SDL3 Support

[RGPaul]

Hey,
thanks for this great Library.

Is there Support for SDL3 planned?
I have some trouble to get the high dpi setup correctly for iOS (touch points are offset).

[texus]

Is there Support for SDL3 planned?

It is definitely planned once SDL3 is released, but I'm not sure if I can keep it supported during its development.
I'm not actively following SDL development (I only read the release notes when they make a new release), so I don't actually know if they expect to break a lot of code or not in SDL3. If the API won't change often then I could perhaps allow the cmake script to find SDL3 as well and only occasionally check if my code still compiles.

Edit: It looks like many functions have already been renamed, so I guess the biggest changes that affect TGUI have already been done. I'll try to have a look soon for making the code compatible with both SDL2 and SDL3.

I have some trouble to get the high dpi setup correctly for iOS (touch points are offset).

This will be tricky for me to solve, because I don't have access to any Apple devices myself.
Are you able to get the correct position from SDL itself? If SDL provides incorrect values then there isn't much that I can do about it, but if SDL is providing correct numbers then you can perhaps show me an example SDL code so that I can figure out the difference with what TGUI is doing now.

[RGPaul]

Edit: It looks like many functions have already been renamed, so I guess the biggest changes that affect TGUI have already been done. I'll try to have a look soon for making the code compatible with both SDL2 and SDL3.

Sounds great.

I have some trouble to get the high dpi setup correctly for iOS (touch points are offset).

This will be tricky for me to solve, because I don't have access to any Apple devices myself. Are you able to get the correct position from SDL itself? If SDL provides incorrect values then there isn't much that I can do about it, but if SDL is providing correct numbers then you can perhaps show me an example SDL code so that I can figure out the difference with what TGUI is doing now.

It seems to be an Issue with SDL2. I had the same problem with my Mac.
I could solve it using this code:

gui.onViewChange([&gui, &window, &renderer] {
        int widthInPixels, heightInPixels;
        SDL_GetWindowSizeInPixels(window, &widthInPixels, &heightInPixels);
        SDL_Log("New Window Size: %d x %d", widthInPixels, heightInPixels);
        SDL_RenderSetLogicalSize(renderer, widthInPixels, heightInPixels);
    });

But that isn't working for iOS.

Edit:
I will check if I can get it working with a plain SDL Application and give feedback or create a pull request if we can adjust TGUI to fix it.

[texus]

The SDL touch event provides values between 0 and 1, and TGUI is multiplying this with the window size. Since the logical and physical window size are different on high-DPI screens, I'm probably just multiplying with the wrong number.

I'm currently multiplying event.tfinger.x and event.tfinger.y with the values returned by SDL_GetWindowSize. I probably need to multiply them with the values returned by SDL_GetWindowSizeInPixels instead. (The relevant lines are found at https://github.com/texus/TGUI/blob/0.10/src/Backend/Window/SDL/BackendGuiSDL.cpp#L333-L386, with m_windowSize and m_framebufferSize containing the values from SDL_GetWindowSize and SDL_GetWindowSizeInPixels respectively)

While that would explain the wrong scaling of touch events, I don't understand how your fix for macOS would work, so maybe the issue is still more complex than this.

[RGPaul]

I can try to adjust that in BackendGuiSDL, but I think using SDL_GetWindowSize is correct. SDL_GetWindowSize should return points instead of pixels.

[RGPaul]

Okay it works correctly (even without SDL_RenderSetLogicalSize mentioned in #182 (comment)) if I change SDL_GetWindowSize to SDL_GetWindowSizeInPixels in BackendGuiSDL.cpp:

void BackendGuiSDL::updateContainerSize()
{
    // We can't do anything yet if we don't have a window
    if (!m_window)
        return;

    SDL_GetWindowSizeInPixels(m_window, &m_windowSize.x, &m_windowSize.y);
    ...

Edit:
macOS still needs the workaround mentioned in #182 (comment)

[texus]

Great, I'll update the code with a similar change later today so that the touch events will work out of the box on iOS.

If you are willing to help figure out why the macOS workaround is needed, I have a few more questions:

• Without the workaround on macOS, are the touch events wrong or is the drawing scaled incorrectly (i.e. does the window contents still look the same with or without that code)?
• Are you passing the SDL_WINDOW_ALLOW_HIGHDPI flag to SDL_CreateWindow?
• Does it make a difference when you call SDL_SetHint(SDL_HINT_WINDOWS_DPI_SCALING, "1"); before SDL_Init? (I'm assuming it makes no difference)
• Could you check what the value of event.tfinger.windowID is when you get a touch event? If it differs from 0 on macOS, then perhaps that is the difference with iOS (as I assume it is 0 on iOS)?

[RGPaul]

If you are willing to help figure out why the macOS workaround is needed, I have a few more questions:

Sure

• Without the workaround on macOS, are the touch events wrong or is the drawing scaled incorrectly (i.e. does the window contents still look the same with or without that code)?

The drawing is correct - just the mouse hit and mouse hover is incorrect.

• Are you passing the SDL_WINDOW_ALLOW_HIGHDPI flag to SDL_CreateWindow?

Yes

• Does it make a difference when you call SDL_SetHint(SDL_HINT_WINDOWS_DPI_SCALING, "1"); before SDL_Init? (I'm assuming it makes no difference)

there is no difference

• Could you check what the value of event.tfinger.windowID is when you get a touch event? If it differs from 0 on macOS, then perhaps that is the difference with iOS (as I assume it is 0 on iOS)?

on macOS I found:
eventSDL.button.windowID: 1

on iOS I found:
eventSDL.tfinger.windowID: 1

Edit:
I don't know if it makes a difference but on macOS the video driver says it is cocoa and on iOS the video driver name is uikit - determined using SDL_GetCurrentVideoDriver

Edit2:
I don't know if you have seen it, but there is an interesting discussion about high dpi about SDL3 (why I thought I need SDL3 Support for iOS): libsdl-org/SDL#7134

[texus]

I didn't realize earlier that on macOS you would be using mouse events instead of touch events, that is the difference between the macOS and iOS issues.

The mouse positions apparently need to be scaled. I didn't understand why it would be different on macOS and Windows, so I booted up my Windows, messed with the scaling, and found that the mouse positions where broken there as well. I've committed a change (1b24db4) that should fix the touch events on iOS and fixes the mouse positions on my Windows with high-DPI. So you should check if it also fixes the issue on macOS.

[RGPaul]

Okay now it works without the workaround! Thanks alot!