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We're in 2022 now, and HTTPS is available in a lot more places in the past. Let's upgrade some links, to protect the privacy of our readers. The links that are left either don't support HTTPS, or are simply dead and needs to be updated anyway. That's besides the scope of this merge-request, so I'm leaving that for someone else. Reviewed-by: David Heidelberg <david.heidelberg@collabora.com> Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/19492>
357 lines
13 KiB
ReStructuredText
357 lines
13 KiB
ReStructuredText
.. _rasterizer:
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Rasterizer
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==========
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The rasterizer state controls the rendering of points, lines and triangles.
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Attributes include polygon culling state, line width, line stipple,
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multisample state, scissoring and flat/smooth shading.
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Linkage
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-------
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clamp_vertex_color
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If set, TGSI_SEMANTIC_COLOR registers are clamped to the [0, 1] range after
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the execution of the vertex shader, before being passed to the geometry
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shader or fragment shader.
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OpenGL: glClampColor(GL_CLAMP_VERTEX_COLOR) in GL 3.0 or GL_ARB_color_buffer_float
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D3D11: seems always disabled
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Note the PIPE_CAP_VERTEX_COLOR_CLAMPED query indicates whether or not the
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driver supports this control. If it's not supported, gallium frontends may
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have to insert extra clamping code.
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clamp_fragment_color
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Controls whether TGSI_SEMANTIC_COLOR outputs of the fragment shader
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are clamped to [0, 1].
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OpenGL: glClampColor(GL_CLAMP_FRAGMENT_COLOR) in GL 3.0 or ARB_color_buffer_float
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D3D11: seems always disabled
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Note the PIPE_CAP_FRAGMENT_COLOR_CLAMPED query indicates whether or not the
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driver supports this control. If it's not supported, gallium frontends may
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have to insert extra clamping code.
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Shading
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-------
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flatshade
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If set, the provoking vertex of each polygon is used to determine the color
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of the entire polygon. If not set, fragment colors will be interpolated
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between the vertex colors.
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The actual interpolated shading algorithm is obviously
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implementation-dependent, but will usually be Gouraud for most hardware.
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.. note::
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This is separate from the fragment shader input attributes
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CONSTANT, LINEAR and PERSPECTIVE. The flatshade state is needed at
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clipping time to determine how to set the color of new vertices.
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:ref:`Draw` can implement flat shading by copying the provoking vertex
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color to all the other vertices in the primitive.
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flatshade_first
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Whether the first vertex should be the provoking vertex, for most primitives.
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If not set, the last vertex is the provoking vertex.
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There are a few important exceptions to the specification of this rule.
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* ``PIPE_PRIMITIVE_POLYGON``: The provoking vertex is always the first
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vertex. If the caller wishes to change the provoking vertex, they merely
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need to rotate the vertices themselves.
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* ``PIPE_PRIMITIVE_QUAD``, ``PIPE_PRIMITIVE_QUAD_STRIP``: The option only has
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an effect if ``PIPE_CAP_QUADS_FOLLOW_PROVOKING_VERTEX_CONVENTION`` is true.
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If it is not, the provoking vertex is always the last vertex.
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* ``PIPE_PRIMITIVE_TRIANGLE_FAN``: When set, the provoking vertex is the
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second vertex, not the first. This permits each segment of the fan to have
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a different color.
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Polygons
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--------
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light_twoside
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If set, there are per-vertex back-facing colors. The hardware
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(perhaps assisted by :ref:`Draw`) should be set up to use this state
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along with the front/back information to set the final vertex colors
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prior to rasterization.
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The frontface vertex shader color output is marked with TGSI semantic
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COLOR[0], and backface COLOR[1].
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front_ccw
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Indicates whether the window order of front-facing polygons is
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counter-clockwise (TRUE) or clockwise (FALSE).
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cull_mode
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Indicates which faces of polygons to cull, either PIPE_FACE_NONE
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(cull no polygons), PIPE_FACE_FRONT (cull front-facing polygons),
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PIPE_FACE_BACK (cull back-facing polygons), or
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PIPE_FACE_FRONT_AND_BACK (cull all polygons).
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fill_front
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Indicates how to fill front-facing polygons, either
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PIPE_POLYGON_MODE_FILL, PIPE_POLYGON_MODE_LINE or
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PIPE_POLYGON_MODE_POINT.
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fill_back
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Indicates how to fill back-facing polygons, either
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PIPE_POLYGON_MODE_FILL, PIPE_POLYGON_MODE_LINE or
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PIPE_POLYGON_MODE_POINT.
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poly_stipple_enable
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Whether polygon stippling is enabled.
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poly_smooth
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Controls OpenGL-style polygon smoothing/antialiasing
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offset_point
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If set, point-filled polygons will have polygon offset factors applied
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offset_line
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If set, line-filled polygons will have polygon offset factors applied
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offset_tri
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If set, filled polygons will have polygon offset factors applied
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offset_units
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Specifies the polygon offset bias
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offset_units_unscaled
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Specifies the unit of the polygon offset bias. If false, use the
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GL/D3D1X behavior. If true, offset_units is a floating point offset
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which isn't scaled (D3D9). Note that GL/D3D1X behavior has different
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formula whether the depth buffer is unorm or float, which is not
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the case for D3D9.
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offset_scale
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Specifies the polygon offset scale
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offset_clamp
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Upper (if > 0) or lower (if < 0) bound on the polygon offset result
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Lines
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-----
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line_width
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The width of lines.
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line_smooth
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Whether lines should be smoothed. Line smoothing is simply anti-aliasing.
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line_stipple_enable
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Whether line stippling is enabled.
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line_stipple_pattern
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16-bit bitfield of on/off flags, used to pattern the line stipple.
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line_stipple_factor
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When drawing a stippled line, each bit in the stipple pattern is
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repeated N times, where N = line_stipple_factor + 1.
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line_last_pixel
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Controls whether the last pixel in a line is drawn or not. OpenGL
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omits the last pixel to avoid double-drawing pixels at the ends of lines
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when drawing connected lines.
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Points
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------
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sprite_coord_enable
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The effect of this state depends on PIPE_CAP_TGSI_TEXCOORD !
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Controls automatic texture coordinate generation for rendering sprite points.
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If PIPE_CAP_TGSI_TEXCOORD is false:
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When bit k in the sprite_coord_enable bitfield is set, then generic
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input k to the fragment shader will get an automatically computed
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texture coordinate.
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If PIPE_CAP_TGSI_TEXCOORD is true:
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The bitfield refers to inputs with TEXCOORD semantic instead of generic inputs.
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The texture coordinate will be of the form (s, t, 0, 1) where s varies
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from 0 to 1 from left to right while t varies from 0 to 1 according to
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the state of 'sprite_coord_mode' (see below).
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If any bit is set, then point_smooth MUST be disabled (there are no
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round sprites) and point_quad_rasterization MUST be true (sprites are
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always rasterized as quads). Any mismatch between these states should
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be considered a bug in the gallium frontend.
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This feature is implemented in the :ref:`Draw` module but may also be
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implemented natively by GPUs or implemented with a geometry shader.
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sprite_coord_mode
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Specifies how the value for each shader output should be computed when drawing
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point sprites. For PIPE_SPRITE_COORD_LOWER_LEFT, the lower-left vertex will
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have coordinates (0,0,0,1). For PIPE_SPRITE_COORD_UPPER_LEFT, the upper-left
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vertex will have coordinates (0,0,0,1).
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This state is used by :ref:`Draw` to generate texcoords.
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point_quad_rasterization
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Determines if points should be rasterized according to quad or point
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rasterization rules.
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(Legacy-only) OpenGL actually has quite different rasterization rules
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for points and point sprites - hence this indicates if points should be
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rasterized as points or according to point sprite (which decomposes them
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into quads, basically) rules. Newer GL versions no longer support the old
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point rules at all.
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Additionally Direct3D will always use quad rasterization rules for
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points, regardless of whether point sprites are enabled or not.
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If this state is enabled, point smoothing and antialiasing are
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disabled. If it is disabled, point sprite coordinates are not
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generated.
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.. note::
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Some renderers always internally translate points into quads; this state
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still affects those renderers by overriding other rasterization state.
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point_tri_clip
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Determines if clipping of points should happen after they are converted
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to "rectangles" (required by d3d) or before (required by OpenGL, though
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this rule is ignored by some IHVs).
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It is not valid to set this to enabled but have point_quad_rasterization
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disabled.
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point_smooth
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Whether points should be smoothed. Point smoothing turns rectangular
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points into circles or ovals.
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point_size_per_vertex
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Whether the vertex shader is expected to have a point size output.
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Undefined behavior is permitted if there is disagreement between
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this flag and the actual bound shader.
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point_size
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The size of points, if not specified per-vertex.
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Other Members
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-------------
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scissor
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Whether the scissor test is enabled.
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multisample
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Whether :term:`MSAA` is enabled.
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half_pixel_center
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When true, the rasterizer should use (0.5, 0.5) pixel centers for
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determining pixel ownership (e.g, OpenGL, D3D10 and higher)::
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0 0.5 1
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0 +-----+
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0.5 | X |
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1 +-----+
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When false, the rasterizer should use (0, 0) pixel centers for determining
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pixel ownership (e.g., D3D9 or ealier)::
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-0.5 0 0.5
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-0.5 +-----+
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0 | X |
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0.5 +-----+
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bottom_edge_rule
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Determines what happens when a pixel sample lies precisely on a triangle
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edge.
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When true, a pixel sample is considered to lie inside of a triangle if it
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lies on the *bottom edge* or *left edge* (e.g., OpenGL drawables)::
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0 x
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0 +--------------------->
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| +=============+
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y V
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When false, a pixel sample is considered to lie inside of a triangle if it
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lies on the *top edge* or *left edge* (e.g., OpenGL FBOs, D3D)::
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0 x
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0 +--------------------->
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y V
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Where:
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- a *top edge* is an edge that is horizontal and is above the other edges;
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- a *bottom edge* is an edge that is horizontal and is below the other
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edges;
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- a *left edge* is an edge that is not horizontal and is on the left side of
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the triangle.
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.. note::
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Actually all graphics APIs use a top-left rasterization rule for pixel
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ownership, but their notion of top varies with the axis origin (which
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can be either at y = 0 or at y = height). Gallium instead always
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assumes that top is always at y=0.
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See also:
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- https://msdn.microsoft.com/en-us/library/windows/desktop/cc627092.aspx
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- https://msdn.microsoft.com/en-us/library/windows/desktop/bb147314.aspx
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clip_halfz
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When true clip space in the z axis goes from [0..1] (D3D). When false
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[-1, 1] (GL)
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depth_clip_near
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When false, the near depth clipping plane of the view volume is disabled.
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depth_clip_far
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When false, the far depth clipping plane of the view volume is disabled.
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depth_clamp
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Whether the depth value will be clamped to the interval defined by the
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near and far depth range at the per-pixel level, after polygon offset has
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been applied and before depth testing. Note that a clamp to [0,1] according
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to GL rules should always happen even if this is disabled.
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clip_plane_enable
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For each k in [0, PIPE_MAX_CLIP_PLANES), if bit k of this field is set,
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clipping half-space k is enabled, if it is clear, it is disabled.
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The clipping half-spaces are defined either by the user clip planes in
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``pipe_clip_state``, or by the clip distance outputs of the shader stage
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preceding the fragment shader.
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If any clip distance output is written, those half-spaces for which no
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clip distance is written count as disabled; i.e. user clip planes and
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shader clip distances cannot be mixed, and clip distances take precedence.
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conservative_raster_mode
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The conservative rasterization mode. For PIPE_CONSERVATIVE_RASTER_OFF,
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conservative rasterization is disabled. For IPE_CONSERVATIVE_RASTER_POST_SNAP
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or PIPE_CONSERVATIVE_RASTER_PRE_SNAP, conservative rasterization is nabled.
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When conservative rasterization is enabled, the polygon smooth, line mooth,
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point smooth and line stipple settings are ignored.
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With the post-snap mode, unlike the pre-snap mode, fragments are never
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generated for degenerate primitives. Degenerate primitives, when rasterized,
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are considered back-facing and the vertex attributes and depth are that of
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the provoking vertex.
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If the post-snap mode is used with an unsupported primitive, the pre-snap
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mode is used, if supported. Behavior is similar for the pre-snap mode.
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If the pre-snap mode is used, fragments are generated with respect to the primitive
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before vertex snapping.
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conservative_raster_dilate
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The amount of dilation during conservative rasterization.
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subpixel_precision_x
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A bias added to the horizontal subpixel precision during conservative rasterization.
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subpixel_precision_y
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A bias added to the vertical subpixel precision during conservative rasterization.
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