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https://github.com/PixarAnimationStudios/OpenSubdiv
synced 2024-11-08 13:30:04 +00:00
Updated Far and Osd user guide docs for 3.4
Updated the Far Overview and Osd Overview and shader interface pages for 3.4 to include a discussion of trianglular patch types and other minor updates.
This commit is contained in:
David G Yu
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95138e680f
@ -294,42 +294,21 @@ to refine primvar data.
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Far::PatchTable
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================
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The patch table is a serialized topology representation. This container is
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generated using *Far::PatchTableFactory* from an instance
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*Far::TopologyRefiner* after a refinement has been applied. The
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FarPatchTableFactory traverses the data-structures of the TopologyRefiner and
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serializes the sub-faces into collections of bi-linear and bi-cubic patches as
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dictated by the refinement mode (uniform or adaptive). The patches are then
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sorted into arrays based on their types.
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PatchTable is the collection of patches derived from the refined faces of a particular mesh topology.
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.. container:: notebox
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**Release Notes (3.0.0)**
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The organization and API of Far::PatchTable is likely to change
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in the 3.1 release to accommodate additional functionality including:
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smooth face-varying interpolation on patches, and dynamic feature
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adaptive isolation (DFAS), and patch evaluation of Loop subdivision
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surfaces.
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This collection is created using *Far::PatchTableFactory* from an instance
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of *Far::TopologyRefiner* after refinement has been applied.
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Patch Arrays
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************
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The patch table is a collection of control vertex indices. Meshes are decomposed
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into a collection of patches, which can be of different types. Each type
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has different requirements for the internal organization of its
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control-vertices. A PatchArray contains a sequence of multiple patches that
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share a common set of attributes.
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The PatchTable is organized into patch arrays. All patches in each array have
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the same type except for face-varying patch arrays which may have a mix of regular and irregular patch types.
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While all patches in a PatchArray will have the same type, each patch in the
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array is associated with a distinct *PatchParam* which specifies additional
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information about the individual patch.
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The *PatchDescriptor* provides the fundamental description of a patch, including the number of control points per patch as well as the basis for patch evaluation.
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Each PatchArray contains a patch *Descriptor* that provides the fundamental
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description of the patches in the array.
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The PatchArray *ArrayRange* provides the indices necessary to track the records
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of individual patches in the table.
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Each patch in the array is associated with a *PatchParam* which
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specifies additional information about the individual patch.
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.. image:: images/far_patchtables.png
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:align: center
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@ -350,19 +329,21 @@ PatchTable:
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+---------------------+------+---------------------------------------------+
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| LINES | 2 | Lines : useful for cage drawing |
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+---------------------+------+---------------------------------------------+
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| QUADS | 4 | Bi-linear quads-only patches |
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| QUADS | 4 | Bi-linear quadrilaterals |
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+---------------------+------+---------------------------------------------+
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| TRIANGLES | 3 | Bi-linear triangles-only mesh |
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| TRIANGLES | 3 | Linear triangles |
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+---------------------+------+---------------------------------------------+
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| LOOP | n/a | Loop patch (currently unsupported) |
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| LOOP | 12 | Quartic triangular Box-spline patches |
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+---------------------+------+---------------------------------------------+
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| REGULAR | 16 | B-spline Basis patches |
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| REGULAR | 16 | Bi-cubic B-spline patches |
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+---------------------+------+---------------------------------------------+
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| GREGORY | 4 | Legacy Gregory patches |
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+---------------------+------+---------------------------------------------+
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| GREGORY_BOUNDARY | 4 | Legacy Gregory Boundary patches |
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+---------------------+------+---------------------------------------------+
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| GREGORY_BASIS | 20 | Gregory Basis patches |
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| GREGORY_BASIS | 20 | Bi-cubic quadrilateral Gregory patches |
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+---------------------+------+---------------------------------------------+
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| GREGORY_TRIANGLE | 18 | Quartic triangular Gregory patches |
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+---------------------+------+---------------------------------------------+
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@ -372,6 +353,10 @@ table as well as the method used to evaluate values.
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Patch Parameterization
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**********************
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Here we describe the encoding of the patch parameterization for
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quadrilateral patches. The encoding for triangular patches is similar,
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please see the API documentation of Far::PatchParam for details.
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Each patch represents a specific portion of the parametric space of the
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coarse topological face identified by the PatchParam FaceId. As topological
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refinement progresses through successive levels, each resulting patch
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@ -435,11 +420,9 @@ sharpness parameter.
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.. container:: notebox
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**Release Notes (3.0.0)**
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**Release Notes (3.x)**
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Currently, the crease sharpness parameter is encoded as a separate
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PatchArray within the PatchTable. This parameter may be combined
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with the other PatchParam values in future releases. Also, evaluation
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Evaluation
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of single-crease patches is currently only implemented for OSD patch
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drawing, but we expect to implement support in all of the evaluation
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code paths for future releases.
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@ -453,15 +436,6 @@ adaptively to the points of the coarse mesh. However, the final patches
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generated from irregular faces, e.g. patches incident on an extraordinary
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vertex might have a representation which requires additional local points.
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.. container:: notebox
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**Release Notes (3.0.0)**
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Currently, representations which require local points also require
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the use of a StencilTable to compute the values of local points.
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This requirement, as well as the rest of the API related to local
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points may change in future releases.
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Legacy Gregory Patches
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**********************
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@ -472,15 +446,6 @@ Legacy Gregory patches are used, the PatchTable must also have an alternative
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representation of the mesh topology encoded as a vertex valence table
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and a quad offsets table.
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.. container:: notebox
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**Release Notes (3.0.0)**
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The encoding and support for Legacy Gregory patches may change
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in future releases. The current encoding of the vertex valence
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and quad offsets tables may be prohibitively expensive for some
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use cases.
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Far::StencilTable
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==================
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@ -42,8 +42,8 @@ The main roles of **Osd** are:
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Compute limit surfaces by limit stencils on CPU/GPU backends
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- **Limit Evaluation with PatchTable**
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Compute limit surfaces by patch evaluation on CPU/GPU backends
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- **OpenGL/DX11 Drawing with hardware tessellation**
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Provide GLSL/HLSL tessellation functions for patch table
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- **OpenGL/DX11/Metal Drawing with hardware tessellation**
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Provide GLSL/HLSL/Metal tessellation functions for patch table
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- **Interleaved/Batched buffer configuration**
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Provide consistent buffer descriptor to deal with arbitrary buffer layout.
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- **Cross-Platform Implementation**
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@ -98,7 +98,8 @@ as a stencil tables as long as Evaluator::EvalStencils() can access the necessar
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+-----------------------------+-----------------------+-------------------------+
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| DX11 ComputeShader (GPU) | D3D11ComputeEvaluator | D3D11StencilTable |
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+-----------------------------+-----------------------+-------------------------+
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| Metal (GPU) | MTLComputeEvaluator | MTLStencilTable |
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+-----------------------------+-----------------------+-------------------------+
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Limit Stencil Evaluation
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========================
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@ -141,17 +142,18 @@ Once all control vertices and local points are resolved by the stencil evaluatio
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| DX11 ComputeShader (GPU) | | D3D11ComputeEvaluator | D3D11PatchTable |
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| | | (*)not yet supported | |
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+-----------------------------+-------------------------+-------------------------+
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| Metal ComputeShader (GPU) | | MTLComputeEvaluator | MTLPatchTable |
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+-----------------------------+-------------------------+-------------------------+
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.. container:: notebox
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**Release Notes (3.0.0)**
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**Release Notes (3.x)**
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* GPU limit evaluation backends (Evaluator::EvalPatches()) only support
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BSpline patches. Clients need to specify BSpline approximation for endcap
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when creating a patch table. See `end capping <far_overview.html#endcap>`__.
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* Osd evaluation backends (Evaluator::EvalPatches()) do not support
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evaluation of single-crease or Legacy Gregory patch types.
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OpenGL/DX11 Drawing with Hardware Tessellation
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==============================================
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OpenGL/DX11/Metal Drawing with Hardware Tessellation
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====================================================
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One of the most interesting use cases of the **Osd** layer is realtime drawing
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of subdivision surfaces using hardware tessellation. This is somewhat similar to
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@ -265,6 +267,8 @@ The methods that need to be implemented for the Evaluators are:
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+-----------------------+------------------------+------------------+
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| D3D11ComputeEvaluator | D3D11 UAV | BindD3D11UAV() |
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+-----------------------+------------------------+------------------+
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| MTLComputeEvaluator | MTLBuffer | BindMTLBuffer() |
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+-----------------------+------------------------+------------------+
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The buffers can use these methods as a trigger of interop. **Osd** provides a default
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implementation of interop buffer for most of the backend combinations.
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@ -50,8 +50,8 @@ The following is a minimal example of GLSL code explaining how client shader cod
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uses OpenSubdiv shader functions to tessellate patches of a patch table.
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Tessellation Control Shader Example (for BSpline patches)
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*********************************************************
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Tessellation Control Shader Example (for B-Spline patches)
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**********************************************************
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.. code:: glsl
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@ -88,8 +88,8 @@ Tessellation Control Shader Example (for BSpline patches)
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Tessellation Evaluation Shader Example (for BSpline patches)
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************************************************************
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Tessellation Evaluation Shader Example (for B-Spline patches)
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*************************************************************
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.. code:: glsl
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@ -160,7 +160,8 @@ are stored in a OsdPerPatchVertexGreogryBasis struct.
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.. code:: glsl
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void OsdComputePerPatchVertexGregoryBasis(
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void
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OsdComputePerPatchVertexGregoryBasis(
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ivec3 patchParam, int ID, vec3 cv, out OsdPerPatchVertexGregoryBasis result)
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The tessellation evaluation shader takes an array of OsdPerPatchVertexGregoryBasis struct,
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@ -174,6 +175,54 @@ and then evaluates the patch using the OsdEvalPatchGregory() function.
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out vec3 N, out vec3 dNu, out vec3 dNv)
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Box-spline Triangle Patch
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*************************
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While regular triangle patches are expressed as triangular box-spline patches in Far::PatchTable,
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the **Osd** shader converts them into triangular Bezier patches for consistency.
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This conversion is performed in the tessellation control stage. The boundary edge evaluation is resolved during this conversion.
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OsdComputePerPatchVertexBoxSplineTriangle() can be used for this process.
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The resulting Bezier control vertices are stored in OsdPerPatchVertexBezier struct.
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.. code:: glsl
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void
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OsdComputePerPatchVertexBoxSplineTriangle(
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ivec3 patchParam, int ID, vec3 cv[12], out OsdPerPatchVertexBezier result);
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The tessellation evaluation shader takes an array of OsdPerPatchVertexBezier struct,
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and then evaluates the patch using the OsdEvalPatchBezierTriangle() function.
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.. code:: glsl
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void OsdEvalPatchBezierTriangle(ivec3 patchParam, vec2 UV,
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OsdPerPatchVertexBezier cv[15],
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out vec3 P, out vec3 dPu, out vec3 dPv,
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out vec3 N, out vec3 dNu, out vec3 dNv)
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Gregory Triangle Patch
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**********************
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OsdComputePerPatchVertexGregoryBasis() can be used for the quartic triangular Gregory patches (although no basis conversion involved for the Gregory triangle patches) and the resulting vertices are stored in a OsdPerPatchVertexGreogryBasis struct.
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.. code:: glsl
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void
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OsdComputePerPatchVertexGregoryBasis(
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ivec3 patchParam, int ID, vec3 cv, out OsdPerPatchVertexGregoryBasis result)
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The tessellation evaluation shader takes an array of OsdPerPatchVertexGregoryBasis struct,
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and then evaluates the patch using the OsdEvalPatchGregoryTriangle() function.
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.. code:: glsl
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void
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OsdEvalPatchGregoryTriangle(ivec3 patchParam, vec2 UV, vec3 cv[18],
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out vec3 P, out vec3 dPu, out vec3 dPv,
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out vec3 N, out vec3 dNu, out vec3 dNv)
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Legacy Gregory Patch (2.x compatibility)
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****************************************
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@ -190,12 +239,6 @@ Tessellation levels
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**Osd** provides both uniform and screen-space adaptive tessellation level computation.
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Uniform tessellation
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OsdGetTessLevelsUniform()
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Screen-space adaptive tessellation
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OsdGetTessLevelsAdaptiveLimitPoints()
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Because of the nature of `feature adaptive subdivision <far_overview.html>`__,
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we need to pay extra attention for a patch's outer tessellation level for the screen-space
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adaptive case so that cracks don't appear.
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@ -212,31 +255,63 @@ as separate levels for the two segments of the edge split at the middle.
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.. image:: images/osd_shader_transition.png
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Then the tessellation evaluation shader takes gl_TessCoord and those two values, and remaps
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gl_TessCoord using OsdGetTessParameterization() to ensure the parameters are consistent
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Tessellation levels at each tessellated vertex
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**********************************************
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The tessellation evaluation shader takes gl_TessCoord and those two values, and remaps
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gl_TessCoord using OsdGetTessParameterization() or OsdGetTessLevelParameterizationTriangle() to ensure the parameters are consistent
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across adjacent patches.
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.. code:: glsl
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vec2 OsdGetTessParameterization(vec2 uv, vec4 tessOuterLo, vec4 tessOuterHi);
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.. code:: glsl
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vec2 OsdGetTessParameterizationTriangle(vec3 uvw, vec4 tessOuterLo, vec4 tessOuterHi);
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.. image:: images/osd_shader_param_remap.png
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.. code:: glsl
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Tessellation levels computed at each patch
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******************************************
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vec2 OsdGetTessParameterization(vec2 uv, vec4 tessOuterLo, vec4 tessOuterHi)
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These tessellation levels can be computed by OsdGetTessLevelsAdaptiveLimitPoints()
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in the tessellation control shader. Note that this function requires all 16 bezier control
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These tessellation levels can be computed the corresponding method in the tesselation control shader. Note that these functions potentially requires all bezier control
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points, you need to call barrier() to ensure the conversion is done for all invocations.
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See osd/glslPatchBSpline.glsl for more details.
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Uniform
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~~~~~~~
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.. code:: glsl
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void OsdGetTessLevelsAdaptiveLimitPoints(OsdPerPatchVertexBezier cpBezier[16],
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ivec3 patchParam,
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out vec4 tessLevelOuter, out vec2 tessLevelInner,
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out vec4 tessOuterLo, out vec4 tessOuterHi)
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void
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OsdGetTessLevelsUniform(ivec3 patchParam,
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out vec4 tessLevelOuter, out vec2 tessLevelInner,
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out vec4 tessOuterLo, out vec4 tessOuterHi)
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.. container:: notebox
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.. code:: glsl
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**Release Notes (3.0.0)**
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void
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OsdGetTessLevelsUniformTriangle(ivec3 patchParam,
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out vec4 tessLevelOuter, out vec2 tessLevelInner,
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out vec4 tessOuterLo, out vec4 tessOuterHi)
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* Currently OsdGetTessParameterization doesn't support fraction spacing.
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It will be fixed in a future release.
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Screenspace
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~~~~~~~~~~~
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.. code:: glsl
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void OsdEvalPatchBezierTessLevels(
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OsdPerPatchVertexBezier cpBezier[16],
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ivec3 patchParam,
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out vec4 tessLevelOuter, out vec2 tessLevelInner,
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out vec4 tessOuterLo, out vec4 tessOuterHi);
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.. code:: glsl
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void OsdEvalPatchBezierTriangleTessLevels(
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vec3 cv[15],
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ivec3 patchParam,
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out vec4 tessLevelOuter, out vec2 tessLevelInner,
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out vec4 tessOuterLo, out vec4 tessOuterHi);
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