Linux Xlib错误的alpha处理

我有两个源代码从stackoverflow和GitHub，它演示了一个Xlib表单上的Alpha通道处理复制。 首先是简单的Xlib，接下来是OpenGL。 但是在我看来，这是错误的。

如果我将alpha通道值设置为0，那么任何颜色都应该是完全透明的，而不仅仅是黑色，但是颜色越接近白色，alpha通道的工作就越less。 如果我将颜色设置为白色，那么窗口完全忽略了Alpha通道。 0x00808080是半透明的。

我不知道我在做什么错，有人可以告诉我什么是问题？ 也许问题出在我的机器上？

这是第一个代码片段：

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#include <X11/Xlib.h> #include <X11/Xutil.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 = 0x00ffffff; 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; } 

这是第二个：

 /* ____ _____ /\__ \ /\ ___\ \/__/\ \ \ \ \__/_ \ \ \ \ \____ \ _\_\ \ \/__/_\ \ /\ _____\ /\ _____\ \/______/ \/______/ Copyright (C) 2011 Joerg Seebohn This program is free software; you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation; either version 2 of the License, or (at your option) any later version. This program demonstrates how an X11 window with OpenGL support can be drawn transparent. The title bar and window border drawn by the window manager are drawn opaque. Only the background of the window which is drawn with OpenGL glClearColor( 0.7, 0.7, 0.7, 0.7) ; glClear(GL_COLOR_BUFFER_BIT) ; is 30% transparent. Compile it with: gcc -std=gnu99 -o test testprogram.c -lX11 -lGL */ #include <X11/Xlib.h> #include <X11/Xatom.h> #include <X11/keysym.h> #include <GL/gl.h> #include <GL/glx.h> #include <stdio.h> #include <stdlib.h> int main(int argc, char* argv[]) { Display * display = XOpenDisplay( 0 ) ; const char * xserver = getenv( "DISPLAY" ) ; if (display == 0) { printf("Could not establish a connection to X-server '%s'\n", xserver ) ; exit(1) ; } // query Visual for "TrueColor" and 32 bits depth (RGBA) XVisualInfo visualinfo ; XMatchVisualInfo(display, DefaultScreen(display), 32, TrueColor, &visualinfo); // create window Window win ; GC gc ; XSetWindowAttributes attr ; attr.colormap = XCreateColormap( display, DefaultRootWindow(display), visualinfo.visual, AllocNone) ; attr.event_mask = ExposureMask | KeyPressMask ; attr.background_pixmap = None ; attr.border_pixel = 0 ; win = XCreateWindow( display, DefaultRootWindow(display), 50, 300, 400, 100, // x,y,width,height : are possibly opverwriteen by window manager 0, visualinfo.depth, InputOutput, visualinfo.visual, CWColormap|CWEventMask|CWBackPixmap|CWBorderPixel, &attr ) ; gc = XCreateGC( display, win, 0, 0) ; // set title bar name of window XStoreName( display, win, "Transparent Window with OpenGL Support" ) ; // say window manager which position we would prefer XSizeHints sizehints ; sizehints.flags = PPosition | PSize ; sizehints.x = 50 ; sizehints.y = 300 ; sizehints.width = 400 ; sizehints.height = 100 ; XSetWMNormalHints( display, win, &sizehints ) ; // Switch On >> If user pressed close key let window manager only send notification >> Atom wm_delete_window = XInternAtom( display, "WM_DELETE_WINDOW", 0) ; XSetWMProtocols( display, win, &wm_delete_window, 1) ; { // change foreground color to brown XColor xcol ; xcol.red = 153 * 256 ; // X11 uses 16 bit colors ! xcol.green = 116 * 256 ; xcol.blue = 65 * 256 ; XAllocColor( display, attr.colormap, &xcol) ; XGCValues gcvalues ; gcvalues.foreground = xcol.pixel ; XChangeGC( display, gc, GCForeground, &gcvalues) ; } // create OpenGL context GLXContext glcontext = glXCreateContext( display, &visualinfo, 0, True ) ; if (!glcontext) { printf("X11 server '%s' does not support OpenGL\n", xserver ) ; exit(1) ; } glXMakeCurrent( display, win, glcontext ) ; // now let the window appear to the user XMapWindow( display, win) ; int isUserWantsWindowToClose = 0 ; while( !isUserWantsWindowToClose ) { int isRedraw = 0 ; /* XPending returns number of already queued events. * If no events are queued XPending sends all queued requests to the X-server * and tries to read new incoming events. */ while( XPending(display) > 0 ) { // process event XEvent event ; XNextEvent( display, &event) ; switch(event.type) { // see 'man XAnyEvent' for a list of available events case ClientMessage: // check if the client message was send by window manager to indicate user wants to close the window if ( event.xclient.message_type == XInternAtom( display, "WM_PROTOCOLS", 1) && event.xclient.data.l[0] == XInternAtom( display, "WM_DELETE_WINDOW", 1) ) { isUserWantsWindowToClose = 1 ; } break; case KeyPress: if (XLookupKeysym(&event.xkey, 0) == XK_Escape) { isUserWantsWindowToClose = 1 ; } break ; case Expose: isRedraw = 1 ; break ; default: // do nothing break ; } } // ... all events processed, now do other stuff ... if (isRedraw) { // needs redraw // use opengl to clear background in (transparent) light grey glClearColor( 1, 1, 1, 0) ; glClear(GL_COLOR_BUFFER_BIT) ; glXSwapBuffers( display, win) ; glXWaitGL() ; // draw string with X11 XDrawString( display, win, gc, 10, 20, "Hello ! ", 7) ; } // ... do something else ... } XDestroyWindow( display, win ) ; win = 0 ; XCloseDisplay( display ) ; display = 0 ; return 0 ; }