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 the PIPE_CAP_VERTEX_COLOR_CLAMPED query indicates whether or not the driver supports this control. If it’s not supported, the state tracker 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 ARB_color_buffer_float

D3D11: seems always disabled

Note the PIPE_CAP_FRAGMENT_COLOR_CLAMPED query indicates whether or not the driver supports this control. If it’s not supported, the state tracker 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 Gourard 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_CAP_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 frontface vertex shader color output is marked with TGSI semantic COLOR[0], and backface 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_units_unscaled
Specifies the unit of the polygon offset bias. If false, use the GL/D3D1X behaviour. If true, offset_units is a floating point offset which isn’t scaled (D3D9). Note that GL/D3D1X behaviour has different formula whether the depth buffer is unorm or float, which is not the case for D3D9.
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_CAP_TGSI_TEXCOORD !

Controls automatic texture coordinate generation for rendering sprite points.

If PIPE_CAP_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_CAP_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 state-tracker.

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 behaviour 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 ealier):

   -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:
clip_halfz
When true clip space in the z axis goes from [0..1] (D3D). When false [-1, 1] (GL)
depth_clip
When false, the near and far depth clipping planes of the view volume are disabled and the depth value will be clamped at the per-pixel level, after polygon offset has been applied and before depth testing.
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.