Bake API - bpy.ops.object.bake()

New operator that can calls a bake function to the current render engine when available. This commit provides no feature for the users, but allows external engines to be accessed by the operator and be integrated with the baking api.

The API itself is simple. Blender sends a populated array of BakePixels to the renderer, and gets back an array of floats with the result.

The Blender Internal (and multires) system is still running independent, but we eventually will pipe it through the API as well. Cycles baking will come next as a separated commit

Python Operator:
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The operator can be called with some arguments, or a user interface can be created for it. In that case the arguments can be ommited and the interface can expose the settings from bpy.context.scene.render.bake

bpy.ops.object.bake(type='COMBINED', filepath="", width=512, height=512, margin=16, use_selected_to_active=False, cage_extrusion=0, cage="", normal_space='TANGENT', normal_r='POS_X', normal_g='POS_Y', normal_b='POS_Z', save_mode='INTERNAL', use_clear=False, use_split_materials=False, use_automatic_name=False)
Note: external save mode is currently disabled.

Supported Features:
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 * Margin - Baked result is extended this many pixels beyond the border of each UV "island," to soften seams in the texture.

 * Selected to Active - bake shading on the surface of selected object to the active object. The rays are cast from the lowpoly object inwards towards the highpoly object. If the highpoly object is not entirely involved by the lowpoly object, you can tweak the rays start point with Cage Extrusion. For even more control of the cage you can use a Cage object.

 * Cage Extrusion - distance to use for the inward ray cast when using selected to active

 * Custom Cage - object to use as cage (instead of the lowpoly object).

 * Normal swizzle - change the axis that gets mapped to RGB

 * Normal space - save as tangent or object normal spaces

Supported Passes:
-----------------
Any pass that is supported by Blender renderlayer system. Though it's up to the external engine to provide a valid enum with its supported passes. Normal passes get a special treatment since we post-process them to converted and "swizzled"

Development Notes for External Engines:
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The Bake API is fully implemented with Python rna functions. The operator expects/call a function:

def  bake(scene, object, pass_type, pixel_array, num_pixels, depth, result)

* scene: current scene (Python object)

* object: object to render (Python object)

* pass_type: pass to render (string, e.g., "COMBINED", "AO", "NORMAL", ...)

* pixel_array: list of primitive ids and barycentric coordinates to bake(Python object, see below)

* num_pixels: size of pixel_array, number of pixels to bake (int)

* depth: depth of pixels to return (int, assuming always 4 now)

* result: array to be populated by the engine (float array, PyLong_AsVoidPtr)

pixel_array is a Python object storing BakePixel elements:

struct BakePixel {
	int primitive_id;
	float u, v;
	float dudx, dudy;
	float dvdx, dvdy;
};

In python you have access to: primitive_id, u, v, du_dx, du_dy, next. Next is a function that returns the next BakePixel in the array.

* For a complete implementation example look at the Cycles Bake commit (next).

Review: D421
Reviewed by: Campbell Barton, Brecht van Lommel, Sergey Sharybin, Thomas Dinge

Normal map pipeline "consulting" by Andy Davies (metalliandy)
Original design by Brecht van Lommel.

The entire commit history can be found on the branch: bake-cycles
Cycles Bake

Expand Cycles to use the new baking API in Blender.

It works on the selected object, and the panel can be accessed in the Render panel (similar to where it is for the Blender Internal).

It bakes for the active texture of each material of the object. The active texture is currently defined as the active Image Texture node present in the material nodetree. If you don't want the baking to override an existent material, make sure the active Image Texture node is not connected to the nodetree. The active texture is also the texture shown in the viewport in the rendered mode.

Remember to save your images after the baking is complete.

Note: This is not supported by Cycles standalone because a lot of the work is done in Blender as part of the operator only, not the engine (Cycles).

Documentation:
http://wiki.blender.org/index.php/User:Dfelinto/CyclesBaking

Supported Passes:
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Data Passes
 * Normal
 * UV
 * Diffuse/Glossy/Transmission/Subsurface/Emit Color

Light Passes
 * AO
 * Combined
 * Shadow
 * Diffuse/Glossy/Transmission/Subsurface/Emit Direct/Indirect
 * Environment

Review: D421
Reviewed by: Campbell Barton, Brecht van Lommel, Sergey Sharybin, Thomas Dinge

Original design by Brecht van Lommel.

The entire commit history can be found on the branch: bake-cycles
Cycles: CUDA changes for kernel evaluation cancel