4 The context object represents the purest, most directly accessible, abilities
5 of the device's 3D rendering pipeline.
13 All CSO state is created, bound, and destroyed, with triplets of methods that
14 all follow a specific naming scheme. For example, ``create_blend_state``,
15 ``bind_blend_state``, and ``destroy_blend_state``.
17 CSO objects handled by the context object:
19 * :ref:`Blend`: ``*_blend_state``
20 * :ref:`Sampler`: These are special; they can be bound to either vertex or
21 fragment samplers, and they are bound in groups.
22 ``bind_fragment_sampler_states``, ``bind_vertex_sampler_states``
23 * :ref:`Rasterizer`: ``*_rasterizer_state``
24 * :ref:`Depth, Stencil, & Alpha`: ``*_depth_stencil_alpha_state``
25 * :ref:`Shader`: These have two sets of methods. ``*_fs_state`` is for
26 fragment shaders, and ``*_vs_state`` is for vertex shaders.
27 * :ref:`Vertex Elements`: ``*_vertex_elements_state``
30 Resource Binding State
31 ^^^^^^^^^^^^^^^^^^^^^^
33 This state describes how resources in various flavours (textures,
34 buffers, surfaces) are bound to the driver.
37 * ``set_constant_buffer`` sets a constant buffer to be used for a given shader
38 type. index is used to indicate which buffer to set (some apis may allow
39 multiple ones to be set, and binding a specific one later, though drivers
40 are mostly restricted to the first one right now).
42 * ``set_framebuffer_state``
44 * ``set_vertex_buffers``
50 These pieces of state are too small, variable, and/or trivial to have CSO
51 objects. They all follow simple, one-method binding calls, e.g.
54 * ``set_stencil_ref`` sets the stencil front and back reference values
55 which are used as comparison values in stencil test.
58 * ``set_polygon_stipple``
59 * ``set_scissor_state`` sets the bounds for the scissor test, which culls
60 pixels before blending to render targets. If the :ref:`Rasterizer` does
61 not have the scissor test enabled, then the scissor bounds never need to
62 be set since they will not be used.
63 * ``set_viewport_state``
69 These are the means to bind textures to shader stages. To create one, specify
70 its format, swizzle and LOD range in sampler view template.
72 If texture format is different than template format, it is said the texture
73 is being cast to another format. Casting can be done only between compatible
74 formats, that is formats that have matching component order and sizes.
76 Swizzle fields specify they way in which fetched texel components are placed
77 in the result register. For example, ``swizzle_r`` specifies what is going to be
78 placed in first component of result register.
80 The ``first_level`` and ``last_level`` fields of sampler view template specify
81 the LOD range the texture is going to be constrained to.
83 * ``set_fragment_sampler_views`` binds an array of sampler views to
84 fragment shader stage. Every binding point acquires a reference
85 to a respective sampler view and releases a reference to the previous
88 * ``set_vertex_sampler_views`` binds an array of sampler views to vertex
89 shader stage. Every binding point acquires a reference to a respective
90 sampler view and releases a reference to the previous sampler view.
92 * ``create_sampler_view`` creates a new sampler view. ``texture`` is associated
93 with the sampler view which results in sampler view holding a reference
94 to the texture. Format specified in template must be compatible
97 * ``sampler_view_destroy`` destroys a sampler view and releases its reference
98 to associated texture.
104 ``clear`` initializes some or all of the surfaces currently bound to
105 the framebuffer to particular RGBA, depth, or stencil values.
107 Clear is one of the most difficult concepts to nail down to a single
108 interface and it seems likely that we will want to add additional
109 clear paths, for instance clearing surfaces not bound to the
110 framebuffer, or read-modify-write clears such as depth-only or
111 stencil-only clears of packed depth-stencil buffers.
117 ``draw_arrays`` draws a specified primitive.
119 This command is equivalent to calling ``draw_arrays_instanced``
120 with ``startInstance`` set to 0 and ``instanceCount`` set to 1.
122 ``draw_elements`` draws a specified primitive using an optional
125 This command is equivalent to calling ``draw_elements_instanced``
126 with ``startInstance`` set to 0 and ``instanceCount`` set to 1.
128 ``draw_range_elements``
130 XXX: this is (probably) a temporary entrypoint, as the range
131 information should be available from the vertex_buffer state.
132 Using this to quickly evaluate a specialized path in the draw
135 ``draw_arrays_instanced`` draws multiple instances of the same primitive.
137 This command is equivalent to calling ``draw_elements_instanced``
138 with ``indexBuffer`` set to NULL and ``indexSize`` set to 0.
140 ``draw_elements_instanced`` draws multiple instances of the same primitive
141 using an optional index buffer.
143 For instanceID in the range between ``startInstance``
144 and ``startInstance``+``instanceCount``-1, inclusive, draw a primitive
145 specified by ``mode`` and sequential numbers in the range between ``start``
146 and ``start``+``count``-1, inclusive.
148 If ``indexBuffer`` is not NULL, it specifies an index buffer with index
149 byte size of ``indexSize``. The sequential numbers are used to lookup
150 the index buffer and the resulting indices in turn are used to fetch
153 If ``indexBuffer`` is NULL, the sequential numbers are used directly
154 as indices to fetch vertex attributes.
156 If a given vertex element has ``instance_divisor`` set to 0, it is said
157 it contains per-vertex data and effective vertex attribute address needs
158 to be recalculated for every index.
160 attribAddr = ``stride`` * index + ``src_offset``
162 If a given vertex element has ``instance_divisor`` set to non-zero,
163 it is said it contains per-instance data and effective vertex attribute
164 address needs to recalculated for every ``instance_divisor``-th instance.
166 attribAddr = ``stride`` * instanceID / ``instance_divisor`` + ``src_offset``
168 In the above formulas, ``src_offset`` is taken from the given vertex element
169 and ``stride`` is taken from a vertex buffer associated with the given
172 The calculated attribAddr is used as an offset into the vertex buffer to
173 fetch the attribute data.
175 The value of ``instanceID`` can be read in a vertex shader through a system
176 value register declared with INSTANCEID semantic name.
182 Queries gather some statistic from the 3D pipeline over one or more
183 draws. Queries may be nested, though no state tracker currently
186 Queries can be created with ``create_query`` and deleted with
187 ``destroy_query``. To start a query, use ``begin_query``, and when finished,
188 use ``end_query`` to end the query.
190 ``get_query_result`` is used to retrieve the results of a query. If
191 the ``wait`` parameter is TRUE, then the ``get_query_result`` call
192 will block until the results of the query are ready (and TRUE will be
193 returned). Otherwise, if the ``wait`` parameter is FALSE, the call
194 will not block and the return value will be TRUE if the query has
195 completed or FALSE otherwise.
197 A common type of query is the occlusion query which counts the number of
198 fragments/pixels which are written to the framebuffer (and not culled by
199 Z/stencil/alpha testing or shader KILL instructions).
202 Conditional Rendering
203 ^^^^^^^^^^^^^^^^^^^^^
205 A drawing command can be skipped depending on the outcome of a query
206 (typically an occlusion query). The ``render_condition`` function specifies
207 the query which should be checked prior to rendering anything.
209 If ``render_condition`` is called with ``query`` = NULL, conditional
210 rendering is disabled and drawing takes place normally.
212 If ``render_condition`` is called with a non-null ``query`` subsequent
213 drawing commands will be predicated on the outcome of the query. If
214 the query result is zero subsequent drawing commands will be skipped.
216 If ``mode`` is PIPE_RENDER_COND_WAIT the driver will wait for the
217 query to complete before deciding whether to render.
219 If ``mode`` is PIPE_RENDER_COND_NO_WAIT and the query has not yet
220 completed, the drawing command will be executed normally. If the query
221 has completed, drawing will be predicated on the outcome of the query.
223 If ``mode`` is PIPE_RENDER_COND_BY_REGION_WAIT or
224 PIPE_RENDER_COND_BY_REGION_NO_WAIT rendering will be predicated as above
225 for the non-REGION modes but in the case that an occulusion query returns
226 a non-zero result, regions which were occluded may be ommitted by subsequent
227 drawing commands. This can result in better performance with some GPUs.
228 Normally, if the occlusion query returned a non-zero result subsequent
229 drawing happens normally so fragments may be generated, shaded and
230 processed even where they're known to be obscured.
239 Resource Busy Queries
240 ^^^^^^^^^^^^^^^^^^^^^
242 ``is_resource_referenced``
249 These methods emulate classic blitter controls. They are not guaranteed to be
250 available; if they are set to NULL, then they are not present.
252 These methods operate directly on ``pipe_surface`` objects, and stand
253 apart from any 3D state in the context. Blitting functionality may be
254 moved to a separate abstraction at some point in the future.
256 ``surface_fill`` performs a fill operation on a section of a surface.
258 ``surface_copy`` blits a region of a surface to a region of another surface,
259 provided that both surfaces are the same format. The source and destination
260 may be the same surface, and overlapping blits are permitted.
262 The interfaces to these calls are likely to change to make it easier
263 for a driver to batch multiple blits with the same source and
270 These methods are used to get data to/from a resource.
272 ``get_transfer`` creates a transfer object.
274 ``transfer_destroy`` destroys the transfer object. May cause
275 data to be written to the resource at this point.
277 ``transfer_map`` creates a memory mapping for the transfer object.
278 The returned map points to the start of the mapped range according to
279 the box region, not the beginning of the resource.
281 .. _transfer_flush_region:
282 ``transfer_flush_region`` If a transfer was created with TRANFER_FLUSH_EXPLICIT,
283 only the region specified is guaranteed to be written to. This is relative to
284 the mapped range, not the beginning of the resource.
286 ``transfer_unmap`` remove the memory mapping for the transfer object.
287 Any pointers into the map should be considered invalid and discarded.
289 ``transfer_inline_write`` performs a simplified transfer for simple writes.
290 Basically get_transfer, transfer_map, data write, transfer_unmap, and
291 transfer_destroy all in one.
298 These flags control the behavior of a transfer object.
300 * ``READ``: resource contents are read at transfer create time.
301 * ``WRITE``: resource contents will be written back at transfer destroy time.
302 * ``MAP_DIRECTLY``: a transfer should directly map the resource. May return
303 NULL if not supported.
304 * ``DISCARD``: The memory within the mapped region is discarded.
305 Cannot be used with ``READ``.
306 * ``DONTBLOCK``: Fail if the resource cannot be mapped immediately.
307 * ``UNSYNCHRONIZED``: Do not synchronize pending operations on the resource
308 when mapping. The interaction of any writes to the map and any
309 operations pending on the resource are undefined. Cannot be used with
311 * ``FLUSH_EXPLICIT``: Written ranges will be notified later with
312 :ref:`transfer_flush_region`. Cannot be used with