From 2bed164bdea04034140b843fc4a3cb20488138b6 Mon Sep 17 00:00:00 2001
From: David Thompson <dthompson2@worcester.edu>
Date: Fri, 5 Mar 2021 08:04:55 -0500
Subject: graphics: Improve error message when prematurely creating GPU
 objects.

---
 chickadee/graphics/buffer.scm      | 2 ++
 chickadee/graphics/engine.scm      | 5 +++++
 chickadee/graphics/framebuffer.scm | 1 +
 chickadee/graphics/shader.scm      | 1 +
 chickadee/graphics/texture.scm     | 1 +
 5 files changed, 10 insertions(+)

diff --git a/chickadee/graphics/buffer.scm b/chickadee/graphics/buffer.scm
index f5ec8c6..37a77e4 100644
--- a/chickadee/graphics/buffer.scm
+++ b/chickadee/graphics/buffer.scm
@@ -204,6 +204,7 @@ USAGE may be:
 
 NAME is simply an arbitrary string for debugging purposes that is
 never sent to the GPU."
+  (assert-current-graphics-engine)
   ;; Weird bugs will occur when creating a new vertex buffer while a
   ;; vertex array is bound.
   (with-graphics-state! ((vertex-array null-vertex-array))
@@ -561,6 +562,7 @@ argument may be overridden.  The following values are supported:
 - triangles
 - triangle-strip
 - triangle-fan"
+  (assert-current-graphics-engine)
   (let ((array (%make-vertex-array (generate-vertex-array)
                                    indices
                                    attributes
diff --git a/chickadee/graphics/engine.scm b/chickadee/graphics/engine.scm
index 4f1250f..1531e3f 100644
--- a/chickadee/graphics/engine.scm
+++ b/chickadee/graphics/engine.scm
@@ -23,6 +23,7 @@
             graphics-engine-guard!
             graphics-engine-reap!
             current-graphics-engine
+            assert-current-graphics-engine
             current-projection
             with-projection
             with-graphics-state
@@ -200,6 +201,10 @@
 
 (define current-graphics-engine (make-parameter #f))
 
+(define-syntax-rule (assert-current-graphics-engine)
+  (unless (current-graphics-engine)
+    (error "No active graphics engine.  Make sure the game loop is running before calling this procedure.")))
+
 (define* (graphics-engine-gl-context #:optional (engine (current-graphics-engine)))
   (%graphics-engine-gl-context engine))
 
diff --git a/chickadee/graphics/framebuffer.scm b/chickadee/graphics/framebuffer.scm
index edf97a2..5a8be8d 100644
--- a/chickadee/graphics/framebuffer.scm
+++ b/chickadee/graphics/framebuffer.scm
@@ -101,6 +101,7 @@
                     (wrap-s 'repeat) (wrap-t 'repeat))
       "Create a new framebuffer that renders to a texture with
 dimensions WIDTH x HEIGHT."
+      (assert-current-graphics-engine)
       (let* ((framebuffer-id (generate-framebuffer))
              (renderbuffer-id (generate-renderbuffer))
              (texture (make-texture #f width height
diff --git a/chickadee/graphics/shader.scm b/chickadee/graphics/shader.scm
index 335f79c..9b2070b 100644
--- a/chickadee/graphics/shader.scm
+++ b/chickadee/graphics/shader.scm
@@ -712,6 +712,7 @@ them into a GPU shader program."
               (error "unsupported attribute size" name size))
             (hash-set! table name (make-attribute name location type)))))
       table))
+  (assert-current-graphics-engine)
   (let ((vertex-id (make-shader-stage (version-2-0 vertex-shader)
                                       vertex-port))
         (fragment-id (make-shader-stage (version-2-0 fragment-shader)
diff --git a/chickadee/graphics/texture.scm b/chickadee/graphics/texture.scm
index 30ae9a0..f056be8 100644
--- a/chickadee/graphics/texture.scm
+++ b/chickadee/graphics/texture.scm
@@ -170,6 +170,7 @@ clamp-to-edge.  FORMAT specifies the pixel format.  Currently only
       ('clamp-to-border (texture-wrap-mode clamp-to-border-sgis))
       ('clamp-to-edge (texture-wrap-mode clamp-to-edge-sgis))))
 
+  (assert-current-graphics-engine)
   (let ((texture (%make-texture (gl-generate-texture) #f
                                 min-filter mag-filter wrap-s wrap-t
                                 0 0 width height
-- 
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