haskell & Gtk2hs : 画布中不显示任何点（平行绘图）

Question

我使用 Gtk2Hs 在 haskell 中编写了一个小程序，它必须显示 mandelbrot 集。

以为没有编译错误，画布中什么都没有显示（点被着色的组件）...

你能帮我调试一下这个逻辑错误吗？

我的代码：

module Main where

import           Control.Monad            (when)
import           Graphics.Rendering.Cairo as C
import           Graphics.UI.Gtk
import           Graphics.UI.Gtk.Builder  ()


main :: IO()
main = do
    _ <- initGUI
    builder <- builderNew
    builderAddFromFile builder "09-mandelbrot.ui"

    window   <- builderGetObject builder castToWindow "Figure de Mandelbrot"
    canvas <- builderGetObject builder castToDrawingArea "drawingarea1"
    _ <- onExpose canvas $ const (updateCanvas canvas)

    widgetShowAll window
    mainGUI


updateCanvas :: DrawingArea -> IO Bool
updateCanvas canvas = do
  win <- widgetGetDrawWindow canvas
  (width, height) <- widgetGetSize canvas
  _ <- mapM_ (affiche win)  (points (fromIntegral width) (fromIntegral height))

  return True

k :: Int
k=100

mandelbrot :: Double -> Double -> Bool
mandelbrot a b =
  let
    mandelrec :: Double -> Double -> Int -> Bool
    mandelrec x y i
      | (x * x + y * y > 4) = False
      | (i==k) && (x * x + y * y <= 4) = True
      | otherwise = mandelrec x' y' (i+1)
            where x' = x * x - y * y + a
                  y' = 2 * x * y + b
  in mandelrec 0 0 0

affiche2 :: DrawWindow -> Double -> Double -> IO()
affiche2 win a b = do
  renderWithDrawable win $ setSourceRGB 0 1 0
  renderWithDrawable win $ setLineWidth 1
  renderWithDrawable win $ C.rectangle a b 1 1 
  renderWithDrawable win stroke


affiche :: DrawWindow -> ((Double,Double), (Double,Double)) -> IO ()
affiche win ((a0,a), (b0,b)) = when (mandelbrot a b) $ postGUIAsync (affiche2 win a0 b0)

colonnes :: Double -> [(Double, Double)]
colonnes w = [ (t,t/w*4-2) | t<-[0..(w-1)] ]

lignes :: Double -> [(Double, Double)]
lignes h = [ (t,t/h*4-2) | t<-[0..(h-1)] ]

points :: Double -> Double -> [((Double, Double), (Double, Double))]
points w h = [ (colonne,ligne)| colonne <- colonnes w,ligne <- lignes h]

main() 并不有趣，它确实有效，我敢肯定。 update_canvas 获取一些值（宽度、高度、胜利）并调用副作用函数 affitche，为其提供“点”中的值（点包含好的值，即 [-2..2] 之间的点的坐标对于 2 个轴。 mandelbrot 很好，因为我成功地绘制了 mandelbrot 集（但所有点都被绘制在一起）。 我认为如果有问题，它可能来自affitche 或affiche2，但我是Gtk 编程的新手。

谢谢。

编辑

嗯，它适用于您的更改，但为什么呢？ 我还有一个问题：如果我将参数 k 提高（比如提高到 1000），则在启动程序后仅 17 秒就会显示该集合，并且显示速度非常快；但这不是我想要的：我希望在计算点后立即绘制这些点。你知道我必须做什么改变吗？

编辑 2

这是一个代码 - 有效：它在

module Main where

import           Control.Monad            (when)
import           Graphics.Rendering.Cairo as C
import           Graphics.UI.Gtk
import           Graphics.UI.Gtk.Builder  ()


main :: IO()
main = do
    _ <- initGUI

    window <- windowNew
    windowSetPosition window WinPosCenter
    windowSetDefaultSize window 500 350
    set window [windowTitle := "Ensemble de Mandelbrot"]
    on window objectDestroy mainQuit

    canvas <- drawingAreaNew
    canvas `on` sizeRequest $ return (Requisition 450 300)
    window `containerAdd` canvas

    _ <- onExpose canvas $ const (updateCanvas canvas)

    widgetShowAll window
    mainGUI


updateCanvas :: DrawingArea -> IO Bool
updateCanvas canvas = do
  win <- widgetGetDrawWindow canvas
  (width, height) <- widgetGetSize canvas
  _ <- mapM_ (affiche win)  (points (fromIntegral width) (fromIntegral height))

  return True

k :: Int
k=100 -- 100 : after launching, u must wait less than 10s

mandelbrot :: Double -> Double -> Bool
mandelbrot a b =
  let
    mandelrec :: Double -> Double -> Int -> Bool
    mandelrec x y i
      | (x * x + y * y > 4) = False
      | (i==k) && (x * x + y * y <= 4) = True
      | otherwise = mandelrec x' y' (i+1)
            where x' = x * x - y * y + a
                  y' = 2 * x * y + b
  in mandelrec 0 0 0

affiche2 :: DrawWindow -> Double -> Double -> IO()
affiche2 win a b = renderWithDrawable win $ do
    setSourceRGB 0 0 0
    setLineWidth 1
    C.rectangle a b 1 1 
    stroke


affiche :: DrawWindow -> ((Double,Double), (Double,Double)) -> IO ()
affiche win ((a0,a), (b0,b)) = when (mandelbrot a b) $ postGUIAsync (affiche2 win a0 b0)

colonnes :: Double -> [(Double, Double)]
colonnes w = [ (t,t/w*4-2) | t<-[0..(w-1)] ]

lignes :: Double -> [(Double, Double)]
lignes h = [ (t,t/h*4-2) | t<-[0..(h-1)] ]

points :: Double -> Double -> [((Double, Double), (Double, Double))]
points w h = [ (colonne,ligne)| colonne <- colonnes w,ligne <- lignes h]

奥利弗

Answer 1

虽然我没有使用过 Gtk2Hs，但我想问题出在affiche2。尝试将其更改为：

affiche2 win a b = do
  renderWithDrawable win $ do
    setSourceRGB 0 1 0
    setLineWidth 1
    C.rectangle a b 1 1 
    stroke