ImGui + SDL z-order

Main.hs

module Main (main) where

import Control.Exception (bracket, bracket_)
import Control.Monad (unless, when)
import Control.Monad.IO.Class ()
import Control.Monad.Managed
import DearImGui
import DearImGui.OpenGL3
import DearImGui.SDL
import DearImGui.SDL.Renderer
import Graphics.GL
import SDL

main :: IO ()
main = do
  -- Initialize SDL
  initializeAll

  runManaged $ do
    -- Create a window using SDL; as we're using OpenGL, we enable OpenGL too
    window <- do
      let title = "Hello, Dear ImGui!"
      let config =
            defaultWindow
              { windowGraphicsContext = OpenGLContext defaultOpenGL
              , windowInitialSize = V2 1024 768
              }
      managed $ bracket (createWindow title config) destroyWindow

    -- Create an OpenGL context
    _glContext <- managed $ bracket (glCreateContext window) glDeleteContext
    -- Create an ImGui context
    _ <- managed $ bracket createContext destroyContext

    -- Initialize ImGui's SDL2 backend
    -- managed_ $ bracket_ (sdl2InitForOpenGL window glContext) sdl2Shutdown

    -- Initialize ImGui's OpenGL backend
    managed_ $ bracket_ openGL3Init openGL3Shutdown

    renderer <-
      managed $
        bracket (createRenderer window -1 defaultRenderer) destroyRenderer

    -- Initialize ImGui's SDL2 backend
    managed_ $ bracket_ (sdl2InitForSDLRenderer window renderer) sdl2Shutdown

    liftIO $ mainLoop window renderer

mainLoop :: Window -> Renderer -> IO ()
mainLoop window renderer = unlessQuit $ do
  -- Tell ImGui we're starting a new frame
  openGL3NewFrame
  sdl2NewFrame
  newFrame

  -- Draw some shapes using SDL. This will draw on the back buffer.
  rendererDrawColor renderer $= V4 64 0 0 255
  -- clear renderer

  rendererDrawColor renderer $= V4 255 0 0 255
  drawLine renderer (P $ V2 100 50) (P $ V2 400 200)
  rendererDrawColor renderer $= V4 0 127 0 127
  fillRect renderer (Just $ Rectangle (P $ V2 500 250) $ V2 100 50)

  -- Build the GUI
  setNextWindowFocus
  withWindowOpen "Hello, ImGui!" $ do
    text "what can we do here!?"
    button "Click me" >>= \clicked ->
      when clicked $ putStrLn "You clicked the button"

  -- Render ImGui stuff to back buffer.
  render

  glClearColor 0 0 0.25 0
  glClear GL_COLOR_BUFFER_BIT

  openGL3RenderDrawData =<< getDrawData

  -- Moving this to above the `openGL3RenderDrawData =<< getDrawData` only
  -- results in the ImGui stuff not being shown at all.
  present renderer

  mainLoop window renderer
  where
    -- Process the event loop
    unlessQuit action = do
      shouldQuit <- gotQuitEvent
      unless shouldQuit action

    gotQuitEvent = do
      ev <- pollEventWithImGui

      case ev of
        Nothing ->
          return False
        Just event ->
          (isQuit event ||) <$> gotQuitEvent

    isQuit event =
      eventPayload event == QuitEvent