Rasterizer — The Mesa 3D Graphics Library latest documentation

# Rasterizer

The rasterizer state controls the rendering of points, lines and triangles. Attributes include polygon culling state, line width, line stipple, multisample state, scissoring and flat/smooth shading.

## Linkage

clamp_vertex_color

  If set, TGSI_SEMANTIC_COLOR registers are clamped to the [0, 1] range after the execution of the vertex shader, before being passed to the geometry shader or fragment shader.

  OpenGL: glClampColor(GL_CLAMP_VERTEX_COLOR) in GL 3.0 or GL_ARB_color_buffer_float

  D3D11: seems always disabled

  Note pipe_caps.vertex_color_clamped indicates whether or not the driver supports this control. If it’s not supported, gallium frontends may have to insert extra clamping code.

clamp_fragment_color

  Controls whether TGSI_SEMANTIC_COLOR outputs of the fragment shader are clamped to [0, 1].

  OpenGL: glClampColor(GL_CLAMP_FRAGMENT_COLOR) in GL 3.0 or GL_ARB_color_buffer_float

  D3D11: seems always disabled

  Note pipe_caps.fragment_color_clamped indicates whether or not the driver supports this control. If it’s not supported, gallium frontends may have to insert extra clamping code.

## Shading

flatshade

  If set, the provoking vertex of each polygon is used to determine the color of the entire polygon. If not set, fragment colors will be interpolated between the vertex colors.

  The actual interpolated shading algorithm is obviously implementation-dependent, but will usually be Gouraud for most hardware.

  Note

  This is separate from the fragment shader input attributes CONSTANT, LINEAR and PERSPECTIVE. The flatshade state is needed at clipping time to determine how to set the color of new vertices.

  Draw can implement flat shading by copying the provoking vertex color to all the other vertices in the primitive.

flatshade_first

  Whether the first vertex should be the provoking vertex, for most primitives. If not set, the last vertex is the provoking vertex.

  There are a few important exceptions to the specification of this rule.

  - `PIPE_PRIMITIVE_POLYGON`: The provoking vertex is always the first vertex. If the caller wishes to change the provoking vertex, they merely need to rotate the vertices themselves.

  - `PIPE_PRIMITIVE_QUAD`, `PIPE_PRIMITIVE_QUAD_STRIP`: The option only has an effect if `pipe_caps.quads_follow_provoking_vertex_convention` is true. If it is not, the provoking vertex is always the last vertex.

  - `PIPE_PRIMITIVE_TRIANGLE_FAN`: When set, the provoking vertex is the second vertex, not the first. This permits each segment of the fan to have a different color.

## Polygons

light_twoside

  If set, there are per-vertex back-facing colors. The hardware (perhaps assisted by Draw) should be set up to use this state along with the front/back information to set the final vertex colors prior to rasterization.

  The front-face vertex shader color output is marked with TGSI semantic COLOR[0], and back-face COLOR[1].

front_ccw

  Indicates whether the window order of front-facing polygons is counter-clockwise (TRUE) or clockwise (FALSE).

cull_mode

  Indicates which faces of polygons to cull, either PIPE_FACE_NONE (cull no polygons), PIPE_FACE_FRONT (cull front-facing polygons), PIPE_FACE_BACK (cull back-facing polygons), or PIPE_FACE_FRONT_AND_BACK (cull all polygons).

fill_front

  Indicates how to fill front-facing polygons, either PIPE_POLYGON_MODE_FILL, PIPE_POLYGON_MODE_LINE or PIPE_POLYGON_MODE_POINT.

fill_back

  Indicates how to fill back-facing polygons, either PIPE_POLYGON_MODE_FILL, PIPE_POLYGON_MODE_LINE or PIPE_POLYGON_MODE_POINT.

poly_stipple_enable

  Whether polygon stippling is enabled.

poly_smooth

  Controls OpenGL-style polygon smoothing/antialiasing

offset_point

  If set, point-filled polygons will have polygon offset factors applied

offset_line

  If set, line-filled polygons will have polygon offset factors applied

offset_tri

  If set, filled polygons will have polygon offset factors applied

offset_units

  Specifies the polygon offset bias

offset_scale

  Specifies the polygon offset scale

offset_clamp

  Upper (if > 0) or lower (if < 0) bound on the polygon offset result

## Lines

line_width

  The width of lines.

line_smooth

  Whether lines should be smoothed. Line smoothing is simply anti-aliasing.

line_stipple_enable

  Whether line stippling is enabled.

line_stipple_pattern

  16-bit bitfield of on/off flags, used to pattern the line stipple.

line_stipple_factor

  When drawing a stippled line, each bit in the stipple pattern is repeated N times, where N = line_stipple_factor + 1.

line_last_pixel

  Controls whether the last pixel in a line is drawn or not. OpenGL omits the last pixel to avoid double-drawing pixels at the ends of lines when drawing connected lines.

## Points

sprite_coord_enable

  The effect of this state depends on pipe_caps.tgsi_texcoord !

  Controls automatic texture coordinate generation for rendering sprite points.

  If pipe_caps.tgsi_texcoord is false: When bit k in the sprite_coord_enable bitfield is set, then generic input k to the fragment shader will get an automatically computed texture coordinate.

  If pipe_caps.tgsi_texcoord is true: The bitfield refers to inputs with TEXCOORD semantic instead of generic inputs.

  The texture coordinate will be of the form (s, t, 0, 1) where s varies from 0 to 1 from left to right while t varies from 0 to 1 according to the state of ‘sprite_coord_mode’ (see below).

  If any bit is set, then point_smooth MUST be disabled (there are no round sprites) and point_quad_rasterization MUST be true (sprites are always rasterized as quads). Any mismatch between these states should be considered a bug in the gallium frontend.

  This feature is implemented in the Draw module but may also be implemented natively by GPUs or implemented with a geometry shader.

sprite_coord_mode

  Specifies how the value for each shader output should be computed when drawing point sprites. For PIPE_SPRITE_COORD_LOWER_LEFT, the lower-left vertex will have coordinates (0,0,0,1). For PIPE_SPRITE_COORD_UPPER_LEFT, the upper-left vertex will have coordinates (0,0,0,1). This state is used by Draw to generate texcoords.

point_quad_rasterization

  Determines if points should be rasterized according to quad or point rasterization rules.

  (Legacy-only) OpenGL actually has quite different rasterization rules for points and point sprites - hence this indicates if points should be rasterized as points or according to point sprite (which decomposes them into quads, basically) rules. Newer GL versions no longer support the old point rules at all.

  Additionally Direct3D will always use quad rasterization rules for points, regardless of whether point sprites are enabled or not.

  If this state is enabled, point smoothing and antialiasing are disabled. If it is disabled, point sprite coordinates are not generated.

  Note

  Some renderers always internally translate points into quads; this state still affects those renderers by overriding other rasterization state.

point_tri_clip

  Determines if clipping of points should happen after they are converted to “rectangles” (required by d3d) or before (required by OpenGL, though this rule is ignored by some IHVs). It is not valid to set this to enabled but have point_quad_rasterization disabled.

point_smooth

  Whether points should be smoothed. Point smoothing turns rectangular points into circles or ovals.

point_size_per_vertex

  Whether the vertex shader is expected to have a point size output. Undefined behavior is permitted if there is disagreement between this flag and the actual bound shader.

point_size

  The size of points, if not specified per-vertex.

## Other Members

scissor

  Whether the scissor test is enabled.

multisample

  Whether MSAA is enabled.

half_pixel_center

  When true, the rasterizer should use (0.5, 0.5) pixel centers for determining pixel ownership (e.g, OpenGL, D3D10 and higher):

          0 0.5 1
       0  +-----+
          |     |
      0.5 |  X  |
          |     |
       1  +-----+

  When false, the rasterizer should use (0, 0) pixel centers for determining pixel ownership (e.g., D3D9 or earlier):

         -0.5 0 0.5
      -0.5 +-----+
           |     |
        0  |  X  |
           |     |
       0.5 +-----+

bottom_edge_rule

  Determines what happens when a pixel sample lies precisely on a triangle edge.

  When true, a pixel sample is considered to lie inside of a triangle if it lies on the bottom edge or left edge (e.g., OpenGL drawables):

        0                    x
      0 +--------------------->
        |
        |  +-------------+
        |  |             |
        |  |             |
        |  |             |
        |  +=============+
        |
      y V

  When false, a pixel sample is considered to lie inside of a triangle if it lies on the top edge or left edge (e.g., OpenGL FBOs, D3D):

        0                    x
      0 +--------------------->
        |
        |  +=============+
        |  |             |
        |  |             |
        |  |             |
        |  +-------------+
        |
      y V

  Where:

    - a top edge is an edge that is horizontal and is above the other edges;

    - a bottom edge is an edge that is horizontal and is below the other edges;

    - a left edge is an edge that is not horizontal and is on the left side of the triangle.

  Note

  Actually all graphics APIs use a top-left rasterization rule for pixel ownership, but their notion of top varies with the axis origin (which can be either at y = 0 or at y = height). Gallium instead always assumes that top is always at y=0.

  See also:

    - https://learn.microsoft.com/en-us/windows/win32/direct3d11/d3d10-graphics-programming-guide-rasterizer-stage-rules

    - https://learn.microsoft.com/en-us/windows/win32/direct3d9/rasterization-rules

clip_halfz

  When true clip space in the z axis goes from [0..1] (D3D). When false [-1, 1] (GL)

depth_clip_near

  When false, the near depth clipping plane of the view volume is disabled.

depth_clip_far

  When false, the far depth clipping plane of the view volume is disabled.

depth_clamp

  Whether the depth value will be clamped to the interval defined by the near and far depth range at the per-pixel level, after polygon offset has been applied and before depth testing. Note that a clamp to [0,1] according to GL rules should always happen even if this is disabled.

clip_plane_enable

  For each k in [0, PIPE_MAX_CLIP_PLANES), if bit k of this field is set, clipping half-space k is enabled, if it is clear, it is disabled. The clipping half-spaces are defined either by the user clip planes in `pipe_clip_state`, or by the clip distance outputs of the shader stage preceding the fragment shader. If any clip distance output is written, those half-spaces for which no clip distance is written count as disabled; i.e. user clip planes and shader clip distances cannot be mixed, and clip distances take precedence.

conservative_raster_mode

  The conservative rasterization mode. For PIPE_CONSERVATIVE_RASTER_OFF, conservative rasterization is disabled. For PIPE_CONSERVATIVE_RASTER_POST_SNAP or PIPE_CONSERVATIVE_RASTER_PRE_SNAP, conservative rasterization is enabled. When conservative rasterization is enabled, the polygon smooth, line smooth, point smooth and line stipple settings are ignored. With the post-snap mode, unlike the pre-snap mode, fragments are never generated for degenerate primitives. Degenerate primitives, when rasterized, are considered back-facing and the vertex attributes and depth are that of the provoking vertex. If the post-snap mode is used with an unsupported primitive, the pre-snap mode is used, if supported. Behavior is similar for the pre-snap mode. If the pre-snap mode is used, fragments are generated with respect to the primitive before vertex snapping.

conservative_raster_dilate

  The amount of dilation during conservative rasterization.

subpixel_precision_x

  A bias added to the horizontal subpixel precision during conservative rasterization.

subpixel_precision_y

  A bias added to the vertical subpixel precision during conservative rasterization.