Blog Archives

Normal Mapping with Partial Derivatives

I have added normal mapping support recently. It is not perfect, but works well with some new models I have obtained from ShareCG (thank you, Nobiax). The model loader still lacks of tangent and binormal processing support (still relying on lowly OBJ files), so I am using partial derivatives to reconstruct T and B from GBuffer and shader parameters.

I have extended the deferred light combiner shader to handle multiple BRDFs with many parameters (diffuse, specular, environment reflection, etc.). The BRDF parameters are organized in a table that is indexed by a field in the GBuffer. Different objects can have different BRDFs, the particular index is an effect parameter. Deferred light combiner shader handles backside lighting (e.g. the sunlight shines through the leaves), controlled by a diffuse parameter in the BRDF table.

Here are some images produced by the current state of the renderer.

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Effects, Passes, Shaders and Parameters

As I promised in an earlier post, this is a short overview about shader support in the engine. Currently Merlin3D supports OpenGL and GLSL. DirectX support is not implemented yet.

Merlin3D uses its own effect files, that describes a particular shader set for the different rendering passes (it has some similarities to .fx files in DirectX, but in OpenGL world there is no effect file support at all). Effect files are in XML format. Each visible scene object has exactly one effect required to render the object in different rendering passes. Multiple scene objects can use the same effect. Anyway, it is the recommended way of effect usage, because the engine tries to group objects by the associated effects to reduce OpenGL state changes.
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