ComboBox clipped by window

[BenBooth1344]

Describe the bug

When a Window has a ComboBox near the bottom some items in the list can be cut off.

To Reproduce
Steps to reproduce the behavior (Bottom clip - 1st screenshot):

• Create a window
• add ui elements using up ~ 300pts of height
• add a ComboBox with a large number of elements
• build & run and click on ComboBox
• bottom of dropdown list is clipped

Steps to reproduce the behavior (Bottom & Side clip 2nd screenshot):

• Create a window with .scroll(true)
• add ui elements using up ~ 600pts of height
• add a ComboBox with a large number of elements (it needs to be located near right edge of window)
• build & run and click on ComboBox
• bottom and right of dropdown list is clipped

Expected behavior
dropdown lists should not be clipped

Cause of issue
clip_rect of parent ui (window or scroll area) is being used to clip the dropdown list

Screenshots

Proposed solution
If the clip_rect of the ui is expanded immediately prior to drawing the dropdown popup and shrunk back afterwards, the problem can be fixed.

The vertical height of the clip_rect needs to be temporally expanded by "ui.spacing().combo_height"
I don't the required width expansion is easily determined

I believe the code change needs to be done in src\containers\popop.popup_below_widget

It might be best to make clip_rect expansion optional

functions to expand/shrink clip_rect:

pub fn expand_ui_clip_rect_y(ui: &mut Ui) {
    let rect = ui.clip_rect();
    ui.set_clip_rect(Rect::from_two_pos(
        rect.min,
        pos2(rect.max.x, rect.max.y + ui.spacing().combo_height),
    ));
}

pub fn shrink_ui_clip_rect_y(ui: &mut Ui) {
    let rect = ui.clip_rect();
    ui.set_clip_rect(Rect::from_two_pos(
        rect.min,
        pos2(rect.max.x, rect.max.y + ui.spacing().combo_height),
    ));
}

Desktop (please complete the following information):

• OS: Windows 10
• eframe : 0.14.0
• Native app

[emilk]

Good find!

The reason that the parent clip rect is respected at all is for the case when the combobox is in a scroll-area. However, maybe it is just easier to always ignore the parent clip rect, and let popups (including comboboxes) "escape" the parent.

See /~https://github.com/emilk/egui/blob/master/egui/src/containers/popup.rs#L288

[emilk]

Another option is to move the popup to be within the parent clip rect, which would also solve #693

[BenBooth1344]

In my case the window is procedurally generated and based on parsed user input. So it's not really an option to move the combo box.

The other issue is I would like to allow the ComboBox to be in a scroll Area since the user can input any number of input blocks which can cause the window to need a scroll bar.

If the ComboBox dropdown being clipped is always bad (at least in y) then you can add a call to "expand_ui_clip_rect_y"
right after line 288
/~https://github.com/emilk/egui/blob/master/egui/src/containers/popup.rs#L288
and a call to "shrink_ui_clip_rect_y" right after line 299 /~https://github.com/emilk/egui/blob/master/egui/src/containers/popup.rs#L299

and that should allow the dropdown to still work with a scroll area

[BenBooth1344]

I misread your comment about moving the ComboBox, if the popup can be automatically moved to within the clip_rect that would solve my issue.

It would also solve the issue with clipping when in a ScrollArea (second screenshot above)

But wouldn't that require knowing how big the popup will be prior to drawing it?