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Rendering System with Lua

Posted by Jason Z, 01 July 2010 · 324 views


Rendering System with Lua


Now that I have a basic Lua interface set up, I added some additional basic functionality, such as attaching two actors together as parent/child, and I also added an interface for the script to modify rendering parameters for a given entity or its material. I figured this was a good time to talk a little bit about render parameters, and how they help make things easier when working with D3D11.

Hieroglyph uses a small class hierarchy based on the RenderParameterDX11 class. This is the base class for the various types of data that can be set in a programmable shader stage. Each one has a type (corresponding to the D3D11 object type) and a name (corresponding to the name of the object in the hlsl file), and each subclass provides the actual data storage. For example, the VectorParameterDX11 class provides a vector. All together, there are currently seven parameter types supported in Hieroglyph 3:

- Vector
- Matrix
- Matrix Array
- Shader Resource
- Unordered Access
- Constant Buffer
- Sampler

There are other possibilities (such as structs of parameters) which I don't currently support, but I haven't found a compelling reason to use them yet.

So these C++ objects are maintained by the renderer, and whatever object is being rendered can set the values in a particular way that it needs to. For example, if an object is going to render itself with a texture, it would set the texture with the correct name into the renderer. When the shader gets loaded and its parameters are configured, the renderer grabs the current value and applies to the named parameter from the shader. Nice and easy from the developer's side.

From my recent work on skinned meshes, I also added the ability of an entity and a material to carry around their own copies of these RenderParameterDX11 instances. This allows for per-material customization and per-object customization to be done, and makes things much easier to work with. The system has been evolving recently regarding cloning of parameters and things like that, but it is more or less where I want it to be now.

As a simple example of these in action, I used my new script interfaces to create a series of cube actors that are randomly oriented and rotated within a window (via the Lua script). This produced the following setup:



I then used my Lua console to modify the 'LightColor' vector parameter of the material to become green. This affects all of the objects sharing that material instance:



All these objects can utilize the same material, and also have individual colors applied to each entity. This in turn override the material RenderParameterDX11 setting, and provides customization. This is now available via script, which opens up quite a bit of data driven control over the rendering process.

I'm still tidying up a few things, but I should have a fresh repository commit in the next few days.




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