I've been trying to implement percentage closer filtering for my shadow mapping as described here Nvidia GPU Gems
When I try to sample my shadow map using a uniform sampler2DShadow and shadow2D or shadow2DProj the GLSL compile fails and gives me the error
shadow2D deprecated after version 120 How would I go about implementing an equivalent solution in GLSL 330+? I'm currently just using a binary texture sample along with Poisson Sampling but the staircase aliasing is pretty bad.
Your title is way off base. sampler2DShadow is not deprecated. The only thing that changed in GLSL 1.30 was that the mess of functions like texture1D, texture2D, textureCube, shadow2D, etc. were all replaced with overloads of texture (...).
texture (...) is equivalent to shadow2D (...):float texture(sampler2DShadow sampler, vec3 P, [float bias]); The texture coordinates used for the lookup using this overload are: P.st and the reference value used for depth comparison is P.r. This overload only works properly when texture comparison is enabled (GL_TEXTURE_COMPARE_MODE == ) for the texture/sampler object bound to the shadow sampler's texture image unit; otherwise the results are undefined.
Beginning with GLSL 1.30, the only time you need to use a different texture lookup function is when you are doing something fundamentally different (e.g. texture projection => textureProj, requesting an exact LOD => textureLod, fetching a texel by its integer coordinates/sample index => texelFetch, etc.). Texture lookup with comparison (shadow sampler) is not considered fundamentally different enough to require its own specialized texture lookup function.
This is all described quite thoroughly on OpenGL's wiki site.
You need to use textureProj, which returns a float rather than a vec4. There's a overview of shadow artifacts and solutions (including Poisson sampling) here.