Setting the Vulkan VkViewport leads to incomplete display of widgets.

[swhoro]

Version/Branch of Dear ImGui:

Version 1.90.9

Back-ends:

no backends

Compiler, OS:

ubuntu 20.04 + gcc 9.4.0

Full config/build information:

No response

Details:

I want the width of a button to fill the window. If I use the normal VkViewport, for example, create a glfw window with width=1280, height=720, set VkViewport{x=0,y=0,width=1280,height=720}, and set io.Displaysize={1280,720}, it display correctly. But if I want the glfw window has 100 padding on x (set VkViewport{x=100,y=0,width=1080,height=720} and io.Displaysize={1080,720}), then the right part of the button is not displayed

Screenshots/Video:

This is the image in which I do not set viewport and button has full width

This is the image I set viewport as I described above and right part of the button is cutted

Minimal, Complete and Verifiable Example code:

https://gist.github.com/swhoro/be2b72efad472558363b6f1debef46a2
This is almost the same as https://github.com/SaschaWillems/Vulkan/blob/master/examples/imgui/main.cpp except line 101, 380, 458, 758 and 761.

[swhoro]

I find it is because in line484, I set wrong scissor.
But why window border can display correctly? It seems when drawing window border, the pcmd->ClipRect is {0,0,1080,720},which is the whole imgui viewport, but when drawing the button, the pcmd->ClipRect is {1,1,499,499}, which only contain the button area. What exactly does pcmd->ClipRect mean?

[ocornut]

Backends don't currently support transforming inputs or render.
You can modify ImDrawData::DisplayPos from (0,0) to (-100,0) and it will look right, but inputs will be incorrect anyhow.

I don't see/understand the reason for setting VkViewport{x=100,y=0,width=1080,height=720} and already DisplayPos. Why not giving access to the full platform window to dear imgui ?

[swhoro]

Backends don't currently support transforming inputs or render. You can modify ImDrawData::DisplayPos from (0,0) to (-100,0) and it will look right, but inputs will be incorrect anyhow.

I don't see/understand the reason for setting VkViewport{x=100,y=0,width=1080,height=720} and already DisplayPos. Why not giving access to the full platform window to dear imgui ?

I am coding for an engine and in that engine, I can only draw on a certain area on the screen.
For example, I write a text_layer for the engine. Every time they use the text_layer, they will tell me where to draw the text, how big it should be and what the content is, but will not give me the screen size. I can only code for the text_layer, and outside the layer, I can not call ImGui::* functions. So for each layer, I maintain a standalone ImGui context, and set the viewport offset and size to what they give.
The code I list above is only a simple example to reproduce the problem what I get in that engine.
It seems a bad design but I can do nothing about this.

By the way, it seems pcmd->ClipRect meaning the "parent" elmenet size? For imgui window, it is the whole imgui viewport, and for a button, it is the window.