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Resources and derived objects
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=============================
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Resources represent objects that hold data: textures and buffers.
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They are mostly modelled after the resources in Direct3D 10/11, but with a
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different transfer/update mechanism, and more features for OpenGL support.
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Resources can be used in several ways, and it is required to specify all planned uses through an appropriate set of bind flags.
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TODO: write much more on resources
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Transfers are the mechanism used to access resources with the CPU.
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OpenGL: OpenGL supports mapping buffers and has inline transfer functions for both buffers and textures
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D3D11: D3D11 lacks transfers, but has special resource types that are mappable to the CPU address space
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TODO: write much more on transfers
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Resource targets determine the type of a resource.
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Note that drivers may not actually have the restrictions listed regarding
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coordinate normalization and wrap modes, and in fact efficient OpenCL
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support will probably require drivers that don't have any of them, which
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will probably be advertised with an appropriate cap.
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TODO: document all targets. Note that both 3D and cube have restrictions
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that depend on the hardware generation.
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Buffer resource: can be used as a vertex, index, constant buffer
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(appropriate bind flags must be requested).
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Buffers do not really have a format, it's just bytes, but they are required
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to have their type set to a R8 format (without a specific "just byte" format,
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R8_UINT would probably make the most sense, but for historic reasons R8_UNORM
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is ok too). (This is just to make some shared buffer/texture code easier so
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format size can be queried.)
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width0 serves as size, most other resource properties don't apply but must be
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set appropriately (depth0/height0/array_size must be 1, last_level 0).
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They can be bound to stream output if supported.
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TODO: what about the restrictions lifted by the several later GL transform feedback extensions? How does one advertise that in Gallium?
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They can be also be bound to a shader stage (for sampling) as usual by
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creating an appropriate sampler view, if the driver supports PIPE_CAP_TEXTURE_BUFFER_OBJECTS.
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This supports larger width than a 1d texture would
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(TODO limit currently unspecified, minimum must be at least 65536).
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Only the "direct fetch" sample opcodes are supported (TGSI_OPCODE_TXF,
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TGSI_OPCODE_SAMPLE_I) so the sampler state (coord wrapping etc.)
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is mostly ignored (with SAMPLE_I there's no sampler state at all).
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They can be also be bound to the framebuffer (only as color render target, not
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depth buffer, also there cannot be a depth buffer bound at the same time) as usual
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by creating an appropriate view (this is not usable in OpenGL).
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TODO there's no CAP bit currently for this, there's also unspecified size etc. limits
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TODO: is there any chance of supporting GL pixel buffer object acceleration with this?
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OpenGL: vertex buffers in GL 1.5 or GL_ARB_vertex_buffer_object
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- Binding to stream out requires GL 3.0 or GL_NV_transform_feedback
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- Binding as constant buffers requires GL 3.1 or GL_ARB_uniform_buffer_object
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- Binding to a sampling stage requires GL 3.1 or GL_ARB_texture_buffer_object
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D3D11: buffer resources
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- Binding to a render target requires D3D_FEATURE_LEVEL_10_0
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PIPE_TEXTURE_1D / PIPE_TEXTURE_1D_ARRAY
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^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
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1D surface accessed with normalized coordinates.
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1D array textures are supported depending on PIPE_CAP_MAX_TEXTURE_ARRAY_LAYERS.
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- If PIPE_CAP_NPOT_TEXTURES is not supported,
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width must be a power of two
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- array_size must be 1 for PIPE_TEXTURE_1D
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- Must use normalized coordinates
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OpenGL: GL_TEXTURE_1D in GL 1.0
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- PIPE_CAP_NPOT_TEXTURES is equivalent to GL 2.0 or GL_ARB_texture_non_power_of_two
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D3D11: 1D textures in D3D_FEATURE_LEVEL_10_0
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2D surface with OpenGL GL_TEXTURE_RECTANGLE semantics.
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- array_size must be 1
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- last_level must be 0
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- Must use unnormalized coordinates
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- Must use a clamp wrap mode
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OpenGL: GL_TEXTURE_RECTANGLE in GL 3.1 or GL_ARB_texture_rectangle or GL_NV_texture_rectangle
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OpenCL: can create OpenCL images based on this, that can then be sampled arbitrarily
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D3D11: not supported (only PIPE_TEXTURE_2D with normalized coordinates is supported)
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PIPE_TEXTURE_2D / PIPE_TEXTURE_2D_ARRAY
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^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
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2D surface accessed with normalized coordinates.
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2D array textures are supported depending on PIPE_CAP_MAX_TEXTURE_ARRAY_LAYERS.
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- If PIPE_CAP_NPOT_TEXTURES is not supported,
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width and height must be powers of two
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- array_size must be 1 for PIPE_TEXTURE_2D
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- Mipmaps can be used
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- Must use normalized coordinates
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- No special restrictions on wrap modes
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OpenGL: GL_TEXTURE_2D in GL 1.0
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- PIPE_CAP_NPOT_TEXTURES is equivalent to GL 2.0 or GL_ARB_texture_non_power_of_two
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OpenCL: can create OpenCL images based on this, that can then be sampled arbitrarily
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- PIPE_CAP_NPOT_TEXTURES is equivalent to D3D_FEATURE_LEVEL_9_3
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3-dimensional array of texels.
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Mipmap dimensions are reduced in all 3 coordinates.
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- If PIPE_CAP_NPOT_TEXTURES is not supported,
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width, height and depth must be powers of two
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- array_size must be 1
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- Must use normalized coordinates
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OpenGL: GL_TEXTURE_3D in GL 1.2 or GL_EXT_texture3D
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- PIPE_CAP_NPOT_TEXTURES is equivalent to GL 2.0 or GL_ARB_texture_non_power_of_two
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- PIPE_CAP_NPOT_TEXTURES is equivalent to D3D_FEATURE_LEVEL_10_0
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PIPE_TEXTURE_CUBE / PIPE_TEXTURE_CUBE_ARRAY
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^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
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Cube maps consist of 6 2D faces.
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The 6 surfaces form an imaginary cube, and sampling happens by mapping an
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input 3-vector to the point of the cube surface in that direction.
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Cube map arrays are supported depending on PIPE_CAP_CUBE_MAP_ARRAY.
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Sampling may be optionally seamless if a driver supports it (PIPE_CAP_SEAMLESS_CUBE_MAP),
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resulting in filtering taking samples from multiple surfaces near to the edge.
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- Width and height must be equal
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- array_size must be a multiple of 6
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- If PIPE_CAP_NPOT_TEXTURES is not supported,
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width and height must be powers of two
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- Must use normalized coordinates
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OpenGL: GL_TEXTURE_CUBE_MAP in GL 1.3 or EXT_texture_cube_map
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- PIPE_CAP_NPOT_TEXTURES is equivalent to GL 2.0 or GL_ARB_texture_non_power_of_two
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- Seamless cube maps require GL 3.2 or GL_ARB_seamless_cube_map or GL_AMD_seamless_cubemap_per_texture
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- Cube map arrays require GL 4.0 or GL_ARB_texture_cube_map_array
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D3D11: 2D array textures with the D3D11_RESOURCE_MISC_TEXTURECUBE flag
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- PIPE_CAP_NPOT_TEXTURES is equivalent to D3D_FEATURE_LEVEL_10_0
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- Cube map arrays require D3D_FEATURE_LEVEL_10_1
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Surfaces are views of a resource that can be bound as a framebuffer to serve as the render target or depth buffer.
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TODO: write much more on surfaces
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OpenGL: FBOs are collections of surfaces in GL 3.0 or GL_ARB_framebuffer_object
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D3D11: render target views and depth/stencil views
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Sampler views are views of a resource that can be bound to a pipeline stage to be sampled from shaders.
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TODO: write much more on sampler views
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OpenGL: texture objects are actually sampler view and resource in a single unit
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D3D11: shader resource views