Xlib â C Language X Interface

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<strong>Xlib</strong> − C LibraryX11, Release 6.7 DRAFTchar dashes;}XGCValues;The default GC values are:ComponentDefaultfunctionGXcopyplane_mask All onesforeground 0background 1line_width 0line_styleLineSolidcap_styleCapButtjoin_styleJoinMiterfill_styleFillSolidfill_ruleEvenOddRulearc_modeArcPieSlicetilePixmap of unspecified size filled with foreground pixel(that is, client specified pixel if any, else 0)(subsequent changes to foreground do not affect this pixmap)stipplePixmap of unspecified size filled with onests_x_origin 0ts_y_origin 0fontsubwindow_mode ClipByChildrengraphics_exposures Trueclip_x_origin 0clip_y_origin 0clip_maskNonedash_offset 0dashes 4 (that is, the list [4, 4])Note that foreground and background are not set to any values likely to be useful in a window.The function attributes of a GC are used when you update a section of a drawable (the destination)with bits from somewhere else (the source). The function in a GC defines how the new destinationbits are to be computed from the source bits and the old destination bits. GXcopy is typicallythe most useful because it will work on a color display, but special applications may useother functions, particularly in concert with particular planes of a color display. The 16 GC functions,defined in , are:Function Name Value OperationGXclear 0x0 0GXand 0x1 src AND dstGXandReverse 0x2 src AND NOT dstGXcopy 0x3 src129
<strong>Xlib</strong> − C LibraryX11, Release 6.7 DRAFTFunction Name Value OperationGXandInverted 0x4 (NOT src) AND dstGXnoop 0x5 dstGXxor 0x6 src XOR dstGXor 0x7 src OR dstGXnor 0x8 (NOT src) AND (NOT dst)GXequiv 0x9 (NOT src) XOR dstGXinvert 0xa NOT dstGXorReverse 0xb src OR (NOT dst)GXcopyInverted 0xc NOT srcGXorInverted 0xd (NOT src) OR dstGXnand 0xe (NOT src) OR (NOT dst)GXset 0xf 1Many graphics operations depend on either pixel values or planes in a GC. The planes attribute isof type long, and it specifies which planes of the destination are to be modified, one bit per plane.Amonochrome display has only one plane and will be the least significant bit of the word. Asplanes are added to the display hardware, they will occupy more significant bits in the planemask.In graphics operations, given asource and destination pixel, the result is computed bitwise on correspondingbits of the pixels. That is, a Boolean operation is performed in each bit plane. Theplane_mask restricts the operation to a subset of planes. Amacro constant AllPlanes can be usedto refer to all planes of the screen simultaneously. The result is computed by the following:((src FUNC dst) AND plane-mask) OR (dst AND (NOT plane-mask))Range checking is not performed on the values for foreground, background, or plane_mask. Theyare simply truncated to the appropriate number of bits. The line-width is measured in pixels andeither can be greater than or equal to one (wide line) or can be the special value zero (thin line).Wide lines are drawn centered on the path described by the graphics request. Unless otherwisespecified by the join-style or cap-style, the bounding box of a wide line with endpoints [x1, y1],[x2, y2] and width w is a rectangle with vertices at the following real coordinates:[x1-(w*sn/2), y1+(w*cs/2)], [x1+(w*sn/2), y1-(w*cs/2)],[x2-(w*sn/2), y2+(w*cs/2)], [x2+(w*sn/2), y2-(w*cs/2)]Here sn is the sine of the angle of the line, and cs is the cosine of the angle of the line. Apixel ispart of the line and so is drawn if the center of the pixel is fully inside the bounding box (which isviewed as having infinitely thin edges). If the center of the pixel is exactly on the bounding box,it is part of the line if and only if the interior is immediately to its right (x increasing direction).Pixels with centers on a horizontal edge are a special case and are part of the line if and only ifthe interior or the boundary is immediately below (yincreasing direction) and the interior or theboundary is immediately to the right (x increasing direction).Thin lines (zero line-width) are one-pixel-wide lines drawn using an unspecified, device-dependentalgorithm. There are only two constraints on this algorithm.1. If aline is drawn unclipped from [x1,y1] to [x2,y2] and if another line is drawn unclippedfrom [x1+dx,y1+dy] to [x2+dx,y2+dy], a point [x,y] is touched by drawing the first line ifand only if the point [x+dx,y+dy] is touched by drawing the second line.130
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AcknowledgmentsThe design and imple
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Release 6Stephen Gildea (X Consorti
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Xlib − C LibraryX11, Release 6.7
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4.2. Translating Screen Coordinates
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10.7. Input Focus Events . . . . .
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13.5.6.1. Input Style . . . . . . .
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