merge gallium docs into main docs

Reviewed-by: Eric Engestrom <eric@engestrom.ch>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/5706>

1 files changed, 207 insertions, 0 deletions

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+.. _resource:
+
+Resources and derived objects
+=============================
+
+Resources represent objects that hold data: textures and buffers.
+
+They are mostly modelled after the resources in Direct3D 10/11, but with a
+different transfer/update mechanism, and more features for OpenGL support.
+
+Resources can be used in several ways, and it is required to specify all planned uses through an appropriate set of bind flags.
+
+TODO: write much more on resources
+
+Transfers
+---------
+
+Transfers are the mechanism used to access resources with the CPU.
+
+OpenGL: OpenGL supports mapping buffers and has inline transfer functions for both buffers and textures
+
+D3D11: D3D11 lacks transfers, but has special resource types that are mappable to the CPU address space
+
+TODO: write much more on transfers
+
+Resource targets
+----------------
+
+Resource targets determine the type of a resource.
+
+Note that drivers may not actually have the restrictions listed regarding
+coordinate normalization and wrap modes, and in fact efficient OpenCL
+support will probably require drivers that don't have any of them, which
+will probably be advertised with an appropriate cap.
+
+TODO: document all targets. Note that both 3D and cube have restrictions
+that depend on the hardware generation.
+
+
+PIPE_BUFFER
+^^^^^^^^^^^
+
+Buffer resource: can be used as a vertex, index, constant buffer
+(appropriate bind flags must be requested).
+
+Buffers do not really have a format, it's just bytes, but they are required
+to have their type set to a R8 format (without a specific "just byte" format,
+R8_UINT would probably make the most sense, but for historic reasons R8_UNORM
+is ok too). (This is just to make some shared buffer/texture code easier so
+format size can be queried.)
+width0 serves as size, most other resource properties don't apply but must be
+set appropriately (depth0/height0/array_size must be 1, last_level 0).
+
+They can be bound to stream output if supported.
+TODO: what about the restrictions lifted by the several later GL transform feedback extensions? How does one advertise that in Gallium?
+
+They can be also be bound to a shader stage (for sampling) as usual by
+creating an appropriate sampler view, if the driver supports PIPE_CAP_TEXTURE_BUFFER_OBJECTS.
+This supports larger width than a 1d texture would
+(TODO limit currently unspecified, minimum must be at least 65536).
+Only the "direct fetch" sample opcodes are supported (TGSI_OPCODE_TXF,
+TGSI_OPCODE_SAMPLE_I) so the sampler state (coord wrapping etc.)
+is mostly ignored (with SAMPLE_I there's no sampler state at all).
+
+They can be also be bound to the framebuffer (only as color render target, not
+depth buffer, also there cannot be a depth buffer bound at the same time) as usual
+by creating an appropriate view (this is not usable in OpenGL).
+TODO there's no CAP bit currently for this, there's also unspecified size etc. limits
+TODO: is there any chance of supporting GL pixel buffer object acceleration with this?
+
+
+OpenGL: vertex buffers in GL 1.5 or GL_ARB_vertex_buffer_object
+
+- Binding to stream out requires GL 3.0 or GL_NV_transform_feedback
+- Binding as constant buffers requires GL 3.1 or GL_ARB_uniform_buffer_object
+- Binding to a sampling stage requires GL 3.1 or GL_ARB_texture_buffer_object
+
+D3D11: buffer resources
+- Binding to a render target requires D3D_FEATURE_LEVEL_10_0
+
+PIPE_TEXTURE_1D / PIPE_TEXTURE_1D_ARRAY
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+1D surface accessed with normalized coordinates.
+1D array textures are supported depending on PIPE_CAP_MAX_TEXTURE_ARRAY_LAYERS.
+
+- If PIPE_CAP_NPOT_TEXTURES is not supported,
+      width must be a power of two
+- height0 must be 1
+- depth0 must be 1
+- array_size must be 1 for PIPE_TEXTURE_1D
+- Mipmaps can be used
+- Must use normalized coordinates
+
+OpenGL: GL_TEXTURE_1D in GL 1.0
+
+- PIPE_CAP_NPOT_TEXTURES is equivalent to GL 2.0 or GL_ARB_texture_non_power_of_two
+
+D3D11: 1D textures in D3D_FEATURE_LEVEL_10_0
+
+PIPE_TEXTURE_RECT
+^^^^^^^^^^^^^^^^^
+2D surface with OpenGL GL_TEXTURE_RECTANGLE semantics.
+
+- depth0 must be 1
+- array_size must be 1
+- last_level must be 0
+- Must use unnormalized coordinates
+- Must use a clamp wrap mode
+
+OpenGL: GL_TEXTURE_RECTANGLE in GL 3.1 or GL_ARB_texture_rectangle or GL_NV_texture_rectangle
+
+OpenCL: can create OpenCL images based on this, that can then be sampled arbitrarily
+
+D3D11: not supported (only PIPE_TEXTURE_2D with normalized coordinates is supported)
+
+PIPE_TEXTURE_2D / PIPE_TEXTURE_2D_ARRAY
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+2D surface accessed with normalized coordinates.
+2D array textures are supported depending on PIPE_CAP_MAX_TEXTURE_ARRAY_LAYERS.
+
+- If PIPE_CAP_NPOT_TEXTURES is not supported,
+      width and height must be powers of two
+- depth0 must be 1
+- array_size must be 1 for PIPE_TEXTURE_2D
+- Mipmaps can be used
+- Must use normalized coordinates
+- No special restrictions on wrap modes
+
+OpenGL: GL_TEXTURE_2D in GL 1.0
+
+- PIPE_CAP_NPOT_TEXTURES is equivalent to GL 2.0 or GL_ARB_texture_non_power_of_two
+
+OpenCL: can create OpenCL images based on this, that can then be sampled arbitrarily
+
+D3D11: 2D textures
+
+- PIPE_CAP_NPOT_TEXTURES is equivalent to D3D_FEATURE_LEVEL_9_3
+
+PIPE_TEXTURE_3D
+^^^^^^^^^^^^^^^
+
+3-dimensional array of texels.
+Mipmap dimensions are reduced in all 3 coordinates.
+
+- If PIPE_CAP_NPOT_TEXTURES is not supported,
+      width, height and depth must be powers of two
+- array_size must be 1
+- Must use normalized coordinates
+
+OpenGL: GL_TEXTURE_3D in GL 1.2 or GL_EXT_texture3D
+
+- PIPE_CAP_NPOT_TEXTURES is equivalent to GL 2.0 or GL_ARB_texture_non_power_of_two
+
+D3D11: 3D textures
+
+- PIPE_CAP_NPOT_TEXTURES is equivalent to D3D_FEATURE_LEVEL_10_0
+
+PIPE_TEXTURE_CUBE / PIPE_TEXTURE_CUBE_ARRAY
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Cube maps consist of 6 2D faces.
+The 6 surfaces form an imaginary cube, and sampling happens by mapping an
+input 3-vector to the point of the cube surface in that direction.
+Cube map arrays are supported depending on PIPE_CAP_CUBE_MAP_ARRAY.
+
+Sampling may be optionally seamless if a driver supports it (PIPE_CAP_SEAMLESS_CUBE_MAP),
+resulting in filtering taking samples from multiple surfaces near to the edge.
+
+- Width and height must be equal
+- depth0 must be 1
+- array_size must be a multiple of 6
+- If PIPE_CAP_NPOT_TEXTURES is not supported,
+      width and height must be powers of two
+- Must use normalized coordinates
+
+OpenGL: GL_TEXTURE_CUBE_MAP in GL 1.3 or EXT_texture_cube_map
+
+- PIPE_CAP_NPOT_TEXTURES is equivalent to GL 2.0 or GL_ARB_texture_non_power_of_two
+- Seamless cube maps require GL 3.2 or GL_ARB_seamless_cube_map or GL_AMD_seamless_cubemap_per_texture
+- Cube map arrays require GL 4.0 or GL_ARB_texture_cube_map_array
+
+D3D11: 2D array textures with the D3D11_RESOURCE_MISC_TEXTURECUBE flag
+
+- PIPE_CAP_NPOT_TEXTURES is equivalent to D3D_FEATURE_LEVEL_10_0
+- Cube map arrays require D3D_FEATURE_LEVEL_10_1
+
+Surfaces
+--------
+
+Surfaces are views of a resource that can be bound as a framebuffer to serve as the render target or depth buffer.
+
+TODO: write much more on surfaces
+
+OpenGL: FBOs are collections of surfaces in GL 3.0 or GL_ARB_framebuffer_object
+
+D3D11: render target views and depth/stencil views
+
+Sampler views
+-------------
+
+Sampler views are views of a resource that can be bound to a pipeline stage to be sampled from shaders.
+
+TODO: write much more on sampler views
+
+OpenGL: texture objects are actually sampler view and resource in a single unit
+
+D3D11: shader resource views