From 92a3951c0823c3be804ca92c78710a6a3d1e7a69 Mon Sep 17 00:00:00 2001
From: David Thompson <dthompson2@worcester.edu>
Date: Thu, 16 Feb 2023 20:51:05 -0500
Subject: Add discard as an alias to empty outputs.

---
 chickadee/graphics/seagull.scm | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/chickadee/graphics/seagull.scm b/chickadee/graphics/seagull.scm
index 515c9e1..c5452b0 100644
--- a/chickadee/graphics/seagull.scm
+++ b/chickadee/graphics/seagull.scm
@@ -39,9 +39,8 @@
 ;;
 ;; TODO:
 ;; - Loops
-;; - discard
 ;; - (define ...) form
-;; - struct field aliases (rgba for vec4, for example)
+;; - struct field aliases (rgba for vec4, for example) maybe a bad idea??
 ;; - Scheme shader type -> GLSL struct translation
 ;; - Dead code elimination (error when a uniform is eliminated)
 ;; - User defined structs
@@ -504,6 +503,10 @@
      (expand:cond clauses stage env))
     (('case key clauses ...)
      (expand:case key clauses stage env))
+    (('discard)
+     (if (eq? stage 'fragment)
+         '(outputs)
+         (seagull-syntax-error "discard not allowed in vertex shader" exp expand)))
     ;; Primitive calls:
     (((? primitive-call-for-stage? operator) args ...)
      (expand:primitive-call operator args stage env))
-- 
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