GBM / DRM / EGL窗口覆盖

如何解决GBM / DRM / EGL窗口覆盖

我正在探索POC的一些图形编程和概念，并且陷入了一个简单的问题。 我有一个带有图形GUI的设备，该图形GUI在KMS + GBM + DRM上运行。现在，我需要创建一个必须在其顶部创建窗口的应用程序。

以下是我正在测试的代码摘录

// Open graphics device
device = open("/dev/dri/card0",O_RDWR);

// Get DRM resources from the graphics card0
//allocates,populates,and returns a drmModeRes structure containing information about the current display configuration
resources = drmModeGetResources(device);

// A method to interate through the connectors and find the correct one
connector = find_connector(resources);

// Get the connector id
connector_id = connector->connector_id;

// Get the connector mode
mode_info = connector->modes[0];

// Get the correct encoder. Inturn calls drmModeGetEncoder
encoder = find_encoder(resources,connector);

// Get original display mode by calling
crtc = drmModeGetCrtc(device,encoder->crtc_id);

// Release encoder 
drmModeFreeEncoder(encoder);

// Release connector
drmModeFreeConnector(connector);

// Release resources
drmModeFreeResources(resources);

// Create GBM device.  Generic Buffer Manager (GBM) device,// since this is the interface that Mesa 
// (the EGL/OpenGL driver we are using) understands.
gbm_device = gbm_create_device(device);

// Set the buffer flag as linear indicating that it is not tiled.
static uint64_t modifiers[] = {GBM_BO_USE_LINEAR};

// Create GBM Surface
gbm_surface = gbm_surface_create_with_modifiers(gbm_device,mode_info.hdisplay,mode_info.vdisplay,GBM_FORMAT_XRGB8888,modifiers,3);

// obtains the EGL display connection for the native display native_display which is GBM device
display = eglGetDisplay(gbm_device);

// Initialize the EGL display connection
eglInitialize(display,NULL,NULL);

// Bind the EGL API
eglBindAPI(EGL_OPENGL_API);

// Returns a list of all EGL frame buffer configurations
// that are available for the specified display
eglGetConfigs(display,&count);

// Allocate memory for the configs
configs = malloc(count * sizeof *configs);

// Chose the appropriate display
eglChooseConfig(display,attributes,configs,count,&num_config);

// Match config to GBM format
config_index = match_config_to_visual(display,num_config);

// Create EGL rendering context for current api
context = eglCreateContext(display,configs[config_index],EGL_NO_CONTEXT,context_attribs);

// Create EGL surface to display the bufffer
egl_surface = eglCreateWindowSurface(display,gbm_surface,NULL);

// Set the current buffer. 
// binds context to the current rendering thread and to the draw and read surfaces 
eglMakeCurrent(display,egl_surface,context);

// Flush the buffers onto the display and surface
eglSwapBuffers(display,egl_surface);

// Lock the front buffer
bo = gbm_surface_lock_front_buffer(gbm_surface);

// Get the handle
handle = gbm_bo_get_handle(bo).u32;

// Get the pitch
pitch = gbm_bo_get_stride(bo);

// Get the framebuffer
fb = drm_fb_get_from_bo(bo);

// Add framebuffer for rendering
drmModeAddFB(device,24,32,pitch,handle,&fb1);  drmModeSetCrtc(device,crtc->crtc_id,fb1,&connector_id,1,&mode_info);

// Paint color
glClearColor(1.0f - 100,100,0.0,1.0);
glClear(GL_COLOR_BUFFER_BIT);

上面的代码在GUI被终止时可以正常工作，但在GUI运行时不起作用。有没有一种方法可以渲染窗口/曲面离屏？ 我尝试将EGL_SURFACE_TYPE设置为EGL_PBUFFER_BIT，如下所示

static const EGLint configAttribs[] = {
      EGL_SURFACE_TYPE,EGL_PBUFFER_BIT,EGL_BLUE_SIZE,8,EGL_GREEN_SIZE,EGL_RED_SIZE,EGL_DEPTH_SIZE,EGL_RENDERABLE_TYPE,EGL_OPENGL_BIT,EGL_NONE
}; 

但是不幸的是，并非所有平台都支持PBuffers。 EGL / GBM不支持Pbuffer。它也不支持Pixmaps。

事实上，除非您使用内核的KMS API将其发布到显示器上，否则我上面的代码所产生的缓冲区将保持在屏幕外。

那么有什么方法可以调用KMS Api将其发布到显示器上？