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,
};