dotnet X11 多次呼叫 XPutImage 是否能做到渲染同步

lindexi發表於2024-08-24

本文將告訴大家我在麒麟系統和統信系統以及分別搭配飛騰和兆芯處理器的裝置上，使用連續的 XPutImage 方法推送介面，測試是否能夠在一次渲染內完成。測試結論是不能做到渲染同步

本文的核心測試程式碼如下

        XPutImage(display, handle, gc, ref xImage, @event.ExposeEvent.x, @event.ExposeEvent.y, @event.ExposeEvent.x, @event.ExposeEvent.y, (uint) @event.ExposeEvent.width,
            (uint) @event.ExposeEvent.height);

        XPutImage(display, handle, gc, ref halfImage, 0, 0, halfWidth, 0, (uint) halfWidth,
            (uint) height);

即連續呼叫兩次 XPutImage 方法，其中最後一次的 XPutImage 方法是讓右半邊覆蓋掉。如果渲染能對齊同步的話，預期右半邊是不會出現閃爍問題，即不會出現先在螢幕顯示首個 XPutImage 繪製的全視窗圖片，再顯示回最後一次的 XPutImage 覆蓋的畫面

然而經過實際測試，視窗顯示的內容將會閃爍，即連續兩次 XPutImage 不能做到渲染同步，這也符合閱讀 XLib 和 XServer 和 KWin 的程式碼瞭解的行為

全部的測試程式碼如下

using CPF.Linux;

using SkiaSharp;

using static CPF.Linux.XLib;

XInitThreads();
var display = XOpenDisplay(IntPtr.Zero);
var screen = XDefaultScreen(display);
var rootWindow = XDefaultRootWindow(display);

XMatchVisualInfo(display, screen, 32, 4, out var info);
var visual = info.visual;

var valueMask =
        //SetWindowValuemask.BackPixmap
        0
        | SetWindowValuemask.BackPixel
        | SetWindowValuemask.BorderPixel
        | SetWindowValuemask.BitGravity
        | SetWindowValuemask.WinGravity
        | SetWindowValuemask.BackingStore
        | SetWindowValuemask.ColorMap
    //| SetWindowValuemask.OverrideRedirect
    ;
var xSetWindowAttributes = new XSetWindowAttributes
{
    backing_store = 1,
    bit_gravity = Gravity.NorthWestGravity,
    win_gravity = Gravity.NorthWestGravity,
    //override_redirect = true, // 設定視窗的override_redirect屬性為True，以避免視窗管理器的干預
    colormap = XCreateColormap(display, rootWindow, visual, 0),
    border_pixel = 0,
    background_pixel = 0,
};

var xDisplayWidth = XDisplayWidth(display, screen);
var xDisplayHeight = XDisplayHeight(display, screen);

var width = xDisplayWidth;
var height = xDisplayHeight;

var handle = XCreateWindow(display, rootWindow, 0, 0, width, height, 5,
    32,
    (int) CreateWindowArgs.InputOutput,
    visual,
    (nuint) valueMask, ref xSetWindowAttributes);

XEventMask ignoredMask = XEventMask.SubstructureRedirectMask | XEventMask.ResizeRedirectMask |
                         XEventMask.PointerMotionHintMask;
var mask = new IntPtr(0xffffff ^ (int) ignoredMask);
XSelectInput(display, handle, mask);

XMapWindow(display, handle);
XFlush(display);

var gc = XCreateGC(display, handle, 0, 0);
var skBitmap = new SKBitmap(width, height, SKColorType.Bgra8888, SKAlphaType.Premul);
var skCanvas = new SKCanvas(skBitmap);
var xImage = CreateImage(skBitmap);

skCanvas.Clear(SKColors.Blue);
skCanvas.Flush();

var halfWidth = width / 2;
var halfSkBitmap = new SKBitmap(halfWidth, height, SKColorType.Bgra8888, SKAlphaType.Premul);
var halfSkCanvas = new SKCanvas(halfSkBitmap);
halfSkCanvas.Clear();
halfSkCanvas.Flush();
var halfImage = CreateImage(halfSkBitmap);

_ = Task.Run(() =>
{
    var newDisplay = XOpenDisplay(IntPtr.Zero);

    while (true)
    {
        Console.ReadLine();

        var xEvent = new XEvent
        {
            ExposeEvent =
            {
                type = XEventName.Expose,
                send_event = true,
                window = handle,
                count = 1,
                display = newDisplay,
                x = 0,
                y = 0,
                width = width,
                height = height,
            }
        };
        // [Xlib Programming Manual: Expose Events](https://tronche.com/gui/x/xlib/events/exposure/expose.html )
        XLib.XSendEvent(newDisplay, handle, propagate: false,
            new IntPtr((int) (EventMask.ExposureMask)),
            ref xEvent);
        
        XFlush(newDisplay);
    }

    XCloseDisplay(newDisplay);
});

while (true)
{
    var xNextEvent = XNextEvent(display, out var @event);

    if (xNextEvent != 0)
    {
        break;
    }

    if (@event.type == XEventName.Expose)
    {
        skCanvas.Clear(new SKColor((uint)Random.Shared.Next()).WithAlpha(0xFF));
        skCanvas.Flush();

        XPutImage(display, handle, gc, ref xImage, @event.ExposeEvent.x, @event.ExposeEvent.y, @event.ExposeEvent.x, @event.ExposeEvent.y, (uint) @event.ExposeEvent.width,
            (uint) @event.ExposeEvent.height);

        XPutImage(display, handle, gc, ref halfImage, 0, 0, halfWidth, 0, (uint) halfWidth,
            (uint) height);
        XFlush(display);
    }
}

static XImage CreateImage(SKBitmap skBitmap)
{
    const int bytePerPixelCount = 4; // RGBA 一共4個 byte 長度
    var bitPerByte = 8;

    var bitmapWidth = skBitmap.Width;
    var bitmapHeight = skBitmap.Height;

    var img = new XImage();
    int bitsPerPixel = bytePerPixelCount * bitPerByte;
    img.width = bitmapWidth;
    img.height = bitmapHeight;
    img.format = 2; //ZPixmap;
    img.data = skBitmap.GetPixels();
    img.byte_order = 0; // LSBFirst;
    img.bitmap_unit = bitsPerPixel;
    img.bitmap_bit_order = 0; // LSBFirst;
    img.bitmap_pad = bitsPerPixel;
    img.depth = bitsPerPixel;
    img.bytes_per_line = bitmapWidth * bytePerPixelCount;
    img.bits_per_pixel = bitsPerPixel;
    XInitImage(ref img);

    return img;
}

本文程式碼放在 github 和 gitee 上，可以使用如下命令列拉取程式碼。我整個程式碼倉庫比較龐大，使用以下命令列可以進行部分拉取，拉取速度比較快

先建立一個空資料夾，接著使用命令列 cd 命令進入此空資料夾，在命令列裡面輸入以下程式碼，即可獲取到本文的程式碼

git init
git remote add origin https://gitee.com/lindexi/lindexi_gd.git
git pull origin b54f37030aec86fda474e99c0ad9ae941e23e1da

以上使用的是國內的 gitee 的源，如果 gitee 不能訪問，請替換為 github 的源。請在命令列繼續輸入以下程式碼，將 gitee 源換成 github 源進行拉取程式碼。如果依然拉取不到程式碼，可以發郵件向我要程式碼

git remote remove origin
git remote add origin https://github.com/lindexi/lindexi_gd.git
git pull origin b54f37030aec86fda474e99c0ad9ae941e23e1da

獲取程式碼之後，進入 X11/ChihewigiKurwawhalcelfe 資料夾，即可獲取到原始碼

更多技術部落格，請參閱 部落格導航

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