docs: clarify point sprite discussion
Plagiarizes email explanation from Roland.
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@ -126,11 +126,15 @@ sprite_coord_enable
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Specifies if a texture unit has its texture coordinates replaced or not. This
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is a packed bitfield containing the enable for all texcoords -- if all bits
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are zero, point sprites are effectively disabled. If any bit is set, then
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point_smooth and point_quad_rasterization are ignored; point smoothing is
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disabled and points are always rasterized as quads. If enabled, the four
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vertices of the resulting quad will be assigned texture coordinates,
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according to sprite_coord_mode.
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are zero, point sprites are effectively disabled.
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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 state-tracker.
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If enabled, the four vertices of the resulting quad will be assigned
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texture coordinates, according to sprite_coord_mode.
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sprite_coord_mode
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^^^^^^^^^^^^^^^^^
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@ -141,20 +145,23 @@ 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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.. note::
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When geometry shaders are available, a special geometry shader could be
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used instead of this functionality, to convert incoming points into quads
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with the proper texture coordinates.
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point_quad_rasterization
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^^^^^^^^^^^^^^^^^^^^^^^^
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Determines if points should be rasterized as quads or points. Certain APIs,
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like Direct3D, always use quad rasterization for points, regardless of
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whether point sprites are enabled or not. If this state is enabled, point
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smoothing and antialiasing are disabled. If it is disabled, point sprite
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coordinates are not generated.
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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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OpenGL actually has quite different rasterization rules for points and
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point sprites - hence this indicates if points should be rasterized as
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points or according to point sprite (which decomposes them into quads,
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basically) rules.
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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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