From df493a7da7251eb5ea33b62a65580d09b440dd74 Mon Sep 17 00:00:00 2001
From: cmitu <31816814+cmitu@users.noreply.github.com>
Date: Wed, 2 Sep 2020 04:27:00 +0100
Subject: [PATCH] add OpenGL shaders versioning for GLSL compatibility

The GL context initialization in 'GLVideoDriver' requests OpenGL (ES) 2.0 from SDL2,
but SDL2 doesn't guarantee the context returned will have the same version [1].

To avoid any compatibility issues with a superior GLSL version, add the GLSL version to the shader code,
depending on the GL context requested (non-ES vs. ES).
 * when expecting an OpenGL 2.0 context, set version to 110
 * when expecting an OpenGL ES 2.0 context, set version to 100

[1] - https://wiki.libsdl.org/SDL_GLattr#OpenGL
---
 gemrb/plugins/SDLVideo/GLSLProgram.cpp  | 10 ++++++++--
 gemrb/plugins/SDLVideo/SDL20GLVideo.cpp |  8 +++++---
 2 files changed, 13 insertions(+), 5 deletions(-)

diff --git a/gemrb/plugins/SDLVideo/GLSLProgram.cpp b/gemrb/plugins/SDLVideo/GLSLProgram.cpp
index 1d5ec51633..34f141002b 100644
--- a/gemrb/plugins/SDLVideo/GLSLProgram.cpp
+++ b/gemrb/plugins/SDLVideo/GLSLProgram.cpp
@@ -102,10 +102,16 @@ GLSLProgram* GLSLProgram::CreateFromFiles(std::string vertexSourceFileName, std:
 	return GLSLProgram::Create(vertexContent, fragmentContent);
 }
 
-GLuint GLSLProgram::buildShader(GLenum type, std::string source)
+GLuint GLSLProgram::buildShader(GLenum type, const std::string source)
 {
+	std::string shader_source = source;
+#ifdef USE_GL
+	shader_source.insert(0, "#version 110\n");
+#else
+	shader_source.insert(0, "#version 100\n");
+#endif
     GLuint id = glCreateShader(type);
-	const char* src = source.c_str();
+	const char* src = shader_source.c_str();
 	glShaderSource(id, 1, &src, 0);
     glCompileShader(id);
     GLint result = GL_FALSE;
diff --git a/gemrb/plugins/SDLVideo/SDL20GLVideo.cpp b/gemrb/plugins/SDLVideo/SDL20GLVideo.cpp
index b28738317e..62eb361238 100644
--- a/gemrb/plugins/SDLVideo/SDL20GLVideo.cpp
+++ b/gemrb/plugins/SDLVideo/SDL20GLVideo.cpp
@@ -66,23 +66,25 @@ int GLVideoDriver::CreateDisplay(int w, int h, int bpp, bool fs, const char* tit
 	window = SDL_CreateWindow(title, SDL_WINDOWPOS_CENTERED, SDL_WINDOWPOS_CENTERED, width, height, winFlags);
 	if (window == NULL) 
 	{
-		Log(ERROR, "SDL 2 GL Driver", "couldnt create window:%s", SDL_GetError());
+		Log(ERROR, "SDL 2 GL Driver", "Unable to create window:%s", SDL_GetError());
 		return GEM_ERROR;
 	}
 
 	context = SDL_GL_CreateContext(window);
 	if (context == NULL) 
 	{
-		Log(ERROR, "SDL 2 GL Driver", "couldnt create GL context:%s", SDL_GetError());
+		Log(ERROR, "SDL 2 GL Driver", "Unable to create GL context:%s", SDL_GetError());
 		return GEM_ERROR;
 	}
 	SDL_GL_MakeCurrent(window, context);
+	Log(MESSAGE, "SDL 2 GL Driver", "OpenGL version: %s, renderer: %s, vendor: %s", glGetString(GL_VERSION), glGetString(GL_RENDERER), glGetString(GL_VENDOR));
+	Log(MESSAGE, "SDL 2 GL Driver", "  GLSL version: %s", glGetString(GL_SHADING_LANGUAGE_VERSION));
 
 	renderer = SDL_CreateRenderer(window, -1, 0);
 
 	if (renderer == NULL) 
 	{
-		Log(ERROR, "SDL 2 GL Driver", "couldnt create renderer:%s", SDL_GetError());
+		Log(ERROR, "SDL 2 GL Driver", "Unable to create renderer:%s", SDL_GetError());
 		return GEM_ERROR;
 	}
 	SDL_RenderSetLogicalSize(renderer, width, height);