Capturing events in vendor:sdl using SetEventFilter?

JPLost · 7 July 2025 15:13

There was some discussion regarding capturing resizing data of sdl window.
For example, if the resize was captured during PollEvent, there would be a momentarily freeze. This is due to OS blocking during PollEvent.

There were two choices given to this. Either use “main callbacks” or use SetEventFilter to make the callback that looks for EVENT_WINDOW_EXPOSED events.

If I want to capture .WINDOW_RESIZED width and height, how should it be set up in Odin?

victhordev · 8 July 2025 08:09

Here’s a code snippet which does just that:

github.com

victor-Lopez25/playlists/blob/sdl3/src/main.odin#L336


      
            }
          
            if ok {
              resize(&app.playlist.songs, len(app.playlist.songData))
              for i := 0; i < len(app.playlist.songData); i += 1 { app.playlist.songs[i] = &app.playlist.songData[i] }
            }
            return ok
          }
          
          EventFilterData :: struct { app: ^AppData, input: ^Input, Context: runtime.Context }
          InputEventFilter :: proc "c"(userdata: rawptr, event: ^sdl.Event) -> bool
          {
            prog := cast(^EventFilterData)userdata
            context = prog.Context
          
            UpdateAndRender :: proc(prog: ^EventFilterData, name: string) {
              // TODO: Figure out what causes the tearing when resizing
              spall.SCOPED_EVENT(&prog.app.spall_ctx, &prog.app.spall_buffer, name)
          
              Update(prog.app, prog.input)

But essentially you want to give it a structure which includes the window width and height and any other data you need for rendering, then inside the function check for the event type you want, I also wanted to render while moving the window and render then.

JPLost · 8 July 2025 16:51

I tried

SDL.SetEventFilter(resize_filter, nil)

resize_filter :: proc "c" (userdata: rawptr, event: ^SDL.Event) -> bool { 
    context = runtime.default_context() 
    if event.type == .WINDOW_RESIZED{ 
        g_ctx.win.w_width = event.window.data1
        g_ctx.win.w_height = event.window.data2
        fmt.printfln("Width = %i, Height = %i", event.window.data1, event.window.data2)
    }
    return true

It basically does the same thing, but still stalls at the beginning of resizing.
The document says that:

SDL_EVENT_WINDOW_EXPOSED
Window has been exposed and should be redrawn, and can be redrawn directly from event watchers for this event. data1 is 1 for live-resize expose events, 0 otherwise.

Now the next question is how to add this to code…

JPLost · 9 July 2025 16:14

This code works fine after adding renderer to window.