diff --git a/src/gl/data/gl_vertexbuffer.cpp b/src/gl/data/gl_vertexbuffer.cpp
index fdce68702..223fb67f8 100644
--- a/src/gl/data/gl_vertexbuffer.cpp
+++ b/src/gl/data/gl_vertexbuffer.cpp
@@ -138,10 +138,21 @@ void FFlatVertexBuffer::ImmRenderBuffer(unsigned int primtype, unsigned int offs
 	// this will only get called if we can't acquire a persistently mapped buffer.
 #ifndef CORE_PROFILE
 	glBegin(primtype);
-	for (unsigned int i = 0; i < count; i++)
+	if (gl.compatibility > CMPT_GL2)
 	{
-		glVertexAttrib2fv(VATTR_TEXCOORD, &map[offset + i].u);
-		glVertexAttrib3fv(VATTR_VERTEX, &map[offset + i].x);
+		for (unsigned int i = 0; i < count; i++)
+		{
+			glVertexAttrib2fv(VATTR_TEXCOORD, &map[offset + i].u);
+			glVertexAttrib3fv(VATTR_VERTEX, &map[offset + i].x);
+		}
+	}
+	else	// no shader means no vertex attributes, so use the old stuff instead.
+	{
+		for (unsigned int i = 0; i < count; i++)
+		{
+			glTexCoord2fv(&map[offset + i].u);
+			glVertex3fv(&map[offset + i].x);
+		}
 	}
 	glEnd();
 #endif
diff --git a/src/gl/renderer/gl_renderstate.cpp b/src/gl/renderer/gl_renderstate.cpp
index 9b9d2d7e5..892e384e7 100644
--- a/src/gl/renderer/gl_renderstate.cpp
+++ b/src/gl/renderer/gl_renderstate.cpp
@@ -279,7 +279,14 @@ void FRenderState::Apply()
 		else mVertexBuffer->BindVBO();
 		mCurrentVertexBuffer = mVertexBuffer;
 	}
-	ApplyShader();
+	if (gl.compatibility > CMPT_GL2) 
+	{
+		ApplyShader();
+	}
+	else
+	{
+		//ApplyFixedFunction();
+	}
 }
 
 
diff --git a/src/gl/shaders/gl_shader.cpp b/src/gl/shaders/gl_shader.cpp
index 493d81818..4a82251d0 100644
--- a/src/gl/shaders/gl_shader.cpp
+++ b/src/gl/shaders/gl_shader.cpp
@@ -59,6 +59,44 @@
 #include "gl/textures/gl_material.h"
 #include "gl/dynlights/gl_lightbuffer.h"
 
+//==========================================================================
+//
+// patch the shader source to work with 
+// GLSL 1.2 keywords and identifiers
+//
+//==========================================================================
+
+void PatchCommon(FString &code)
+{
+	code.Substitute("precision highp int;", "");
+	code.Substitute("precision highp float;", "");
+}
+
+void PatchVertShader(FString &code)
+{
+	PatchCommon(code);
+	code.Substitute("out vec", "varying vec");
+	code.Substitute("gl_ClipDistance", "//");
+}
+
+void PatchFragShader(FString &code)
+{
+	PatchCommon(code);
+	code.Substitute("out vec4 FragColor;", "");
+	code.Substitute("FragColor", "gl_FragColor");
+	code.Substitute("in vec", "varying vec");
+	// this patches the switch statement to if's.
+	code.Substitute("break;", "");
+	code.Substitute("switch (uFixedColormap)", "int i = uFixedColormap;");
+	code.Substitute("case 0:", "if (i == 0)");
+	code.Substitute("case 1:", "else if (i == 1)");
+	code.Substitute("case 2:", "else if (i == 2)");
+	code.Substitute("case 3:", "else if (i == 3)");
+	code.Substitute("case 4:", "else if (i == 4)");
+	code.Substitute("case 5:", "else if (i == 5)");
+	code.Substitute("texture(", "texture2D(");
+}
+
 //==========================================================================
 //
 //
@@ -95,6 +133,10 @@ bool FShader::Load(const char * name, const char * vert_prog_lump, const char *
 		{
 			vp_comb = "#version 130\n";
 		}
+		else
+		{
+			vp_comb = "#define GLSL12_COMPATIBLE\n";
+		}
 	}
 	else
 	{
@@ -159,6 +201,12 @@ bool FShader::Load(const char * name, const char * vert_prog_lump, const char *
 		}
 	}
 
+	if (gl.compatibility < CMPT_GL3)
+	{
+		PatchVertShader(vp_comb);
+		PatchFragShader(fp_comb);
+	}
+
 	hVertProg = glCreateShader(GL_VERTEX_SHADER);
 	hFragProg = glCreateShader(GL_FRAGMENT_SHADER);	
 
@@ -391,7 +439,7 @@ static const FEffectShader effectshaders[]=
 
 FShaderManager::FShaderManager()
 {
-	CompileShaders();
+	if (gl.compatibility > CMPT_GL2) CompileShaders();
 }
 
 //==========================================================================
@@ -402,7 +450,7 @@ FShaderManager::FShaderManager()
 
 FShaderManager::~FShaderManager()
 {
-	Clean();
+	if (gl.compatibility > CMPT_GL2) Clean();
 }
 
 //==========================================================================
@@ -544,25 +592,35 @@ EXTERN_CVAR(Int, gl_fuzztype)
 
 void FShaderManager::ApplyMatrices(VSMatrix *proj, VSMatrix *view)
 {
-	for (int i = 0; i < 4; i++)
+	if (gl.compatibility == CMPT_GL2)
 	{
-		mTextureEffects[i]->ApplyMatrices(proj, view);
-		mTextureEffectsNAT[i]->ApplyMatrices(proj, view);
+		glMatrixMode(GL_PROJECTION);
+		glLoadMatrixf(proj->get());
+		glMatrixMode(GL_MODELVIEW);
+		glLoadMatrixf(view->get());
 	}
-	mTextureEffects[4]->ApplyMatrices(proj, view);
-	if (gl_fuzztype != 0)
+	else
 	{
-		mTextureEffects[4+gl_fuzztype]->ApplyMatrices(proj, view);
+		for (int i = 0; i < 4; i++)
+		{
+			mTextureEffects[i]->ApplyMatrices(proj, view);
+			mTextureEffectsNAT[i]->ApplyMatrices(proj, view);
+		}
+		mTextureEffects[4]->ApplyMatrices(proj, view);
+		if (gl_fuzztype != 0)
+		{
+			mTextureEffects[4 + gl_fuzztype]->ApplyMatrices(proj, view);
+		}
+		for (unsigned i = 12; i < mTextureEffects.Size(); i++)
+		{
+			mTextureEffects[i]->ApplyMatrices(proj, view);
+		}
+		for (int i = 0; i < MAX_EFFECTS; i++)
+		{
+			mEffectShaders[i]->ApplyMatrices(proj, view);
+		}
+		if (mActiveShader != NULL) mActiveShader->Bind();
 	}
-	for (unsigned i = 12; i < mTextureEffects.Size(); i++)
-	{
-		mTextureEffects[i]->ApplyMatrices(proj, view);
-	}
-	for (int i = 0; i < MAX_EFFECTS; i++)
-	{
-		mEffectShaders[i]->ApplyMatrices(proj, view);
-	}
-	if (mActiveShader != NULL) mActiveShader->Bind();
 }
 
 //==========================================================================
diff --git a/src/gl/system/gl_interface.cpp b/src/gl/system/gl_interface.cpp
index d057ad140..d2b69ad0a 100644
--- a/src/gl/system/gl_interface.cpp
+++ b/src/gl/system/gl_interface.cpp
@@ -152,7 +152,6 @@ void gl_LoadExtensions()
 	// Buffer lighting is only feasible with GLSL 1.3 and higher, even if 1.2 supports the extension.
 	if (gl.version > 3.0f && (gl.version >= 3.3f || CheckExtension("GL_ARB_uniform_buffer_object")))
 	{
-		gl.flags |= RFL_SAMPLER_OBJECTS;
 		gl.lightmethod = LM_DEFERRED;
 	}
 
@@ -161,9 +160,10 @@ void gl_LoadExtensions()
 
 	if (Args->CheckParm("-noshader"))
 	{
+		gl.version = 2.1f;
 		gl.compatibility = CMPT_GL2;	// force the low end path
 	}
-	if (gl.version < 3.0f)
+	else if (gl.version < 3.0f)
 	{
 		if (CheckExtension("GL_NV_GPU_shader4") || CheckExtension("GL_EXT_GPU_shader4")) gl.compatibility = CMPT_GL2_SHADER;	// for pre-3.0 drivers that support capable hardware. Needed for Apple.
 		else gl.compatibility = CMPT_GL2;
@@ -172,6 +172,7 @@ void gl_LoadExtensions()
 	{
 		if (strstr(gl.vendorstring, "ATI Tech")) 
 		{
+			gl.version = 2.1f;
 			gl.compatibility = CMPT_GL2_SHADER;	// most of these drivers are irreperably broken with GLSL 1.3 and higher.
 			gl.lightmethod = LM_SOFTWARE;		// do not use uniform buffers with the fallback shader, it may cause problems.
 		}
@@ -198,6 +199,7 @@ void gl_LoadExtensions()
 		}
 		else
 		{
+			gl.version = 3.3f;
 			gl.compatibility = CMPT_GL3;
 		}
 	}
diff --git a/src/gl/textures/gl_hqresize.cpp b/src/gl/textures/gl_hqresize.cpp
index 55cf88fb1..993e9f138 100644
--- a/src/gl/textures/gl_hqresize.cpp
+++ b/src/gl/textures/gl_hqresize.cpp
@@ -263,6 +263,10 @@ unsigned char *gl_CreateUpsampledTextureBuffer ( const FTexture *inputTexture, u
 	if ( inputTexture->bHasCanvas )
 		return inputBuffer;
 
+	// [BB] Don't upsample non-shader handled warped textures. Needs too much memory and time
+	if (gl.compatibility == CMPT_GL2 && inputTexture->bWarped)
+		return inputBuffer;
+
 	// already scaled?
 	if (inputTexture->Scale.X >= 2 && inputTexture->Scale.Y >= 2)
 		return inputBuffer;
diff --git a/src/gl/textures/gl_hwtexture.cpp b/src/gl/textures/gl_hwtexture.cpp
index c855ef285..02ed64290 100644
--- a/src/gl/textures/gl_hwtexture.cpp
+++ b/src/gl/textures/gl_hwtexture.cpp
@@ -424,6 +424,7 @@ int FHardwareTexture::GetDepthBuffer()
 void FHardwareTexture::BindToFrameBuffer()
 {
 	glFramebufferTexture2D(GL_FRAMEBUFFER, GL_COLOR_ATTACHMENT0, GL_TEXTURE_2D, glDefTex.glTexID, 0);
-	glFramebufferRenderbuffer(GL_FRAMEBUFFER, GL_DEPTH_STENCIL_ATTACHMENT, GL_RENDERBUFFER, GetDepthBuffer()); 
+	glFramebufferRenderbuffer(GL_FRAMEBUFFER, GL_DEPTH_ATTACHMENT, GL_RENDERBUFFER, GetDepthBuffer());
+	glFramebufferRenderbuffer(GL_FRAMEBUFFER, GL_STENCIL_ATTACHMENT, GL_RENDERBUFFER, GetDepthBuffer());
 }
 
diff --git a/src/win32/win32gliface.cpp b/src/win32/win32gliface.cpp
index 4ba6ad300..9ce3c8837 100644
--- a/src/win32/win32gliface.cpp
+++ b/src/win32/win32gliface.cpp
@@ -782,7 +782,6 @@ bool Win32GLVideo::InitHardware (HWND Window, int multisample)
 
 	if (!SetupPixelFormat(multisample))
 	{
-		I_Error ("R_OPENGL: Unabl...\n");
 		return false;
 	}
 
diff --git a/wadsrc/static/shaders/glsl/main.fp b/wadsrc/static/shaders/glsl/main.fp
index f6273fc09..af5b30a03 100644
--- a/wadsrc/static/shaders/glsl/main.fp
+++ b/wadsrc/static/shaders/glsl/main.fp
@@ -170,7 +170,7 @@ vec4 getLightColor(float fogdist, float fogfactor)
 		float newlightlevel = 1.0 - R_DoomLightingEquation(uLightLevel, gl_FragCoord.z);
 		color.rgb *= newlightlevel;
 	}
-	else if (uFogEnabled > 0.0)
+	else if (uFogEnabled > 0)
 	{
 		// brightening around the player for light mode 2
 		if (fogdist < uLightDist)