Port path stroke shader to Seagull.

1 files changed, 68 insertions, 4 deletions

diff --git a/chickadee/graphics/path.scm b/chickadee/graphics/path.scm
index f97ca4a..f6bfcdb 100644
--- a/chickadee/graphics/path.scm
+++ b/chickadee/graphics/path.scm
@@ -1221,9 +1221,74 @@
 ;;; Rendering
 ;;;
 
+(define-vertex-shader stroke-vertex
+  ((in vec2 position)
+   (in vec2 tex)
+   (in float stroke-length)
+   (out vec2 frag-tex)
+   (out float frag-stroke-length)
+   (uniform mat4 mvp)
+   (uniform vec4 color))
+  ;; Short-circuit because the fragments will just be discarded
+  ;; anyway.
+  (if (<= (-> color w) 0.0)
+      (outputs
+       (vertex:position (vec4 0.0 0.0 0.0 1.0)))
+      (outputs
+       (vertex:position (* mvp (vec4 (-> position x) (-> position y) 0.0 1.0)))
+       (frag-tex tex)
+       (frag-stroke-length stroke-length))))
+
+(define-fragment-shader stroke-fragment
+  ((in vec2 frag-tex)
+   (in float frag-stroke-length)
+   (out vec4 frag-color)
+   (uniform vec4 color)
+   (uniform float feather)
+   (uniform int stroke-closed)
+   (uniform float stroke-width)
+   (uniform int stroke-cap)
+   (uniform float stroke-miter-limit))
+  (if (<= (-> color w) 0.0)
+      (outputs)
+      (let* ((infinity (/ 1.0 0.0))
+             (hw (/ stroke-width 2.0))
+             (u (-> frag-tex x))
+             (v (-> frag-tex y))
+             (dx (if (< u 0.0) (abs u) (- u frag-stroke-length)))
+             (dy (abs v))
+             ;; Signed distance function that applies end cap styles.
+             (d (if (or (< u 0.0) (> u frag-stroke-length))
+                    (case stroke-cap
+                      ((0) ; none
+                       infinity)
+                      ((1) ; butt (hehe)
+                       (max (- (+ dx hw) (* 2.0 feather)) dy))
+                      ((2) ; square
+                       (max dx dy))
+                      ((3) ; round
+                       (sqrt (+ (* dx dx) (* dy dy))))
+                      ((4) ; triangle out
+                       (+ dx dy))
+                      ((5) ; triangle in
+                       (max dy (- hw (+ feather dx) dy)))
+                      (else ; unknown
+                       0.0))
+                    dy))
+             (color* (if (<= d hw)
+                         color
+                         (vec4 (-> color x)
+                               (-> color y)
+                               (-> color z)
+                               (* (-> color w)
+                                  (- 1.0 (/ (- d hw) feather)))))))
+        (if (<= (-> color w) 0.0)
+            (outputs)
+            (outputs
+             (frag-color color*))))))
+
 (define-graphics-variable stroke-shader
-  (load-shader (scope-datadir "shaders/path-stroke-vert.glsl")
-               (scope-datadir "shaders/path-stroke-frag.glsl")))
+  (compile-shader stroke-vertex stroke-fragment))
 
 (define-vertex-shader fill-vertex
   ((in vec2 position)
@@ -1258,8 +1323,7 @@
                                          0.0 1.0)))
                           (mix color end-color t)))))
     (if (<= (-> color w) 0.0)
-        (outputs
-         (frag-color (vec4 1.0 1.0 1.0 1.0)))
+        (outputs)
         (outputs
          (frag-color
           (case mode