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The X Rendering Extension Version 0.11 2009-07-15 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 tessellation 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, Multiply, Screen, Overlay, Darken, Lighten, ColorDodge, ColorBurn, HardLight, SoftLight, Difference, Exclusion, HSLHue, HSLSaturation, HSLColor, HSLLuminosity } 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) 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 four options for pixel values which fall outside the drawable (this includes pixels within a window geometry obscured by other windows). + None. Missing values are replaced with transparent. + Pad. Replace missing pixels with the nearest available pixel. Where multiple pixels are equidistant, select those with smallest Y and then smallest X coordinates + Normal. 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. * Reflect. Select the pixel which would appear were the drawable tiled to enclose the missing coordinate in such a way that tiles in even numbered columns are reflected in the Y axis, and tiles in even numbered rows are reflected in the X axis. Tiles that in both an even numbered row and an even numbered column are reflected in both axes. To construct the source and mask operands, the computed pixels values are transformed through a homogeneous matrix, filtered and then used in the fundamental 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 invariant. 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 -> formats: LISTofPICTFORMINFO screens: LISTofPICTSCREEN ndepths: CARD32 nvisuals: CARD32 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 total number of PICTDEPTH and PICTVISUAL objects is this reply is given in 'ndepths' and 'nvisuals'. 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 This request gets the names of available filters that can be used on the given drawable. Filters are applied using a SetPictureFilter request. 'aliases' contains a value for each filter name which is the index into 'filters' if this name is an alias. Non-aliased filter have this value set to 0xFFFF. 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, Repeat indicates how the drawable contents should be extended 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 and clip mask 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). If the alpha-map picture itself already has an alpha-map, the result is undefined. 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 the picture. 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. Transformations, filters and repeat modes do not affect the clip mask. When a window is used as a destination, the subwindow_mode determines what happens to pixels obscured by inferior windows. For ClipByChildren the window is clipped by inferiors and siblings. For IncludeInferior, the window is clipped by siblings, but not by inferiors. When a window is used as source or mask, the subwindow_mode is ignored. Pixels that are obscured by other windows, whether siblings or inferiors, have undefined contents. The graphics-exposures flag is ignored. GraphicsExposure events are never generated by this extension. Poly-edge and poly-mode control the rasterization of polygons as described above. Dither is ignored. 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 None clip-x-origin 0 clip-y-origin 0 clip-mask None subwindow-mode ClipByChildren poly-edge Smooth poly-mode Precise 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 picture after transformations and repeats have been applied. The rectangle coordinates are interpreted relative to the clip origin. 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. 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) (The Trapezoids request is deprecated) 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) 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. 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 glyphcmds: LISTofGLYPHITEM8 CompositeGlyphs8 glyphcmds: LISTofGLYPHITEM16 CompositeGlyphs16 glyphcmds: LISTofGLYPHITEM32 CompositeGlyphs32 Errors: Picture, PictOp, PictFormat, GlyphSet, Glyph The src-x and src-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 glyphset 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. CreateLinearGradient pid: PICTURE p1, p2: POINTFIX nstops: CARD32 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 nstops: CARD32 stops: LISTofFIXED stop_colors: LISTofCOLOR Errors: Alloc, Value Creates a source picture representing a radial 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 nstops: CARD32 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 provided. 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. 0.11: Blend mode operators
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