Resolve symbols in pattern values to Fontconfig constants

README.md

@@ -6,13 +6,13 @@ The actor responds to observations of font properties by asserting what it deter
 
 The assertion format is `<fontconfig {pattern…} {attributes…}>` (see [protocol.prs](./protocol.prs)). The `pattern` field is a dictionary of properties to match fonts against and the `attributes` field is a dictionary of the properties of a font selected by Fontconfig. An application observes a `pattern` and takes the `file` and `index` fields of a corresponding assertion and reads font data from the file-system. In the case that `pattern` does not match any fonts an assertion will still be made, so it is possible that all of the properties in `pattern` will be contradicted in `attributes`.
 
-For a list of possibly supported properties see the [Fontconfig documentation](https://www.freedesktop.org/software/fontconfig/fontconfig-devel/x19.html).
+For a list of possibly supported properties see the [Fontconfig documentation](https://www.freedesktop.org/software/fontconfig/fontconfig-devel/x19.html). When the value of a property is a Preserves symbol (rather than a string in double-quotes) it will be resolved to a Fontconfig constant if possible. Constants are not resolved from integers to symbols in the `attributes` field. For example, `{slant: oblique}` is transformed to `{slant: 110}` from `pattern` to `attributes`.
 
 Example [Syndicate server](https://git.syndicate-lang.org/syndicate-lang/syndicate-rs) configuration:
 ```
 <require-service <daemon fontconfig_actor>>
 <daemon fontconfig_actor {
-  argv: [ "/home/emery/src/bin/fontconfig_actor" ]
+  argv: [ "/usr/local/bin/fontconfig_actor" ]
   protocol: application/syndicate
 }>
 
@@ -24,8 +24,8 @@ let ?fontspace = dataspace
 ]
 
 $fontspace [
-  ? <fontconfig {family: "Gentium Book Plus"} ?attributes> [
-    $log ! <log "-" { line: <fontconfig $attributes> }>
+  ? <fontconfig {size: 8.0, spacing: proportional} ?properties> [
+    $log ! <log "-" { line: <fontconfig $properties> }>
   ]
 ]
 ```

src/fontconfig_actor.nim

@@ -1,7 +1,7 @@
 # SPDX-FileCopyrightText: ☭ Emery Hemingway
 # SPDX-License-Identifier: Unlicense
 
-import std/[asyncdispatch, options, os, strutils, tables]
+import std/[asyncdispatch, options, os, tables]
 import preserves, syndicate, syndicate/[patterns]
 import ./protocol
 
@@ -47,6 +47,9 @@ type
 
   FcConfig = distinct pointer
 
+  FcConstant {.importc.} = ptr object
+    value: cint
+
 const
   (FcFalse, FcTrue) = (cint 0, cint 1)
 
@@ -61,7 +64,7 @@ proc PatternAddDouble(p: FcPattern; obj: cstring; d: cdouble): FcBool {.importFc
 proc PatternAddString(p: FcPattern; obj: cstring; s: cstring): FcBool {.importFc.}
 proc PatternAddBool(p: FcPattern; obj: cstring; b: bool): FcBool {.importFc.}
 proc DefaultSubstitute(p: FcPattern) {.importFc.}
-proc PatternPrint(p: FcPattern) {.importFc.}
+# proc PatternPrint(p: FcPattern) {.importFc.}
 
 proc FontMatch(cfg: FcConfig; p: FcPattern; r: var FcResult): FcPattern {.importFc.}
 
@@ -72,6 +75,10 @@ proc PatternIterIsValid(p: FcPattern; iter: ptr FcPatternIter): FcBool {.importF
 proc PatternIterGetObject(p: FcPattern; iter: ptr FcPatternIter): cstring {.importFc.}
 proc PatternIterGetValue(p: FcPattern; iter: ptr FcPatternIter; id: cint; v: ptr FcValue; b: pointer): FcResult {.importFc.}
 
+# proc NameGetConstantFor(str: ptr FcChar8; obj: cstring): FcConstant {.importFc.}
+proc NameGetConstant(str: cstring): FcConstant {.importFc,
+  deprecated: "update to Fontconfig 2.14.2 API and use NameGetConstantFor".}
+
 proc getValue(pat: FcPattern; iter: ptr FcPatternIter; i: cint):  Option[Preserve[void]] =
   var fcVal: FcValue
   if PatternIterGetValue(pat, iter, i, addr fcVal, nil) == FcResultMatch:
@@ -118,17 +125,23 @@ proc fillPattern(properties: Properties): FcPattern =
       of pkSignedInteger: PatternAddInteger(result, key, cint val.int)
       of pkString:
         PatternAddString(result, key, val.string)
+      of pkSymbol:
+        let constant = NameGetConstant(val.symbol.cstring)
+        if not constant.isNil: PatternAddInteger(result, key, constant.value)
+        else:
+          logError("invalid constant: ", val)
+          FcFalse
       else:
         logError("invalid property: ", val)
         FcFalse
     if recognized == FcFalse:
-      logError("unrecognized property: ", key.escape)
+      logError("unrecognized property {", key, ": ", val, "}")
   DefaultSubstitute(result)
 
 template withFontconfig(body: untyped): untyped =
   ## Initialize and deinitialize the Fontconfig library for the scope of `body`.
   if Init() == FcFalse:
-    quit"Failed to initialize FontConfig"
+    logError "Failed to initialize FontConfig"
   else:
     body
   Fini()