeadf4a 100644
--- a/crates/egui_demo_lib/src/demo/table_demo.rs
+++ b/crates/egui_demo_lib/src/demo/table_demo.rs
@@ -127,6 +127,7 @@ impl TableDemo {
         let mut table = TableBuilder::new(ui)
             .striped(self.striped)
             .resizable(self.resizable)
+            .drag_to_scroll(false)
             .cell_layout(egui::Layout::left_to_right(egui::Align::Center))
             .column(Column::auto())
             .column(Column::initial(100.0).range(40.0..=300.0))

I failed to notice any difference between the cases — I was always able to scroll the table by dragging its body:

2023-06-26.23-34-12.mp4

@KYovchevski What is the desired effect?

[KYovchevski]

@vvv The desired effect is to expose the body's underlying ScrollArea's drag_to_scroll option by adding a builder function that allows it to be set and passed down to the ScrollArea

I just tested on both master and my branch with the patch you provided, and the behaviour is as intended:

• On master, the table can be scrolled by dragging on it with the mouse, and this fact cannot be changed.
• On my branch, running with .drag_to_scroll(false) causes the dragging on the table body to not scroll it. I also tested the same property with true, which results in the same behaviour as master.

[vvv]

@KYovchevski Ah, I understand why it didn't work for me! I used “two fingers scrolling” gesture on MacBook's trackpad. That is equivalent to scrolling with mouse's wheel. It is not the same as dragging.

When I use a mouse or click-and-drag properly with a trackpad, the PR works as intended.

Sorry for the noise.

[emilk]

I'm not sure why the CI isn't kicking in. Perhaps try merging in latest master and see if it helps?