From a38e873f8aee88f3cd17a4290d8b172c35701227 Mon Sep 17 00:00:00 2001
From: Sandy Carter <bwrsandman@gmail.com>
Date: Fri, 25 Oct 2019 14:56:54 +0200
Subject: [PATCH] rebind instance data buffer if index buffer changes

Fix case of drawing different indices of same vertex buffer using same
instance data.

This can happen in the case of conditionally drawing subsets of vertex
buffer stored in different index buffers while re-using non-transient
instance buffers.
---
 src/renderer_gl.cpp | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/src/renderer_gl.cpp b/src/renderer_gl.cpp
index 89f3ff8c8..8aa9f950c 100644
--- a/src/renderer_gl.cpp
+++ b/src/renderer_gl.cpp
@@ -7195,6 +7195,8 @@ namespace bgfx { namespace gl
 
 					{
 						bool diffStreamHandles = false;
+						bool diffIndexBuffer = false;
+
 						for (uint32_t idx = 0, streamMask = draw.m_streamMask
 							; 0 != streamMask
 							; streamMask >>= 1, idx += 1
@@ -7252,6 +7254,8 @@ namespace bgfx { namespace gl
 							{
 								GL_CHECK(glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, 0) );
 							}
+
+							diffIndexBuffer = true;
 						}
 
 						if (0 != currentState.m_streamMask)
@@ -7308,7 +7312,10 @@ namespace bgfx { namespace gl
 								}
 
 								program.bindAttributesEnd();
+							}
 
+							if (bindAttribs || diffStartVertex || diffIndexBuffer)
+							{
 								if (isValid(draw.m_instanceDataBuffer) )
 								{
 									GL_CHECK(glBindBuffer(GL_ARRAY_BUFFER, m_vertexBuffers[draw.m_instanceDataBuffer.idx].m_id) );