Deprecated ImGui::Begin(...) and ImGui::SetNextWindowBgAlpha(...) handle alpha<0 differently

[Flix01]

Basically, as far as I can understand, now ImGui::SetNextWindowBgAlpha(bg_alpha); is used when the deprecated version of ImGui::Begin(...,bg_alpha,...) gets called.

But now if we pass for example bg_alpha=-1.f we get a transparent window.
Previously the default alpha value of 0.7f (as far as I remember) was used.

In short I think this is breaking some old deprecated code, unless we handle negative values correctly in ImGui::SetNextWindowBgAlpha(bg_alpha);.

[ocornut]

Hmm, I think you shouldn't need/want to call SetNextWindowBgAlpha(-1.0f), perhaps we could assert for that?

Previously the default alpha value of 0.7f (as far as I remember) was used.

It was using the normal alpha from the corresponding window background color, most often ImGuiCol_WindowBg.

[ocornut]

Oh I see the problem, sorry. It is a problem when called through the old Begin() signature. Fixing now!

[Flix01]

Thank you!

[ocornut]

Fixed, my bad.