From 9753201b2180c7c0236f6e18180829b788be4a6f Mon Sep 17 00:00:00 2001
From: Dunfan Lu <dunfanlu@meta.com>
Date: Fri, 15 Sep 2023 14:21:19 -0700
Subject: [PATCH] Always use GLSL ES 100 shaders in swift shaders

Summary:
OpenGL ES 3 on rainbow has a bug, which originates from a bug in swiftshaders.

the issue is that swiftshaders is returning -1 when we use
```
glGetActiveUniformsiv(,..,GL_UNIFORM_OFFSET, ...)
```
to query the offset of a member in a uniform buffer. We believe this is a swift shaders bug, so we work around this by always using GLSL es 100 shaders on rainbow

Reviewed By: dmannemela, syeh1

Differential Revision: D49329247

fbshipit-source-id: 54a8245704d932e7984e7521bef9d28367d1e416
---
 src/igl/opengl/Version.cpp | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/src/igl/opengl/Version.cpp b/src/igl/opengl/Version.cpp
index 6b7084cff2..3bd52fcb3d 100644
--- a/src/igl/opengl/Version.cpp
+++ b/src/igl/opengl/Version.cpp
@@ -223,6 +223,13 @@ GLVersion getGLVersion(const char* version, bool constrain) {
 }
 
 ShaderVersion getShaderVersion(GLVersion version) {
+#if IGL_PLATFORM_LINUX_SWIFTSHADER
+  // Swiftshader has a bug when it comes to uniform blocks. When calling
+  // `glGetActiveUniformsiv(,..,GL_UNIFORM_OFFSET, ...)`, it always returns -1. We work around this
+  // by forcing GLSL ES 100 shaders in swiftshaders.
+  // TODO(dunfanlu): consider patching swift shaders to fix this.
+  return {ShaderFamily::GlslEs, 1, 0};
+#else
   // TODO: Return proper GLSL ES versions
   switch (version) {
   case GLVersion::v2_0_ES:
@@ -263,6 +270,7 @@ ShaderVersion getShaderVersion(GLVersion version) {
     IGL_ASSERT_NOT_REACHED();
     return {};
   }
+#endif
 }
 
 std::string getStringFromShaderVersion(ShaderVersion version) {