implement display rotation

ssd1306.c

@@ -63,6 +63,7 @@ bool ssd1306_init(ssd1306_t *p, uint16_t width, uint16_t height, uint8_t address
     p->height=height;
     p->pages=height/8;
     p->address=address;
+    p->rotation=ROT_0;
 
     p->i2c_i=i2c_instance;
 
@@ -140,13 +141,36 @@ inline void ssd1306_clear(ssd1306_t *p) {
     memset(p->buffer, 0, p->bufsize);
 }
 
+inline void ssd1306_set_rotation(ssd1306_t *p, rotation_t rotation) {
+    p->rotation = rotation;
+}
+
+void rotate_coordinates(ssd1306_t *p, uint32_t* x, uint32_t* y) {
+    uint32_t tmp_x = *x;
+    if(p->rotation == ROT_90) {
+        *x = p->height - *y - 1;
+        *y = tmp_x;
+    } else if(p->rotation == ROT_180) {
+        *x = p->width - *x - 1;
+        *y = p->height - *y - 1;
+    } else if(p->rotation == ROT_270) {
+        *x = *y;
+        *y = p->width - tmp_x - 1;
+    }
+    // Keep coordinates as is for ROT_0
+}
+
 void ssd1306_clear_pixel(ssd1306_t *p, uint32_t x, uint32_t y) {
+    rotate_coordinates(p, &x, &y);
+
     if(x>=p->width || y>=p->height) return;
 
     p->buffer[x+p->width*(y>>3)]&=~(0x1<<(y&0x07));
 }
 
 void ssd1306_draw_pixel(ssd1306_t *p, uint32_t x, uint32_t y) {
+    rotate_coordinates(p, &x, &y);
+
     if(x>=p->width || y>=p->height) return;
 
     p->buffer[x+p->width*(y>>3)]|=0x1<<(y&0x07); // y>>3==y/8 && y&0x7==y%8

ssd1306.h

@@ -56,6 +56,17 @@ typedef enum {
     SET_CHARGE_PUMP = 0x8D
 } ssd1306_command_t;
 
+/**
+ * @brief defines rotations/orientations
+ */
+typedef enum {
+    ROT_0 = 0,
+    ROT_90 = 1,
+    ROT_180 = 2,
+    ROT_270 = 3,
+} rotation_t;
+
+
 /**
 *	@brief holds the configuration
 */
@@ -68,6 +79,7 @@ typedef struct {
     bool external_vcc; 	/**< whether display uses external vcc */ 
     uint8_t *buffer;	/**< display buffer */
     size_t bufsize;		/**< buffer size */
+    rotation_t rotation; /**< rotation of display */
 } ssd1306_t;
 
 /**
@@ -143,6 +155,14 @@ void ssd1306_show(ssd1306_t *p);
 */
 void ssd1306_clear(ssd1306_t *p);
 
+/**
+  @brief sets the rotation for
+
+  @param[in] p : instance of display
+  @param[in] rotation : rotation angle
+*/
+void ssd1306_set_rotation(ssd1306_t *p, rotation_t rotation);
+
 /**
 	@brief clear pixel on buffer