如何在XLib中创建半透明的白色窗口

问题描述

我想在XLib中创建一个半透明的白色窗口，但是该窗口不是半透明的，它仍然是完全不透明的。我使用compton合成器，并且系统中有透明的窗口，因此问题出在代码中：

I would like to create a semi transparent white window in XLib, but the window is not semi translucent, it remains fully opaque. I use the compton compositor and there are transparent windows in the system, so the problem is in the code:

#include <X11/Xlib.h>
#include <X11/Xutil.h>
#include <stdio.h>

int main(int argc, char* argv[])
{
    Display* display = XOpenDisplay(NULL);

    XVisualInfo vinfo;

    XMatchVisualInfo(display, DefaultScreen(display), 32, TrueColor, &vinfo);

    XSetWindowAttributes attr;
    attr.colormap = XCreateColormap(display, DefaultRootWindow(display), vinfo.visual, AllocNone);
    attr.border_pixel = 0;
    attr.background_pixel = 0x80ffffff;

    Window win = XCreateWindow(display, DefaultRootWindow(display), 0, 0, 300, 200, 0, vinfo.depth, InputOutput, vinfo.visual, CWColormap | CWBorderPixel | CWBackPixel, &attr);
    XSelectInput(display, win, StructureNotifyMask);
    GC gc = XCreateGC(display, win, 0, 0);

    Atom wm_delete_window = XInternAtom(display, "WM_DELETE_WINDOW", 0);
    XSetWMProtocols(display, win, &wm_delete_window, 1);

    XMapWindow(display, win);

    int keep_running = 1;
    XEvent event;

    while (keep_running) {
        XNextEvent(display, &event);

        switch(event.type) {
            case ClientMessage:
                if (event.xclient.message_type == XInternAtom(display, "WM_PROTOCOLS", 1) && (Atom)event.xclient.data.l[0] == XInternAtom(display, "WM_DELETE_WINDOW", 1))
                    keep_running = 0;

                break;

            default:
                break;
        }
    }

    XDestroyWindow(display, win);
    XCloseDisplay(display);
    return 0;
}

推荐答案

X11期望 pre相乘的颜色，即真正的不透明颜色需要乘以alpha值（并相应缩放，即当通道宽度为8位时除以256）。当您需要组合多个级别时，此格式更易于使用。请参见的公式。

X11 expects pre-multiplied colours, i.e. real opaque colours need to be multiplied by the alpha value (and scaled accordingly, i.e. divided by 256 when channel widths is 8 bits). This format is easier to work with when you need to combine many levels. See formulas here. There's less computation when everything is pre-multiplied.

因此，您需要将每个R，G和B通道乘以alpha值（0x80），然后除以256，从而减少了计算量。

So you need to multiply each of your R, G and B channels by the alpha value (0x80) and divide by 256.

将背景设置为0x80808080即可得到所需的结果：

Setting the background to 0x80808080 gives the desired result:

请注意，结果与@patthoyts所建议的不同：此处仅窗口是半透明的，WM装饰保持不透明在那里，适当的窗户和装饰都由WM透明化了（WM进行了必要的颜色混合）。

Note the result is different from what @patthoyts suggests: here only the window proper is semi-transparent, the WM decoration stays opaque; there both the window proper and the decoration are made transparent by the WM (and the WM does the necessary colour blending).

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