From 40b43110df468c72c8d90c34d559e2725fe05e42 Mon Sep 17 00:00:00 2001
From: David Thompson <dthompson2@worcester.edu>
Date: Wed, 26 Aug 2020 21:36:10 -0400
Subject: render: buffer: Support vertex arrays with no index buffer.

---
 chickadee/graphics.scm        | 12 ++++++------
 chickadee/graphics/buffer.scm | 35 ++++++++++++++++++++---------------
 chickadee/graphics/sprite.scm |  1 +
 3 files changed, 27 insertions(+), 21 deletions(-)

diff --git a/chickadee/graphics.scm b/chickadee/graphics.scm
index a41739e..1a2917f 100644
--- a/chickadee/graphics.scm
+++ b/chickadee/graphics.scm
@@ -182,20 +182,20 @@
          (set-uniform-value! shader uniform (uniform-value uniform))))
      shader)))
 
-(define-syntax-rule (gpu-apply* shader vertex-array count . uniforms)
+(define-syntax-rule (gpu-apply* shader vertex-array offset count . uniforms)
   (begin
     (gpu-prepare shader vertex-array uniforms)
-    (render-vertices vertex-array count)))
+    (render-vertices vertex-array #:count count #:offset offset)))
 
 (define-syntax-rule (gpu-apply shader vertex-array uniforms ...)
-  (gpu-apply* shader vertex-array #f uniforms ...))
+  (gpu-apply* shader vertex-array #f 0 uniforms ...))
 
-(define-syntax-rule (gpu-apply/instanced* shader vertex-array count instances .
+(define-syntax-rule (gpu-apply/instanced* shader vertex-array offset count instances .
                                           uniforms)
   (begin
     (gpu-prepare shader vertex-array uniforms)
-    (render-vertices/instanced vertex-array instances count)))
+    (render-vertices/instanced vertex-array instances #:count count #:offset offset)))
 
 (define-syntax-rule (gpu-apply/instanced shader vertex-array instances
                                          uniforms ...)
-  (gpu-apply/instanced* shader vertex-array #f instances uniforms ...))
+  (gpu-apply/instanced* shader vertex-array #f 0 instances uniforms ...))
diff --git a/chickadee/graphics/buffer.scm b/chickadee/graphics/buffer.scm
index cfb541f..9e5a791 100644
--- a/chickadee/graphics/buffer.scm
+++ b/chickadee/graphics/buffer.scm
@@ -571,7 +571,7 @@ argument may be overridden.  The following values are supported:
                 ((index . buffer-view)
                  (apply-buffer-view buffer-view index)))
               attributes)
-    (apply-buffer-view indices)
+    (when indices (apply-buffer-view indices))
     (set-gpu-vertex-array! (current-gpu) null-vertex-array)
     array))
 
@@ -585,21 +585,26 @@ argument may be overridden.  The following values are supported:
     ('triangle-strip (begin-mode triangle-strip))
     ('triangle-fan (begin-mode triangle-fan))))
 
-(define* (render-vertices array #:optional count)
+(define* (render-vertices array #:key count (offset 0))
   (set-gpu-vertex-array! (current-gpu) array)
   (let ((indices (vertex-array-indices array)))
-    (gl-draw-elements (vertex-array-mode-gl array)
-                      (or count
-                          (buffer-view-length indices))
-                      (buffer-view-type-gl indices)
-                      %null-pointer)))
-
-(define* (render-vertices/instanced array instances #:optional count)
+    (if indices
+        (gl-draw-elements (vertex-array-mode-gl array)
+                          (or count
+                              (buffer-view-length indices))
+                          (buffer-view-type-gl indices)
+                          %null-pointer)
+        (gl-draw-arrays (vertex-array-mode-gl array) offset count))))
+
+(define* (render-vertices/instanced array instances #:key count (offset 0))
   (set-gpu-vertex-array! (current-gpu) array)
   (let ((indices (vertex-array-indices array)))
-    (gl-draw-elements-instanced (vertex-array-mode-gl array)
-                                (or count
-                                    (buffer-view-length indices))
-                                (buffer-view-type-gl indices)
-                                %null-pointer
-                                instances)))
+    (when indices
+      (gl-draw-elements-instanced (vertex-array-mode-gl array)
+                                  (or count
+                                      (buffer-view-length indices))
+                                  (buffer-view-type-gl indices)
+                                  %null-pointer
+                                  instances)
+      (gl-draw-arrays-instanced (vertex-array-mode-gl array)
+                                offset count instances))))
diff --git a/chickadee/graphics/sprite.scm b/chickadee/graphics/sprite.scm
index 5fc3203..7c36623 100644
--- a/chickadee/graphics/sprite.scm
+++ b/chickadee/graphics/sprite.scm
@@ -460,6 +460,7 @@ void main (void) {
         (with-texture 0 (sprite-batch-texture batch)
           (gpu-apply* (force batched-sprite-shader)
                       (sprite-batch-vertex-array batch)
+                      0
                       (* (sprite-batch-size batch) 6)
                       #:mvp mvp))))))
 
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