render: viewport: Make applying the null viewport a no-op.

* chickadee/render/viewport.scm (apply-viewport): Don't do anything if
the viewport being applied is the null viewport.

1 files changed, 11 insertions, 10 deletions

diff --git a/chickadee/render/viewport.scm b/chickadee/render/viewport.scm
index 6789766..ad057d1 100644
--- a/chickadee/render/viewport.scm
+++ b/chickadee/render/viewport.scm
@@ -96,16 +96,17 @@ CLEAR-FLAGS are 'color-buffer', 'depth-buffer', 'accum-buffer', and
 (define (apply-viewport viewport)
   "Set the OpenGL state for VIEWPORT.  Clip rendering to the viewport
 area, set the clear color, and clear necessary buffers."
-  (let ((x (viewport-x viewport))
-        (y (viewport-y viewport))
-        (w (viewport-width viewport))
-        (h (viewport-height viewport))
-        (c (viewport-clear-color viewport)))
-    (gl-enable (enable-cap scissor-test))
-    (gl-viewport x y w h)
-    (gl-scissor x y w h)
-    (gl-clear-color (color-r c) (color-g c) (color-b c) (color-a c))
-    (gl-clear (clear-buffer-mask (viewport-clear-flags viewport)))))
+  (unless (eq? viewport null-viewport)
+    (let ((x (viewport-x viewport))
+          (y (viewport-y viewport))
+          (w (viewport-width viewport))
+          (h (viewport-height viewport))
+          (c (viewport-clear-color viewport)))
+      (gl-enable (enable-cap scissor-test))
+      (gl-viewport x y w h)
+      (gl-scissor x y w h)
+      (gl-clear-color (color-r c) (color-g c) (color-b c) (color-a c))
+      (gl-clear (clear-buffer-mask (viewport-clear-flags viewport))))))
 
 (define *viewport-state*
   (make-gpu-state apply-viewport null-viewport))