我编写了一个可视化氢原子电子云的程序。
import System.Exit
import Graphics.UI.GLUT
probDensity :: Double -> Double
probDensity r = abs $ (1 - r) * exp (-r/2.0)
myInit :: IO ()
myInit = clearColor $= Color4 1 1 1 0
grid :: [(GLint,GLint)]
grid = [(x,y) | x <- [-200..200],y <- [-200..200]]
density :: [Double]
density = map (\(i',j') -> probDensity $ sqrt $ (fromIntegral i' ** 2 + fromIntegral j' ** 2 ) / 324) grid
cloud = zip density grid
display :: DisplayCallback
display = do
clear [ColorBuffer]
color $ Color4 1 1 1 (0::GLfloat)
renderPrimitive Points $
mapM_ (\(c,(x,y)) -> color (Color3 c c 0) >> vertex (Vertex2 x y)) cloud
flush
idle :: IdleCallback
idle =
postRedisplay Nothing
reshape :: ReshapeCallback
reshape (Size _ _) = do
viewport $= (Position 0 0, Size 400 400)
matrixMode $= Projection
loadIdentity
ortho2D (-200.0) 200.0 (-200.0) 200.0
matrixMode $= Modelview 0
loadIdentity
keyboard :: KeyboardMouseCallback
keyboard (Char '\27') Down _ _ = exitSuccess
keyboard _ _ _ _ = return ()
main :: IO ()
main = do
(_, _args) <- getArgsAndInitialize
initialDisplayMode $= [ RGBMode ]
initialWindowSize $= Size 400 400
initialWindowPosition $= Position 100 100
_ <- createWindow "Cloud"
shadeModel $= Smooth
myInit
displayCallback $= display
reshapeCallback $= Just reshape
keyboardMouseCallback $= Just keyboard
idleCallback $= Just idle
mainLoop
但结果在图表的右侧有很多行。
我一次又一次检查了我的代码,找不到任何错误。 这是包的错误吗?
答案 0 :(得分:4)
我猜这是因为浮点错误导致光栅化过程中遗漏了某些列。您有超过400列像素的401列样本,并且您的顶点位置将作为整数发送。当整数在图形管道中转换为浮点数时,they will not be exact。如果您将视口和窗口大小更改为其他内容,它应该看起来很好:
399x399:
400x400:
401x401(一对一像素到样本):
402x402:
注意,如果你增加你正在采集的样本数量,这也可以正常工作:
grid = [(x,y) | x <- [-400..400],y <- [-400..400]]
density = map (\(i',j') -> probDensity $ sqrt $
(fromIntegral i' ** 2 + fromIntegral j' ** 2 ) / 648) grid
renderPrimitive Points $
mapM_ (\(c,(x,y)) -> do
color (Color3 c c 0)
vertex (Vertex2 (fromIntegral x / 2) (fromIntegral y / 2) :: Vertex2 GLfloat)) cloud
另一种解决方法是使用浮点顶点位置定位像素中心。变化
vertex (Vertex2 x y)
到
vertex (Vertex2 (fromIntegral x + 0.5) (fromIntegral y + 0.5) :: Vertex2 GLfloat)