I'm trying to come up with a good design for a convenient and low-overhead shader library abstracting away low-level graphics API details and allowing me to focus on shaders/game renderer development.

Basically, i'm pursuing the following goals:

1) minimal memory footprint - no string names at run-time, minimal amount of metadata if any;

2) support for hot-reloading modified shader files;

3) support for caching compiled shader bytecode and filtering out duplicates;

How are such shader libraries usually built and how should it be used in actual engine code?

Are there any more performant alternatives to DirectX effects?

The first problem can be solved by storing name hashes instead of full strings (in C++ code compile-time string hashing could be used).

The second one is tough for me, because my shader techniques can depend on global stuff (constant buffers, sampler states and shader resources) and before reloading changed technique i'll have to 'link' it (to avoid recreating those globals).

Right now, my pipeline structure conceptually looks like this:

struct Pipeline
{
              // global stuff
	Array< RenderTargetResource >		renderTargets;
	Array< DepthStencilStateResource >	depthStencilStates;
	Array< RasterizerStateResource >	rasterizerStates;
	Array< SamplerStateResource >		samplerStates;
	Array< BlendStateResource >		blendStates;
	Array< StateBlock >			stateBlocks;

	Array< CBufferResource >	constantBuffers;       //<= global constant buffers (e.g. cbPerFrame, per-view, per-instance)
             // handles to shader sampler states are stored in the 'samplerStates' array above
	Array< ShaderResource >	shaderResources;   //<= 

	Array< ShaderTechnique >	techniques;

              // all created shader programs (VS/GS/PS) for fixing-up HShaderProgram handles in technique passes (when serialized, they store indices into this array in place of handles)
	Array< HShaderProgram >	programs[ ShaderType::Count ];

	// this is used for locating shader cache on disk
	String		name;
};

// technique: name and array of passes

// pass - array of shader instances (combinations, identified by a bitmask), default shader instance id,
// and parameter bindings info (cbuffers,samplers,textures) in the form {array, start, count}

Global shader resources are shared between different shader programs, e.g. updating a global constant buffer would look so:

SetStateBlock(Default); // Default is LessEqZNoStencil, NoBlending, CullBack.

CBuffer& perFrame = pipeline.GetCBufferByName("cbPerFrame");

cbPerFrame* data = cast(cbPerFrame*) perFrame.ToPtr();

...

perFrame.Commit();

What's the most efficient way to do redundancy checking (to avoid extraneous Direct3D API function calls for binding pipeline resources) ?

my goal is to minimize the low-level graphics wrapper overhead as much as possible.

(i use small integer handles everywhere instead of pointers. i decided to use 8-bit handles for all immutable render states (DepthStencil, Rasterizer, Sampler and Blend - they are created at the start) and all constant buffers (i have a fixed pool of CBs). i can only have 8 CBs/samplers bound simultaneously so i can concatenate the whole pipeline state into a few 64-bit integers and use bitwise instructions to calculate 'delta' and issue the corresponding Set* calls if needed.)

Are there open-source implementations of stateless, 'packetized' renderers that i can learn from?

Could you give me an example of a stateless low-level graphics API? What functions should it contain?