如何在Raspberry Pi上使用DispmanX显示到/ dev / fb1

Question

我正在Raspberry Pi 3上使用2个显示器，运行不带X的Raspbian（内核4.14）

一个是1280x720分辨率的HDMI，另一个是SPI 720x480分辨率。

两个显示均在引导时显示控制台输出。

我可以使用以下命令在SPI显示器上正确显示随机噪声 cat /dev/urandom >/dev/fb1

我需要使用C ++在SPI显示器上显示图像

我正在运行测试代码，该代码在HDI显示器上显示测试模式 Source Link

问题是，无论我输入什么uint32_t displayNumber = 0; \\=1; =2; etc..，它始终显示在HDMI显示屏上。 info.width和info.height始终显示1920x1080

如果我断开HDMI显示器的连接，然后再次尝试为uint32_t displayNumber = 0;输入不同的数字，我会得到 info.width和info.height始终显示720x480

但是SPI显示屏上仍然没有任何显示。

看来vc_dispmanx_display_open(displayNumber);不在乎它作为输入参数是什么。

我的问题是，如何正确地将dispmanx从/dev/fb0切换到/dev/fb1？

谢谢

int main(int argc, char *argv[])
{
    uint32_t displayNumber = 0;
    VC_IMAGE_TYPE_T type = VC_IMAGE_RGBA32;
    bcm_host_init();
    DISPMANX_DISPLAY_HANDLE_T display
        = vc_dispmanx_display_open(displayNumber);
    assert(display != 0);
    DISPMANX_MODEINFO_T info;
    int result = vc_dispmanx_display_get_info(display, &info);
    assert(result == 0);
    uint32_t vc_image_ptr;
    DISPMANX_RESOURCE_HANDLE_T bgResource =
        vc_dispmanx_resource_create(type, 1, 1, &vc_image_ptr);
    assert(bgResource != 0);
    DISPMANX_RESOURCE_HANDLE_T resource =
        vc_dispmanx_resource_create(type, 2, 2, &vc_image_ptr);
    assert(resource != 0);
    VC_RECT_T src_rect;
    VC_RECT_T dst_rect;
    vc_dispmanx_rect_set(&dst_rect, 0, 0, 1, 1);
    uint32_t background = 0;
    result = vc_dispmanx_resource_write_data(bgResource,
        type,
        sizeof(background),
        &background,
        &dst_rect);
    assert(result == 0);
    uint32_t image[32];

    memset(image, 0, sizeof(image));
    image[0] = 0xFF0000FF;
    image[1] = 0xFF00FFFF;
    image[16] = 0xFFFF0000;
    image[17] = 0xFFFFFF00;

    vc_dispmanx_rect_set(&dst_rect, 0, 0, 2, 2);

    result = vc_dispmanx_resource_write_data(resource,
        type,
        16 * sizeof(uint32_t),
        image,
        &dst_rect);
    assert(result == 0);
    DISPMANX_UPDATE_HANDLE_T update = vc_dispmanx_update_start(0);
    assert(update != 0);
    VC_DISPMANX_ALPHA_T alpha =
    {
        DISPMANX_FLAGS_ALPHA_FIXED_ALL_PIXELS, 
        255,
        /*alpha 0->255*/
        0
    };
    vc_dispmanx_rect_set(&src_rect, 0, 0, 1, 1);
    vc_dispmanx_rect_set(&dst_rect, 0, 0, 0, 0);
    DISPMANX_ELEMENT_HANDLE_T bgElement =
        vc_dispmanx_element_add(update,
        display,
        1,
         // layer
        &dst_rect,
        bgResource,
        &src_rect,
        DISPMANX_PROTECTION_NONE,
        &alpha,
        NULL,
         // clamp
        DISPMANX_NO_ROTATE);
    assert(bgElement != 0);
    vc_dispmanx_rect_set(&src_rect, 0, 0, 2 << 16, 2 << 16);
    vc_dispmanx_rect_set(&dst_rect,
        (info.width - info.height) / 2,
        0,
        info.height,
        info.height);

    DISPMANX_ELEMENT_HANDLE_T element =
        vc_dispmanx_element_add(update,
        display,
        2,
         // layer
        &dst_rect,
        resource,
        &src_rect,
        DISPMANX_PROTECTION_NONE,
        &alpha,
        NULL,
         // clamp
        DISPMANX_NO_ROTATE);
    assert(element != 0);
    result = vc_dispmanx_update_submit_sync(update);
    assert(result == 0);

    //---------------------------------------------------------------------
    usleep(1000000);
    //---------------------------------------------------------------------

    update = vc_dispmanx_update_start(0);
    assert(update != 0);
    result = vc_dispmanx_element_remove(update, element);
    assert(result == 0);
    result = vc_dispmanx_element_remove(update, bgElement);
    assert(result == 0);
    result = vc_dispmanx_update_submit_sync(update);
    assert(result == 0);
    result = vc_dispmanx_resource_delete(resource);
    assert(result == 0);
    result = vc_dispmanx_resource_delete(bgResource);
    assert(result == 0);
    result = vc_dispmanx_display_close(display);
    assert(result == 0);
    return 0;
}