X11 app in Kotln/Native

main.kt

package com.github.kropp

import kotlinx.cinterop.*
import x11.*

const val APPLICATION_NAME = "spotlight"
const val SIZE = 800


@ExperimentalUnsignedTypes
data class Size(val width: UInt, val height: UInt) {
    companion object {
        val EMPTY = Size(0u, 0u)
    }
}

@ExperimentalUnsignedTypes
fun screenSize(display: CPointer<Display>): Size {
    val screen = XDefaultScreenOfDisplay(display) ?: return Size.EMPTY
    val screenWidth = screen.pointed.width.toUInt()
    val screenHeight = screen.pointed.height.toUInt()
    XFree(screen)
    return Size(screenWidth, screenHeight)
}

@kotlin.ExperimentalUnsignedTypes
fun main() {
    val display = XOpenDisplay(null) ?: error("Can't open display")
    val screenNumber = XDefaultScreen(display)

    val screen = screenSize(display)

    val window = memScoped {
        val visualInfo = alloc<XVisualInfo>()
        XMatchVisualInfo(display, screenNumber, 32, TrueColor, visualInfo.ptr)

        val attrs = alloc<XSetWindowAttributes> {
            override_redirect = 1
            colormap = XCreateColormap(display, XDefaultRootWindow(display), visualInfo.visual, AllocNone)
            border_pixel = 0UL
            background_pixel = 0xffffffUL
        }.ptr
        XCreateWindow(display, XRootWindow(display, screenNumber), 0, 0, screen.width, screen.height, 0, visualInfo.depth, CopyFromParent.toUInt(),
            visualInfo.visual, (CWColormap or CWBorderPixel or CWBackPixel or CWOverrideRedirect).toULong(), attrs)
    }

    XStoreName(display, window, APPLICATION_NAME)

    XMapWindow(display, window)
    XRaiseWindow(display, window)
    XFlush(display)

    val mouse = MousePointer(display, window)

    memScoped {
        val hint = alloc<XClassHint> {
            res_name = APPLICATION_NAME.cstr.ptr
            res_class = APPLICATION_NAME.cstr.ptr
        }
        XSetClassHint(display, window, hint.ptr)
    }

    val gc = memScoped {
        val values = alloc<XGCValues> { graphics_exposures = False }.ptr
        XCreateGC(display, window, 0UL, values)
    }

    memScoped {
        // Keep the window on top
        val e = alloc<XEvent> {
            xclient.apply {
                type = ClientMessage
                message_type = XInternAtom(display, "_NET_WM_STATE", False)
                this.display = display
                this.window = window
                format = 32
                serial = 0UL
                data.l[0] = 1
                data.l[1] = XInternAtom(display, "_NET_WM_STATE_STAYS_ON_TOP", False).toLong()
            }
        }
        XSendEvent(display, XRootWindow(display, screenNumber), False, SubstructureRedirectMask, e.ptr)

        XSetForeground(display, gc, 0x55000000UL)
        XFillRectangle(display, window, gc, 0, 0, screen.width, screen.height)
        XFlush(display)

        XSelectInput(display, window, PointerMotionMask or ButtonPressMask or ButtonReleaseMask or KeyPressMask or KeyReleaseMask)

        val event = alloc<XEvent>()

        mouse.hide()
        while (true) {
            XNextEvent(display, event.ptr)

            XSetForeground(display, gc, 0xdd000000UL)
            XFillRectangle(display, window, gc, 0, 0, screen.width, screen.height)
            if (event.type == MotionNotify) {
                XSetForeground(display, gc, 0x00000000UL)
                XFillArc(display, window, gc, event.xmotion.x - SIZE / 2, event.xmotion.y - SIZE / 2, SIZE.toUInt(), SIZE.toUInt(), 0, 360 * 64)
                XFlush(display)
            }
        }
    }
}

@kotlin.ExperimentalUnsignedTypes
class MousePointer(private val display: CPointer<Display>, private val window: Window) {
    fun hide() = memScoped {
        val bitmap = XCreateBitmapFromData(display, window, ByteArray(8) { 0 }.toCValues(), 8, 8)

        val black = alloc<XColor> {
            red = 0U
            green = 0U
            blue = 0U
        }
        val cursor = XCreatePixmapCursor(display, bitmap, bitmap, black.ptr, black.ptr, 0, 0)

        XDefineCursor(display, window, cursor)

        XFreeCursor(display, cursor)
        XFreePixmap(display, bitmap)
    }

    fun show() {
        XUndefineCursor(display, window)
    }
}

x11.def

package = x11
headers = X11/Xlib.h X11/Xutil.h X11/Xatom.h
headerFilter = X11/*
compilerOpts = -I/usr/include/ -I/usr/include/x86_64-linux-gnu
linkerOpts = -lX11 -L/usr/lib/x86_64-linux-gnu/
noStringConversion = XCreateBitmapFromData