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| author | David Thompson <dthompson2@worcester.edu> | 2014-08-03 20:34:33 -0400 |
|---|---|---|
| committer | David Thompson <dthompson2@worcester.edu> | 2014-08-25 19:33:07 -0400 |
| commit | e8f5b8cca92c41cd4a9a62c297ec01a38c786063 (patch) | |
| tree | a975592f1397965a4bcb6ab6ff14aba200704db5 | |
| parent | 1963e911026046f528a2923a924a39b55947558e (diff) | |
Simplify perspective-projection implementation.
* sly/math.scm (cotan): New procedure.
* sly/transform.scm (perspective-projection): Simplify.
| -rw-r--r-- | sly/math.scm | 5 | ||||
| -rw-r--r-- | sly/transform.scm | 25 |
2 files changed, 10 insertions, 20 deletions
diff --git a/sly/math.scm b/sly/math.scm index 1a5f2c6..8dc5cbf 100644 --- a/sly/math.scm +++ b/sly/math.scm @@ -30,6 +30,7 @@ cos-degrees tan-degrees atan-degrees + cotan clamp linear-scale)) @@ -85,6 +86,10 @@ "Compute the arctangent in degrees of the coordinates Y and X." (radians->degrees (atan y x))) +(define (cotan z) + "Return the cotangent of Z." + (/ 1 (tan z))) + (define (clamp min max x) "Restrict X to the range defined by MIN and MAX. Assumes that MIN is actually less than MAX." diff --git a/sly/transform.scm b/sly/transform.scm index ece4b06..f8bba23 100644 --- a/sly/transform.scm +++ b/sly/transform.scm @@ -213,23 +213,8 @@ FAR." "Return a new transform that represents a perspective projection with a FIELD-OF-VISION in degrees, the desired ASPECT-RATIO, and the depth clipping plane NEAR and FAR." - (let ((size (* near (tan (/ (degrees->radians field-of-vision) 2))))) - (let ((left (- size)) - (right size) - (top (/ size aspect-ratio)) - (bottom (/ (- size) aspect-ratio))) - (make-transform (/ (* 2 near) (- right left)) ;; First row - 0 - (/ (+ right left) (- right left)) - 0 - ;; Second row - 0 - (/ (* 2 near) (- top bottom)) - (/ (+ top bottom) (- top bottom)) - 0 - ;; Third row - 0 0 - (- (/ (+ far near) (- far near))) - (- (/ (* 2 far near) (- far near))) - ;; Fourth row - 0 0 -1 0)))) + (let ((f (cotan (/ (degrees->radians field-of-vision) 2)))) + (make-transform (/ f aspect-ratio) 0 0 0 + 0 f 0 0 + 0 0 (/ (+ far near) (- near far)) -1 + 0 0 (/ (* 2 far near) (- near far)) 0))) |