gallium/docs: updated/improve sampler state documentation

src/gallium/docs/source/cso/sampler.rst

@@ -13,38 +13,94 @@ Members
 -------
 
 wrap_s
-    How to wrap the S coordinate. One of PIPE_TEX_WRAP.
+    How to wrap the S coordinate. One of PIPE_TEX_WRAP_*.
 wrap_t
-    How to wrap the T coordinate. One of PIPE_TEX_WRAP.
+    How to wrap the T coordinate. One of PIPE_TEX_WRAP_*.
 wrap_r
-    How to wrap the R coordinate. One of PIPE_TEX_WRAP.
+    How to wrap the R coordinate. One of PIPE_TEX_WRAP_*.
+
+The wrap modes are:
+
+* ``PIPE_TEX_WRAP_REPEAT``: Standard coord repeat/wrap-around mode.
+* ``PIPE_TEX_WRAP_CLAMP_TO_EDGE``: Clamp coord to edge of texture, the border
+  color is never sampled.
+* ``PIPE_TEX_WRAP_CLAMP_TO_BORDER``: Clamp coord to border of texture, the
+  border color is sampled when coords go outside the range [0,1].
+* ``PIPE_TEX_WRAP_CLAMP``: The coord is clamped to the range [0,1] before
+  scaling to the texture size.  This corresponds to the legacy OpenGL GL_CLAMP
+  texture wrap mode.  Historically, this mode hasn't acted consistantly across
+  all graphics hardware.  It sometimes acts like CLAMP_TO_EDGE or
+  CLAMP_TO_BORDER.  The behaviour may also vary depending on linear vs.
+  nearest sampling mode.
+* ``PIPE_TEX_WRAP_MIRROR_REPEAT``: If the integer part of the coordinate
+  is odd, the coord becomes (1 - coord).  Then, normal texture REPEAT is
+  applied to the coord.
+* ``PIPE_TEX_WRAP_MIRROR_CLAMP_TO_EDGE``: First, the absolute value of the
+  coordinate is computed.  Then, regular CLAMP_TO_EDGE is applied to the coord.
+* ``PIPE_TEX_WRAP_MIRROR_CLAMP_TO_BORDER``: First, the absolute value of the
+  coordinate is computed.  Then, regular CLAMP_TO_BORDER is applied to the
+  coord.
+* ``PIPE_TEX_WRAP_MIRROR_CLAMP``: First, the absolute value of the coord is
+  computed.  Then, regular CLAMP is applied to the coord.
+
+
 min_img_filter
-    The filter to use when minifying texels. One of PIPE_TEX_FILTER.
+    The image filter to use when minifying texels. One of PIPE_TEX_FILTER_*.
+mag_img_filter
+    The image filter to use when magnifying texels. One of PIPE_TEX_FILTER_*.
+
+The texture image filter modes are:
+
+* ``PIPE_TEX_FILTER_NEAREST``: One texel is fetched from the texture image
+  at the texture coordinate.
+* ``PIPE_TEX_FILTER_LINEAR``: Two, four or eight texels (depending on the
+  texture dimensions; 1D/2D/3D) are fetched from the texture image and
+  linearly weighted and blended together.
+
 min_mip_filter
     The filter to use when minifying mipmapped textures. One of
-    PIPE_TEX_FILTER.
+    PIPE_TEX_MIPFILTER_*.
-mag_img_filter
+
-    The filter to use when magnifying texels. One of PIPE_TEX_FILTER.
+The texture mip filter modes are:
+
+* ``PIPE_TEX_MIPFILTER_NEAREST``: A single mipmap level/image is selected
+  according to the texture LOD (lambda) value.
+* ``PIPE_TEX_MIPFILTER_LINEAR``: The two mipmap levels/images above/below
+  the texture LOD value are sampled from.  The results of sampling from
+  those two images are blended together with linear interpolation.
+* ``PIPE_TEX_MIPFILTER_NONE``: Mipmap filtering is disabled.  All texels
+  are taken from the level 0 image.
+
+
 compare_mode
-    If set to PIPE_TEX_COMPARE_R_TO_TEXTURE, texture output is computed
+    If set to PIPE_TEX_COMPARE_R_TO_TEXTURE, the result of texture sampling
-    according to compare_func, using r coord and the texture value as operands.
+    is not a color but a true/false value which is the result of comparing the
+    sampled texture value (typically a Z value from a depth texture) to the
+    texture coordinate's R component.
     If set to PIPE_TEX_COMPARE_NONE, no comparison calculation is performed.
 compare_func
-    How the comparison is computed. One of PIPE_FUNC.
+    The inequality operator used when compare_mode=1.  One of PIPE_FUNC_x.
 normalized_coords
-    Whether the texture coordinates are normalized. If normalized, they will
+    If set, the incoming texture coordinates (nominally in the range [0,1])
-    always be in [0, 1]. If not, they will be in the range of each dimension
+    will be scaled by the texture width, height, depth to compute texel
-    of the loaded texture.
+    addresses.  Otherwise, the texture coords are used as-is (they are not
+    scaled by the texture dimensions).
 lod_bias
-    The bias to apply to the level of detail.
+    Bias factor which is added to the computed level of detail.
+    The normal level of detail is computed from the partial derivatives of
+    the texture coordinates and/or the fragment shader TEX/TXB/TXL
+    instruction.
 min_lod
-    Minimum level of detail, used to clamp LoD after bias.
+    Minimum level of detail, used to clamp LOD after bias.  The LOD values
+    correspond to mipmap levels where LOD=0 is the level 0 mipmap image.
 max_lod
-    Maximum level of detail, used to clamp LoD after bias.
+    Maximum level of detail, used to clamp LOD after bias.
 border_color
-    RGBA color used for out-of-bounds coordinates.
+    RGBA color used for texel coordinates that are outside the [0,width-1],
+    [0, height-1] or [0, depth-1] ranges.
 max_anisotropy
-    Maximum filtering to apply anisotropically to textures. Setting this to
+    Maximum anistropy ratio to use when sampling from textures.  For example,
-    0 disables anisotropic filtering. Any other setting enables anisotropic
+    if max_anistropy=4, a region of up to 1 by 4 texels will be sampled.
-    filtering, however it's not unexpected some drivers only will change their
+    Set to zero to disable anisotropic filtering.  Any other setting enables
-    filtering with a setting of 2 and higher.
+    anisotropic filtering, however it's not unexpected some drivers only will
+    change their filtering with a setting of 2 and higher.