Compute height of pixel at distance.

1 files changed, 7 insertions, 0 deletions

diff --git a/MeshSketch.hs b/MeshSketch.hs
index 02c813d..0c1b4a2 100644
--- a/MeshSketch.hs
+++ b/MeshSketch.hs
@@ -471,6 +471,13 @@ onResize glarea realized w h = do
 unit :: (Linear t c, Fractional t, Normed (c t)) => c t -> c t
 unit v = scale (1/realToFrac (norm_2 v)) v
 
+-- | Compute the height of a pixel at the given 3d point.
+pixelDelta :: Camera -> Vector Float -> Float
+pixelDelta cam x = realToFrac $ frustumHeight eyeToPoint / realToFrac (camHeight cam)
+ where
+    eyeToPoint = norm_2 (x - camPos cam)
+    frustumHeight d = 2 * d * tan (realToFrac $ camHeightAngle cam / 2)
+
 -- This computes a point in world coordinates on the view screen if
 -- we assume the camera is located at the origin.
 computeDirection :: Camera -> Double -> Double -> Vector Float