implemented extended postfx

src/extras/shaders/contrast_fs_gl3.inc

@@ -0,0 +1,20 @@
+const char *contrast_frag_src =
+"uniform sampler2D tex0;\n"
+"uniform vec3 u_contrastAdd;\n"
+"uniform vec3 u_contrastMult;\n"
+
+"in vec4 v_color;\n"
+"in vec2 v_tex0;\n"
+"in float v_fog;\n"
+
+"out vec4 color;\n"
+
+"void\n"
+"main(void)\n"
+"{\n"
+"	vec4 dst = texture(tex0, vec2(v_tex0.x, 1.0-v_tex0.y));\n"
+"	color.rgb = dst.rgb*u_contrastMult + u_contrastAdd;\n"
+"	color.a = 1.0f;\n"
+"}\n"
+
+;