基于BetaFlight开源代码框架简介的框架设计，逐步分析内部模块功能设计。
描述：主要是将系统信息叠加到视频流上，以便更加便捷的通过眼镜了解飞控实时状态。
src/main/
├── /osd/
│ ├── osd.c/h
│ ├── osd_elements.c/h
│ └── osd_warnings.c/h
└── /driver/
└── display.c/h
注：这里主要是VTX上的OSD，而OLED显示设备并非OSD叠加，而是DashBoard显示。
osd.c主要描述了状态机的整体情况，详见：BetaFlight模块设计之十六：OSD更新任务分析。
\src\main\osd\osd_warnings.h
#define OSD_WARNINGS_MAX_SIZE 12
#define OSD_FORMAT_MESSAGE_BUFFER_SIZE (OSD_WARNINGS_MAX_SIZE + 1)
void renderOsdWarning(char *warningText, bool *blinking, uint8_t *displayAttr);
注：OSD检查子模块主要是在osdUpdate中被调用，定期调度执行：
osdUpdate–>osdDrawNextActiveElement–>osdDrawSingleElement–>osdElementDrawFunction[OSD_WARNINGS]–>osdElementWarnings–>renderOsdWarning
主要用于衔接osd状态机与OSD适配设备的作用。
\src\main\osd\osd_elements.h
//使用适配层进行OSD显示
bool osdDrawNextActiveElement(displayPort_t *osdDisplayPort, timeUs_t currentTimeUs);
void osdDrawActiveElementsBackground(displayPort_t *osdDisplayPort);
//OSD Element参数格式化和状态管理函数
int osdConvertTemperatureToSelectedUnit(int tempInDegreesCelcius);
void osdFormatDistanceString(char *result, int distance, char leadingSymbol);
bool osdFormatRtcDateTime(char *buffer);
void osdFormatTime(char * buff, osd_timer_precision_e precision, timeUs_t time);
void osdFormatTimer(char *buff, bool showSymbol, bool usePrecision, int timerIndex);
float osdGetMetersToSelectedUnit(int32_t meters);
char osdGetMetersToSelectedUnitSymbol(void);
int32_t osdGetSpeedToSelectedUnit(int32_t value);
char osdGetSpeedToSelectedUnitSymbol(void);
char osdGetTemperatureSymbolForSelectedUnit(void);
void osdAddActiveElements(void);
uint8_t osdGetActiveElement();
uint8_t osdGetActiveElementCount();
void osdElementsInit(bool backgroundLayerFlag);
void osdSyncBlink();
void osdResetAlarms(void);
void osdUpdateAlarms(void);
bool osdElementsNeedAccelerometer(void);
注：Kakute F7 AIO的板子用的是7456芯片。
主要就是三种OSD设备，其中AUTO只是三种设备自动侦测。详见：void init(void)
\src\main\osd\osd.h
typedef enum {
OSD_DISPLAYPORT_DEVICE_NONE = 0,
OSD_DISPLAYPORT_DEVICE_AUTO,
OSD_DISPLAYPORT_DEVICE_MAX7456,
OSD_DISPLAYPORT_DEVICE_MSP,
OSD_DISPLAYPORT_DEVICE_FRSKYOSD,
} osdDisplayPortDevice_e;
这里以Kakute F7使用的7456芯片为例。
\src\main\io\displayport_max7456.c
static const displayPortVTable_t max7456VTable = {
.grab = grab,
.release = release,
.clearScreen = clearScreen,
.drawScreen = drawScreen,
.screenSize = screenSize,
.writeString = writeString,
.writeChar = writeChar,
.isTransferInProgress = isTransferInProgress,
.heartbeat = heartbeat,
.redraw = redraw,
.isSynced = isSynced,
.txBytesFree = txBytesFree,
.layerSupported = layerSupported,
.layerSelect = layerSelect,
.layerCopy = layerCopy,
.writeFontCharacter = writeFontCharacter,
.checkReady = checkReady,
.setBackgroundType = setBackgroundType,
};
bool max7456DisplayPortInit(const vcdProfile_t *vcdProfile, displayPort_t **displayPort)
该适配模型在max7456DisplayPortInit里面已经初始化：displayInit(&max7456DisplayPort, &max7456VTable, DISPLAYPORT_DEVICE_TYPE_MAX7456);
\src\main\drivers\display.h
typedef enum {
DISPLAYPORT_ATTR_NONE = 0,
DISPLAYPORT_ATTR_INFO,
DISPLAYPORT_ATTR_WARNING,
DISPLAYPORT_ATTR_CRITICAL,
} displayPortAttr_e;
typedef struct displayPortVTable_s {
int (*grab)(displayPort_t *displayPort);
int (*release)(displayPort_t *displayPort);
int (*clearScreen)(displayPort_t *displayPort, displayClearOption_e options);
bool (*drawScreen)(displayPort_t *displayPort);
int (*screenSize)(const displayPort_t *displayPort);
int (*writeString)(displayPort_t *displayPort, uint8_t x, uint8_t y, uint8_t attr, const char *text);
int (*writeChar)(displayPort_t *displayPort, uint8_t x, uint8_t y, uint8_t attr, uint8_t c);
bool (*isTransferInProgress)(const displayPort_t *displayPort);
int (*heartbeat)(displayPort_t *displayPort);
void (*redraw)(displayPort_t *displayPort);
bool (*isSynced)(const displayPort_t *displayPort);
uint32_t (*txBytesFree)(const displayPort_t *displayPort);
bool (*layerSupported)(displayPort_t *displayPort, displayPortLayer_e layer);
bool (*layerSelect)(displayPort_t *displayPort, displayPortLayer_e layer);
bool (*layerCopy)(displayPort_t *displayPort, displayPortLayer_e destLayer, displayPortLayer_e sourceLayer);
bool (*writeFontCharacter)(displayPort_t *instance, uint16_t addr, const struct osdCharacter_s *chr);
bool (*checkReady)(displayPort_t *displayPort, bool rescan);
void (*beginTransaction)(displayPort_t *displayPort, displayTransactionOption_e opts);
void (*commitTransaction)(displayPort_t *displayPort);
bool (*getCanvas)(struct displayCanvas_s *canvas, const displayPort_t *displayPort);
void (*setBackgroundType)(displayPort_t *displayPort, displayPortBackground_e backgroundType);
} displayPortVTable_t;
void displayGrab(displayPort_t *instance);
void displayRelease(displayPort_t *instance);
void displayReleaseAll(displayPort_t *instance);
bool displayIsGrabbed(const displayPort_t *instance);
void displayClearScreen(displayPort_t *instance, displayClearOption_e options);
bool displayDrawScreen(displayPort_t *instance);
int displayScreenSize(const displayPort_t *instance);
void displaySetXY(displayPort_t *instance, uint8_t x, uint8_t y);
int displayWrite(displayPort_t *instance, uint8_t x, uint8_t y, uint8_t attr, const char *s);
int displayWriteChar(displayPort_t *instance, uint8_t x, uint8_t y, uint8_t attr, uint8_t c);
bool displayIsTransferInProgress(const displayPort_t *instance);
bool displayHeartbeat(displayPort_t *instance);
void displayRedraw(displayPort_t *instance);
bool displayIsSynced(const displayPort_t *instance);
uint16_t displayTxBytesFree(const displayPort_t *instance);
bool displayWriteFontCharacter(displayPort_t *instance, uint16_t addr, const struct osdCharacter_s *chr);
bool displayCheckReady(displayPort_t *instance, bool rescan);
void displayBeginTransaction(displayPort_t *instance, displayTransactionOption_e opts);
void displayCommitTransaction(displayPort_t *instance);
bool displayGetCanvas(struct displayCanvas_s *canvas, const displayPort_t *instance);
void displayInit(displayPort_t *instance, const displayPortVTable_t *vTable, displayPortDeviceType_e deviceType);
bool displayLayerSupported(displayPort_t *instance, displayPortLayer_e layer);
bool displayLayerSelect(displayPort_t *instance, displayPortLayer_e layer);
bool displayLayerCopy(displayPort_t *instance, displayPortLayer_e destLayer, displayPortLayer_e sourceLayer);
void displaySetBackgroundType(displayPort_t *instance, displayPortBackground_e backgroundType);
bool displaySupportsOsdSymbols(displayPort_t *instance);