SCREEN basic programming

Basic steps of SCREEN programming

Here we take the ssplash application in the Qualcomm 8155 software baseline as an example for analysis.

Basic process:

Introducing these steps, we will introduce two problems in screen application programming from the two dimensions of why and how : why do you want to do this? How to do?

1. Wait for the /dev/screen node

why : The screen application depends on the screen service, so it must wait for the screen service to be ready.

how : You can use the waitfor or waitfor_attach interface to wait for the screen directory node to be generated (the generation of the screen directory node means that the screen service is ready), for example, the waitfor_attach interface used below waits for the screen service to be ready, and the timeout period is 5000ms.

    /*Wait till "/dev/screen" shows up */
    waitfor_attach ( "/dev/screen", 5000 );

2. Create screen context

Why: All screen API interfaces (except screen events) need to interact with the screen server through the context, so the first step in screen programming is to create a screen context to establish a connection between the application and the screen.

how: Please refer to the code below. There are various types of parameter flags required by the interface. For ordinary screen applications, select SCREEN_APPLICATION_CONTEXT. If you need power on display, you also need to set SCREEN_POWER_MANAGER_CONTEXT. The meaning of these two flags is: this is an application-level screen program with power on display permissions. For other flag information, please refer to Screen con in the developer manual. text types section .

    screen_context_t screen_ctx;
    /*Create a screen context*/
    if ( EOK != ( rc = screen_create_context(&screen_ctx, 
                    SCREEN_APPLICATION_CONTEXT | 
                    SCREEN_POWER_MANAGER_CONTEXT ))) 
    {   
        ERROR("screen_create_context(0x%x) failed, err=%d", 
                SCREEN_APPLICATION_CONTEXT|SCREEN_POWER_MANAGER_CONTEXT, 
                errno);
        goto exit1;
    }

3. Create a render target

why : It can be understood as the target you want to render through the screen. If the target needs to be displayed on the screen, it is usually a window window. If it does not need to be displayed on the screen, it can be a stream/pixmap.

how : Refer to the following example to create a windows instance.

    /*Create a window on which we will show the splash*/
    if ( EOK != ( rc = screen_create_window(&screen_win, screen_ctx))) {
        ERROR("create win failed, err=%d", errno ) ;
        goto exit3;
    }

4. Set the target attribute

Why: Similar to framebuffer programming, you need to configure parameters for the target you want to display, such as display position, size, alpha, etc.

how: Refer to the example below.

    if ( EOK != ( rc = screen_get_window_property_iv(screen_win,
            SCREEN_PROPERTY_BUFFER_SIZE, rect+2)))
    {
        ERROR("GET SCREEN_PROPERTY_SIZE failed, err=%d", errno);
        goto exit4;
    }

    position[0] = dims[0]/2 - rect[2]/2;
    position[1] = dims[1]/2 - rect[3]/2;
    if ( EOK != ( rc = screen_set_window_property_iv(screen_win,
            SCREEN_PROPERTY_POSITION , position )))
    {
        ERROR("SET SCREEN_PROPERTY_POSITION failed, err=%d", errno);
        goto exit4;
    }

    if ( EOK != ( rc = screen_set_window_property_iv(screen_win,
            SCREEN_PROPERTY_STATIC , &static_content)))
    {
        ERROR("SET SCREEN_PROPERTY_STATIC failed, err=%d", errno);
        goto exit4;
    }

5. Create a render buffer

why : used to store the image data content to be displayed

how : Refer to the code below

    /*Create one buffer*/
    if (EOK != (rc = screen_create_window_buffers(screen_win, 1))){
        ERROR("screen_create_window_buffers(1) failed, err=%d", errno);
        goto error;
    }

6，render target

why : render may be the most complicated part of the screen. There are many ways to implement render here, and there are also various operations, such as re-sizing the screen, using GPU to render and modify the content data of the screen, etc.

how : Refer to Chapter 3 Rendering in the developer manual 

7. Push the rendered data

why : Push the rendered data to the screen

how : refer to the following code

    /*Final call to post the window*/
    if (EOK != ( rc = screen_post_window(screen_win,
                    screen_buf, 1, rect, 0)))
    {
        ERROR("screen_post_window failed, err=%d",errno);
        goto exit4;
    }

8. Handle input events (if necessary)

reference

https://blog.csdn.net/suixing_yuan/category_10911939.html

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