From 3bbb377e2ceecea3c1ed7abdad7db6f506f70f20 Mon Sep 17 00:00:00 2001
From: David Thompson <dthompson2@worcester.edu>
Date: Mon, 10 May 2021 17:12:11 -0400
Subject: graphics: buffer: Fix indexed rendering with a byte offset.

Need to pass in the byte offset as a pointer to gl-draw-elements
rather than using the null pointer aka an offset of 0 bytes.
---
 chickadee/graphics/buffer.scm | 14 ++++++++------
 1 file changed, 8 insertions(+), 6 deletions(-)

diff --git a/chickadee/graphics/buffer.scm b/chickadee/graphics/buffer.scm
index 52c1293..89ee376 100644
--- a/chickadee/graphics/buffer.scm
+++ b/chickadee/graphics/buffer.scm
@@ -380,12 +380,13 @@ resized."
     ('double 8)))
 
 (define-record-type <buffer-view>
-  (%make-buffer-view name buffer offset component-type
+  (%make-buffer-view name buffer offset offset-pointer component-type
                      normalized? length type max min sparse divisor)
   buffer-view?
   (name buffer-view-name)
   (buffer buffer-view->buffer)
   (offset buffer-view-offset)
+  (offset-pointer buffer-view-offset-pointer)
   (component-type buffer-view-component-type)
   (normalized? buffer-view-normalized?)
   (length buffer-view-length)
@@ -453,8 +454,9 @@ divisor of 0 means that a single element is used for every instance
 and is used for the data being instanced.  A divisor of 1 means that
 each element is used for 1 instance.  A divisor of 2 means that each
 element is used for 2 instances, and so on."
-  (%make-buffer-view name buffer offset component-type
-                     normalized? length type max min sparse divisor))
+  (let ((offset-ptr (make-pointer offset)))
+    (%make-buffer-view name buffer offset offset-ptr component-type
+                       normalized? length type max min sparse divisor)))
 
 (define (display-buffer-view buffer-view port)
   (format port "#<buffer-view name: ~s buffer: ~a type: ~s component-type: ~s length: ~d offset: ~d divisor: ~d>"
@@ -496,7 +498,7 @@ element is used for 2 instances, and so on."
                                 (buffer-view-type-gl buffer-view)
                                 (buffer-view-normalized? buffer-view)
                                 (buffer-view-stride buffer-view)
-                                (make-pointer (buffer-view-offset buffer-view)))
+                                (buffer-view-offset-pointer buffer-view))
       (let ((divisor (buffer-view-divisor buffer-view)))
         (when divisor
           (gl-vertex-attrib-divisor attribute-index divisor))))))
@@ -600,7 +602,7 @@ argument may be overridden.  The following values are supported:
                               (or count
                                   (buffer-view-length indices))
                               (buffer-view-type-gl indices)
-                              %null-pointer))
+                              (buffer-view-offset-pointer indices)))
           (gl-draw-arrays (vertex-array-mode-gl array)
                           offset
                           (or count
@@ -618,7 +620,7 @@ argument may be overridden.  The following values are supported:
                                         (or count
                                             (buffer-view-length indices))
                                         (buffer-view-type-gl indices)
-                                        %null-pointer
+                                        (buffer-view-offset-pointer indices)
                                         instances))
           (gl-draw-arrays-instanced (vertex-array-mode-gl array)
                                     offset count instances)))))
-- 
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