Question

I want to use Haskell’s SDL-binding for drawing simple objects (triangle, circles and the like). There is a function for drawing rectangles in Graphics.UI.SDL.Video that works ok. But I can’t get the functions I found for drawing other primitives (in Graphics.UI.SDL.Primitives) to work. The following code only draws a rectangle. Any ideas what I missed?

module Main where

import Graphics.UI.SDL as SDL
import Graphics.UI.SDL.Color
import Graphics.UI.SDL.Primitives

main = do
    SDL.init [SDL.InitVideo]
    screen <- SDL.setVideoMode 500 500 32 [SDL.HWSurface]

    SDL.fillRect screen Nothing (SDL.Pixel 0x0000FF) 

    fillRect screen (Just (SDL.Rect 10 10 30 30)) (SDL.Pixel 0x00FF0000)
    filledCircle screen 40 40 50 (SDL.Pixel 0x00FF0000)

    SDL.flip screen

    delay 2000

    SDL.quit

Answer 1

The pixel color you give filledCircle and fillRect has its alpha component set to zero; try SDL.Pixel 0x00FF00FF instead. filledCircle seems to respect the color’s alpha component whereas fillRect apparently does not.