XRender 创建离屏图片

Question

我正在尝试创建一个合成窗口管理器。到目前为止它可以工作，但是当一个窗口覆盖另一个窗口时，它会像疯了一样闪烁。我发现这是因为我正在创建一个Picture，然后在它上面绘画，这导致它在屏幕上绘画。

我想要的行为是有一个Picture可以绘制的屏幕外，然后使用 XComposite 将其绘制到屏幕窗口。有没有办法让屏幕外Picture的大小与根窗口相同？

到目前为止（这段代码在无限循环中运行）：

Window root, parent, *children;
uint children_count;
XQueryTree(disp, DefaultRootWindow(disp), &root, &parent, &children, &children_count);

// I'd like the following picture to be offscreen.
// I suspect that I have to put else something where rootPicture is
// Currently, when I draw to this picture, X11 renders it to the screen immediately, which is what I don't want.
Picture pictureBuf = XRenderCreatePicture(disp, /* rootPicture */, XRenderFindVisualFormat(disp, DefaultVisual(disp, DefaultScreen(disp))), CPSubwindowMode, &RootAttributes);

for (uint i = 0; i < children_count; i++) {
    // collapsed some stuff that doesn't matter
    Picture picture = XRenderCreatePicture(disp, children[i], pictureFormat, CPSubwindowMode, &pictureAttributes);

    // The following line should composite to an offscreen picture
    XRenderComposite(disp, hasAlpha ? PictOpOver : PictOpSrc, picture, None, pictureBuf, 0, 0, 0, 0, windowRect.x(), windowRect.y(), windowRect.width(), windowRect.height());
    // collapsed some stuff that doesn't matter
}

// The following line should composite from the offscreen picture to an onscreen picture
XRenderComposite(disp, PictOpSrc, pictureBuf, None, rootPicture, 0, 0, 0, 0, RootAttr.x, RootAttr.y, RootAttr.width, RootAttr.height);

Answer 1

我最近正在研究类似的事情，并想我会回复。下面的代码片段显示了如何从现有窗口创建新的像素图，而不直接绘制到该窗口。希望这有帮助。

Pixmap new_pixmap;
new_pixmap = XCompositeNameWindowPixmap( display, src_window);
Drawable draw = new_pixmap;
if (!draw) draw = src_window;
Picture origin;
origin = XRenderCreatePicture( display, draw, format, CPSubWindowMode, &attributes);