src/core/packages/capture.sgl

1;;; Screen capture.

2;;;

3;;; grim is a Wayland screenshot client. It is in this channel for two

4;;; reasons, and the second is the one worth reading.

5;;;

6;;; 1. IT IS A SECOND WAYLAND CLIENT. Everything else in the Wayland half of

7;;; this channel exists to serve foot, which makes it hard to tell whether

8;;; `wayland`, `pixman` and `wayland-protocols` are packaged correctly or

9;;; merely packaged the way foot happens to need. A second, unrelated

10;;; consumer answers that.

11;;;

12;;; 2. IT MAKES A DIFFERENTIAL TEST POSSIBLE -- AND IT MUST NOT BE MISTAKEN

13;;; FOR AN INSTRUMENT. foot's acceptance evidence is a screenshot of a

14;;; nested compositor, and that screenshot is deliberately taken with the

15;;; HOST's grim, not this one. The observer has to be independent of the

16;;; observed: a grim built from the SAME pixman and the SAME wayland-client

17;;; as foot could be wrong in a correlated way, agree with foot, and produce

18;;; a convincing green. What this package is good for is the other

19;;; direction -- run both grims on the same frame and compare. Agreement is

20;;; then evidence that the channel's Wayland and pixman stack behaves like

21;;; the host's, which is a measurement rather than a caveat.

22;;;

23;;; grim vendors the `wlr-screencopy` protocol XML it needs under `protocol/`,

24;;; so it does not drag wlroots into this channel.

25(define-library (core packages capture)

26 (import (sigil core)

27 (core build-environments)

28 (core packages compression)

29 (core packages graphics)

30 (core packages wayland)

31 (core packages ffi)

32 (core packages build-tools)

33 (core packages python)

34 (sigil env package)

35 (sigil build external))

36 (export grim)

37 (begin

38 (define grim

39 (package

40 name: "grim"

41 version: "1.4.0"

42 source: (external-source

43 location: "https://github.com/emersion/grim/releases/download/v1.4.0/grim-1.4.0.tar.gz"

44 sha256: "b6786e889ed93568634189a59f6b6429c041bf74883c10e8b6e2ed6772ae7ffb")

45 buildenv: core-buildenv

46 ;; zlib is reached through libpng.pc's `Requires:` chain -- see the

47 ;; note on `fontconfig` in (core packages fonts) for why a

48 ;; grand-dependency has to be named here.

49 dependencies: (list libpng pixman wayland wayland-protocols libffi zlib)

50 ;; WAYLAND IS A DEPENDENCY ONLY, AND THE SCANNER IS POINTED AT

51 ;; EXPLICITLY. The obvious move -- naming `wayland` in BOTH

52 ;; `dependencies:` and `build-inputs:`, since grim needs the library

53 ;; linked and the `wayland-scanner` program run -- IS REFUSED:

54 ;;

55 ;; package: duplicate input name: wayland

56 ;;

57 ;; and there is no way round it by declaration. Only build inputs put

58 ;; a `bin/` on PATH, and a dependency cannot export one either, because

59 ;; `PATH` is builder-owned and a `search-paths:` export naming it is

60 ;; refused as well.

61 ;;

62 ;; foot does not hit this: it reads the scanner's absolute path out of

63 ;; pkg-config (`wscanner.get_variable('wayland_scanner')`). grim's

64 ;; `protocol/meson.build:3` does a plain

65 ;; `find_program('wayland-scanner')`, which searches PATH:

66 ;;

67 ;; Run-time dependency wayland-client found: YES 1.24.0

68 ;; Program wayland-scanner found: NO

69 ;;

70 ;; The library is found and the program is not, from the same package,

71 ;; one line apart.

72 ;;

73 ;; The answer is meson's own mechanism for exactly this -- a native

74 ;; file naming the binary -- fed from `${wayland}`, which interpolates

75 ;; because wayland IS a declared dependency. No patch to grim, no

76 ;; second declaration, and the path is derived from the closure rather

77 ;; than searched for.

78 build-inputs: (list meson samurai python)

79 phases: (list

80 (external-phase

81 kind: 'run

82 args: (list "sh" "-c"

83 (string-append

84 "set -eu\n"

85 "cat > native.ini <<'NF'\n"

86 "[binaries]\n"

87 "wayland-scanner = '${wayland}/bin/wayland-scanner'\n"

88 "NF\n"

89 "meson setup build --native-file native.ini"

90 " --prefix=${out}"

91 " --buildtype=plain"

92 " --default-library=static"

93 ;; `-Dprefer_static=true` MAKES MESON ASK

94 ;; PKG-CONFIG THE STATIC QUESTION, and without it

95 ;; a fully static link fails at the last step.

96 ;;

97 ;; A `.pc` file splits its link line: `Libs:` is

98 ;; what a SHARED consumer needs, `Libs.private:`

99 ;; and `Requires.private:` are the extra

100 ;; transitive libraries a STATIC consumer needs.

101 ;; fontconfig lists expat under

102 ;; `Requires.private:`, so a default

103 ;; `dependency('fontconfig')` emits no `-lexpat`

104 ;; -- correct for a shared link, fatal here:

105 ;;

106 ;; ld.lld: error: undefined symbol: XML_ErrorString

107 ;; >>> referenced by fcxml.c

108 ;; >>> fcxml.o in archive libfontconfig.a

109 ;;

110 ;; The symbol is missing from the LINK, not from

111 ;; the closure: expat is declared, built, and

112 ;; present. Only the query was the wrong one.

113 ;; This is the same `Requires.private:` line that

114 ;; had to be satisfied at CONFIGURE time; it bites

115 ;; twice, in two different ways, and fixing the

116 ;; first does not fix the second.

117 " -Dprefer_static=true"

118 ;; JPEG output would add libjpeg for a format

119 ;; nothing here reads.

120 ;; UPSTREAM'S WARNINGS-AS-ERRORS IS TURNED OFF,

121 ;; and this is a compiler-set difference rather

122 ;; than a defect in grim. grim's meson sets

123 ;; `werror=true`, and this toolchain's clang

124 ;; warns where the author's compiler did not:

125 ;;

126 ;; ../write_ppm.c:32:23: error: unused variable

127 ;; 'format' [-Werror,-Wunused-variable]

128 ;;

129 ;; The variable really is unused, in a PPM writer

130 ;; nothing in this channel calls. Distributions

131 ;; disable `werror` for exactly this reason: a

132 ;; project's warning policy is calibrated to the

133 ;; compilers its authors use, and turning a

134 ;; foreign compiler's extra warnings into build

135 ;; failures makes the package unbuildable for

136 ;; reasons unrelated to correctness.

137 ;;

138 ;; NOTE THAT FOOT DOES NOT NEED THIS. foot also

139 ;; sets `werror=true` and compiles clean under

140 ;; the same clang, so this is not a blanket

141 ;; concession -- it is one package's warning.

142 " -Dwerror=false"

143 " -Djpeg=disabled"

144 ;; man pages want scdoc.

145 " -Dman-pages=disabled\n"

146 "echo GRIM-CONFIGURED\n")))

147 (external-phase

148 kind: 'run

149 args: (list "sh" "-c"

150 (string-append

151 "set -eu\n"

152 "meson compile -C build\n"

153 "echo GRIM-COMPILED\n")))

154 (external-phase

155 kind: 'run

156 args: (list "sh" "-c"

157 (string-append

158 "set -eu\n"

159 "d=\"$(dirname \"$PWD\")/install-root\"\n"

160 "DESTDIR=\"$d\" meson install -C build --no-rebuild\n"

161 "test -x \"$d${out}/bin/grim\"\n"

162 "echo GRIM-INSTALLED\n"))))))))