From 6b7675df78a5afc3f7b8b3c4a1943bc02f82ca66 Mon Sep 17 00:00:00 2001
From: Pavel Rojtberg <rojtberg@gmail.com>
Date: Mon, 9 Sep 2024 18:43:46 +0200
Subject: [PATCH] GL3Plus: offset mesh SSBO binding by 3

to give room for meshlet buffers. Also UBOs work now with gl_spirv
---
 Docs/src/high-level-programs.md                           | 2 +-
 RenderSystems/GL3Plus/src/OgreGL3PlusRenderSystem.cpp     | 2 +-
 Samples/Media/materials/programs/GLSL400/MeshProgram.glsl | 8 ++------
 3 files changed, 4 insertions(+), 8 deletions(-)

diff --git a/Docs/src/high-level-programs.md b/Docs/src/high-level-programs.md
index 01a2f6b4291..6476d6523b3 100644
--- a/Docs/src/high-level-programs.md
+++ b/Docs/src/high-level-programs.md
@@ -131,7 +131,7 @@ refer to the following table for the location indices and names to use:
 
 ## Buffers in Mesh Shaders {#GLSL-Mesh-Shaders}
 
-With mesh shaders the input assembly stage is skipped and hence the vertex attributes are not available. Instead, %Ogre will bind the vertex buffers as SSBOs to a binding point defined by the Ogre::VertexBufferBinding index.
+With mesh shaders the input assembly stage is skipped and hence the vertex attributes are not available. Instead, %Ogre will bind the vertex buffers as SSBOs to a binding point defined by the Ogre::VertexBufferBinding index, offset by 3.
 
 In the shader you can access the buffer as follows:
 
diff --git a/RenderSystems/GL3Plus/src/OgreGL3PlusRenderSystem.cpp b/RenderSystems/GL3Plus/src/OgreGL3PlusRenderSystem.cpp
index 0bb4878018f..2bd7d3bcfd3 100644
--- a/RenderSystems/GL3Plus/src/OgreGL3PlusRenderSystem.cpp
+++ b/RenderSystems/GL3Plus/src/OgreGL3PlusRenderSystem.cpp
@@ -1009,7 +1009,7 @@ namespace Ogre {
             for(auto it : op.vertexData->vertexBufferBinding->getBindings())
             {
                 auto buf = it.second->_getImpl<GL3PlusHardwareBuffer>();
-                buf->setGLBufferBinding(it.first, GL_SHADER_STORAGE_BUFFER);
+                buf->setGLBufferBinding(it.first + 3, GL_SHADER_STORAGE_BUFFER);
             }
         }
 
diff --git a/Samples/Media/materials/programs/GLSL400/MeshProgram.glsl b/Samples/Media/materials/programs/GLSL400/MeshProgram.glsl
index 0f3e2008d73..d77b14731f1 100644
--- a/Samples/Media/materials/programs/GLSL400/MeshProgram.glsl
+++ b/Samples/Media/materials/programs/GLSL400/MeshProgram.glsl
@@ -17,13 +17,13 @@ layout(location=0) out PerVertexData
     vec3 color;
 } v_out[];
 
-#ifdef VULKAN
 layout(binding=0, row_major) uniform OgreUniforms
 {
     mat4 MVP;
     float t;
 };
 
+#ifdef VULKAN
 // SSBOs cannot be used with Vulkan yet
 float data[] = {
     -100, -100, 0,  // pos
@@ -40,13 +40,9 @@ float data[] = {
     0,0
 };
 #else
-// UBOs cannot be used with gl_spirv yet
-layout(location=0) uniform mat4 MVP;
-layout(location=4) uniform float t;
-
 //![vertexbuffer]
 // buffer at index 0, which is expected to contain float data
-layout(binding = 0) buffer VertexDataIn
+layout(binding = 3) readonly buffer VertexDataIn
 {
     float data[];
 };