Added FXAA post-processing

Implementation of Fast Approximate Anti-Aliasing is based on nVidia sample:
https://github.com/NVIDIAGameWorks/GraphicsSamples/tree/master/samples/es3-kepler/FXAA

src/gl/shaders/gl_fxaashader.cpp

@@ -0,0 +1,99 @@
+//
+//---------------------------------------------------------------------------
+//
+// Copyright(C) 2016 Alexey Lysiuk
+// All rights reserved.
+//
+// This program is free software: you can redistribute it and/or modify
+// it under the terms of the GNU Lesser General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// This program is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU Lesser General Public License for more details.
+//
+// You should have received a copy of the GNU Lesser General Public License
+// along with this program.  If not, see http://www.gnu.org/licenses/
+//
+//--------------------------------------------------------------------------
+//
+
+//
+// Fast approXimate Anti-Aliasing (FXAA) post-processing
+//
+
+#include "gl/system/gl_system.h"
+#include "gl/shaders/gl_fxaashader.h"
+
+EXTERN_CVAR(Int, gl_fxaa)
+
+void FFXAALumaShader::Bind()
+{
+	if (!mShader)
+	{
+		mShader.Compile(FShaderProgram::Vertex, "shaders/glsl/screenquad.vp", "", 330);
+		mShader.Compile(FShaderProgram::Fragment, "shaders/glsl/fxaa.fp", "#define FXAA_LUMA_PASS\n", 330);
+		mShader.SetFragDataLocation(0, "FragColor");
+		mShader.Link("shaders/glsl/fxaa");
+		mShader.SetAttribLocation(0, "PositionInProjection");
+		InputTexture.Init(mShader, "InputTexture");
+	}
+
+	mShader.Bind();
+}
+
+static int GetMaxVersion()
+{
+	return gl.glslversion >= 4.f ? 400 : 330;
+}
+
+static FString GetDefines()
+{
+	int quality;
+
+	switch (gl_fxaa)
+	{
+	default:
+	case FFXAAShader::Low:     quality = 10; break;
+	case FFXAAShader::Medium:  quality = 12; break;
+	case FFXAAShader::High:    quality = 29; break;
+	case FFXAAShader::Extreme: quality = 39; break;
+	}
+
+	const int gatherAlpha = GetMaxVersion() >= 400 ? 1 : 0;
+
+	// TODO: enable FXAA_GATHER4_ALPHA on OpenGL earlier than 4.0
+	// when GL_ARB_gpu_shader5/GL_NV_gpu_shader5 extensions are supported
+
+	FString result;
+	result.Format(
+		"#define FXAA_QUALITY__PRESET %i\n"
+		"#define FXAA_GATHER4_ALPHA %i\n",
+		quality, gatherAlpha);
+
+	return result;
+}
+
+void FFXAAShader::Bind()
+{
+	assert(gl_fxaa > 0 && gl_fxaa < Count);
+	FShaderProgram &shader = mShaders[gl_fxaa];
+
+	if (!shader)
+	{
+		const FString defines = GetDefines();
+		const int maxVersion = GetMaxVersion();
+
+		shader.Compile(FShaderProgram::Vertex, "shaders/glsl/screenquad.vp", "", 330);
+		shader.Compile(FShaderProgram::Fragment, "shaders/glsl/fxaa.fp", defines, maxVersion);
+		shader.SetFragDataLocation(0, "FragColor");
+		shader.Link("shaders/glsl/fxaa");
+		shader.SetAttribLocation(0, "PositionInProjection");
+		InputTexture.Init(shader, "InputTexture");
+		ReciprocalResolution.Init(shader, "ReciprocalResolution");
+	}
+
+	shader.Bind();
+}