Context ======= The context object represents the purest, most directly accessible, abilities of the device's 3D rendering pipeline. Methods ------- CSO State ^^^^^^^^^ All CSO state is created, bound, and destroyed, with triplets of methods that all follow a specific naming scheme. For example, ``create_blend_state``, ``bind_blend_state``, and ``destroy_blend_state``. CSO objects handled by the context object: * :ref:`Blend`: ``*_blend_state`` * :ref:`Sampler`: These are special; they can be bound to either vertex or fragment samplers, and they are bound in groups. ``bind_fragment_sampler_states``, ``bind_vertex_sampler_states`` * :ref:`Rasterizer`: ``*_rasterizer_state`` * :ref:`Depth, Stencil, & Alpha`: ``*_depth_stencil_alpha_state`` * :ref:`Shader`: These have two sets of methods. ``*_fs_state`` is for fragment shaders, and ``*_vs_state`` is for vertex shaders. * :ref:`Vertex Elements`: ``*_vertex_elements_state`` Resource Binding State ^^^^^^^^^^^^^^^^^^^^^^ This state describes how resources in various flavours (textures, buffers, surfaces) are bound to the driver. * ``set_constant_buffer`` sets a constant buffer to be used for a given shader type. index is used to indicate which buffer to set (some apis may allow multiple ones to be set, and binding a specific one later, though drivers are mostly restricted to the first one right now). * ``set_framebuffer_state`` * ``set_vertex_buffers`` Non-CSO State ^^^^^^^^^^^^^ These pieces of state are too small, variable, and/or trivial to have CSO objects. They all follow simple, one-method binding calls, e.g. ``set_blend_color``. * ``set_stencil_ref`` sets the stencil front and back reference values which are used as comparison values in stencil test. * ``set_blend_color`` * ``set_clip_state`` * ``set_polygon_stipple`` * ``set_scissor_state`` sets the bounds for the scissor test, which culls pixels before blending to render targets. If the :ref:`Rasterizer` does not have the scissor test enabled, then the scissor bounds never need to be set since they will not be used. * ``set_viewport_state`` Sampler Views ^^^^^^^^^^^^^ These are the means to bind textures to shader stages. To create one, specify its format, swizzle and LOD range in sampler view template. If texture format is different than template format, it is said the texture is being cast to another format. Casting can be done only between compatible formats, that is formats that have matching component order and sizes. Swizzle fields specify they way in which fetched texel components are placed in the result register. For example, ``swizzle_r`` specifies what is going to be placed in first component of result register. The ``first_level`` and ``last_level`` fields of sampler view template specify the LOD range the texture is going to be constrained to. * ``set_fragment_sampler_views`` binds an array of sampler views to fragment shader stage. Every binding point acquires a reference to a respective sampler view and releases a reference to the previous sampler view. * ``set_vertex_sampler_views`` binds an array of sampler views to vertex shader stage. Every binding point acquires a reference to a respective sampler view and releases a reference to the previous sampler view. * ``create_sampler_view`` creates a new sampler view. ``texture`` is associated with the sampler view which results in sampler view holding a reference to the texture. Format specified in template must be compatible with texture format. * ``sampler_view_destroy`` destroys a sampler view and releases its reference to associated texture. Clearing ^^^^^^^^ ``clear`` initializes some or all of the surfaces currently bound to the framebuffer to particular RGBA, depth, or stencil values. Clear is one of the most difficult concepts to nail down to a single interface and it seems likely that we will want to add additional clear paths, for instance clearing surfaces not bound to the framebuffer, or read-modify-write clears such as depth-only or stencil-only clears of packed depth-stencil buffers. Drawing ^^^^^^^ ``draw_arrays`` draws a specified primitive. This command is equivalent to calling ``draw_arrays_instanced`` with ``startInstance`` set to 0 and ``instanceCount`` set to 1. ``draw_elements`` draws a specified primitive using an optional index buffer. This command is equivalent to calling ``draw_elements_instanced`` with ``startInstance`` set to 0 and ``instanceCount`` set to 1. ``draw_range_elements`` XXX: this is (probably) a temporary entrypoint, as the range information should be available from the vertex_buffer state. Using this to quickly evaluate a specialized path in the draw module. ``draw_arrays_instanced`` draws multiple instances of the same primitive. This command is equivalent to calling ``draw_elements_instanced`` with ``indexBuffer`` set to NULL and ``indexSize`` set to 0. ``draw_elements_instanced`` draws multiple instances of the same primitive using an optional index buffer. For instanceID in the range between ``startInstance`` and ``startInstance``+``instanceCount``-1, inclusive, draw a primitive specified by ``mode`` and sequential numbers in the range between ``start`` and ``start``+``count``-1, inclusive. If ``indexBuffer`` is not NULL, it specifies an index buffer with index byte size of ``indexSize``. The sequential numbers are used to lookup the index buffer and the resulting indices in turn are used to fetch vertex attributes. If ``indexBuffer`` is NULL, the sequential numbers are used directly as indices to fetch vertex attributes. ``indexBias`` is a value which is added to every index read from the index buffer before fetching vertex attributes. ``minIndex`` and ``maxIndex`` describe minimum and maximum index contained in the index buffer. If a given vertex element has ``instance_divisor`` set to 0, it is said it contains per-vertex data and effective vertex attribute address needs to be recalculated for every index. attribAddr = ``stride`` * index + ``src_offset`` If a given vertex element has ``instance_divisor`` set to non-zero, it is said it contains per-instance data and effective vertex attribute address needs to recalculated for every ``instance_divisor``-th instance. attribAddr = ``stride`` * instanceID / ``instance_divisor`` + ``src_offset`` In the above formulas, ``src_offset`` is taken from the given vertex element and ``stride`` is taken from a vertex buffer associated with the given vertex element. The calculated attribAddr is used as an offset into the vertex buffer to fetch the attribute data. The value of ``instanceID`` can be read in a vertex shader through a system value register declared with INSTANCEID semantic name. Queries ^^^^^^^ Queries gather some statistic from the 3D pipeline over one or more draws. Queries may be nested, though no state tracker currently exercises this. Queries can be created with ``create_query`` and deleted with ``destroy_query``. To start a query, use ``begin_query``, and when finished, use ``end_query`` to end the query. ``get_query_result`` is used to retrieve the results of a query. If the ``wait`` parameter is TRUE, then the ``get_query_result`` call will block until the results of the query are ready (and TRUE will be returned). Otherwise, if the ``wait`` parameter is FALSE, the call will not block and the return value will be TRUE if the query has completed or FALSE otherwise. The most common type of query is the occlusion query, ``PIPE_QUERY_OCCLUSION_COUNTER``, which counts the number of fragments which are written to the framebuffer without being culled by :ref:`Depth, Stencil, & Alpha` testing or shader KILL instructions. Another type of query, ``PIPE_QUERY_TIME_ELAPSED``, returns the amount of time, in milliseconds, the context takes to perform operations. Gallium does not guarantee the availability of any query types; one must always check the capabilities of the :ref:`Screen` first. Conditional Rendering ^^^^^^^^^^^^^^^^^^^^^ A drawing command can be skipped depending on the outcome of a query (typically an occlusion query). The ``render_condition`` function specifies the query which should be checked prior to rendering anything. If ``render_condition`` is called with ``query`` = NULL, conditional rendering is disabled and drawing takes place normally. If ``render_condition`` is called with a non-null ``query`` subsequent drawing commands will be predicated on the outcome of the query. If the query result is zero subsequent drawing commands will be skipped. If ``mode`` is PIPE_RENDER_COND_WAIT the driver will wait for the query to complete before deciding whether to render. If ``mode`` is PIPE_RENDER_COND_NO_WAIT and the query has not yet completed, the drawing command will be executed normally. If the query has completed, drawing will be predicated on the outcome of the query. If ``mode`` is PIPE_RENDER_COND_BY_REGION_WAIT or PIPE_RENDER_COND_BY_REGION_NO_WAIT rendering will be predicated as above for the non-REGION modes but in the case that an occulusion query returns a non-zero result, regions which were occluded may be ommitted by subsequent drawing commands. This can result in better performance with some GPUs. Normally, if the occlusion query returned a non-zero result subsequent drawing happens normally so fragments may be generated, shaded and processed even where they're known to be obscured. Flushing ^^^^^^^^ ``flush`` Resource Busy Queries ^^^^^^^^^^^^^^^^^^^^^ ``is_resource_referenced`` Blitting ^^^^^^^^ These methods emulate classic blitter controls. They are not guaranteed to be available; if they are set to NULL, then they are not present. These methods operate directly on ``pipe_surface`` objects, and stand apart from any 3D state in the context. Blitting functionality may be moved to a separate abstraction at some point in the future. ``surface_fill`` performs a fill operation on a section of a surface. ``surface_copy`` blits a region of a surface to a region of another surface, provided that both surfaces are the same format. The source and destination may be the same surface, and overlapping blits are permitted. The interfaces to these calls are likely to change to make it easier for a driver to batch multiple blits with the same source and destination. Transfers ^^^^^^^^^ These methods are used to get data to/from a resource. ``get_transfer`` creates a transfer object. ``transfer_destroy`` destroys the transfer object. May cause data to be written to the resource at this point. ``transfer_map`` creates a memory mapping for the transfer object. The returned map points to the start of the mapped range according to the box region, not the beginning of the resource. ``transfer_unmap`` remove the memory mapping for the transfer object. Any pointers into the map should be considered invalid and discarded. ``transfer_inline_write`` performs a simplified transfer for simple writes. Basically get_transfer, transfer_map, data write, transfer_unmap, and transfer_destroy all in one. .. _transfer_flush_region: transfer_flush_region %%%%%%%%%%%%%%%%%%%%% If a transfer was created with ``FLUSH_EXPLICIT``, it will not automatically be flushed on write or unmap. Flushes must be requested with ``transfer_flush_region``. Flush ranges are relative to the mapped range, not the beginning of the resource. .. _pipe_transfer: PIPE_TRANSFER ^^^^^^^^^^^^^ These flags control the behavior of a transfer object. * ``READ``: resource contents are read at transfer create time. * ``WRITE``: resource contents will be written back at transfer destroy time. * ``MAP_DIRECTLY``: a transfer should directly map the resource. May return NULL if not supported. * ``DISCARD``: The memory within the mapped region is discarded. Cannot be used with ``READ``. * ``DONTBLOCK``: Fail if the resource cannot be mapped immediately. * ``UNSYNCHRONIZED``: Do not synchronize pending operations on the resource when mapping. The interaction of any writes to the map and any operations pending on the resource are undefined. Cannot be used with ``READ``. * ``FLUSH_EXPLICIT``: Written ranges will be notified later with :ref:`transfer_flush_region`. Cannot be used with ``READ``.