path: root/src/gallium/docs/source/screen.rst

.. _screen:

Screen
======

A screen is an object representing the context-independent part of a device.

Flags and enumerations
----------------------

XXX some of these don't belong in this section.


.. _pipe_cap:

PIPE_CAP_*
^^^^^^^^^^

Capability queries return information about the features and limits of the
driver/GPU.  For floating-point values, use :ref:`get_paramf`, and for boolean
or integer values, use :ref:`get_param`.

The integer capabilities:

* ``PIPE_CAP_NPOT_TEXTURES``: Whether :term:`NPOT` textures may have repeat modes,
  normalized coordinates, and mipmaps.
* ``PIPE_CAP_TWO_SIDED_STENCIL``: Whether the stencil test can also affect back-facing
  polygons.
* ``PIPE_CAP_MAX_DUAL_SOURCE_RENDER_TARGETS``: How many dual-source blend RTs are support.
  :ref:`Blend` for more information.
* ``PIPE_CAP_ANISOTROPIC_FILTER``: Whether textures can be filtered anisotropically.
* ``PIPE_CAP_POINT_SPRITE``: Whether point sprites are available.
* ``PIPE_CAP_MAX_RENDER_TARGETS``: The maximum number of render targets that may be
  bound.
* ``PIPE_CAP_OCCLUSION_QUERY``: Whether occlusion queries are available.
* ``PIPE_CAP_QUERY_TIME_ELAPSED``: Whether PIPE_QUERY_TIME_ELAPSED queries are available.
* ``PIPE_CAP_TEXTURE_SHADOW_MAP``: indicates whether the fragment shader hardware
  can do the depth texture / Z comparison operation in TEX instructions
  for shadow testing.
* ``PIPE_CAP_TEXTURE_SWIZZLE``: Whether swizzling through sampler views is
  supported.
* ``PIPE_CAP_MAX_TEXTURE_2D_LEVELS``: The maximum number of mipmap levels available
  for a 2D texture.
* ``PIPE_CAP_MAX_TEXTURE_3D_LEVELS``: The maximum number of mipmap levels available
  for a 3D texture.
* ``PIPE_CAP_MAX_TEXTURE_CUBE_LEVELS``: The maximum number of mipmap levels available
  for a cubemap.
* ``PIPE_CAP_TEXTURE_MIRROR_CLAMP``: Whether mirrored texture coordinates with clamp
  are supported.
* ``PIPE_CAP_BLEND_EQUATION_SEPARATE``: Whether alpha blend equations may be different
  from color blend equations, in :ref:`Blend` state.
* ``PIPE_CAP_SM3``: Whether the vertex shader and fragment shader support equivalent
  opcodes to the Shader Model 3 specification. XXX oh god this is horrible
* ``PIPE_CAP_MAX_STREAM_OUTPUT_BUFFERS``: The maximum number of stream buffers.
* ``PIPE_CAP_PRIMITIVE_RESTART``: Whether primitive restart is supported.
* ``PIPE_CAP_INDEP_BLEND_ENABLE``: Whether per-rendertarget blend enabling and channel
  masks are supported. If 0, then the first rendertarget's blend mask is
  replicated across all MRTs.
* ``PIPE_CAP_INDEP_BLEND_FUNC``: Whether per-rendertarget blend functions are
  available. If 0, then the first rendertarget's blend functions affect all
  MRTs.
* ``PIPE_CAP_MAX_TEXTURE_ARRAY_LAYERS``: The maximum number of texture array
  layers supported. If 0, the array textures are not supported at all and
  the ARRAY texture targets are invalid.
* ``PIPE_CAP_TGSI_FS_COORD_ORIGIN_UPPER_LEFT``: Whether the TGSI property
  FS_COORD_ORIGIN with value UPPER_LEFT is supported.
* ``PIPE_CAP_TGSI_FS_COORD_ORIGIN_LOWER_LEFT``: Whether the TGSI property
  FS_COORD_ORIGIN with value LOWER_LEFT is supported.
* ``PIPE_CAP_TGSI_FS_COORD_PIXEL_CENTER_HALF_INTEGER``: Whether the TGSI
  property FS_COORD_PIXEL_CENTER with value HALF_INTEGER is supported.
* ``PIPE_CAP_TGSI_FS_COORD_PIXEL_CENTER_INTEGER``: Whether the TGSI
  property FS_COORD_PIXEL_CENTER with value INTEGER is supported.
* ``PIPE_CAP_DEPTH_CLIP_DISABLE``: Whether the driver is capable of disabling
  depth clipping (through pipe_rasterizer_state)
* ``PIPE_CAP_SHADER_STENCIL_EXPORT``: Whether a stencil reference value can be
  written from a fragment shader.
* ``PIPE_CAP_TGSI_INSTANCEID``: Whether TGSI_SEMANTIC_INSTANCEID is supported
  in the vertex shader.
* ``PIPE_CAP_VERTEX_ELEMENT_INSTANCE_DIVISOR``: Whether the driver supports
  per-instance vertex attribs.
* ``PIPE_CAP_FRAGMENT_COLOR_CLAMPED``: Whether fragment color clamping is
  supported.  That is, is the pipe_rasterizer_state::clamp_fragment_color
  flag supported by the driver?  If not, the state tracker will insert
  clamping code into the fragment shaders when needed.

* ``PIPE_CAP_MIXED_COLORBUFFER_FORMATS``: Whether mixed colorbuffer formats are
  supported, e.g. RGBA8 and RGBA32F as the first and second colorbuffer, resp.
* ``PIPE_CAP_VERTEX_COLOR_UNCLAMPED``: Whether the driver is capable of
  outputting unclamped vertex colors from a vertex shader. If unsupported,
  the vertex colors are always clamped. This is the default for DX9 hardware.
* ``PIPE_CAP_VERTEX_COLOR_CLAMPED``: Whether the driver is capable of
  clamping vertex colors when they come out of a vertex shader, as specified
  by the pipe_rasterizer_state::clamp_vertex_color flag.  If unsupported,
  the vertex colors are never clamped. This is the default for DX10 hardware.
  If both clamped and unclamped CAPs are supported, the clamping can be
  controlled through pipe_rasterizer_state.  If the driver cannot do vertex
  color clamping, the state tracker may insert clamping code into the vertex
  shader.
* ``PIPE_CAP_GLSL_FEATURE_LEVEL``: Whether the driver supports features
  equivalent to a specific GLSL version. E.g. for GLSL 1.3, report 130.
* ``PIPE_CAP_QUADS_FOLLOW_PROVOKING_VERTEX_CONVENTION``: Whether quads adhere to
  the flatshade_first setting in ``pipe_rasterizer_state``.
* ``PIPE_CAP_USER_VERTEX_BUFFERS``: Whether the driver supports user vertex
  buffers.  If not, the state tracker must upload all data which is not in hw
  resources.  If user-space buffers are supported, the driver must also still
  accept HW resource buffers.
* ``PIPE_CAP_VERTEX_BUFFER_OFFSET_4BYTE_ALIGNED_ONLY``: This CAP describes a hw
  limitation.  If true, pipe_vertex_buffer::buffer_offset must always be aligned
  to 4.  If false, there are no restrictions on the offset.
* ``PIPE_CAP_VERTEX_BUFFER_STRIDE_4BYTE_ALIGNED_ONLY``: This CAP describes a hw
  limitation.  If true, pipe_vertex_buffer::stride must always be aligned to 4.
  If false, there are no restrictions on the stride.
* ``PIPE_CAP_VERTEX_ELEMENT_SRC_OFFSET_4BYTE_ALIGNED_ONLY``: This CAP describes
  a hw limitation.  If true, pipe_vertex_element::src_offset must always be
  aligned to 4.  If false, there are no restrictions on src_offset.
* ``PIPE_CAP_COMPUTE``: Whether the implementation supports the
  compute entry points defined in pipe_context and pipe_screen.
* ``PIPE_CAP_USER_INDEX_BUFFERS``: Whether user index buffers are supported.
  If not, the state tracker must upload all indices which are not in hw
  resources.  If user-space buffers are supported, the driver must also still
  accept HW resource buffers.
* ``PIPE_CAP_USER_CONSTANT_BUFFERS``: Whether user-space constant buffers
  are supported.  If not, the state tracker must put constants into HW
  resources/buffers.  If user-space constant buffers are supported, the
  driver must still accept HW constant buffers also.
* ``PIPE_CAP_CONSTANT_BUFFER_OFFSET_ALIGNMENT``: Describes the required
  alignment of pipe_constant_buffer::buffer_offset.
* ``PIPE_CAP_START_INSTANCE``: Whether the driver supports
  pipe_draw_info::start_instance.
* ``PIPE_CAP_QUERY_TIMESTAMP``: Whether PIPE_QUERY_TIMESTAMP and
  the pipe_screen::get_timestamp hook are implemented.
* ``PIPE_CAP_TEXTURE_MULTISAMPLE``: Whether all MSAA resources supported
  for rendering are also supported for texturing.
* ``PIPE_CAP_MIN_MAP_BUFFER_ALIGNMENT``: The minimum alignment that should be
  expected for a pointer returned by transfer_map if the resource is
  PIPE_BUFFER. In other words, the pointer returned by transfer_map is
  always aligned to this value.
* ``PIPE_CAP_TEXTURE_BUFFER_OFFSET_ALIGNMENT``: Describes the required
  alignment for pipe_sampler_view::u.buf.first_element, in bytes.
  If a driver does not support first/last_element, it should return 0.
* ``PIPE_CAP_TGSI_TEXCOORD``: This CAP describes a hw limitation.
  If true, the hardware cannot replace arbitrary shader inputs with sprite
  coordinates and hence the inputs that are desired to be replaceable must
  be declared with TGSI_SEMANTIC_TEXCOORD instead of TGSI_SEMANTIC_GENERIC.
  The rasterizer's sprite_coord_enable state therefore also applies to the
  TEXCOORD semantic.
  Also, TGSI_SEMANTIC_PCOORD becomes available, which labels a fragment shader
  input that will always be replaced with sprite coordinates.
* ``PIPE_CAP_PREFER_BLIT_BASED_TEXTURE_TRANSFER``: Whether it is preferable
  to use a blit to implement a texture transfer which needs format conversions
  and swizzling in state trackers. Generally, all hardware drivers with
  dedicated memory should return 1 and all software rasterizers should return 0.
* ``PIPE_CAP_QUERY_PIPELINE_STATISTICS``: Whether PIPE_QUERY_PIPELINE_STATISTICS
  is supported.
* ``PIPE_CAP_TEXTURE_BORDER_COLOR_QUIRK``: Bitmask indicating whether special
  considerations have to be given to the interaction between the border color
  in the sampler object and the sampler view used with it.
  If PIPE_QUIRK_TEXTURE_BORDER_COLOR_SWIZZLE_R600 is set, the border color
  may be affected in undefined ways for any kind of permutational swizzle
  (any swizzle XYZW where X/Y/Z/W are not ZERO, ONE, or R/G/B/A respectively)
  in the sampler view.
  If PIPE_QUIRK_TEXTURE_BORDER_COLOR_SWIZZLE_NV50 is set, the border color
  state should be swizzled manually according to the swizzle in the sampler
  view it is intended to be used with, or herein undefined results may occur
  for permutational swizzles.
* ``PIPE_CAP_MAX_TEXTURE_BUFFER_SIZE``: The maximum accessible size with
  a buffer sampler view, in bytes.
* ``PIPE_CAP_MAX_VIEWPORTS``: The maximum number of viewports (and scissors
  since they are linked) a driver can support. Returning 0 is equivalent
  to returning 1 because every driver has to support at least a single
  viewport/scissor combination.  
* ''PIPE_CAP_ENDIANNESS``:: The endianness of the device.  Either
  PIPE_ENDIAN_BIG or PIPE_ENDIAN_LITTLE.
* ``PIPE_CAP_MIXED_FRAMEBUFFER_SIZES``: Whether it is allowed to have
  different sizes for fb color/zs attachments. This controls whether
  ARB_framebuffer_object is provided.
* ``PIPE_CAP_TGSI_VS_LAYER``: Whether TGSI_SEMANTIC_LAYER is supported
  as a vertex shader output.


.. _pipe_capf:

PIPE_CAPF_*
^^^^^^^^^^^^^^^^

The floating-point capabilities are:

* ``PIPE_CAPF_MAX_LINE_WIDTH``: The maximum width of a regular line.
* ``PIPE_CAPF_MAX_LINE_WIDTH_AA``: The maximum width of a smoothed line.
* ``PIPE_CAPF_MAX_POINT_WIDTH``: The maximum width and height of a point.
* ``PIPE_CAPF_MAX_POINT_WIDTH_AA``: The maximum width and height of a smoothed point.
* ``PIPE_CAPF_MAX_TEXTURE_ANISOTROPY``: The maximum level of anisotropy that can be
  applied to anisotropically filtered textures.
* ``PIPE_CAPF_MAX_TEXTURE_LOD_BIAS``: The maximum :term:`LOD` bias that may be applied
  to filtered textures.
* ``PIPE_CAPF_GUARD_BAND_LEFT``,
  ``PIPE_CAPF_GUARD_BAND_TOP``,
  ``PIPE_CAPF_GUARD_BAND_RIGHT``,
  ``PIPE_CAPF_GUARD_BAND_BOTTOM``: TODO


.. _pipe_shader_cap:

PIPE_SHADER_CAP_*
^^^^^^^^^^^^^^^^^

These are per-shader-stage capabitity queries. Different shader stages may
support different features.

* ``PIPE_SHADER_CAP_MAX_INSTRUCTIONS``: The maximum number of instructions.
* ``PIPE_SHADER_CAP_MAX_ALU_INSTRUCTIONS``: The maximum number of arithmetic instructions.
* ``PIPE_SHADER_CAP_MAX_TEX_INSTRUCTIONS``: The maximum number of texture instructions.
* ``PIPE_SHADER_CAP_MAX_TEX_INDIRECTIONS``: The maximum number of texture indirections.
* ``PIPE_SHADER_CAP_MAX_CONTROL_FLOW_DEPTH``: The maximum nested control flow depth.
* ``PIPE_SHADER_CAP_MAX_INPUTS``: The maximum number of input registers.
* ``PIPE_SHADER_CAP_MAX_CONSTS``: The maximum number of constants.
* ``PIPE_SHADER_CAP_MAX_CONST_BUFFERS``: Maximum number of constant buffers that can be bound
  to any shader stage using ``set_constant_buffer``. If 0 or 1, the pipe will
  only permit binding one constant buffer per shader, and the shaders will
  not permit two-dimensional access to constants.
  
If a value greater than 0 is returned, the driver can have multiple
constant buffers bound to shader stages. The CONST register file can
be accessed with two-dimensional indices, like in the example below.

DCL CONST[0][0..7]       # declare first 8 vectors of constbuf 0
DCL CONST[3][0]          # declare first vector of constbuf 3
MOV OUT[0], CONST[0][3]  # copy vector 3 of constbuf 0

For backwards compatibility, one-dimensional access to CONST register
file is still supported. In that case, the constbuf index is assumed
to be 0.
  
* ``PIPE_SHADER_CAP_MAX_TEMPS``: The maximum number of temporary registers.
* ``PIPE_SHADER_CAP_MAX_ADDRS``: The maximum number of address registers.
* ``PIPE_SHADER_CAP_MAX_PREDS``: The maximum number of predicate registers.
* ``PIPE_SHADER_CAP_TGSI_CONT_SUPPORTED``: Whether the continue opcode is supported.
* ``PIPE_SHADER_CAP_INDIRECT_INPUT_ADDR``: Whether indirect addressing
  of the input file is supported.
* ``PIPE_SHADER_CAP_INDIRECT_OUTPUT_ADDR``: Whether indirect addressing
  of the output file is supported.
* ``PIPE_SHADER_CAP_INDIRECT_TEMP_ADDR``: Whether indirect addressing
  of the temporary file is supported.
* ``PIPE_SHADER_CAP_INDIRECT_CONST_ADDR``: Whether indirect addressing
  of the constant file is supported.
* ``PIPE_SHADER_CAP_SUBROUTINES``: Whether subroutines are supported, i.e.
  BGNSUB, ENDSUB, CAL, and RET, including RET in the main block.
* ``PIPE_SHADER_CAP_INTEGERS``: Whether integer opcodes are supported.
  If unsupported, only float opcodes are supported.
* ``PIPE_SHADER_CAP_MAX_TEXTURE_SAMPLERS``: The maximum number of texture
  samplers.
* ``PIPE_SHADER_CAP_PREFERRED_IR``: Preferred representation of the
  program.  It should be one of the ``pipe_shader_ir`` enum values.
* ``PIPE_SHADER_CAP_MAX_SAMPLER_VIEWS``: The maximum number of texture
  sampler views. Must not be lower than PIPE_SHADER_CAP_MAX_TEXTURE_SAMPLERS.


.. _pipe_compute_cap:

PIPE_COMPUTE_CAP_*
^^^^^^^^^^^^^^^^^^

Compute-specific capabilities. They can be queried using
pipe_screen::get_compute_param.

* ``PIPE_COMPUTE_CAP_IR_TARGET``: A description of the target of the form
  ``processor-arch-manufacturer-os`` that will be passed on to the compiler.
  This CAP is only relevant for drivers that specify PIPE_SHADER_IR_LLVM for
  their preferred IR.
  Value type: null-terminated string.
* ``PIPE_COMPUTE_CAP_GRID_DIMENSION``: Number of supported dimensions
  for grid and block coordinates.  Value type: ``uint64_t``.
* ``PIPE_COMPUTE_CAP_MAX_GRID_SIZE``: Maximum grid size in block
  units.  Value type: ``uint64_t []``.
* ``PIPE_COMPUTE_CAP_MAX_BLOCK_SIZE``: Maximum block size in thread
  units.  Value type: ``uint64_t []``.
* ``PIPE_COMPUTE_CAP_MAX_THREADS_PER_BLOCK``: Maximum number of threads that
  a single block can contain.  Value type: ``uint64_t``.
  This may be less than the product of the components of MAX_BLOCK_SIZE and is
  usually limited by the number of threads that can be resident simultaneously
  on a compute unit.
* ``PIPE_COMPUTE_CAP_MAX_GLOBAL_SIZE``: Maximum size of the GLOBAL
  resource.  Value type: ``uint64_t``.
* ``PIPE_COMPUTE_CAP_MAX_LOCAL_SIZE``: Maximum size of the LOCAL
  resource.  Value type: ``uint64_t``.
* ``PIPE_COMPUTE_CAP_MAX_PRIVATE_SIZE``: Maximum size of the PRIVATE
  resource.  Value type: ``uint64_t``.
* ``PIPE_COMPUTE_CAP_MAX_INPUT_SIZE``: Maximum size of the INPUT
  resource.  Value type: ``uint64_t``.
* ``PIPE_COMPUTE_CAP_MAX_MEM_ALLOC_SIZE``: Maximum size of a memory object
  allocation in bytes.  Value type: ``uint64_t``.

.. _pipe_bind:

PIPE_BIND_*
^^^^^^^^^^^

These flags indicate how a resource will be used and are specified at resource
creation time. Resources may be used in different roles
during their lifecycle. Bind flags are cumulative and may be combined to create
a resource which can be used for multiple things.
Depending on the pipe driver's memory management and these bind flags,
resources might be created and handled quite differently.

* ``PIPE_BIND_RENDER_TARGET``: A color buffer or pixel buffer which will be
  rendered to.  Any surface/resource attached to pipe_framebuffer_state::cbufs
  must have this flag set.
* ``PIPE_BIND_DEPTH_STENCIL``: A depth (Z) buffer and/or stencil buffer. Any
  depth/stencil surface/resource attached to pipe_framebuffer_state::zsbuf must
  have this flag set.
* ``PIPE_BIND_BLENDABLE``: Used in conjunction with PIPE_BIND_RENDER_TARGET to
  query whether a device supports blending for a given format.
  If this flag is set, surface creation may fail if blending is not supported
  for the specified format. If it is not set, a driver may choose to ignore
  blending on surfaces with formats that would require emulation.
* ``PIPE_BIND_DISPLAY_TARGET``: A surface that can be presented to screen. Arguments to
  pipe_screen::flush_front_buffer must have this flag set.
* ``PIPE_BIND_SAMPLER_VIEW``: A texture that may be sampled from in a fragment
  or vertex shader.
* ``PIPE_BIND_VERTEX_BUFFER``: A vertex buffer.
* ``PIPE_BIND_INDEX_BUFFER``: An vertex index/element buffer.
* ``PIPE_BIND_CONSTANT_BUFFER``: A buffer of shader constants.
* ``PIPE_BIND_TRANSFER_WRITE``: A transfer object which will be written to.
* ``PIPE_BIND_TRANSFER_READ``: A transfer object which will be read from.
* ``PIPE_BIND_STREAM_OUTPUT``: A stream output buffer.
* ``PIPE_BIND_CUSTOM``:
* ``PIPE_BIND_SCANOUT``: A front color buffer or scanout buffer.
* ``PIPE_BIND_SHARED``: A sharable buffer that can be given to another
  process.
* ``PIPE_BIND_GLOBAL``: A buffer that can be mapped into the global
  address space of a compute program.
* ``PIPE_BIND_SHADER_RESOURCE``: A buffer or texture that can be
  bound to the graphics pipeline as a shader resource.
* ``PIPE_BIND_COMPUTE_RESOURCE``: A buffer or texture that can be
  bound to the compute program as a shader resource.

.. _pipe_usage:

PIPE_USAGE_*
^^^^^^^^^^^^

The PIPE_USAGE enums are hints about the expected usage pattern of a resource.

* ``PIPE_USAGE_DEFAULT``: Expect many uploads to the resource, intermixed with draws.
* ``PIPE_USAGE_DYNAMIC``: Expect many uploads to the resource, intermixed with draws.
* ``PIPE_USAGE_STATIC``: Same as immutable (?)
* ``PIPE_USAGE_IMMUTABLE``: Resource will not be changed after first upload.
* ``PIPE_USAGE_STREAM``: Upload will be followed by draw, followed by upload, ...


Methods
-------

XXX to-do

get_name
^^^^^^^^

Returns an identifying name for the screen.

get_vendor
^^^^^^^^^^

Returns the screen vendor.

.. _get_param:

get_param
^^^^^^^^^

Get an integer/boolean screen parameter.

**param** is one of the :ref:`PIPE_CAP` names.

.. _get_paramf:

get_paramf
^^^^^^^^^^

Get a floating-point screen parameter.

**param** is one of the :ref:`PIPE_CAP` names.

context_create
^^^^^^^^^^^^^^

Create a pipe_context.

**priv** is private data of the caller, which may be put to various
unspecified uses, typically to do with implementing swapbuffers
and/or front-buffer rendering.

is_format_supported
^^^^^^^^^^^^^^^^^^^

Determine if a resource in the given format can be used in a specific manner.

**format** the resource format

**target** one of the PIPE_TEXTURE_x flags

**sample_count** the number of samples. 0 and 1 mean no multisampling,
the maximum allowed legal value is 32.

**bindings** is a bitmask of :ref:`PIPE_BIND` flags.

**geom_flags** is a bitmask of PIPE_TEXTURE_GEOM_x flags.

Returns TRUE if all usages can be satisfied.


can_create_resource
^^^^^^^^^^^^^^^^^^^

Check if a resource can actually be created (but don't actually allocate any
memory).  This is used to implement OpenGL's proxy textures.  Typically, a
driver will simply check if the total size of the given resource is less than
some limit.


.. _resource_create:

resource_create
^^^^^^^^^^^^^^^

Create a new resource from a template.
The following fields of the pipe_resource must be specified in the template:

**target** one of the pipe_texture_target enums.
Note that PIPE_BUFFER and PIPE_TEXTURE_X are not really fundamentally different.
Modern APIs allow using buffers as shader resources.

**format** one of the pipe_format enums.

**width0** the width of the base mip level of the texture or size of the buffer.

**height0** the height of the base mip level of the texture
(1 for 1D or 1D array textures).

**depth0** the depth of the base mip level of the texture
(1 for everything else).

**array_size** the array size for 1D and 2D array textures.
For cube maps this must be 6, for other textures 1.

**last_level** the last mip map level present.

**nr_samples** the nr of msaa samples. 0 (or 1) specifies a resource
which isn't multisampled.

**usage** one of the PIPE_USAGE flags.

**bind** bitmask of the PIPE_BIND flags.

**flags** bitmask of PIPE_RESOURCE_FLAG flags.



resource_destroy
^^^^^^^^^^^^^^^^

Destroy a resource. A resource is destroyed if it has no more references.



get_timestamp
^^^^^^^^^^^^^

Query a timestamp in nanoseconds. The returned value should match
PIPE_QUERY_TIMESTAMP. This function returns immediately and doesn't
wait for rendering to complete (which cannot be achieved with queries).



get_driver_query_info
^^^^^^^^^^^^^^^^^^^^^

Return a driver-specific query. If the **info** parameter is NULL,
the number of available queries is returned.  Otherwise, the driver
query at the specified **index** is returned in **info**.
The function returns non-zero on success.
The driver-specific query is described with the pipe_driver_query_info
structure.