I am trying to use opengl to make isometric drawings.
According to: http://en.wikipedia.org/wiki/Isometric_projection#Mathematics
"this is done by first looking straight towards one face. Next the cube is rotated ±45° about the vertical axis, followed by a rotation of approximately ±35.264° (precisely arcsin(tan 30°) or arctan(sin 45°) ) about the horizontal axis."
But clearly I am missing some detail. This code sort of works but it is at a strange angle. The yellow should be the bottom most line.
import Graphics.UI.GLFW
import Graphics.Rendering.OpenGL
main :: IO ()
main = do
initialize
openWindow (Size 800 600) [] Window
windowTitle $= "Test Projection"
clearColor $= Color4 0 0 0 1
pointSize $= 3
lineWidth $= 1
blend $= Enabled
blendFunc $= (SrcAlpha, OneMinusSrcAlpha)
viewport $= (Position 0 0, Size 800 600)
matrixMode $= Projection
loadIdentity
-- ortho (-2) (2) (-2) 2 (-20.0) 20.0
matrixMode $= Modelview 0
loadIdentity
rotate (35.264) (Vector3 1.0 0.0 0.0 :: Vector3 GLfloat)
rotate (-45) (Vector3 0.0 1.0 0.0 :: Vector3 GLfloat)
clear [ColorBuffer]
renderPrimitive Lines $ do
color $ Color3 1 zero zero
vertex' (0,0,0)
vertex' (1,0,0)
color $ Color3 zero 1 zero
vertex' (0,0,0)
vertex' (0,1,0)
color $ Color3 zero zero 1
vertex' (0,0,0)
vertex' (0,0,1)
color $ Color3 1 1 zero
vertex' (1,0,0)
vertex' (0,1,0)
swapBuffers
getChar
return ()
vertex' :: Integral a => (a, a, a) -> IO ()
vertex' (x, y, z) = vertex (Vertex3 (f x) (f y) (f z))
where f p = fromIntegral p :: GLint
zero :: GLfloat
zero = 0.0
Actually your code is correct. You just went for some misconception of OpenGLs default coordinate system. In OpenGL's standard coordinate system X goes right, Y goes up and Z points out of the screen. Your yellow line goes from (1,0,0) to (1,0,0), i.e. from a point to the right to a point up. It's perfectly correct.