Fix ImGuiKey mapping for SDL2 and SDL3

[eszdman]

Since ImGui requires untranslated ImGuiKey values, we should use scancode mapping instead of symbols, as referred to in SDL2 documentation SDL_Keycode

[ocornut]

Thanks for the PR! Where did you see that it require untranslated keys? I think we should explicitly state we try to use translate ones?

[eszdman]

Thanks for the PR! Where did you see that it require untranslated keys? I think we should explicitly state we try to use translate ones?

I tried to use it with not English locale settings in my system (arch,KDE), without fix it won't work at all, only chars queue and functional keys
Meanwhile glfw works well

[ocornut]

You are suggesting something different now. Do you mean that you are not receiving any SDL valid key-code from SDL on those keys?
Can you add some printing of all values in the event handler and confirm them?

[eszdman]

You are suggesting something different now. Do you mean that you are not receiving any SDL valid key-code from SDL on those keys? Can you add some printing of all values in the event handler and confirm them?

Sure, I tried it with demo window, Keys down method not working
This problem only appears when starting with another language, after startup with en I can use any layout
I tried to print ImGui_ImplSDL2_KeycodeToImGuiKey argument without fix and get 1094 instead of 119

[ocornut]

Can you add some printing of all values in the event handler and confirm them for a range of keys?

[eszdman]

Can you add some printing of all values in the event handler and confirm them for a range of keys?

Yes, I'm pressing QWERTYUIOP:
Startup with us:

keycode: 113:q
keycode: 113:q
keycode: 119:w
keycode: 119:w
keycode: 101:e
keycode: 101:e
keycode: 114:r
keycode: 114:r
keycode: 116:t
keycode: 116:t
keycode: 121:y
keycode: 121:y
keycode: 117:u
keycode: 117:u
keycode: 105:i
keycode: 105:i
keycode: 111:o
keycode: 111:o
keycode: 112:p
keycode: 112:p

Startup with ru:

keycode: 1081:9
keycode: 1081:9
keycode: 1094:F
keycode: 1094:F
keycode: 1091:C
keycode: 1091:C
keycode: 1082::
keycode: 1082::
keycode: 1077:5
keycode: 1077:5
keycode: 1085:=
keycode: 1085:=
keycode: 1075:3
keycode: 1075:3
keycode: 1096:H
keycode: 1096:H
keycode: 1097:I
keycode: 1097:I
keycode: 1079:7
keycode: 1079:7

scancode is the same so I print only SDL_Keycode sym
std::cout<<"keycode: "<<keycode<<":"<<char(keycode)<<std::endl;

[eszdman]

Another possible workaround is to try symbols first and then scancode but you will get issues with qwertz layout

            ImGuiKey key = ImGui_ImplSDL2_KeycodeToImGuiKeySym(event->key.keysym.sym);
            if(key == ImGuiKey_None)
                key = ImGui_ImplSDL2_KeycodeToImGuiKey(event->key.keysym.scancode);

Or implement similar method like in glfw backend - ImGui_ImplGlfw_TranslateUntranslatedKey

[ocornut]

First check what those keycode correspond to in SDL mapping.

[eszdman]

First check what those keycode correspond to in SDL mapping.

I implemented ImGui_ImplSDL2_TranslateUntranslatedKey it works well but I get error when change locale at runtime
void ImGui::UpdateKeyboardInputs(): Assertion (io.KeysDown[n] == false || IsKeyDown((ImGuiKey)n)) && "Backend needs to either only use io.AddKeyEvent(), either only fill legacy io.KeysDown[] + io.KeyMap[]. Not both!" failed.

Edit: figured it out

[eszdman]

Will open new PR with translated solution