path: root/renderproto.txt

			The X Rendering Extension
			      Version 0.9
			        2004-7-23
			      Keith Packard
			    keithp@keithp.com

1. Introduction

The X Rendering Extension (Render) introduces digital image composition as
the foundation of a new rendering model within the X Window System.
Rendering geometric figures is accomplished by client-side tesselation into
either triangles or trapezoids.  Text is drawn by loading glyphs into the
server and rendering sets of them.

2. Acknowledgments

This extension was the work of many people, in particular:

 +	Thomas Porter and Tom Duff for their formal description
	of image compositing.

 +	Rob Pike and Russ Cox who designed the Plan 9 window system from
	which the compositing model was lifted.

 +	Juliusz Chroboczek and Raph Levien whose proposal for client-side
	glyph management eliminated font handling from the X server.

 +	Jon Leech, Brad Grantham and Allen Akin for patiently explaining
	how OpenGL works.

 +	Carl Worth for providing the sample implementation of
 	trapezoid rendering and showing how broken the spec was

 +	Sam Pottle and Jamey Sharp for helping demonstrate the correctness
 	of the trapezoid specification.

 +	Owen Taylor for helping specify projective transformations

3. Rendering Model

Render provides a single rendering operation which can be used in a variety of
ways to generate images:

	dest = (source IN mask) OP dest

Where 'IN' is the Porter/Duff operator of that name and 'OP' is any of the
list of compositing operators described below, among which can be found all
of the Porter/Duff binary operators.

To use this operator several additional values are required:

 +	The destination rectangle.  This is a subset of the destination
 	within which the rendering is performed.

 +	The source location. This identifies the coordinate in the
 	source aligned with the upper left corner of the
	destination rectangle.

 +	The mask location. This identifies the coordinate in the
 	mask aligned with the upper left corner of the
	destination rectangle.

 +	A clip list.  This limits the rendering to the intersection of the
 	destination rectangle with this clip list.

 +	The OP to use

 +	Whether the source should be repeated to cover the destination
 	rectangle, extended with a constant pixel value or extended by
	using the nearest available source pixel.

 +	Whether the mask should be repeated to cover the destination
 	rectangle, extended with a constant pixel value or extended by
	using the nearest available mask pixel.

 +	Whether the mask has a single alpha value for all four channels or
 	whether each mask channel should affect the associated source/dest
	channels.

 +	Whether the source should be reshaped with a projective
        transformation, and if so, what filter to apply while
	resampling the data.
	
 +	Whether the mask should be reshaped with a projective
        transformation, and if so, what filter to apply while
	resampling the data.
	
These parameters are variously attached to the operands or included in each
rendering request.

4. Data types

The core protocol rendering system uses a pixel model and applies color only
in the final generation of the video signal.  A compositing model operates
on colors, not pixel values so a new datatype is needed to interpret data as
color instead of just bits.

The "PictFormat" object holds information needed to translate pixel values
into red, green, blue and alpha channels.  The server has a list of picture
formats corresponding to the various visuals on the screen.  There are two
classes of formats, Indexed and Direct.  Indexed PictFormats hold a list of
pixel values and RGBA values while Direct PictFormats hold bit masks for each
of R, G, B and A.

The "Picture" object contains a Drawable, a PictFormat and some
rendering state.  More than one Picture can refer to the same Drawable.

5. Errors

Errors are sent using core X error reports.

PictFormat
	A value for a PICTFORMAT argument does not name a defined PICTFORMAT.

Picture
	A value for a PICTURE argument does not name a defined PICTURE.

PictOp
	A value for a PICTOP argument does not name a defined PICTOP.

GlyphSet
	A value for a GLYPHSET argument does not name a defined GLYPHSET.

Glyph
	A value for a GLYPH argument does not name a defined GLYPH in the
	glyphset.

6. Protocol Types

PICTURE		32-bit value (top three bits guaranteed to be zero)
PICTFORMAT	32-bit value (top three bits guaranteed to be zero)
PICTTYPE	{ Indexed, Direct }
PICTOP		{ Clear, Src, Dst, Over, OverReverse, In, InReverse,
		  Out, OutReverse, Atop, AtopReverse, Xor, Add, Saturate,
		  DisjointClear, DisjointSrc, DisjointDst, DisjointOver,
		  DisjointOverReverse, DisjointIn, DisjointInReverse,
		  DisjointOut, DisjointOutReverse, DisjointAtop,
		  DisjointAtopReverse, DisjointXor,
		  ConjointClear, ConjointSrc, ConjointDst, ConjointOver,
		  ConjointOverReverse, ConjointIn, ConjointInReverse,
		  ConjointOut, ConjointOutReverse, ConjointAtop,
		  ConjointAtopReverse, ConjointXor }
SUBPIXEL	{ Unknown, HorizontalRGB, HorizontalBGR, 
		  VerticalRGB, VerticalBGR, None
		}
COLOR		[	
			red, green, blue, alpha: CARD16
		]
CHANNELMASK	[
			shift, mask: CARD16
		]
DIRECTFORMAT	[
			red, green, blue, alpha: CHANNELMASK 
		]
INDEXVALUE	[ 
			pixel: Pixel; 
			red, green, blue, alpha: CARD16 
		]
PICTFORMINFO	[
			id:		PICTFORMAT
			type:		PICTTYPE
			depth:		CARD8
			direct:		DIRECTFORMAT
			colormap:	COLORMAP or None
		]

PICTVISUAL	[
			visual:		VISUALID or None
			format:		PICTFORMAT
		]

PICTDEPTH	[
			depth:		CARD8
			visuals:	LISTofPICTVISUAL
		]

PICTSCREEN	LISTofPICTDEPTH

FIXED		32-bit value (top 16 are integer portion, bottom 16 are fraction)
TRANSFORM	[
			p11, p12, p13:	FIXED
			p21, p22, p23:	FIXED
			p31, p32, p33:	FIXED
		]
POINTFIX	[
			x, y: FIXED
		]
POLYEDGE	{ Sharp, Smooth }
POLYMODE	{ Precise, Imprecise }
REPEAT          { None, Regular, Pad, Reflect }
COLORPOINT	[
			point:		POINTFIX
			color:		COLOR
		]
SPANFIX		[
			left, right, y: FIXED
		]
COLORSPANFIX	[
			left, right, y: FIXED
			left_color:	COLOR
			right_color:	COLOR
QUAD		[
			p1, p2, p3, p4:	POINTFIX
		]
TRIANGLE	[
			p1, p2, p3:	POINTFIX
		]
LINEFIX		[
			p1, p2:		POINTFIX
		]
TRAP		[
			top, bottom:	SPANFIX
		]
TRAPEZOID	[
			top, bottom:	FIXED
			left, right:	LINEFIX
		]
(TRAPEZOID is deprecated)
COLORTRIANGLE	[
			p1, p2, p3:	COLORPOINT
		]
COLORTRAP	[
			top, bottom:	COLORSPANFIX
		]
GLYPHSET	32-bit value (top three bits guaranteed to be zero)
GLYPH		32-bit value
GLYPHINFO	[
			width, height:	CARD16
			x, y:		INT16
			off-x, off-y:	INT16
		]
PICTGLYPH	[
			info:		GLYPHINFO
			x, y:		INT16
		]
GLYPHABLE	GLYPHSET or FONTABLE
GLYPHELT8	[
			dx, dy:		INT16
			glyphs:		LISTofCARD8
		]
GLYPHITEM8	GLYPHELT8 or GLYPHABLE
GLYPHELT16	[
			dx, dy:		INT16
			glyphs:		LISTofCARD16
		]
GLYPHITEM16	GLYPHELT16 or GLYPHABLE
GLYPHELT32	[
			dx, dy:		INT16
			glyphs:		LISTofCARD32
		]
GLYPHITEM32	GLYPHELT32 or GLYPHABLE

ANIMCURSORELT	[
			cursor:		CURSOR
			delay:		CARD32
		]
7. Standard PictFormats

The server must support a Direct PictFormat with 8 bits each of red, green,
blue and alpha as well as a Direct PictFormat with 8 bits of red, green and
blue and 0 bits of alpha.  The server must also support Direct PictFormats
with 1, 4 and 8 bits of alpha and 0 bits of r, g and b.

Pixel component values lie in the close range [0,1].  These values are
encoded in a varying number of bits.  Values are encoded in a straight
forward manner.  For a component encoded in m bits, a binary encoding b
is equal to a component value of b/(2^m-1).

A Direct PictFormat with zero bits of alpha component is declared to have
alpha == 1 everywhere.  A Direct PictFormat with zero bits of red, green and
blue is declared to have red, green, blue == 0 everywhere.  If any of red,
green or blue components are of zero size, all are of zero size.  Direct
PictFormats never have colormaps and are therefore screen independent.

Indexed PictFormats never have alpha channels and the direct component is all
zeros.  Indexed PictFormats always have a colormap in which the specified
colors are allocated read-only and are therefore screen dependent.  Drawing
to in Indexed Picture uses only pixel values listed by QueryPictIndexValues.
Reading from an Indexed Picture uses red, green and blue values from the
colormap and alpha values from those listed by QueryPictIndexValues.  Pixel
values not present in QueryPictIndexValues are given alpha values of 1.

8. Compositing Operators

For each pixel, the four channels of the image are computed with:

	C = Ca * Fa + Cb * Fb

where C, Ca, Cb are the values of the respective channels and Fa and Fb
come from the following table:

	PictOp			Fa			Fb
	--------------------------------------------------
	Clear			0			0
	Src			1			0
	Dst			0			1
	Over			1			1-Aa
	OverReverse		1-Ab			1
	In			Ab			0
	InReverse		0			Aa
	Out			1-Ab			0
	OutReverse		0			1-Aa
	Atop			Ab			1-Aa
	AtopReverse		1-Ab			Aa
	Xor			1-Ab			1-Aa
	Add			1			1
	Saturate		min(1,(1-Ab)/Aa)	1
	DisjointClear		0			0
	DisjointSrc		1			0
	DisjointDst		0			1
	DisjointOver		1			min(1,(1-Aa)/Ab)
	DisjointOverReverse	min(1,(1-Ab)/Aa)	1
	DisjointIn		max(1-(1-Ab)/Aa,0)	0
	DisjointInReverse	0			max(1-(1-Aa)/Ab,0)
	DisjointOut		min(1,(1-Ab)/Aa)	0
	DisjointOutReverse	0			min(1,(1-Aa)/Ab)
	DisjointAtop		max(1-(1-Ab)/Aa,0)	min(1,(1-Aa)/Ab)
	DisjointAtopReverse	min(1,(1-Ab)/Aa)	max(1-(1-Aa)/Ab,0)
	DisjointXor		min(1,(1-Ab)/Aa)	min(1,(1-Aa)/Ab)
	ConjointClear		0			0
	ConjointSrc		1			0
	ConjointDst		0			1
	ConjointOver		1			max(1-Aa/Ab,0)
	ConjointOverReverse	max(1-Ab/Aa,0)		1
	ConjointIn		min(1,Ab/Aa)		0
	ConjointInReverse	0			min(Aa/Ab,1)
	ConjointOut		max(1-Ab/Aa,0)		0
	ConjointOutReverse	0			max(1-Aa/Ab,0)
	ConjointAtop		min(1,Ab/Aa)		max(1-Aa/Ab,0)
	ConjointAtopReverse	max(1-Ab/Aa,0)		min(1,Aa/Ab)
	ConjointXor		max(1-Ab/Aa,0)		max(1-Aa/Ab,0)

Saturate and DisjointOverReverse are the same.  They match OpenGL
compositing with FUNC_ADD, SRC_ALPHA_SATURATE, ONE, except that Render uses
premultiplied alpha while Open GL uses non-premultiplied alpha.

The result of any compositing operator is always limited to the range
[0,1] for each component.  Components whose value would be greater than 1
are set to 1.

For operations involving division, when the divisor is zero, define the
quotient to be positive infinity.  The result is always well defined
because the division is surrounded with a max or min operator which will
give a finite result.

When the mask contains separate alpha values for each channel, the
alpha value resulting from the combination of that value with the source
alpha channel is used in the final image composition.

9. Source and Mask Transformations

When fetching pixels from the source or mask pictures, Render provides three
options for pixel values which fall outside the drawable (this includes
pixels within a window geometry obscured by other windows).

 +	Transparent.  Missing values are replaced with transparent.
 
 +	Nearest.  Replace missing pixels with the nearest available
 	pixel.  Where multiple pixels are equidistant, select
	those with smallest Y and then smallest X coordinates

 +	Tile.  Select the pixel which would appear were the
 	drawable tiled to enclose the missing coordinate.  If
	the tiling doesn't cover the coordinate, use the
	selected Constant or Nearest mode.

When GraphicsExposures are selected in the destination picture, a region
containing at least the union of all destination pixel values affected by
data replaced as above is delivered after each compositing operation.  If
the resulting region is empty, a NoExpose event is delivered instead.

To construct the source and mask operands, the computed pixels values are
transformed through a homogeneous matrix, filtered and then used in the
fundemental rendering operator described above.  Each screen provides a list
of supported filter names. There are a few required filters, and several
required filter alias which must map to one of the available filters.

10. Polygon Rasterization

Render provides only two kinds of polygons, trapezoids and triangles.  To
improve efficiency, several different wire encodings exist for each. 

All trapezoids must be convex.  Rendering of concave trapezoids is unspecified
except that the result must obey the clipping rules.

Composite
Polygons are rasterized by implicit generating an alpha mask and using that
in the general compositing operator along with a supplied source image:

	tmp = Rasterize (polygon)
	Composite (op, dst, src, tmp)

When rasterized with Sharp edges, the mask is computed with a depth of 1 so
that all of the mask values are either 0 or 1.

When rasterized with Smooth edges, the mask is generated by creating a square
around each pixel coordinate and computing the amount of that square covered
by the polygon.  This ignores sampling theory but it provides a precise
definition which is close to the right answer.  This value is truncated to
the alpha width in the fallback format before application of the compositing
operator.

Rasterization
Alpha values are generated by point sampling the coverage of a square
surrounding the center of each pixel by the polygon. 

In Precise poly mode, the sample points are located in a regular grid.  When
alpha depth 'e' is even, the regular grid is 2**(e/2) + 1 samples wide and
2**(e/2) -1 samples high.  For odd alpha depth 'o', the sample grid is 2**o
- 1 samples wide and 1 sample high.  Note that odd alpha depth usually
occurs only at depth 1, so this misshapen sample grid has no ill effects.
The sample grid is centered within the pixel and then each sample point is
rounded down to a point on the sub-pixel coordinate grid.

In Imprecise mode, the location of the sample points is not specified, but
the implementation must conform to the following constraints:

 +	Abutting edges must match precisely.  When specifying two polygons
	abutting along a common edge, if that edge is specified with the
	same coordinates in each polygon then the sum of alpha values for
	pixels inside the union of the two polygons must be precisely one.

 +	Translationally invarient.  The pixelization of the polygon must
	be the same when either the polygon or the target drawable
	are translated by any whole number of pixels in any direction.

 +	Sharp edges are honored.  When the polygon is rasterized with Sharp
	edges, the implicit alpha mask will contain only 1 or 0 for
	each pixel.

 +	Order independent. Two identical polygons specified with vertices
	in different orders must generate identical results.

11. Image Filtering

When computing pixels from source and mask images, a filter may be applied
to the data.  This is usually used with a non-identity transformation
matrix, but filtering may be applied with an identity transformation.

Each filter is given a unique name encoded as an ISO Latin-1 string.
Filters may be configured with a list of fixed point values; the number of
parameters and their interpretation is currently left to conventions passed
outside of the protocol.  A set of standard filters are required to be
provided:

	Filter Name	Description

	nearest		Nearest neighbor filtering
	bilinear	Linear interpolation in two dimensions

Additional names may be provided for any filter as aliases.  A set of
standard alias names are required to be mapped to a provided filter so that
applications can use the alias names without checking for availability.

	Alias name	Intended interpretation
	
	fast		High performance, quality similar to Nearest
	good		Reasonable performance, quality similar to Bilinear
	best		Highest quality available, performance may not
			be suitable for interactive use

Aliases must map directly to a non-aliased filter name.

There is also a set of standard filters which are not required but may be
provided.  If they are provided, using the standard name, they must match
the definition specified here.

	Filter Name	Description
	
	convolution	MxN convolution filter.  The values specified
			in SetPictureFilter are M, N and then M * N
			filter parameters.  M and N must be integers
			represented as fixed point numbers.
	gaussian	Gaussian blur.  The value specified is a radius
			in pixels (which can be fractional).  A standard
			Gaussian 2D convolution filter will be applied.
	binomial	Binomial blur. An approximation of a Gaussian
			blur using binomial coefficients

12. Glyph Rendering

Glyphs are small alpha masks which can be stored in the X server and
rendered by referring to them by name.  A set of glyphs can be rendered in a
single request.  Glyphs are positioned by subtracting the x, y elements of
the GLYPHINFO from the requested rendering position.  The next glyph
rendering position is set to the current rendering position plus the off-x
and off-y elements.

Glyphs are stored in GlyphSets and are named within the GlyphSet with
client-specified 32-bit numbers.

Glyphs can be stored in any PictFormat supported by the server.  All glyphs
in a GlyphSet are stored in the same format.

13. Extension Initialization

The client must negotiate the version of the extension before executing
extension requests.  Behavior of the server is undefined otherwise.

QueryVersion

	client-major-version:		CARD32
	client-minor-version:		CARD32

	->

	major-version:			CARD32
	minor-version:			CARD32

	The client sends the highest supported version to the server and
	the server sends the highest version it supports, but no higher than
	the requested version.  Major versions changes can introduce
	incompatibilities in existing functionality, minor version
	changes introduce only backward compatible changes.  It is
	the clients responsibility to ensure that the server supports
	a version which is compatible with its expectations.

QueryPictFormats

	->

	fallback:	PICTFORMAT
	formats:	LISTofPICTFORMINFO
	screens:	LISTofPICTSCREEN
	subpixels:	LISTofSUBPIXEL

	Errors:
		<none>

	The server responds with a list of supported PictFormats and
	a list of which PictFormat goes with each visual on each screen.
	Every PictFormat must match a supported depth, but not every
	PictFormat need have a matching visual.

	The fallback format is used as an intermediate representation
	in cases where there is no ideal choice.

	The relationship between the red, green and blue elements making
	up each pixel indexed by screen is returned in subpixels.
	This list is not present in servers advertising protocol
	versions earlier than 0.6.  This list may be shorter than
	the number of screens, in which case the remaining screens
	are given sub pixel order Unknown.

QueryPictIndexValues

	format:		PICTFORMAT

	->

	values:		LISTofINDEXVALUE

	Errors:
		PictFormat, Match

	Returns the mapping from pixel values to RGBA values for the
	specified Indexed PictFormat.  If 'format' does not refer to
	an Indexed PictFormat a Match error is generated.

QueryFilters

	drawable:	DRAWABLE

	->

	filters:	LISTofSTRING8
	aliases:	LISTofCARD16

	
14. Extension Requests

CreatePicture

	pid:		PICTURE
	drawable:	DRAWABLE
	format:		PICTFORMAT
	value-mask:	BITMASK
	value-list:	LISTofVALUE

	Errors:
		Alloc, Drawable, IDChoice, Match, Pixmap, Picture,
		PictFormat, Value

	This request creates a Picture object associated with the specified
	drawable and assigns the identifier pid to it.  Pixel data in the
	image are interpreted according to 'format'.  It is a Match error
	to specify a format with a different depth than the drawable.  If
	the drawable is a Window then the Red, Green and Blue masks must
	match those in the visual for the window else a Match error is
	generated.

	The value-mask and value-list specify attributes of the picture that
	are to be explicitly initialized.  The possible values are:
	
	repeat:			REPEAT
	alpha-map:		PICTURE or None
	alpha-x-origin:		INT16
	alpha-y-origin:		INT16
	clip-x-origin:		INT16
	clip-y-origin:		INT16
	clip-mask:		PIXMAP or None
	graphics-exposures:	BOOL
	subwindow-mode:		{ ClipByChildren, IncludeInferiors }
	poly-edge:		POLYEDGE
	poly-mode:		POLYMODE
	dither:			ATOM or None
	component-alpha:	BOOL
	
	When used as a source or mask operand, the repeat and fill-constant
	values control how pixels outside the geometry of the drawable are
	computed.
	
	Repeat indicates how the drawable contents should be extented
	in both directions.  
	
	The alpha channel of alpha-map is used in place of any alpha channel
	contained within the drawable for all rendering operations.  The
	alpha-mask origin is interpreted relative to the origin of drawable.
	Rendering is additionally clipped by the geometry of alpha-map.
	Exposures to the window do not affect the contents of alpha-map.
	Alpha-map must refer to a picture containing a Pixmap, not a Window
	(or a Match error results).

	The clip-mask restricts reads and writes to drawable.  Only pixels
	where the clip-mask has bits set to 1 are read or written.  Pixels
	are not accessed outside the area covered by the clip-mask or where
	the clip-mask has bits set to 0.  The clip-mask affects all graphics
	requests, including sources.  The clip-mask origin is interpreted
	relative to the origin of drawable.  If a pixmap is specified as the
	clip-mask, it must have depth 1 and have the same root as the
	drawable (or a Match error results).  If clip-mask is None, then
	pixels are always drawn, regardless of the clip origin.  The
	clip-mask can also be set with the SetPictureClipRectangles request.
	
	For ClipByChildren, both source and destination windows are
	additionally clipped by all viewable InputOutput children.  For
	IncludeInferiors , neither source nor destination window is clipped
	by inferiors.  This will result in including subwindow contents in
	the source and drawing through subwindow boundaries of the
	destination.  The use of IncludeInferiors with a source or
	destination window of one depth with mapped inferiors of differing
	depth is not illegal, but the semantics are undefined by this
	extension.

	The graphics-exposures flag controls GraphicsExposure event
	generation for Composite requests (and any similar requests
	defined by additional extensions).

	Poly-edge and poly-mode control the rasterization of polygons
	as described above.

	Dither selects which of the available dither patterns should
	be used.  If dither is None, no dithering will be done.

	Component-alpha indicates whether each image component is
	intended as a separate alpha value when the picture is used
	as a mask operand.

	The default component values are

		Component		Default
		-------------------------------
		repeat			False
		fill-nearest:		False
		clip-x-origin        	0
		clip-y-origin          	0
		clip-mask		None
		graphics-exposures	True
		subwindow-mode		ClipByChildren
		poly-edge		Smooth
		poly-mode		Precise
		dither			None
		component-alpha		False

ChangePicture

	pid:		PICTURE
	value-mask:     BITMASK
	value-list:     LISTofVALUE

	Errors:
		Picture, Alloc, Pixmap, PictOp, Value

	The value-mask and value-list specify which attributes are to be
	changed.  The values and restrictions are the same as for 
	CreatePicture.

SetPictureClipRectangles

	picture:	PICTURE
	clip-x-origin:	INT16
	clip-y-origin:	INT16
	rectangles:	LISTofRECTANGLE

	Errors:
		Alloc, Picture

	This request changes clip-mask in picture to the specified list of
	rectangles and sets the clip origin.  Input and output will be
	clipped to remain contained within the rectangles.  The clip origin
	is interpreted relative to the origin of the drawable associated
	with picture.  The rectangle coordinates are interpreted relative to
	the clip origin.  Note that the list of rectangles can be empty,
	which effectively disables output.  This is the opposite of passing
	None as the clip-mask in CreatePicture and ChangePicture.
	
	Note that output is clipped to the union of all of the rectangles
	and that no particular ordering among the rectangles is required.

SetPictureTransform

	picture:	PICTURE
	transform:	TRANSFORM

	Errors:
		Alloc, Value, Picture

	This request changes the projective transformation used to
	map coordinates when 'picture' is used as the source or
	mask in any compositing operation.  The transform
	maps from destination pixel geometry back to the source pixel
	geometry.

	The matrix must be invertable, else a Value error is generated.

SetPictureFilter

	picture:	PICTURE
	filter:		STRING8
	values:		LISTofFIXED

	Errors:
		Value, Match, Picture

	This request sets the current filter used when picture is a source
	or mask operand.  Filter must be one of the filters supported
	for the screen associated with picture, else a Match error
	is generated.  If the filter accepts additional parameters,
	they can be provided in values, incorrect values generate Value
	errors, too many values generate Match errors.  Too few values
	cause the filter to assume default values for the missing
	parameters.

	When created, Pictures are set to the Nearest filter.

FreePicture

	pid:		PICTURE

	Errors:
		Picture

	This request deletes the association between the resource ID and the
	picture.  The picture storage will be freed when no other resource
	references it.

Composite

	op:		PICTOP
	src:		PICTURE
	mask:		PICTURE or None
	dst:		PICTURE
	src-x, src-y:	INT16
	mask-x, mask-y:	INT16
	dst-x, dst-y:	INT16
	width, height:	CARD16

	This request combines the specified rectangle of the transformed
	src and mask operands with the specified rectangle of dst using op
	as the compositing operator.  The coordinates are relative their
	respective (transformed) drawable's origin.  Rendering is clipped
	to the geometry of the dst drawable and then to the dst clip-list.

	Pixels outside the geometry of src or mask needed for this
	computation are substituted as described in the Source and Mask
	Transformations section above.
	
	If src, mask and dst are not in the same format, and one of their
	formats can hold all without loss of precision, they are converted
	to that format.  Alternatively, the server will convert each
	operand to the fallback format.

	If mask is None, it is replaced by a constant alpha value of 1.

	When dst has graphics-exposures true, a region covering all dst
	pixels affected by substitutions performed on src or mask pixels
	outside their respective geometries is computed.  If that region is
	empty, a NoExpose event is sent.  Otherwise, a sequence of
	GraphicsExpose events are sent covering that region.

FillRectangles

	op:		PICTOP
	dst:		PICTURE
	color:		COLOR
	rects:		LISTofRECTANGLE

	This request combines color with the destination drawable in the
	area specified by rects.  Each rectangle is combined separately;
	overlapping areas will be rendered multiple times.  The effect is
	equivalent to compositing with a repeating source picture filled with
	the specified color.

Trapezoids

	op:		PICTOP
	src:		PICTURE
	src-x, src-y:   INT16
	dst:		PICTURE
	mask-format:	PICTFORMAT or None
	traps:		LISTofTRAPEZOID

	This request rasterizes the list of trapezoids.
	
	For each trap, the area between the left and right edges is filled
	from the top to the bottom.  src-x and src-y register the pattern to
	the floor of the top x and y coordinate of the left edge of the
	first trapezoid, they are adjusted for subsequent trapezoids so that
	the pattern remains globally aligned within the destination.

	When mask-format is not None, trapezoids are rendered in the
	following way with the effective mask computed in mask-format:

		tmp = temporary alpha picture (in mask-format)
		Combine (Zero, tmp, tmp, None)
		for each trapezoid
			Combine (Add, tmp, trapezoid, None)
		Combine (op, dst, source, tmp)

	When mask-format is None, trapezoids are rendered in the order
	specified directly to the destination:

		for each trapezoid
			Combine (op, dst, source, trapezoid)

Triangles

	op:		PICTOP
	src:		PICTURE
	src-x, src-y:   INT16
	dst:		PICTURE
	mask-format:	PICTFORMAT or None
	triangles:	LISTofTRIANGLE

	This request rasterizes the list of triangles in the order they
	occur in the list.

	When mask-format is not None, triangles are rendered in the
	following way with the effective mask computed in mask-format:

		tmp = temporary alpha picture (in mask-format)
		Combine (Zero, tmp, tmp, None)
		for each triangle
			Combine (Add, tmp, triangle, None)
		Combine (op, dst, source, tmp)

	When mask-format is None, triangles are rendered in the order
	specified directly to the destination:

		for each triangle
			Combine (op, dst, source, triangle)

TriStrip

	op:		PICTOP
	src:		PICTURE
	src-x, src-y:   INT16
	dst:		PICTURE
	mask-format:	PICTFORMAT or None
	points:		LISTofPOINTFIX

	Triangles are formed by initially using the first three points and
	then by eliminating the first point and appending the next point in
	the list. If fewer than three points are provided, this request does
	nothing.

	When mask-format is not None, triangles are rendered in the
	following way with the effective mask computed in mask-format:

		tmp = temporary alpha picture (in mask-format)
		Combine (Zero, tmp, tmp, None)
		for each triangle
			Combine (Add, tmp, triangle, None)
		Combine (op, dst, source, tmp)

	When mask-format is None, triangles are rendered in the order
	specified directly to the destination:

		for each triangle
			Combine (op, dst, source, triangle)

TriFan
	op:		PICTOP
	src:		PICTURE
	src-x, src-y:   INT16
	dst:		PICTURE
	mask-format:	PICTFORMAT or None
	points:		LISTofPOINTFIX

	Triangles are formed by initially using the first three points and
	then by eliminating the second point and appending the next point
	int the list. If fewer than three points are provided, this request
	does nothing.

	When mask-format is not None, triangles are rendered in the
	following way with the effective mask computed in mask-format:

		tmp = temporary alpha picture (in mask-format)
		Combine (Zero, tmp, tmp, None)
		for each triangle
			Combine (Add, tmp, triangle, None)
		Combine (op, dst, source, tmp)

	When mask-format is None, triangles are rendered in the order
	specified directly to the destination:

		for each triangle
			Combine (op, dst, source, triangle)

ColorTrapezoids

	op:		PICTOP
	dst:		PICTURE
	trapezoids:	LISTofCOLORTRAP

	The geometry of the trapezoids must meet the same requirements as
	for the Trapezoids request.  The trapezoids are filled in the order
	they occur in the list.

ColorTriangles

	op:		PICTOP
	dst:		PICTURE
	triangles:	LISTofCOLORTRIANGLE

	The colored triangles are rasterized in the order they occur in the
	list.

???

Should I included compressed triangle representations here?

???

CreateGlyphSet

	gsid:		GLYPHSET
	format:		PICTFORMAT

	Errors:
		Alloc, IDChoice, PictFormat, Match

	This request creates a container for glyphs.  The glyphset and
	all contained glyphs are destroyed when gsid and any other names
	for the glyphset are freed.  Format must be a Direct format, when
	it contains RGB values, the glyphs are composited using
	component-alpha True, otherwise they are composited using
	component-alpha False.

ReferenceGlyphSet

	gsid:		GLYPHSET
	existing:	GLYPHSET

	Errors:
		Alloc, IDChoice, GlyphSet

	This request creates an additional name for the existing glyphset.
	The glyphset will not be freed until all references to it are
	destroyed.

FreeGlyphSet

	glyphset:	GLYPHSET

	Errors:
		GlyphSet

	This request frees the name for the glyphset.  When all names have
	been freed, the glyphset and all contained glyphs are freed.

AddGlyphs
	glyphset:	GLYPHSET
	glyphids:	LISTofCARD32
	glyphs:		LISTofGLYPHINFO
	data:		LISTofBYTE

	Errors:
		GlyphSet, Alloc

	This request adds glyphs to glyphset.  The image for the glyphs
	are stored with each glyph in a separate Z-format image padded to a
	32-bit boundary.  Existing glyphs with the same names are replaced.

AddGlyphsFromPicture

	glyphset:	GLYPHSET
	src:		PICTURE
	glyphs:		LISTofPICTGLYPH

	Errors:
		GlyphSet, Alloc

	This request adds glyphs to glyphset by copying them from src from
	the locations included in glyphs.  Existing glyphs with the same
	names are replaced.  Src may be in a different PictFormat than
	glyphset, in which case the images are converted to the glyphset
	format.
	
FreeGlyphs

	glyphset:	GLYPHSET
	glyphs:		LISTofGLYPH

	Errors:
		GlyphSet, Match

	This request removes glyphs from glyphset.  Each glyph must exist
	in glyphset (else a Match error results).

CompositeGlyphs8
CompositeGlyphs16
CompositeGlyphs32

	op:		PICTOP
	src:		PICTURE
	dst:		PICTURE
	mask-format:	PICTFORMAT or None
	glyphset:	GLYPHABLE
	src-x, src-y:	INT16
	dst-x, dst-y:	INT16
	glyphcmds:	LISTofGLYPHITEM8	CompositeGlyphs8
	glyphcmds:	LISTofGLYPHITEM16	CompositeGlyphs16
	glyphcmds:	LISTofGLYPHITEM32	CompositeGlyphs32

	Errors:
		Picture, PictOp, PictFormat, GlyphSet, Glyph

	The dst-x and dst-y coordinates are relative to the drawable's
	origin and specify the baseline starting position (the initial glyph
	origin).  Each glyph item is processed in turn.  A glyphset item
	causes the glyhpset to be used for subsequent glyphs.  Switching
	among glyphsets does not affect the next glyph origin.  A glyph
	element delta-x and delta-y specify additional changes in the
	position along the x and y axes before the string is drawn; the
	deltas are always added to the glyph origin.

	All contained GLYPHSETs are always transmitted most significant byte
	first.  
	
	If a GlyphSet error is generated for an item, the previous items may
	have been drawn.
	
	When mask-format is not None, glyphs are rendered in the following
	way with the effective mask computed in mask-format:

		tmp = temporary alpha picture
		Combine (Zero, tmp, tmp, None)
		for each glyph
			Combine (Add, tmp, glyph, None)
		Combine (op, dst, source, tmp)

	When mask-format is None, glyphs are rendered in the order specified
	directly to the destination:

		for each glyph
			Combine (op, dst, source, glyph)

CreateCursor

	cid:		CURSOR
	source:		PICTURE
	x, y:		CARD16

	Errors:		Alloc, IDChoice, Match, Picture

	This request creates a cursor and associates identifier cid with it.
	The x and y coordinates define the hotspot relative to the source's
	origin and must be a point within the source (or a Match error
	results).  The resulting picture will nominally be drawn to the
	screen with PictOpOver. 
	
	The components of the cursor may be transformed arbitrarily to meet
	display limitations.  In particular, if the display supports only
	two colors cursors without translucency, the cursor will be
	transformed so that areas less than .5 alpha will be transparent,
	else opaque, and areas darker than 50% gray will be black else white.

	The source picture can be freed immediately if no further explicit
	references to it are to be made.

	Subsequent drawing in the source has an undefined effect on the
	cursor.  The server might or might not make a copy of the picture.

CreateAnimCursor
	cid:		CURSOR
	cursors:	LISTofANIMCURSORELT

	Errors:		Alloc, IDChoice, Cursor

	This request creates a cursor and associates identifier cid with it.
	When active, the cursor image on the screen will cycle through
	'cursors', showing each cursor in the element for the number of
	milliseconds indicated by the 'delay' member of that element.

AddTraps
	picture:	PICTURE
	off-x, off-y:	INT16
	trapezoids:	LISTofTRAP

	Errors:		Match

	Each trap is PictOpAdd'ed to 'picture'.  'off-x', 'off-y'
	are added to each coordinate.

	'picture' must be an alpha-only picture else a 'Match' error is
	returned.
	
CreateSolidFill
	pid: 		PICTURE
	color:		COLOR	

	Creates a Source picture that represents a solid fill with
	the specified color. color is assumed to be non premultiplied.

CreateLinearGradient
	pid:		PICTURE
	p1, p2:		POINTFIX
	spread:		CARD16
	nstops:		CARD16
	stops:		LISTofFIXED
	stop_colors:	LISTofCOLOR

	Errors:		Alloc, Value

	Creates a source picture representing a linear Gradient. The gradients
	bounds are defined by the two end points p1 and p2. 

	The gradient has nstops stop points between 0 and 1, each
	having a stop color defined in stop_colors.

	The array of stops has to contain values between 0 and 1 (inclusive) and
	has to be ordered in increasing size or a Value error is generated. If 
	p1 == p2 a Value error is generated.

	The colors are non premultiplied.

CreateRadialGradient
	pid:		PICTURE
	inner_center:	POINTFIX
	outer_center:	POINTFIX
	inner_radius:	FIXED
	outer_radius:	FIXED
	spread:		CARD16
	nstops:		CARD16
	stops:		LISTofFIXED
	stop_colors:	LISTofCOLOR

	Errors:		Alloc, Value

	Creates a source picture representing a linear Gradient. The
	gradients bounds are defined by a center point, a focal point and a
	radius around the center.

	The gradient has nstops stop points between 0 and 1, each
	having a stop color defined in stop_colors.

	The array of stops has to contain values between 0 and 1 (inclusive) and
	has to be ordered in increasing size or a Value error is generated. The inner
	circle has to be completely contained inside the outer one or a Value error is 
	generated. 

	The colors are non premultiplied.

CreateConicalGradient
	pid:		PICTURE
	center:		POINTFIX
	angle:		FIXED
	spread:		CARD16
	nstops:		CARD16
	stops:		LISTofFIXED
	stop_colors:	LISTofCOLOR

	Errors:		Alloc, Value

	Creates a source picture representing a conical Gradient. The
	gradient is defined by a center point and an angle (in degrees).

	The gradient has nstops stop points between 0 and 1, each
	having a stop color defined in stop_colors.

	The array of stops has to contain values between 0 and 1 (inclusive) and
	has to be ordered in increasing size or a Value error is generated.

	The colors are non premultiplied.

	
15. Extension Versioning

The Render extension was developed in parallel with the implementation to
ensure the feasibility of various portions of the design.  As portions of
the extension are implemented, the version number of the extension has
changed to reflect the portions of the standard provied.  This document
describes the intent for version 1.0 of the specification, the partial
implementations have version numbers less than that.  Here's a list of
what each version before 1.0 implemented:

	0.0:	
		No disjoint/conjoint operators
		No component alpha
		Composite
		CreateGlyphSet
		FreeGlyphSet
		AddGlyphs
		CompositeGlyphs

	0.1:
		Component alpha
		FillRectangles

	0.2:
		Disjoint/Conjoint operators

	0.3:
		FreeGlyphs

	0.4:
		Trapezoids
		Triangles
		TriStrip
		TriFan

	0.5:
		CreateCursor

	0.6:
		SetPictureTransform
		QueryFilters
		SetPictureFilter
		subpixels member of QueryPictFormats

	0.7:
		QueryPictIndexValues
	0.8:
		CreateAnimCursor
	0.9:
		AddTrapezoids

	0.10:	
		CreateSolidFill
		CreateLinearGradient
		CreateRadialGradient
		CreateConicalGradient

		The repeat picture attribute now supports Pad and
		Reflect, older versions only supported None and Normal.