Write the PID on a semi-transparent DirectFB Window.

fb_image.c

#include <directfb.h>
#include <stdio.h>
#include <unistd.h>


#define DFBCHECK(x...)                          \
do {                                            \
    DFBResult err = x;                          \
    if (err != DFB_OK) {                        \
        printf("%s <%i>:", __FILE__, __LINE__); \
        DirectFBErrorFatal( #x, err );          \
    }                                           \
} while (0)


int main(int argc, char **argv) {
    // Initialize DirectFB.
    DFBCHECK( DirectFBInit(&argc, &argv) );

    // Get the main interface.
    IDirectFB *dfb = NULL;
    DFBCHECK( DirectFBCreate(&dfb) );

    // Get the primary layer.
    IDirectFBDisplayLayer *layer = NULL;
    DFBCHECK( dfb->GetDisplayLayer(dfb, DLID_PRIMARY, &layer) );
    DFBCHECK( layer->SetCooperativeLevel(layer, DLSCL_ADMINISTRATIVE) );

    // Get the surface of the primary layer.
    IDirectFBSurface *surface = NULL;
    DFBCHECK( layer->GetSurface(layer, &surface) );

    // Load JPG image.
    IDirectFBImageProvider *provider = NULL;
    DFBCHECK( dfb->CreateImageProvider(dfb,
        "/usr/share/directfb-examples/wood_andi.jpg", &provider) );

    // Render JPG to surface.
    DFBCHECK( provider->RenderTo(provider, surface, NULL) );

    // Flip the surface.
    DFBCHECK( surface->Flip(surface, NULL, DSFLIP_WAITFORSYNC) );

    getchar();

    // Cleanup.
    DFBCHECK( provider->Release(provider) );
    DFBCHECK( layer->Release(layer) );
    DFBCHECK( dfb->Release(dfb) );

    return 0;
}

fb_window_test.c

#include <directfb.h>
#include <sys/types.h>
#include <time.h>
#include <stdlib.h>
#include <unistd.h>
#include <stdio.h>


#define DFBCHECK(x...)                          \
do {                                            \
    DFBResult err = x;                          \
    if (err != DFB_OK) {                        \
        printf("%s <%i>:", __FILE__, __LINE__); \
        DirectFBErrorFatal( #x, err );          \
    }                                           \
} while (0)


int main(int argc, char **argv) {
    // Initialize randomness seed.
    srand(time(NULL));

    // Initialize DirectFB.
    DFBCHECK( DirectFBInit(&argc, &argv) );

    // Get the main interface.
    IDirectFB *dfb = NULL;
    DFBCHECK( DirectFBCreate(&dfb) );

    // Get the primary layer.
    IDirectFBDisplayLayer *layer = NULL;
    DFBCHECK( dfb->GetDisplayLayer(dfb, DLID_PRIMARY, &layer) );
    DFBCHECK( layer->SetCooperativeLevel(layer, DLSCL_ADMINISTRATIVE) );

    // Create a 1280 x 720 window, with alpha.
    IDirectFBWindow *window = NULL;
    DFBWindowDescription window_desc = {
        .flags = DWDESC_POSX | DWDESC_POSY | DWDESC_WIDTH | DWDESC_HEIGHT |
                 DWDESC_CAPS | DWDESC_SURFACE_CAPS,
        .caps = DWCAPS_ALPHACHANNEL | DWCAPS_DOUBLEBUFFER | DWCAPS_NODECORATION,
        .surface_caps = DSCAPS_PRIMARY | DSCAPS_PREMULTIPLIED | DSCAPS_VIDEOONLY,
        .posx = 0,
        .posy = 0,
        .width = 1280,
        .height = 720
    };
    DFBCHECK( layer->CreateWindow(layer, &window_desc, &window) );

    // Set the window opacity to 50%, so we can see all windows.
    DFBCHECK( window->SetOpacity(window, 0x80) );

    // Get the primary surface.
    IDirectFBSurface *surface;
    DFBCHECK( window->GetSurface(window, &surface) );

    // Set basic drawing flags.
    DFBCHECK( surface->SetPorterDuff(surface, DSPD_SRC_OVER) );
    DFBCHECK( surface->SetBlittingFlags(surface, DSBLIT_BLEND_ALPHACHANNEL) );
    DFBCHECK( surface->SetDrawingFlags(surface, DSDRAW_BLEND) );

    // Clear the screen with black.
    DFBCHECK( surface->Clear(surface, 0x0, 0x0, 0x0, 0xFF) );
    DFBCHECK( surface->Flip(surface, NULL, DSFLIP_WAITFORSYNC) );
    DFBCHECK( surface->Clear(surface, 0x0, 0x0, 0x0, 0xFF) );

    // Create a font.
    IDirectFBFont *font = NULL;
    DFBFontDescription font_dsc = {
      .flags = DFDESC_HEIGHT,
      .height = 48
    };
    DFBCHECK( dfb->CreateFont(dfb,
        "/usr/share/directfb-examples/fonts/decker.ttf", &font_dsc, &font) );

    // Set it as the surface font.
    DFBCHECK( surface->SetFont(surface, font) );

    // Draw the PID in white.
    char pid_string[20] = {0};
    snprintf(pid_string, 19, "Process: %i", getpid());
    DFBCHECK( surface->SetColor(surface, 0xFF, 0xFF, 0xFF, 0xFF) );
    DFBCHECK( surface->DrawString(surface, pid_string, -1, rand() % 1000,
        rand() % 600, DSTF_LEFT) );

    // Flip the surface.
    DFBCHECK( surface->Flip(surface, NULL, DSFLIP_WAITFORSYNC) );

    getchar();

    // Cleanup.
    DFBCHECK( window->Release(window) );
    DFBCHECK( layer->Release(layer) );
    DFBCHECK( font->Release(font) );
    DFBCHECK( dfb->Release(dfb) );

    return 0;
}