第二部分 overlay 架构初探

1 overlay可能支持的颜色格式
/* possible overlay formats可能支持的颜色格式 */
enum {
    OVERLAY_FORMAT_RGBA_8888    = HAL_PIXEL_FORMAT_RGBA_8888,
    OVERLAY_FORMAT_RGB_565      = HAL_PIXEL_FORMAT_RGB_565,
    OVERLAY_FORMAT_BGRA_8888    = HAL_PIXEL_FORMAT_BGRA_8888,
    OVERLAY_FORMAT_YCbCr_422_SP = HAL_PIXEL_FORMAT_YCbCr_422_SP,
    OVERLAY_FORMAT_YCbCr_420_SP = HAL_PIXEL_FORMAT_YCbCr_420_SP,
    OVERLAY_FORMAT_YCbYCr_422_I = HAL_PIXEL_FORMAT_YCbCr_422_I,
    OVERLAY_FORMAT_YCbYCr_420_I = HAL_PIXEL_FORMAT_YCbCr_420_I,
    OVERLAY_FORMAT_CbYCrY_422_I = HAL_PIXEL_FORMAT_CbYCrY_422_I,
    OVERLAY_FORMAT_CbYCrY_420_I = HAL_PIXEL_FORMAT_CbYCrY_420_I,
    OVERLAY_FORMAT_DEFAULT      = 99    // The actual color format is determined
                                        // by the overlay
};

2 overlay_control_device_t结构的子函数

/* get static informations about the capabilities of the overlay engine 获取overlay引擎的固定信息*/
    int (*get)(struct overlay_control_device_t *dev, int name);

/* creates an overlay matching the given parameters as closely as possible.根据所给的参数，尽可能得创建一个overlay。
     * returns an error if no more overlays are available. The actual 如果没有更多的overlay可获取，返回错误。
     * size and format is returned in overlay_t. 实际的尺寸和格式通过overlay_t结构返回*/
    overlay_t* (*createOverlay)(struct overlay_control_device_t *dev,
            uint32_t w, uint32_t h, int32_t format);
   
    /* destroys an overlay. This call releases all 销毁一个overlay，释放所有资源
     * resources associated with overlay_t and make it invalid */
    void (*destroyOverlay)(struct overlay_control_device_t *dev,
            overlay_t* overlay);

/* set position and scaling of the given overlay as closely as possible. 根据所给的参数，尽可能的设置坐标和缩放。
     * if scaling cannot be performed, overlay must be centered. 如果无法执行尺寸变化，必须为中心覆盖*/
    int (*setPosition)(struct overlay_control_device_t *dev,
            overlay_t* overlay,
            int x, int y, uint32_t w, uint32_t h);

/* returns the actual position and size of the overlay 获取overlay的实际位置*/
    int (*getPosition)(struct overlay_control_device_t *dev,
            overlay_t* overlay,
            int* x, int* y, uint32_t* w, uint32_t* h);

/* sets configurable parameters for this overlay. returns an error if not设置配置参数，如果不支持返回错误
     * supported. */
    int (*setParameter)(struct overlay_control_device_t *dev,
            overlay_t* overlay, int param, int value);
/*以下两个函数没有实现*/
    int (*stage)(struct overlay_control_device_t *dev, overlay_t* overlay);
    int (*commit)(struct overlay_control_device_t *dev, overlay_t* overlay);

3、 overlay_data_device_t结构体函数子函数
    /* initialize the overlay from the given handle. this associates this通过传入的handle初始化overlay
     * overlay data module to its control module将data模块附加到控制模块上 */
    int (*initialize)(struct overlay_data_device_t *dev,
            overlay_handle_t handle);

/* can be called to change the width and height of the overlay.改变overlay的宽度和高度 */
    int (*resizeInput)(struct overlay_data_device_t *dev,
            uint32_t w, uint32_t h);
/*以下三个函数没有实现*/
    int (*setCrop)(struct overlay_data_device_t *dev,
            uint32_t x, uint32_t y, uint32_t w, uint32_t h) ;

int (*getCrop)(struct overlay_data_device_t *dev,
       uint32_t* x, uint32_t* y, uint32_t* w, uint32_t* h) ;

int (*setParameter)(struct overlay_data_device_t *dev,
            int param, int value);

/* blocks until an overlay buffer is available and return that buffer.阻塞直到一个overlay释放buffer */
    int (*dequeueBuffer)(struct overlay_data_device_t *dev,
           overlay_buffer_t *buf);

/* release the overlay buffer and post it释放overlay buffer，post我理解是贴到screen上 */
    int (*queueBuffer)(struct overlay_data_device_t *dev,
            overlay_buffer_t buffer);

/* returns the address of a given buffer if supported, NULL otherwise.返回given buffer的地址 */
    void* (*getBufferAddress)(struct overlay_data_device_t *dev,
            overlay_buffer_t buffer);
/*暂未实现*/
    int (*getBufferCount)(struct overlay_data_device_t *dev);

4、get()函数可以提供的种类
enum {
    /* Maximum amount of minification supported by the hardware硬件支持的最大缩小倍数*/
    OVERLAY_MINIFICATION_LIMIT      = 1,
    /* Maximum amount of magnification supported by the hardware硬件支持的最大放大倍数 */
    OVERLAY_MAGNIFICATION_LIMIT     = 2,
    /* Number of fractional bits support by the overlay scaling engine 缩放引擎支持的小数位数 */
    OVERLAY_SCALING_FRAC_BITS       = 3,
    /* Supported rotation step in degrees. 旋转步进*/
    OVERLAY_ROTATION_STEP_DEG       = 4,
    /* horizontal alignment in pixels 像素中的水平对齐？*/
    OVERLAY_HORIZONTAL_ALIGNMENT    = 5,
    /* vertical alignment in pixels 像素中的垂直对齐*/
    OVERLAY_VERTICAL_ALIGNMENT      = 6,
    /* width alignment restrictions. negative number for max. power-of-two 宽度对齐限制。负数为最大值。双功率？*/
    OVERLAY_WIDTH_ALIGNMENT         = 7,
    /* height alignment restrictions. negative number for max. power-of-two 高度对齐限制。负数为最大值。双功率？*/
    OVERLAY_HEIGHT_ALIGNMENT        = 8,
};

5、设置setParameter()函数可设置的种类
enum {
    /* rotation of the source image in degrees (0 to 359)源图像旋转角度（0 到 359）6410好像还不支持任意角度旋转 */
    OVERLAY_ROTATION_DEG = 1,
    /* enable or disable dithering */
    OVERLAY_DITHER        = 3,
    /* transformation applied (this is a superset of COPYBIT_ROTATION_DEG) */
    OVERLAY_TRANSFORM    = 4,
};