Return each X11 monitor so games can choose where to open

.github/workflows/build.yml

@@ -35,6 +35,17 @@ jobs:
     - run: nim r -d:useCpu tests/test_cpu_pixels.nim
       if: matrix.os == 'windows-latest'
 
+    - name: Check two X11 monitors
+      if: matrix.os == 'ubuntu-latest'
+      run: |
+        sudo apt-get update -qq
+        sudo apt-get install -y x11-xserver-utils
+        xvfb-run -a -s "-noreset -screen 0 1600x600x24" sh -ec '
+          xrandr --setmonitor LEFT 800/200x600/150+0+0 screen
+          xrandr --setmonitor RIGHT 800/200x600/150+800+0 none
+          nim r --parallelBuild:1 tests/test_screens.nim
+        '
+
     # Build native examples.
     - run: nim c examples/basic.nim
     - run: nim c examples/basic_boxy.nim

examples/screens.nim

@@ -1,8 +1,4 @@
 import windy
 
-when defined(windows) or defined(macosx):
-  # Screens API only currently supported on Windows and macOS
-
-  let screens = getScreens()
-  for screen in screens:
-    echo screen
+for screen in getScreens():
+  echo screen

src/windy/platforms/linux/x11.nim

@@ -2,7 +2,7 @@ import
   std/[os, osproc, sequtils, sets, strformat, strutils, times, unicode, uri, pathnorm],
   ../../[common, internal],
   vmath, pixie,
-  x11/[glx, keysym, x, xevent, xlib, xcursor]
+  x11/[glx, keysym, x, xevent, xlib, xcursor, xrandr]
 
 import ../../http
 export http
@@ -625,6 +625,27 @@ proc `title=`*(window: Window, v: string) =
   window.handle.setProperty(xaNetWMIconName, xaUTF8String, 8, v)
   display.Xutf8SetWMProperties(window.handle, v, v, nil, 0, nil, nil, nil)
 
+proc getScreens*(): seq[common.Screen] =
+  ## Returns active X11 monitors and their desktop positions (RandR 1.5).
+  init()
+  var major, minor, count: cint
+  if display.XRRQueryVersion(major.addr, minor.addr) == 0 or
+      (major == 1 and minor < 5) or major < 1:
+    raise WindyError.newException("Screen enumeration requires RandR 1.5")
+  let monitors = display.XRRGetMonitors(display.defaultRootWindow, 1, count.addr)
+  if monitors == nil:
+    return
+  defer: XRRFreeMonitors(monitors)
+  for i in 0 ..< count:
+    let monitor = monitors[i]
+    result.add common.Screen(
+      left: monitor.x,
+      top: monitor.y,
+      right: monitor.x + monitor.width,
+      bottom: monitor.y + monitor.height,
+      primary: monitor.primary != 0
+    )
+
 proc contentScale*(window: Window): float32 =
   const defaultScreenDpi = 96.0
 

src/windy/platforms/linux/x11/xrandr.nim

@@ -0,0 +1,15 @@
+import x, xlib
+
+type
+  XRRMonitorInfo* {.bycopy.} = object
+    name*: Atom
+    primary*, automatic*, noutput*: cint
+    x*, y*, width*, height*, mwidth*, mheight*: cint
+    outputs*: ptr culong
+
+{.push cdecl, dynlib: "libXrandr.so.2", importc.}
+proc XRRQueryVersion*(display: Display, major, minor: ptr cint): cint
+proc XRRGetMonitors*(display: Display, window: Window, active: cint,
+    count: ptr cint): ptr UncheckedArray[XRRMonitorInfo]
+proc XRRFreeMonitors*(monitors: ptr UncheckedArray[XRRMonitorInfo])
+{.pop.}

tests/test_screens.nim

@@ -0,0 +1,10 @@
+## Run on the two-monitor Xvfb layout configured by the build workflow.
+import windy, std/algorithm
+var screens = getScreens()
+screens.sort(proc(a, b: Screen): int = cmp(a.left, b.left))
+doAssert screens.len == 2, "each monitor must be returned separately"
+doAssert screens[0].left == 0 and screens[0].right == 800
+doAssert screens[1].left == 800 and screens[1].right == 1600
+for screen in screens:
+  doAssert screen.top == 0 and screen.bottom == 600
+echo "Two distinct X11 monitor bounds passed"